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Thread: Is time travel possible

  1. #1 Is time travel possible 
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    To the future , then yes.
    But to the past that is quite impossible.Because that will create a circumstance that you go back to the past and kill your grandfather. But however there was a theories, multi universe, it said that when you go back to the past and try to kill your grand father then it will separate into 2 universe , I don't know much about this but you can search online.
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    Quote Originally Posted by VIJAY
    Is time travel possible?
    Time travel is not possible it is "required". The only things that does not travel through time are mass less things.

    Everything is moving at cosmic speed limit c trough space-time. That is a fixed positive speed for everything.

    What the talk expose is that when you are accelerating from one particular FoR (the earth for example) you still goes at c, and the earth still goes at c in spacetime (a 4D space velocity, not a 3D velocity)
    But what happens is that the more your space-like velocity is big (the 3D part of the 4D) the less your time-like velocity is. Because the total is always c. So you time-like distance slow compared to earth.

    So what really happen is NOT some kind of discontinuous jump, but just a detour, another path to get from A to B, longer in space, shorter in time.
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    VIJAY: no, time travel is not possible. See time travel is a fantasy. The TEDed video is popscience I'm afraid. Time dilation is not time travel. If you move fast and suffer time-dilation, you don't end up in the middle of next week. You merely suffer less local motion. You can emulate that using a refrigerator.

    Re the post above, everything is NOT moving at c through space-time. Spacetime is a mathematical model that presents all times at once. We draw worldlines in it, but there is no motion in it. It is static.
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    Quote Originally Posted by Farsight View Post
    VIJAY: no, time travel is not possible. See time travel is a fantasy. The TEDed video is popscience I'm afraid. Time dilation is not time travel. If you move fast and suffer time-dilation, you don't end up in the middle of next week. You merely suffer less local motion. You can emulate that using a refrigerator.
    Indeed, no one skips any time, per SR. It's always continuously and contiguously passing oneself per oneself, at seemingly steady rate, and there are no exceptions.

    Quote Originally Posted by Farsight View Post
    Re the post above, everything is NOT moving at c through space-time. Spacetime is a mathematical model that presents all times at once. We draw worldlines in it, but there is no motion in it. It is static.
    Well, spacetime is 4-dimensional. On a spacetime diagram, the figure is static, correct. The relative motions are indicated by the relative angular orientations between worldlines, per POV. As such, motion is inherent in the static 4d perspective. We experience motion because time passes us by, because with time's passage we can experience change. To model the motion on a 4d spacetime diagram, one must consider the "advancement of time" in conjunction with the relative angular orientations between worldlines. IOW, the upward steady advancement of lines-of-simultaneity, upward being toward higher entropy (ie the future). How fast do lines-of-simultaneity advance? At the rate of proper time, per the observer assigned that line-of-simultaneity. How fast is that? We do not know, however the Minkowski model suggests that the advancement of proper-time may be taken as something equivalent to the rate of c. Why? Well, because you hold yourself stationary, advancing only thru proper time at steady rate. Someone moving at a virtual c holds himself "passing only thru time" and you moving at a virtual c thru 3-space ... and so what you consider your own velocity thru time, is considered by he as your velocity (~c) thru spacetime, and vice versa. Therefore, your own time vector may be considered to have a magnitude of ~c, whilst you do no't realize it. As such, all entity travels through the spacetime continuum at the rate of c, and relative material motion is then the result of worldlines being non-parallel ... If parallel velocity 4-vectors then the relative v=0, and if unparallel then v>0. The more unparallel, the greater the relative v, c being the cosmologic speed limit.

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    I don't think that I'd want to dismiss it outright,because one can imagine a very nontrivial space-time topology that allows it. But how likely such a topology can be is another question -- and I don't see any straightforward way of producing it.
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    VIJAY, if you look at that video, you'll see what is meant by traveling.

    You cannot go anywhere but in the future at speed c. It is very important to understand that the universe isn't a static 3D picture with a universal ticking clock.
    Measuring distance is the only thing that one can do with regards to travelling. And the only thing travelers could do is to choose a path with more or less time. The "could do" in this case is using a powerful rocket, giving you enough energy to choose the most shorter "time" travel.

    Quote Originally Posted by lpetrich
    I don't think that I'd want to dismiss it outright,because one can imagine a very nontrivial space-time topology that allows it
    I've always be dubious about this wormhole notion. Dismissing the idea that somehow it is possible to shortcut'ing' only through space, and not time, requires some discontinuity, 'rips' more then 'holes'.

    In a more general sense, I fell like a more extended version of the causality principle is at play. I can 'imagine' in some way receiving 'news' from ultra distant planet without breaking causality. But I cannot imagine receiving a box of cakes from the same place.

    Things 'popping' into existence, would requires some breaking in the conservation of 'things'. So I would say it is only possible if I had sent the exact same box of cakes on the other ends. I could also describe this event like this: 'nothing happens'. So if I wanted to receive news from ultra distant planet, I should be able to sent then at the same time.


    That is also how I interpret the quantum fluctuation. When things have been borrow from the future and the past, and then merging to 'restore the balance'. Those event being at the very bottom of each light cone, below Planck length, where travelers can tunnel beyond or below C.
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    Quote Originally Posted by SinceYouAsked View Post
    Well, spacetime is 4-dimensional. On a spacetime diagram, the figure is static, correct. The relative motions are indicated by the relative angular orientations between worldlines, per POV. As such, motion is inherent in the static 4d perspective.
    Yes, but this motion is through space, not spacetime. If you're sitting still we draw a vertical worldline, but you aren't actually moving through spacetime.

    Quote Originally Posted by SinceYouAsked View Post
    We experience motion because time passes us by, because with time's passage we can experience change.
    We experience motion and change, but we don't actually experience time passing us by or time's passage. Such is just a figure of speech.

    Quote Originally Posted by SinceYouAsked View Post
    To model the motion on a 4d spacetime diagram, one must consider the "advancement of time" in conjunction with the relative angular orientations between worldlines. IOW, the upward steady advancement of lines-of-simultaneity, upward being toward higher entropy (ie the future). How fast do lines-of-simultaneity advance? At the rate of proper time, per the observer assigned that line-of-simultaneity. How fast is that? We do not know, however the Minkowski model suggests that the advancement of proper-time may be taken as something equivalent to the rate of c. Why? Well, because you hold yourself stationary, advancing only thru proper time at steady rate. Someone moving at a virtual c holds himself "passing only thru time" and you moving at a virtual c thru 3-space ... and so what you consider your own velocity thru time, is considered by he as your velocity (~c) thru spacetime, and vice versa.
    It's all abstraction, SinceYouAsked. You really aren't really "advancing through proper time". Your clock is ticking because inside it something is moving. And you are alive and conscious because inside your brain electrochemical signals are moving from synapse to synapse, and inside your chest your heart is beating. Moving. Your blood is moving. Etc.

    Quote Originally Posted by SinceYouAsked View Post
    Therefore, your own time vector may be considered to have a magnitude of ~c, whilst you do no't realize it. As such, all entity travels through the spacetime continuum at the rate of c
    No, they don't. Again, spacetime is a static mathematical model. You aren't travelling through anything at the speed of light.


    Quote Originally Posted by lpetrich
    I don't think that I'd want to dismiss it outright, because one can imagine a very nontrivial space-time topology that allows it.
    It doesn't allow it. Spacetime is an abstract static thing. A closed timelike curve in spacetime isn't time travel. It's not even like Groundhog Day. It would be where your life was one day long and causeless. You don't travel through spacetime, you don't go round and round the loop. See page 142 of Palle Yourgrau's book where he says Wheeler conflated a circle with a cycle.
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    Quote Originally Posted by Farsight View Post
    Yes, but this motion is through space, not spacetime. If you're sitting still we draw a vertical worldline, but you aren't actually moving through spacetime.
    While stationary, you are moving through spacetime because your clock continues to tick. You are unaware you are moving, because of three reasons ... (1) you do not feel your own inertia when inertial, and (2) others comoving with you in your locale never change in relative position wrt your own 3-space. So your motion through spacetime goes casually unbeknownst.

    Quote Originally Posted by Farsight View Post
    We experience motion and change, but we don't actually experience time passing us by or time's passage. Such is just a figure of speech.
    It's not that I completely disagree with your point here. It does have some merit. However, how do you define motion or change, if time does not exist?

    Quote Originally Posted by Farsight View Post
    It's all abstraction, SinceYouAsked. You really aren't really "advancing through proper time". Your clock is ticking because inside it something is moving. And you are alive and conscious because inside your brain electrochemical signals are moving from synapse to synapse, and inside your chest your heart is beating. Moving. Your blood is moving. Etc.
    Again, how do all these things exist, if there is no passage of time? Your clock's hands going round in a circle requires a passage of time, just like the motion of a planet about its star. How do you define motion, in the absence of time? Please show your mathematical model. Also, I'm curious ... how is it that one can be so sure that space exists, and that time does not? Change and motion cannot exist without space as much as without time.

    Quote Originally Posted by Farsight View Post
    No, they don't. Again, spacetime is a static mathematical model. You aren't travelling through anything at the speed of light.
    How can you know this? Spacetime is transparent. You don't feel your own inertia when inertial. Those comoving with you never change in their relative position. How can you be so sure you are not traveling through the frictionless continuum?

    Quote Originally Posted by Farsight View Post
    It doesn't allow it. Spacetime is an abstract static thing. A closed timelike curve in spacetime isn't time travel. It's not even like Groundhog Day. It would be where your life was one day long and causeless. You don't travel through spacetime, you don't go round and round the loop. See page 142 of Palle Yourgrau's book where he says Wheeler conflated a circle with a cycle.
    Well, I would agree in that spacetime coordinates are man made, but this does not change the fact that events in spacetime are measurable, predictable, and thus real, using them. Spacetime (ie spacetime systems) is our measure of the medium (the spacetime continuum), whatever it is. It exists because we know we can measure it, quantify it, and predict it, consistently.

    Far as a closed time-like curve in spacetime goes, none exists far as we know. It's a theoretical speculation. There are various professional opinions as to what the outcome would be. For example, you could not kill your grandfather no matter how hard you tried. Or, you could, but an alternate universe is generated. I might add, if you went back in time to a year earlier, there would be 2 versions of you there, and so you yourself do not keep repeating the circle back in time. That'd be the prior version of yourself. Each second of the day there exists cause and effect, and so I don't quite see how the time-loop would be causeless, if it were possible. It may well be that if wormholes exist, they cannot connect you to any prior event within the lightcone, then there is never a problem.

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    Use Google to look up time travel and cosmic strings. I've heard that time travel is possible using two parallel cosmic strings passing by each other at near light speeds. It's highly impractical of course since nobody has ever detected a cosmic string and it we did they'd be so far away that they'd be too difficult to get to. Not to mention that you can't control what a cosmic string is doing.
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    Quote Originally Posted by SinceYouAsked View Post
    While stationary, you are moving through spacetime because your clock continues to tick.
    I'm not moving through spacetime at all. There's something moving inside my clock, that's all.

    Quote Originally Posted by SinceYouAsked View Post
    You are unaware you are moving, because of three reasons ... (1) you do not feel your own inertia when inertial, and (2) others comoving with you in your locale never change in relative position wrt your own 3-space. So your motion through spacetime goes casually unbeknownst.
    You can say that about my motion through space, but not about motion through spacetime. There isn't any motion through spacetime. It's the block universe. All times at once. It's static.

    Quote Originally Posted by SinceYouAsked View Post
    It's not that I completely disagree with your point here. It does have some merit. However, how do you define motion or change, if time does not exist?
    Empirically. You hold your hands up a yard apart and say that's distance then you waggle your hands and say that's motion.

    Quote Originally Posted by SinceYouAsked View Post
    Again, how do all these things exist, if there is no passage of time? Your clock's hands going round in a circle requires a passage of time, just like the motion of a planet about its star. How do you define motion, in the absence of time? Please show your mathematical model. Also, I'm curious ... how is it that one can be so sure that space exists, and that time does not? Change and motion cannot exist without space as much as without time.
    Nobody is saying time doesn't exist. A hundred years will kill you just as surely as a 100 degrees C. But time just isn't something that literally passes. That's just a figure of speech. Your clock's hands go round in circles because they're moving, and you label their current location the time now. You define motion empirically, see above.

    Quote Originally Posted by SinceYouAsked View Post
    How can you know this? Spacetime is transparent. You don't feel your own inertia when inertial. Those comoving with you never change in their relative position. How can you be so sure you are not traveling through the frictionless continuum?
    Because spacetime is static. You're referring to space as if its spacetime.

    Quote Originally Posted by SinceYouAsked View Post
    Well, I would agree in that spacetime coordinates are man made, but this does not change the fact that events in spacetime are measurable, predictable, and thus real, using them. Spacetime (ie spacetime systems) is our measure of the medium (the spacetime continuum), whatever it is. It exists because we know we can measure it, quantify it, and predict it, consistently.
    The events and the motion and the change are all happening in space. Spacetime is this big static "map" thingy, and the map is not the territory. You draw worldlines in spacetime to denote motion through space over time. But space isn't what spacetime is. You don't see any worldliness in space because they're abstract, like spacetime.

    Quote Originally Posted by SinceYouAsked View Post
    As far as a closed time-like curve in spacetime goes, none exists far as we know. It's a theoretical speculation.
    It's a myth. You don't travel up a worldline. If it curved round on itself you don't travel round it ad infinitum.

    Quote Originally Posted by SinceYouAsked View Post
    There are various professional opinions as to what the outcome would be. For example, you could not kill your grandfather no matter how hard you tried. Or, you could, but an alternate universe is generated. I might add, if you went back in time to a year earlier, there would be 2 versions of you there, and so you yourself do not keep repeating the circle back in time. That'd be the prior version of yourself. Each second of the day there exists cause and effect, and so I don't quite see how the time-loop would be causeless, if it were possible. It may well be that if wormholes exist, they cannot connect you to any prior event within the lightcone, then there is never a problem.
    All this stuff is science fiction. You can't travel to the past because you don't really "travel" to the future.
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    Farsight,

    Most of what you say there, I really don't entirely disagree with. There is the camp who says time exists, and the camp who says time does not exist. The former camp, is the consensus in physics today. It may be that eventually, the latter camp overthrows the former. Hasn't happened yet though.

    Let's say time does not exist in the way we presume, as a fundamental dimension. That instead, that which we call time is actually "something else". That something else, must do everything that time does. Now, one may argue that motion (or change) and space is all that exists. That time is just a mathematical construct used to aid in quantifying existence. I'm somewhat fine with that, however, one must still address that which we call "the passage of time", something we directly experience. And, it must be addressed under the context of relativity theory, since that theory has been consistently proven true to date, and accepted accordingly. How do you explain the passage of time, if everything in existence is static? Are you saying that nothing moves in spacetime, or are you saying you reject the spacetime model, and prefer an unfused space and time? If everything were static, why then do we experience things to move, including light? What produced the experience we have "of change"? It is insufficient to just say "change exists, and let's leave it at that then".

    Regarding spacetime diagrams ... Simply because ink does not move on a piece of paper, does not lead that lines-of-simultaneity should be considered "not to advance" with proper-time's passage on a spacetime figure. One can certainly imagine they do advance, as consistent with time's passage toward the future in everyday experience. For example, this spacetime figure below shows the heavens "during the passage of his own proper time" per a properly accelerating observer. With PC animations, we no longer need to imagine, and the page of paper need not remain static, although we unfortunately don't have animations for every scenario we choose to discuss ...

    http://upload.wikimedia.org/wikipedi...world_line.gif

    Now, that animation shows the POV of the properly accelerating observer as the reference for all motion (ie stationary). This does not lead that he is not traveling through the 4-space, but the animation shows what is always allowed per relativity ... to assume oneself the stationary and all else in motion. That animation could be redone to show the observer moving upward along his time axis (away from t'=0) representing a progression thru time toward the future, and all the relative positions of the heavens would not change as he goes (compared to what the posted animation shows). It's an arbitrary choice. The question is, which arbitrary choice best represents mother nature?

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    Quote Originally Posted by Farsight
    I'm not moving through spacetime at all. There's something moving inside my clock, that's all.
    You either forgot or didn't notice that all parts of the human body are clocks. The heart itself can be considered a clock since it beats. It's not a good clock, but it's still a clock.
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    No problem, Physicist. Galilieo used his own pulse as a kind of clock. I had that in mind when I said this the other day: "Your clock is ticking because inside it something is moving. And you are alive and conscious because inside your brain electrochemical signals are moving from synapse to synapse, and inside your chest your heart is beating. Moving. Your blood is moving. Etc."
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    Quote Originally Posted by SinceYouAsked View Post
    Most of what you say there, I really don't entirely disagree with. There is the camp who says time exists, and the camp who says time does not exist. The former camp, is the consensus in physics today. It may be that eventually, the latter camp overthrows the former. Hasn't happened yet though.
    I don't think it's quite like that. In fact, I think time exists like heat exists. Heat is very real, heat will kill you. So will time. But you know how we talk about a higher temperature? Nobody thinks you can literally climb up to a higher temperature. IMHO the "latter camp" are the people who say time is real like heat is real, but you can't travel in time just as you can't climb to a higher temperature.

    Quote Originally Posted by SinceYouAsked View Post
    Let's say time does not exist in the way we presume, as a fundamental dimension. That instead, that which we call time is actually "something else". That something else, must do everything that time does. Now, one may argue that motion (or change) and space is all that exists. That time is just a mathematical construct used to aid in quantifying existence.
    I wouldn't want to get rid of time, but I would like to make it clear that time isn't something you can travel through. It's a dimension of measure, not one that offers freedom of motion.

    Quote Originally Posted by SinceYouAsked View Post
    I'm somewhat fine with that, however, one must still address that which we call "the passage of time", something we directly experience. And, it must be addressed under the context of relativity theory, since that theory has been consistently proven true to date, and accepted accordingly. How do you explain the passage of time, if everything in existence is static?
    Everything in existence isn't static!

    Quote Originally Posted by SinceYouAsked View Post
    Are you saying that nothing moves in spacetime, or are you saying you reject the spacetime model, and prefer an unfused space and time?
    I'm saying nothing moves in spacetime because it's an "all times at once" model of reality. It's a model that works, there's no need to reject it, but there is a need to avoid confusing the model with the reality. We don't live in some static "all times at once" reality.

    Quote Originally Posted by SinceYouAsked View Post
    If everything were static, why then do we experience things to move, including light?
    Because everything isn't static, things do move.

    Quote Originally Posted by SinceYouAsked View Post
    What produced the experience we have "of change"? It is insufficient to just say "change exists, and let's leave it at that then".
    All I can say to that is that things move and change happens. Light moves, planets move, hearts move, blood moves, electrochemical signals move, and so on.

    Quote Originally Posted by SinceYouAsked View Post
    Regarding spacetime diagrams ... Simply because ink does not move on a piece of paper, does not lead that lines-of-simultaneity should be considered "not to advance" with proper-time's passage on a spacetime figure.
    They don't advance, they can't advance, because they need time to do that, and spacetime models all times at once. It's static. If you sit on your chair you aren't travelling up some worldline at the speed of light. That worldline doesn't actually exist. It's just an abstract concept in a mathematical model. You're just sitting in your chair. You aren't going anywhere at the speed of light.

    Quote Originally Posted by SinceYouAsked View Post
    One can certainly imagine they do advance, as consistent with time's passage toward the future in everyday experience.
    You can, but it's the wrong concept, as is "time's passage". Things move. Shit happens. That's it.

    Quote Originally Posted by SinceYouAsked View Post
    For example, this spacetime figure below shows the heavens "during the passage of his own proper time" per a properly accelerating observer. With PC animations, we no longer need to imagine, and the page of paper need not remain static, although we unfortunately don't have animations for every scenario we choose to discuss ...



    Now, that animation shows the POV of the properly accelerating observer as the reference for all motion (ie stationary). This does not lead that he is not traveling through the 4-space, but the animation shows what is always allowed per relativity ... to assume oneself the stationary and all else in motion. That animation could be redone to show the observer moving upward along his time axis
    It's misleading. The observer isn't moving up his time axis, he isn't moving up his worldline, his worldline isn't moving down through him, and he isn't stationary. He's moving through space, and he's changing his motion through space, whereupon his measurements of space and time, made using the motion of light, change.

    Quote Originally Posted by SinceYouAsked View Post
    It's an arbitrary choice. The question is, which arbitrary choice best represents mother nature?
    Spacetime is fine provided you don't confuse it with space and think it's something you can move through. You can't move through spacetime just as you can't move through time.
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    The Ted lesson discussion conclusion leads to a contrarian view. Pls go through,Is time travel possible? - Colin Stuart | TED-Ed is astonishing to note that ,the Special Relativity Theory Equations are incongruous beyond half the speed of light, by mere Number Theory considerations ,specifically ‘time dilation’ and ‘length contraction’ equations
    Nevertheless, there is an exception to this theory,for particles of masses less than

    1kg, or time intervals between events which are less than 1s or length

    contraction less than 300000km ,where it could be absolutely accurate as

    Einstein predicted and therefore it implies,these could change upto only

    13.3%,approximately.Pls go through my publication,the link of which ishttp://www.ijser.org/onlineResearchPaperViewer.aspx?Domain-of-Relativistic-Mechanics.
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    Quote Originally Posted by Farsight View Post
    I'm saying nothing moves in spacetime because it's an "all times at once" model of reality.
    That's totally dumb. That's a "look from outside" view of space-time, when we live on the inside of it.

    Hermann Minkowski, Space and Time: "Henceforth, space for itself, and time for itself shall completely reduce to a mere shadow, and only some sort of union of the two shall preserve independence." So if you deny a unified space-time, you deny Minkowski and you don't qualify as a physicist.

    Actually, that's not the way that a real physicist would work, even if it is the sort of argument that I've seen a lot of here.


    Space-time has local Poincaré symmetry. I say local because in general relativity, it is curved, typically reducing its overall symmetry. Only in flat space-time is Poincaré symmetry global. Poincaré symmetry is defined by transforms (R,D) where R is a 4*4 matrix and D is a 4-vector. It turns space-time 4-vector x into x':
    x' = R.x + D

    The R's satisfy RT.g.R = g where g is a constant symmetric 4*4 matrix. For (space 1, space 2, space 3, time) and c = 1, g = diag(1,1,1,-1) or diag(-1,-1,-1,1). So there isn't any fundamental difference between space and time, though spacelike, null, and timelike directions are distinct, and null and timelike ones can be further subdivided into forward and backward ones.
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    Quote Originally Posted by lpetrich View Post
    That's totally dumb. That's a "look from outside" view of space-time, when we live on the inside of it. Hermann Minkowski, Space and Time: "Henceforth, space for itself, and time for itself shall completely reduce to a mere shadow, and only some sort of union of the two shall preserve independence." So if you deny a unified space-time, you deny Minkowski and you don't qualify as a physicist.
    What are you on about, lpetrich? Nobody is denying spacetime. All we're saying is that it isn't space. You move through space over time. You don't move through spacetime over time, because time is already in spacetime. So it's static.

    Quote Originally Posted by lpetrich View Post
    Space-time has local Poincaré symmetry. I say local because in general relativity, it is curved, typically reducing its overall symmetry. Only in flat space-time is Poincaré symmetry global. Poincaré symmetry is defined by transforms (R,D) where R is a 4*4 matrix and D is a 4-vector. It turns space-time 4-vector x into...
    You're lost in maths. Understand this: spacetime is the map, space is the territory. Motion occurs in this territory, over time. But the map is not the territory. Take a look at Inhomogeneous Vacuum: An Alternative Interpretation of Curved Spacetime - Abstract - Chinese Physics Letters - IOPscience. Inhomogeneous space is the real thing that underlies "curved spacetime". Imagine you were swimming through inhomogeneous water. Like water that was saltier and denser on the left than on the right. You'd find yourself veering left. That's like light curving in a gravitational field. See Professor Ned Wright's deflection and delay of light. Pay special attention to "In a very real sense, the delay experienced by light passing a massive object is responsible for the deflection of the light."

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    Farsight, so per your last post, I summarize your position as follow ...

    Regarding time ...

    Time exists.
    Time is a dimension of measure.
    Time is not that which allows for motion.
    Things move through space, but not through time.

    Regarding spacetime ...

    Spacetime is static, and nothing can move through it.
    The spacetime model works, but does not represent "true reality".
    Spacetime implies "all times at once".
    Lines-of-simultaneity cannot advance.
    Stationary observers do not travel up a worldline, let alone at light speed.
    Worldlines do not travel down thru a stationary observer.
    Worldlines do not actually exist, and are man made abstracts.
    Spacetime is fine, provided you don't confuse it with space and think you can move through time similarly.
    You cannot move through spacetime or time, but you can move through space.

    Sound about right, per your prior post?

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    Quote Originally Posted by Farsight View Post
    What are you on about, lpetrich? Nobody is denying spacetime. All we're saying is that it isn't space.
    It isn't 3-space because 3-space is a subset of spacetime. One can foliate or slice space-time into a set of 3-space hypersurfaces. Doing so is arbitrary, though one may use appropriate features of the space-time if they are available.

    Also, saying that 3-space is fundamental while time is not is essentially denying space-time, because in relativity, space and time are coequal in it.

    Inhomogeneous space is the real thing that underlies "curved spacetime".
    Whatever "inhomogeneous" is supposed to mean in this context. I'd like to see it worked out mathematically. Quoting Einstein isn't enough. In his Leyden address, he was trying to explain general relativity in nonmathematical terms, and he may have been imprecise, like using "space" instead of "space-time". So I don't see why it qualifies as as a literally-true inspired text.
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    Quote Originally Posted by SinceYouAsked View Post
    Farsight, so per your last post, I summarize your position as follow ...

    Regarding time ...

    Time exists.
    Time is a dimension of measure.
    Time is not that which allows for motion.
    Things move through space, but not through time.
    Pretty close. Maybe time is not that which allows for motion needs a polish, because time is derived from motion. I can waggle my hands and show you motion. It's empirical. But I can't show you time.

    Quote Originally Posted by SinceYouAsked View Post
    Regarding spacetime ...

    Spacetime is static, and nothing can move through it.
    The spacetime model works, but does not represent "true reality".
    Spacetime implies "all times at once".
    Lines-of-simultaneity cannot advance.
    Stationary observers do not travel up a worldline, let alone at light speed.
    Worldlines do not travel down thru a stationary observer.
    Worldlines do not actually exist, and are man made abstracts.
    Spacetime is fine, provided you don't confuse it with space and think you can move through time similarly.
    You cannot move through spacetime or time, but you can move through space.

    Sound about right, per your prior post?
    Yep, pretty much. Though your second line could maybe do with a tweak. Maybe like this: The spacetime model works, and it does represent the true reality, but spacetime is not the true reality, just as the map is not the territory.
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    Quote Originally Posted by SinceYouAsked View Post
    Far as a closed time-like curve in spacetime goes, none exists far as we know. It's a theoretical speculation. There are various professional opinions as to what the outcome would be. For example, you could not kill your grandfather no matter how hard you tried. Or, you could, but an alternate universe is generated. I might add, if you went back in time to a year earlier, there would be 2 versions of you there, and so you yourself do not keep repeating the circle back in time. That'd be the prior version of yourself. Each second of the day there exists cause and effect, and so I don't quite see how the time-loop would be causeless, if it were possible. It may well be that if wormholes exist, they cannot connect you to any prior event within the lightcone, then there is never a problem.
    One can arbitrarily decree that space-time has a form that permits closed timelike loops, but the real challenge is to get such a space-time as a result of the sort of Universe we live in. It is apparently *very* difficult, though I don't know if anyone has proved that it is impossible.
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    Quote Originally Posted by lpetrich View Post
    It isn't 3-space because 3-space is a subset of spacetime. One can foliate or slice space-time into a set of 3-space hypersurfaces. Doing so is arbitrary, though one may use appropriate features of the space-time if they are available.
    That's circular logic that elevates abstraction above reality. Space is empirical. Hold your hands out, there's a space between them. Now waggle your hands. That's motion, that's empirical too. Time isn't, nor is spacetime. Don't let your your schooling cloud your scientific rationality on this kind of thing.

    Quote Originally Posted by lpetrich View Post
    Also, saying that 3-space is fundamental while time is not is essentially denying space-time, because in relativity, space and time are coequal in it.
    Nobody is "denying spacetime". I'm just telling you how to understand it. You can see space and motion, but not time. So you give more priority to space and motion. For example, go and open up a clock, and appreciate that there isn't any time flowing through it. Then appreciate that a clock clocks up local motion, so if you move fast through space it of necessity clocks up less, because the maximum motion is the speed of light.

    Quote Originally Posted by lpetrich View Post
    Whatever "inhomogeneous" is supposed to mean in this context. I'd like to see it worked out mathematically. Quoting Einstein isn't enough. In his Leyden address, he was trying to explain general relativity in nonmathematical terms, and he may have been imprecise, like using "space" instead of "space-time". So I don't see why it qualifies as as a literally-true inspired text.
    Go and do some research and read stuff like Inhomogeneous Vacuum: An Alternative Interpretation of Curved Spacetime and Inhomogeneous and interacting vacuum energy. The important thing to appreciate is that light curves because the speed of light varies with position. Because space isn't uniform. It doesn't curve because "spacetime is curved". That confuses cause and effect. A concentration of energy causes the surrounding space to be inhomogeneous, not curved. Then light "veers" like a car veers when it encounters mud at the side of the road. We model the motion of light through this space over time as curved spacetime. But see Baez and note not the curvature of space, but of spacetime. Space isn't curved, it's inhomogeneous.

    Quote Originally Posted by lpetrich
    One can arbitrarily decree that space-time has a form that permits closed timelike loops...
    Only that yields a causeless mayfly life that lasted a day and is ancient history. Not time travel. You don't go round and round the loop. Because you don't travel along your worldline. By and large, the length of your worldline represents elapsed time. And if it's a loop that is one light-day long, your life lasted a day. And it isn't a Groundhog day that you live over and over. It lasted a day. Full stop. That's it. You lived a day. You weren't born, you didn't die. But you only lived a day. And it's all just science fiction and fantasy, not physics.
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    Quote Originally Posted by lpetrich View Post
    One can arbitrarily decree that space-time has a form that permits closed timelike loops, but the real challenge is to get such a space-time as a result of the sort of Universe we live in. It is apparently *very* difficult, though I don't know if anyone has proved that it is impossible.
    Indeed. It is all a theoretical possibility based upon an interpretation of the general theory. I'm trying to separate these 2 issues mentioned by Farsight ...

    (1) a closed-time-loop, in the sense backward travel thru time & repeating it.
    (2) the accurateness of the 4 dimension spacetime model as it relates to reality.

    Discussing (1) is not helpful in discussing (2). We use (2), but we do not even know if (1) is possible.

    Farsight does not believe we travel thru time. He believes time exists, but that we don't travel through it, nor does it pass us by. He says that time does not allow for motion (or change). Then, what is time? To simply call time "the NOW", seems insufficient, and rather redundant. It seems that Farsight is saying that all that exists is "space and change", and time merely a man made measuring tool of sort. That's an argument that many make today, that time is not a fundamental dimension. At any rate, Farsight's is a reasonable position if one ignores the requirements of the accepted spacetime theory of the day. Relativity theory requires that space and time be fused, and that all points in time coexist as do the inches on a ruler do. This means there are countless Farsights from his birth to his death, all coexisting and passing thru spacetime unbeknownst to each other, each living out their unchanging NOW as it happens and unawares of the future. This requires a 4 dimensional continuum of fused spacetime, which spacetime diagrams model. Given all moments in time coexist casually unbeknownst to us, then Farsight's opinion that only the everchanging NOW exists is a shortsighted one, per the accepted theory. Yet, I'd have to consider Farsight's version of reality and give it its fair due, because we don't understand what time really is even though we quantify it very well. That leaves the door open, so to speak, for alternate theories of spacetime.

    Again, IMO, it is insufficient to say ... "only space and change exist, and that's that". Whoever says that, must show mathematically how anything can change (or move) without the use of time. We measure space, just as we measure time. If space must be used to model motion, and space is considered real, then why should time be considered "something less than space"? The only fellow I know of who has given these a fair address, is Julian Barbour. He suggests that time's passage is a manifestation of brain processing, that the passage of time is more an illusionary effect. That the passage of time is akin to flipping still pages in a rotary movie machine. Other that that, I have not heard a good explanation of how time arises, assuming it is not real. Yet, I must then ask, why would out brains sequence though contiguous snapshots of reality in the first place, if time did not pass?

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    (Me on space as a slice of space-time)
    Quote Originally Posted by Farsight View Post
    That's circular logic that elevates abstraction above reality.
    There is a lot of stuff about space-time foliations or slicings in the professional general-relativity literature. general relativity - What does "foliation" mean in the context of a "foliation of spacetime?" - Physics Stack Exchange is the simplest introduction that I could find.

    Space is empirical. Hold your hands out, there's a space between them. Now waggle your hands. That's motion, that's empirical too. Time isn't, nor is spacetime.
    By your argument about time, space isn't empirical either. All one perceives are variations in incoming light as a function of space and time. Thus, space is derived from variation.

    Furthermore, we have a sense of time: Timing and time perception: A review of recent behavioral and neuroscience findings and theoretical directions - Springer

    For example, go and open up a clock, and appreciate that there isn't any time flowing through it.
    What gives you the idea that there ought to be time flowing through it?

    The important thing to appreciate is that light curves because the speed of light varies with position.
    Locally, it is constant, but nonlocally, it is poorly defined. To lowest order, the nonlocal measured velocity differs from c by around c*(curvature)*(size of measurement path)^2.

    A concentration of energy causes the surrounding space to be inhomogeneous, not curved.
    Completely contrary to general relativity, and no amount of scriptural exegesis can change that. I studied GR long ago, and my knowledge of it has stayed with me. Matter-energy makes space-time curve; that's the meaning of
    (Einstein curvature tensor) = (gravitational constant) * (energy-momentum tensor)

    The Einstein curvature tensor is derived from the more-general Riemann one, and that in turn is derived from the space-time metric.

    (closed timelike loop)
    Only that yields a causeless mayfly life that lasted a day and is ancient history. Not time travel.
    Except that a closed timelike loop suggests the feasibility of an almost-closed one, one which avoids that difficulty.
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    Quote Originally Posted by Farsight View Post
    That's circular logic that elevates abstraction above reality. Space is empirical. Hold your hands out, there's a space between them. Now waggle your hands. That's motion, that's empirical too.
    I have heard the claim that motion is empirical. However, the only way I know of for testing claims about motion involve comparing different locations at different times. Every test of general relativity requires this.

    Is there some way to represent motion without time? What is motion without time? What is empirical about motion without time? What is motion?
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  27. #27 A mere 7% relativistic effects,due to special theory of relativity,has it been ever observed for either 2 second events or 2 kg masses 
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    Quote Originally Posted by PhysBang View Post
    I have heard the claim that motion is empirical. However, the only way I know of for testing claims about motion involve comparing different locations at different times. Every test of general relativity requires this.

    Is there some way to represent motion without time? What is motion without time? What is empirical about motion without time? What is motion?
    If the same has not taken place the reason is: Mathematical proof is given below
    Domain of Relativistic Mechanics.
    Pradeep Koshy
    Abstract : .It is astonishing to note that ,the Special Relativity Theory Equations
    are incongruous beyond one-third the speed of light, by mere Number Theory
    considerations ,specifically ‘time dilation’ and ‘length contraction’ equations.
    Nevertheless, there is an exception to this theory,for particles of masses less than
    1kg, or time intervals between events which are less than 1s or length
    contraction less than 300000km ,where it could be absolutely accurate as
    Einstein predicted and therefore it implies,these could change upto only
    6.07%,approximately.
    Keywords: Relativity,time dilation,length contraction,mass variance,
    number theory,algebraic formulae.
    Proof
    Introduction
    Since the mathematicians invaded Relativity,I do not understand it anymore--- Albert Einstein.
    This statement by Einstein,gives the general feeling that he was not convinced that the Theory of
    Relativity was absolute.The onus is on me,therefore to prove that the Special Theory of
    Relativity,has limitations and domain of relativistic mechanics is one-third the speed of light.,for
    particles of masses greater than 1 kg, time events greater than 1second as well as length
    contraction greater than 300000kms(approx.)
    I will start with Einstein’s own words
    “If you can’t explain it simply,you don’t understand it well enough.”
    Time travel is therefore an illusion. Science is really about demystification.The crowning glory of
    my achievement is merely Number Theory and Miracle Equation are utilized to achieve
    this. Miracle Equation is an equation,capable of solving 3variables in a single equation—
    Incredulous isn’t it. Abstract:
    Before 2013, you required 3 equations to solve 3 variables. Now it isn’t necessary.
    .
    PROOF
    MIRACLE EQUATION-CAN BE USED TO SOLVE 3 VARIABLES IN A SINGLE EQUATION.
    SEEMS IMPOSSIBLE.
    BUT HERE IS THE PROOF
    MIRACLE EQUATION:
    [(NX )² ― {(N―2) X }² ] =[N―(1―X²)]²―[N―(1+X²)]²
    The above equation which is true for all real values of N and X,is actually analogous to the equation
    [A²―B²] = C ²―D ² where A= NX,B=(N―2) X,C=[N―(1―X²)] & D=[N―(1+X²)] where .A,B.C & D are all variables.One way of analyzing the same is,if anyone chooses one of these variables,the remaining 3
    variables can be found out.The second case is given below.
    Now ,there is an interesting application wherein ,we can utilize this equation to solve 3 unknown
    variables in a single equation.
    Assuming the 3 variabled equation is of the form
    ax+by+dz=k where a,b,d are coefficients,x,y,z are variables and k is the constant.Solution is given
    by x= A²/a,y= B²/(-b) and z= D ² /d
    Hence the solution to the equation 2x+3y+4z=16
    HERE C= 4 . Arbitrarily selected values of N=1, X=2 to satisfy C=[ N―(1―X²)]
    Ergo , x=2, y = - 4/3 and z=4.Substituting different satisfying values(any real number) to N and X to make C = 4,(for instance you could generate different values of N = C+1- X² ,corresponding to X equal any real number)we can threreby get infinite solutions to this equation.We could resort to algorithm and programming at this stage,since a general equation is involved and a trinitarian aspect could be proved.
    PN:When k is a perfect square,calculations are simple. Otherwise,multiply k by itself.For the equation
    to remain unchanged multiply each term of LHS by k and then resort to the steps like below
    Suppose one need to solve
    2x+3y+4z=13 Taking the necessary steps the equation becomes
    26x+39y+52 z= 169,therefore x= A²/a,y= B²/(-b) and z= D ² /d
    HERE C= 13,Arbitrarily selected values of N=10 and X=2
    Therefore x= 400/26=200/13,y=256/-39= -256/39 and z= 25/52 We should also be educated in the Pythagoras Theorem to achieve the same. Abstract:
    It is astonishing to note that the 2500 year old,Pythagoras Theorem could be revolutionarily
    analysed and interpreted, in a two variable case and in a one variable case ,with the aid of
    axioms that have been deduced by me.
    PROOF
    Revoutionary analysing and interpreting the 2500 year old Pythagoras theorm.
    Understanding the Pythagoras theorm,is essential or played a very great role in my analyzing the
    Special Theory Of Relativity.Now,what I have deduced regarding the Pythagoras theorem
    .If the hypotenuse of a right triangle,is the average of two numbers say .A and B ie (A+B)/2,then
    the legs are (A-B)/2 and √(AB)
    .
    Another way of stating the Pythagoras theorem is, if the hypotenuse is product of two real
    numbers N and X ie (NX),then the legs are,the smaller leg is {2 X √(N-1)} and the longer leg is
    {X(N-2)},for large values of hypotenuse,where definitely, X<1.
    Earlier, I reduced it to a two variable case.Now,I have reduced it to a single variable case.In that
    case X is any real number and need not be less than 1. The hypotenuse is A and the legs are
    (n-2)(A/n) and {2(A/n) √(n-1)} what I have done is substitued N=n and X= A/n and removed the
    condition X<1.Also,note here n can be any whole number we substitute .
    .
    One could also,have the hypotenuse as [(N-1)+X²] and then the legs could be [(N-1)-X²] and {2
    X √(N-1)}
    Putting suitable values in the above Pythagorean triplets can be generated
    TIME DILATON EQUATION
    t = t′ /[√ (1― v²/c²) ]
    where t is the time measured in S frame is slower than the time t′ measured in inertial frame S′
    by time dilation equations.In all these cases, c stands for velocity of light and equal to it,whereas
    v is the velocity of the frame S′ with respect to S. On rearranging the relativistic
    equation ,simplifies to( t′c)²=(tc )²―(tv)²,which finally leads to
    (t′)²=(t)²―( tv/c)²
    Note that each term in the modified form of the TIME DILATION EQUATION has the same
    units.Units have no relevance and it can now be considered part of Number Theory.Comparing
    both these equations,MIRACLE EQUATION and modified form of TIME DILATION
    EQUATION.vital observations
    are made ie
    Miracle Equation reduces to
    [(NX )² ― {(N―2) X }² ] =4(N-1) X², tv/c corresponds or is equal to(N―2) X and t corresponds to(N) X
    Ie( tv/c)/t =(N―2) X /(N)X
    Ie v/c=(N―2)/N Therefore Ie v/c=(N―2)/N ie c stands for 3 meaning 300000 kms/s,N=3 therefore v= 3-2=1 meaning 100000kms/, therefore the Special Relativity Theory Equations
    are incongruous beyond one-third the speed of light, by mere Number Theory
    considerations ,specifically ‘time dilation’ and ‘length contraction’ equations.
    Nevertheless, there is an exception to this theory,for particles of masses less than
    1kg, or time intervals between events which are less than 1s or length
    contraction less than 300000km ,where it could be absolutely accurate as
    Einstein predicted and therefore it implies,these could change upto only
    6.07%,approximately.For proof to the exception and v/c <(0.5) go to the journal link attached below Domain of Relativistic Mechanics - IJSER Journal Publication
    .Please note two very important
    points.Firstly,presently we see ,highest common factor of (t′),(t)&( tv/c) is 1.This has to be
    understood in its context.Secondly,the Miracle Equation both sides has to be multiplied by
    k,where k stands for any positive number,whatever possible values it can assume,so that it
    becomes fully identical to modified form of TIME DILATION EQUATION and therefore(t′),
    (t)&( tv/c) can attain any variations of values that may be possible.
    (hence concluded.)
    11.References
    [1]University Physics by Sears,Zemanski &Young.
    [2]The Feynmann Lectures by Richard P.Feynmann,Matthew W.Sands &Robert B.
    Leighton.
    [3]Special Theory of Relativity by Resnick.
    [4]Fundamentals of Physics by Halliday,Resnick &Walker.
    Author
    Pradeep Koshy,
    Independent Researcher,
    Cochin, Kerala, India
    Mob:+91-9895854062
    Email:koshy68@gmail.com
    Domain of Relativistic Mechanics - IJSER Journal Publication
    IJSER is an open access international journal online facilitating the publication of scholarly, peer reviewed journals in the field of science & engineering.
    IJSER.ORG
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    Quote Originally Posted by SinceYouAsked View Post
    Farsight does not believe we travel thru time. He believes time exists, but that we don't travel through it, nor does it pass us by.
    Yep.

    Quote Originally Posted by SinceYouAsked View Post
    He says that time does not allow for motion (or change).
    Hmmn. What I'm really saying is that time is motion. Or change. A clock is alleged to measure the passage of time, but actually it "clocks up" some kind of regular cyclical motion and shows you a cumulative result that you call "the time".

    Quote Originally Posted by SinceYouAsked View Post
    Then, what is time?
    A cumulative measure of local motion.

    Quote Originally Posted by SinceYouAsked View Post
    To simply call time "the NOW", seems insufficient, and rather redundant. It seems that Farsight is saying that all that exists is "space and change", and time merely a man made measuring tool of sort.
    Remember I said time exists. It exists like heat exists. At the sub-atomic level there is no such thing as heat. A "hot" particle is merely a fast-moving particle. But if you've ever touched a hot stove, you know that heat exists. Heat will burn you. Heat will kill you. Heat exists. So does time, because a hundred years will kill you just as surely as 100°C.

    Quote Originally Posted by SinceYouAsked View Post
    That's an argument that many make today, that time is not a fundamental dimension. At any rate, Farsight's is a reasonable position if one ignores the requirements of the accepted spacetime theory of the day. Relativity theory requires that space and time be fused
    And that they are. Because when you move fast through space your measurement of local motion changes, because the total motion can't exceed c. See the simple inference of time dilation due to relative velocity. The Lorentz factor is essentially Pythagoras' theorem. The light path is the hypotenuse, the base is your speed as a fraction of c, the height is the Lorentz factor with a reciprocal to distinguish length contraction from time dilation. It's really simple.

    Quote Originally Posted by SinceYouAsked View Post
    and that all points in time coexist as do the inches on a ruler do. This means there are countless Farsights from his birth to his death, all coexisting and passing thru spacetime unbeknownst to each other, each living out their unchanging NOW as it happens and unawares of the future.
    Relativity just doesn't say this.

    Quote Originally Posted by SinceYouAsked View Post
    This requires a 4 dimensional continuum of fused spacetime, which spacetime diagrams model. Given all moments in time coexist
    But they don't all coexist. That's science fiction territory. Some events have happened. Other haven't.

    Quote Originally Posted by SinceYouAsked View Post
    casually unbeknownst to us, then Farsight's opinion that only the everchanging NOW exists is a shortsighted one, per the accepted theory. Yet, I'd have to consider Farsight's version of reality and give it its fair due, because we don't understand what time really is even though we quantify it very well. That leaves the door open, so to speak, for alternate theories of spacetime.
    You don't need any alternate theories of spacetime. You just need to understand it. And to do that you need to appreciate that it's the map, and the map is not the territory. We live in a world of space and motion, not in a static world of lightcones and worldlines where all times coexist and where there are countless Farsights. That just isn't how it is.

    Quote Originally Posted by SinceYouAsked View Post
    Again, IMO, it is insufficient to say ... "only space and change exist, and that's that". Whoever says that, must show mathematically how anything can change (or move) without the use of time.
    No. Nobody can show this mathematically. They can however only show space and motion empirically. Such that you can see them with your own eyes. Then when nobody can show you time in similar vein, that should be sufficient.

    Quote Originally Posted by SinceYouAsked View Post
    We measure space, just as we measure time.
    Using the motion of light through space.

    Quote Originally Posted by SinceYouAsked View Post
    If space must be used to model motion, and space is considered real, then why should time be considered "something less than space"?
    Because I can hold my hands up and show you the space between them. But you can't show me time.

    Quote Originally Posted by SinceYouAsked View Post
    The only fellow I know of who has given these a fair address, is Julian Barbour. He suggests that time's passage is a manifestation of brain processing, that the passage of time is more an illusionary effect. That the passage of time is akin to flipping still pages in a rotary movie machine.
    See Wikipedia: "It is all an illusion: there is no motion and no change." Julian Barbour is wrong. There is motion. There is change. Time exists. But it just isn't something you can move through, because it's a cumulative measure of motion. You can't move through motion.

    Quote Originally Posted by SinceYouAsked View Post
    Other that that, I have not heard a good explanation of how time arises, assuming it is not real. Yet, I must then ask, why would out brains sequence though contiguous snapshots of reality in the first place, if time did not pass?
    It's real because shit happens. Accept it. And then appreciate that things change and move, but time itself doesn't. Time does not literally pass or flow, and you cannot travel through it.
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    Quote Originally Posted by PhysBang View Post
    I have heard the claim that motion is empirical. However, the only way I know of for testing claims about motion involve comparing different locations at different times. Every test of general relativity requires this.
    And those different times are measured on clocks. Which feature cogs moving in some regular cyclical fashion. Or crystals vibrating in some regular cyclical fashion. Or microwaves generated in some regular cyclical fashion. In the end you test your claims about motion using "different times" that are calibrated against the motion of light. It always comes back to motion.

    Quote Originally Posted by PhysBang View Post
    Is there some way to represent motion without time? What is motion without time? What is empirical about motion without time? What is motion?
    Motion is where some thing gradually changes its location or orientation in space. And this thing might be an electron, which was made in pair production. Starting with a photon. Which we could have converted into the motion of electrons via repeated Compton scatters. So in a way, an electron is made of motion. And so are you.
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    Hi 07CAUCHY,
    Your noetical observations,if it is absolute will transmogrify existing views of Special Theory of Relativity.I will ask cognoscenti to give their views on the same.
    Regards
    VIJAY
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    Quote Originally Posted by lpetrich View Post
    By your argument about time, space isn't empirical either. All one perceives are variations in incoming light as a function of space and time. Thus, space is derived from variation.
    It isn't true. You don't just perceive incoming light. Hold your hands up, palms pressed together. There is no space between them, and you can feel your palms touching. Now repeat, but this time with your hands a yard apart. This time there is a space between them. You can feel the difference, and you can see the difference. It is empirical.

    That's just a figure of speech. You don't have a sense of time. You have a sense of smell, you have vision, hearing, touch, and taste. You have five senses. You do not have a sixth sense that is a sense of time.

    Quote Originally Posted by lpetrich View Post
    What gives you the idea that there ought to be time flowing through it?
    I don't have that idea. But other people do. Ask them what a clock does and they'll say "measure the flow of time". As if the clock is some kind of cosmic gas meter with time flowing through it. It isn't. It just clocks up some kind of regular cyclical motion and gives a cumulative display.

    Quote Originally Posted by lpetrich View Post
    Locally, it is constant, but nonlocally, it is poorly defined. To lowest order, the nonlocal measured velocity differs from c by around c*(curvature)*(size of measurement path)^2.
    Let's save that for a different thread.

    Quote Originally Posted by lpetrich View Post
    Completely contrary to general relativity, and no amount of scriptural exegesis can change that. I studied GR long ago, and my knowledge of it has stayed with me. Matter-energy makes space-time curve; that's the meaning of (Einstein curvature tensor) = (gravitational constant) * (energy-momentum tensor) The Einstein curvature tensor is derived from the more-general Riemann one, and that in turn is derived from the space-time metric.
    As above. Do appreciate that some things that you take for granted are not correct.

    Quote Originally Posted by lpetrich View Post
    Except that a closed timelike loop suggests the feasibility of an almost-closed one, one which avoids that difficulty.
    It's still the stuff of fantasy. Spacetime depicts our world of space and motion. There is no way you can move to get into a situation where everything is somehow back where it was, and didn't move to where it did.
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    Quote Originally Posted by SYA View Post
    And that all points in time coexist as do the inches on a ruler do. This means there are countless Farsights from his birth to his death, all coexisting and passing thru spacetime unbeknownst to each other, each living out their unchanging NOW as it happens and unawares of the future.

    Quote Originally Posted by Farsight View Post
    Relativity just doesn't say this.
    Link -> Eternalism (philosophy of time) - Wikipedia, the free encyclopedia.

    Quote Originally Posted by SYA View Post
    This requires a 4 dimensional continuum of fused spacetime, which spacetime diagrams model. Given all moments in time coexist.
    Quote Originally Posted by Farsight View Post
    But they don't all coexist. That's science fiction territory. Some events have happened. Other haven't.
    See the above hyperlink reference.

    Quote Originally Posted by SYA View Post
    Given all moments in time coexist casually unbeknownst to us, then Farsight's opinion that only the everchanging NOW exists is a shortsighted one, per the accepted theory. Yet, I'd have to consider Farsight's version of reality and give it its fair due, because we don't understand what time really is even though we quantify it very well. That leaves the door open, so to speak, for alternate theories of spacetime.

    Quote Originally Posted by Farsight View Post
    You don't need any alternate theories of spacetime. You just need to understand it. And to do that you need to appreciate that it's the map, and the map is not the territory. We live in a world of space and motion, not in a static world of lightcones and worldlines where all times coexist and where there are countless Farsights. That just isn't how it is.
    You say you don't need any alternate theories of spacetime, but yet you do not know of eternalism. Worldlines are static in 4-space, but our progression along them is not. Repeating that worldlines are static, will never change that.

    OK, so the measure of time may be defined as the relative comparison of motions in space, one motion being hopefully of uniform cyclic nature. However, what allows anything "to move" in the very first place? The answer ... no one has any idea how to explain that without the use of TIME. Given such, what is the standard reply? "Well, motion simply exists, and that's that as they say". Not good enough. Folks will have to do better, as they say.

    Again, please show mathematically how motion is described given time exists but does not pass by. If math cannot describe existence, then what else?

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    Quote Originally Posted by Farsight View Post
    And those different times are measured on clocks. Which feature cogs moving in some regular cyclical fashion. Or crystals vibrating in some regular cyclical fashion. Or microwaves generated in some regular cyclical fashion. In the end you test your claims about motion using "different times" that are calibrated against the motion of light. It always comes back to motion.
    Then you have a number of tasks to do.

    1) Show that everything is light. (A fairly difficult task, since contemporary physics rejects this claim.)
    2) Show us a definition of motion that does not use time, since you are claiming that time is secondary. (A task that you seem to have dodged for years.)
    3) Show us that Einstein knew these two things specifically and in the same way. (You are claiming that you are not presenting your theory, a claim that seems demonstrably false for over a decade.)

    Motion is where some thing gradually changes its location or orientation in space.
    You have used the language of time there. So it seems that you do believe in time after all. It seems that you believe in one universal standard for space and time. It is interesting that not-your-theory seems to contradict so completely with general relativity. However, since you haven't got a physics theory yet, contradictions or not are irrelevant.
    And this thing might be an electron, which was made in pair production. Starting with a photon. Which we could have converted into the motion of electrons via repeated Compton scatters. So in a way, an electron is made of motion. And so are you.
    Can you turn this bad poetry into something that we can measure? If we are to do physics, we need to be able to do precise measurements. So far, you have given us religious sounding claims without any way to use them in physics. Let's see you defend your claims with physics, not evangelism.
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    Quote Originally Posted by SinceYouAsked View Post
    Link -> Eternalism (philosophy of time) - Wikipedia, the free encyclopedia. See the above hyperlink reference.
    I know about Eternalism. I'm the Time Explained guy. The opposing view is Presentism.

    Quote Originally Posted by SinceYouAsked View Post
    You say you don't need any alternate theories of spacetime, but yet you do not know of eternalism. Worldlines are static in 4-space, but our progression along them is not. Repeating that worldlines are static, will never change that.
    Worldlines don't actually exist. They're abstract things in a static mathematical model. You don't actually progress along a worldline. The map is not the territory. You're moving, your heart is beating, your blood is flowing, the wind is blowing, trucks move, the Earth turns, light moves, everything moves. We live in a world of space and motion, not in a world of lightcones and worldlines.

    Quote Originally Posted by SinceYouAsked View Post
    OK, so the measure of time may be defined as the relative comparison of motions in space, one motion being hopefully of uniform cyclic nature. However, what allows anything "to move" in the very first place? The answer ... no one has any idea how to explain that without the use of TIME. Given such, what is the standard reply? "Well, motion simply exists, and that's that as they say". Not good enough. Folks will have to do better, as they say.
    It will have to do. Waggle your hands. That's motion. It isn't there because of something called time that you can neither see nor demonstrate. It's there because that's how the world is.

    Quote Originally Posted by SinceYouAsked View Post
    Again, please show mathematically how motion is described given time exists but does not pass by. If math cannot describe existence, then what else?
    Again, I can't show you mathematically. Nobody can show you mathematically that time passes, and nobody can show you mathematically that it doesn't. Mathematics just can't show you either way. But empirical evidence can. Go and find a mechanical clock and open it up. See those cogs whirring? That's motion. The clock is clocking it up, and the little hand and the big hand are moving. It isn't measuring the passage of time. There is no time flowing through that clock. The clock isn't some kind of cosmic gas meter measuring time passing through it. See? See what's there, and do not let the things you cannot see stop you seeing what's there.
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    Quote Originally Posted by PhysBang View Post
    Then you have a number of tasks to do.

    1) Show that everything is light. (A fairly difficult task, since contemporary physics rejects this claim.)
    I can't. Neutrinos aren't light. A black hole isn't light. Dark energy isn't light.

    Quote Originally Posted by PhysBang View Post
    2) Show us a definition of motion that does not use time, since you are claiming that time is secondary. (A task that you seem to have dodged for years.)
    I just gave you one. A gradual change in position or orientation.

    Quote Originally Posted by PhysBang View Post
    3) Show us that Einstein knew these two things specifically and in the same way. (You are claiming that you are not presenting your theory, a claim that seems demonstrably false for over a decade.)
    Everything isn't light. But see A World Without Time: The Forgotten Legacy of Gödel and Einstein for what Einstein knew about time.

    Quote Originally Posted by PhysBang View Post
    You have used the language of time there. So it seems that you do believe in time after all.
    Huh? I've always said time exists. But it isn't something you can move through, because it's a cumulative measure of motion. Go and look at what a clock actually does.

    Quote Originally Posted by PhysBang View Post
    It seems that you believe in one universal standard for space and time.
    Huh? We use the motion of light to define our metre and our second.

    Quote Originally Posted by PhysBang View Post
    It is interesting that not-your-theory seems to contradict so completely with general relativity. However, since you haven't got a physics theory yet, contradictions or not are irrelevant.
    It isn't my theory. I didn't invent presentism. It wasn't me walking home in Princeton with Gödel talking about the nature of time.

    Quote Originally Posted by PhysBang View Post
    Can you turn this bad poetry into something that we can measure? If we are to do physics, we need to be able to do precise measurements. So far, you have given us religious sounding claims without any way to use them in physics. Let's see you defend your claims with physics, not evangelism.
    Religious? Evangelism? Bad poetry? What are you on about? Are you so bereft of counterargument that you have to make specious claims?
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    Quote Originally Posted by Farsight View Post
    It isn't true. You don't just perceive incoming light. Hold your hands up, palms pressed together. There is no space between them, and you can feel your palms touching. Now repeat, but this time with your hands a yard apart. This time there is a space between them. You can feel the difference, and you can see the difference. It is empirical.
    So rainbows and clouds are solid objects? That's because they look like solid objects when you look at them.

    I wish to note that one does not directly perceive space, and that one does not even directly perceive 3D positions. Our spatial senses are either of angles and the like (proprioception), 2D positions (skin senses), or directions (vision).

    (sense of time)
    Quote Originally Posted by Farsight
    That's just a figure of speech. You don't have a sense of time. You have a sense of smell, you have vision, hearing, touch, and taste. You have five senses. You do not have a sixth sense that is a sense of time.
    We have more than the traditional five senses. I'll quote the abstract of the article that I linked to:
    The aim of the present review article is to guide the reader through portions of the human time perception, or temporal processing, literature. After distinguishing the main contemporary issues related to time perception, the article focuses on the main findings and explanations that are available in the literature on explicit judgments about temporal intervals. The review emphasizes studies that are concerned with the processing of intervals lasting a few milliseconds to several seconds and covers studies issuing from either a behavioral or a neuroscience approach. It also discusses the question of whether there is an internal clock (pacemaker counter or oscillator device) that is dedicated to temporal processing and reports the main hypotheses regarding the involvement of biological structures in time perception.
    Clocks mark out time with their actions, and we seem to have some internal way of marking out time.

    Quote Originally Posted by lpetrich
    I studied GR long ago, and my knowledge of it has stayed with me. Matter-energy makes space-time curve; that's the meaning of (Einstein curvature tensor) = (gravitational constant) * (energy-momentum tensor) The Einstein curvature tensor is derived from the more-general Riemann one, and that in turn is derived from the space-time metric.
    Quote Originally Posted by Farsight
    Do appreciate that some things that you take for granted are not correct.
    I was stating in words Equation 96, page 89, The Meaning of Relativity by Albert Einstein. Here is what he had stated:


    R = Riemann curvature tensor
    g = metric
    κ = gravitational constant: 8π*G(Newtonian)
    T = energy-momentum tensor
    μ,ν = space-time indices

    I'm sure that I might be told that it's a math dump. But it's Albert Einstein's math, math that I had quoted from the Einsteinian Scriptures. So if one denies that math, one denies Einstein.
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    Quote Originally Posted by Farsight View Post
    I can't. Neutrinos aren't light. A black hole isn't light. Dark energy isn't light.
    OK, so then we have to explain why all these things obey the same changes of time. If we just accept that there is time in spacetime, then we can explain how the timing of all things work out fine. Where is your alternative and can it do as well as contemporary theories?
    I just gave you one. A gradual change in position or orientation.
    "gradual" is a term that uses time. So, please, try again; this time use something that we can attach numbers to so that we could conceivably use it in physics.
    Everything isn't light. But see A World Without Time: The Forgotten Legacy of Gödel and Einstein for what Einstein knew about time.
    It's good that you know how to produce a hyperlink, but that isn't evidence. There seems to be nothing in that book that matches your claims.
    Huh? I've always said time exists. But it isn't something you can move through, because it's a cumulative measure of motion. Go and look at what a clock actually does.
    You need to translate this statement into physics.
    Huh? We use the motion of light to define our metre and our second.
    You are still claiming that there is a secret time against which we could compare these. Regardless, until you have physics claims, you still only have (bad) poetry.
    It isn't my theory. I didn't invent presentism. It wasn't me walking home in Princeton with Gödel talking about the nature of time.
    You are not peddling presentism, you appear to be peddling a vague religion of an Einstein-like figure. I say Einstein-like, because you are adopting an absolute hidden reference frame, something that Einstein does not appear to have done. If you would like to talk physics, please show us some numbers.
    Religious? Evangelism? Bad poetry? What are you on about? Are you so bereft of counterargument that you have to make specious claims?
    I am merely pointing out that you have yet to show us anything that we could use to do physics. Until you do so, your claims cannot be considered physics. The counter-arguments to your claims is this: your claims cannot be compared in detail with any theories of physics or even any physical events, your claims cannot be considered physics. All you have are qualitative claims of clocks going slower, whereas contemporary theories (even rivals to GR) have detailed descriptions and predictions about measurable changes to not only clocks, but every physical process.

    For example, you evangelize against dark matter, claiming that all physicists and astronomers are wrong in their calculations of galaxy rotation curves. You evangelize to others about the great Einstein, who knew the real answer, inhomogeneous space! You claim (without evidence) that all physicists and astronomers use the heretical "raisin in the cake" analogy in their calculations of galaxy rotation curves, forgetting the holy words of Einstein that "gravity shall act as any other energy"! Yet you have never, not one single time, demonstrated where a physicist or astronomer uses this analogy in their calculations. You have never not one single time, demonstrated how to use the holy words of Einstein in a calculation of galaxy rotation curves.

    It is not enough to cite the holy words of Einstein. We have to look at how the physics actually works in applications. Because Einstein was not a master of all knowledge with some divine gift: we believe in his physics, when we do, because of the measurement evidence.

    Einstein made some major mistakes: Controversy Einstein's Endorsement of Psychic Upton Sinclair Defends | New Republic
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    Quote Originally Posted by lpetrich View Post
    So rainbows and clouds are solid objects?
    No. Where do that come from? It isn't relevant. And nor is anything else you've said. Are you trying to derail the thread?

    Quote Originally Posted by PhysBang
    ...For example, you evangelize against dark matter, claiming that all physicists and astronomers are wrong in their calculations of galaxy rotation curves. You evangelize to others about the great Einstein, who knew the real answer, inhomogeneous space! You claim (without evidence) that all physicists and astronomers use the heretical "raisin in the cake" analogy in their calculations of galaxy rotation curves, forgetting the holy words of Einstein that "gravity shall act as any other energy"! Yet you have never, not one single time, demonstrated where a physicist or astronomer uses this analogy in their calculations. You have never not one single time, demonstrated how to use the holy words of Einstein in a calculation of galaxy rotation curves. It is not enough to cite the holy words of Einstein...
    You clearly are.

    This thread is about time travel and the nature of time. Please try to stay on topic.
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    Quote Originally Posted by Farsight View Post
    This thread is about time travel and the nature of time. Please try to stay on topic.
    You mean, stay on topic and not avoid the inconvenient questions?

    Quote Originally Posted by Farsight View Post
    I can't. Neutrinos aren't light. A black hole isn't light. Dark energy isn't light.
    OK, so then we have to explain why all these things obey the same changes of time. If we just accept that there is time in spacetime, then we can explain how the timing of all things work out fine. Where is your alternative and can it do as well as contemporary theories?
    I just gave you one. A gradual change in position or orientation.
    "gradual" is a term that uses time. So, please, try again; this time use something that we can attach numbers to so that we could conceivably use it in physics.
    Everything isn't light. But see A World Without Time: The Forgotten Legacy of Gödel and Einstein for what Einstein knew about time.
    It's good that you know how to produce a hyperlink, but that isn't evidence. There seems to be nothing in that book that matches your claims.
    Huh? I've always said time exists. But it isn't something you can move through, because it's a cumulative measure of motion. Go and look at what a clock actually does.
    You need to translate this statement into physics.
    Huh? We use the motion of light to define our metre and our second.
    You are still claiming that there is a secret time against which we could compare these. Regardless, until you have physics claims, you still only have (bad) poetry.
    It isn't my theory. I didn't invent presentism. It wasn't me walking home in Princeton with Gödel talking about the nature of time.
    You are not peddling presentism, you appear to be peddling a vague religion of an Einstein-like figure. I say Einstein-like, because you are adopting an absolute hidden reference frame, something that Einstein does not appear to have done. If you would like to talk physics, please show us some numbers.
    Religious? Evangelism? Bad poetry? What are you on about? Are you so bereft of counterargument that you have to make specious claims?
    I am merely pointing out that you have yet to show us anything that we could use to do physics. Until you do so, your claims cannot be considered physics. The counter-arguments to your claims is this: your claims cannot be compared in detail with any theories of physics or even any physical events, your claims cannot be considered physics. All you have are qualitative claims of clocks going slower, whereas contemporary theories (even rivals to GR) have detailed descriptions and predictions about measurable changes to not only clocks, but every physical process.

    For example, you evangelize against dark matter, claiming that all physicists and astronomers are wrong in their calculations of galaxy rotation curves. You evangelize to others about the great Einstein, who knew the real answer, inhomogeneous space! You claim (without evidence) that all physicists and astronomers use the heretical "raisin in the cake" analogy in their calculations of galaxy rotation curves, forgetting the holy words of Einstein that "gravity shall act as any other energy"! Yet you have never, not one single time, demonstrated where a physicist or astronomer uses this analogy in their calculations. You have never not one single time, demonstrated how to use the holy words of Einstein in a calculation of galaxy rotation curves.

    It is not enough to cite the holy words of Einstein. We have to look at how the physics actually works in applications. Because Einstein was not a master of all knowledge with some divine gift: we believe in his physics, when we do, because of the measurement evidence.

    Einstein made some major mistakes: Controversy Einstein's Endorsement of Psychic Upton Sinclair Defends | New Republic
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    All: PhysBang's post is one long diatribe. IMHO he has no sincere desire to discuss the matter in hand, and is deliberately trying to derail the thread with accusations and argument that other posters will find off-putting. So I've put him on ignore. I suggest you do the same.
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    I agree: if you want the sort of physics that Farsight offers, put me on ignore.
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    Quote Originally Posted by Farsight View Post
    All: PhysBang's post is one long diatribe. IMHO he has no sincere desire to discuss the matter in hand, and is deliberately trying to derail the thread with accusations and argument that other posters will find off-putting. So I've put him on ignore. I suggest you do the same.
    IMNHO, you are using the forum to present monologues only. Any questions directed at getting you to be quantitative (i.e., do real physics) are ignored by you. PhysBang is trying to engage you in a real conversation. You only dodge.

    One wonders why.

    Then after wondering, one draws inferences. These are not favourable to your ideas.
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    All: PhysBang's post is one long diatribe. IMHO he has no sincere desire to discuss the matter in hand, and is deliberately trying to derail the thread with accusations and argument that other posters will find off-putting. So I've put him on ignore. I suggest you do the same
    Warning: Hello Farsight. Let me introduce myself. I am the new Sheriff in town. I don't know you. I don't know how accurate your assessment of PhysBang's post is. I don't know PhysBang.

    I do know Markus posted a very clear admonition the other day requesting and demanding an improvement in posting behaviour. Your post is an excellent example of what is not acceptable. I do not want to see a post from you that includes speculation on the motives, mindset or meanderings of other members. Ever. This is my first day on the job so I am going to be generous and not ban you for the post - perhaps you missed Markus's appeal. Find it now, read it, understand it, follow his request, or find the way to the exit.

    Do not, under any circumstances, comment on this post within this thread. If you disagree with any part of it, or wish to make some comment you may pm me, or another moderator or admin, or you may report the post. That goes for everyone else. Thank you.
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    Quote Originally Posted by Farsight View Post
    I know about Eternalism. I'm the Time Explained guy. The opposing view is Presentism.
    OK, so 2 observers (A & B) move relatively and are momentarily co-located on flyby. They both then consider a remotely located observer (C) who moves wrt both of them. A says C's clock then reads 10am. B says C's clock then reads 2pm. The LTs confirm this, and that they are each correct even though they disagree on C's clock reading. Eternalism says that C really does exist at 10am per A, and really does exist at 2pm per B, when A & B are momentarily co-located. All are correct.

    Now then, how do you explain this using the PRESENTIST philosophy of time, in a way that LT solns are real vs illusionary effect?

    Quote Originally Posted by Farsight View Post
    Worldlines don't actually exist. They're abstract things in a static mathematical model. You don't actually progress along a worldline. The map is not the territory. You're moving, your heart is beating, your blood is flowing, the wind is blowing, trucks move, the Earth turns, light moves, everything moves. We live in a world of space and motion, not in a world of lightcones and worldlines.
    But the eternalist philosophy supports all your highlighted points here, as you move along your own static worldline as time progresses.

    Quote Originally Posted by Farsight View Post
    It will have to do. Waggle your hands. That's motion. It isn't there because of something called time that you can neither see nor demonstrate. It's there because that's how the world is.
    Again, show the mathematical model that explains motion in the absence of time. If you cannot, please adequately explain why you (or anyone else) cannot show the math.

    Quote Originally Posted by Farsight View Post
    Again, I can't show you mathematically. Nobody can show you mathematically that time passes, and nobody can show you mathematically that it doesn't. Mathematics just can't show you either way. But empirical evidence can. Go and find a mechanical clock and open it up. See those cogs whirring? That's motion. The clock is clocking it up, and the little hand and the big hand are moving. It isn't measuring the passage of time. There is no time flowing through that clock. The clock isn't some kind of cosmic gas meter measuring time passing through it. See? See what's there, and do not let the things you cannot see stop you seeing what's there.
    For a traversal of 1 ls at v=0.866c ls/s, the time that passes is ... t = x/v = 1/0.866 = 1.154s. If you are a spectator on the side of the race track, then you will experience (ie feel) that passage of time, and your clock validates the traversal and experience. See how easy that was.

    Don't get me wrong Farsight, it's not as though I don't recognize your points. Many today argue your same points, and there exist fairly logical arguments that support them. However, one will have to do better than to say ... "motion just exists, time is not required, and that's that". At the very least, one must explain why time (used in calculations) "holds an equal footing with space as a dimension", given time is not a real or fundamental dimension, while space is.

    Now far as time travel goes, the PRESENTIST philosophy cannot support it, because only a present ever changing moment ever exists in the space continuum. Per the ETERNALISM philosophy, all moments in time really do exist within the continuum, on equal footing. So per GR, all that's required is that the spacetime medium at 2 remotely separated locations connect via a major curvature of the medium. Then, those 2 distinct moments in (space)time connect, since they coexist in the very first place. No one knows of it's possible, but theory allows for the possibility given the required circumstances exist.

    Thank You,
    SinceYouAsked
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    Quote Originally Posted by SinceYouAsked View Post
    OK, so 2 observers (A & B) move relatively and are momentarily co-located on flyby. They both then consider a remotely located observer (C) who moves wrt both of them. A says C's clock then reads 10am. B says C's clock then reads 2pm. The LTs confirm this, and that they are each correct even though they disagree on C's clock reading. Eternalism says that C really does exist at 10am per A, and really does exist at 2pm per B, when A & B are momentarily co-located. All are correct. Now then, how do you explain this using the PRESENTIST philosophy of time, in a way that LT solns are real vs illusionary effect?
    I don't think your scenario is correct. Light is moving back and forth inside C's clock, and light moves from C's clock to the A&B point. A and B both see this light, so they agree on the clock reading.

    Quote Originally Posted by SinceYouAsked View Post
    But the eternalist philosophy supports all your highlighted points here, as you move along your own static worldline as time progresses.
    It doesn't. Spacetime is static. There's no motion in it. Your worldline is an abstract thing, you don't move along it. Your heart beats, the Earth turns, etc. But all this motion is through space, not spacetime. How can I get this across? Imagine I throw a red ball across the room and you film it with an old-style movie camera. Then you develop the film and cut it into individual frames. Then you form them into a block. There's a red streak in this block. That's like the worldline of the ball. And it depicts the ball at all times. The ball isn't moving up through the block.

    Quote Originally Posted by SinceYouAsked View Post
    Again, show the mathematical model that explains motion in the absence of time. If you cannot, please adequately explain why you (or anyone else) cannot show the math.
    I can't show a mathematical model that explains motion in the absence of time. There is no such mathematical model. Mathematics doesn't explain this sort of thing. I can show you motion, and demonstrate that it's empirical. But I can't show you time passing. Nobody can. And nor can I show you a mathematical model that explains what we can see in the absence of something we can't. All I can do is point to the existing mathematical model, remind you that I said time exists, and then show you inside a clock, where you see cogs moving rather than time flowing. Then I can tell you that time t is a cumulative measure of the motion of those cogs rather than a cumulative measure of something flowing or passing through the clock.

    Quote Originally Posted by SinceYouAsked View Post
    For a traversal of 1 ls at v=0.866c ls/s, the time that passes is ... t = x/v = 1/0.866 = 1.154s. If you are a spectator on the side of the race track, then you will experience (ie feel) that passage of time, and your clock validates the traversal and experience. See how easy that was.
    There's no issue with time dilation. But look at your language. You don't actually "feel that passage of time". That's just a figure of speech. Time isn't literally passing, instead things like light and hearts are moving. You experience less local motion when you go fast because the total motion is limited to c.

    Quote Originally Posted by SinceYouAsked View Post
    Don't get me wrong Farsight, it's not as though I don't recognize your points. Many today argue your same points, and there exist fairly logical arguments that support them. However, one will have to do better than to say ... "motion just exists, time is not required, and that's that". At the very least, one must explain why time (used in calculations) "holds an equal footing with space as a dimension", given time is not a real or fundamental dimension, while space is.
    It doesn't hold an equal footing. There's a minus sign on the t term in the spacetime interval expression below:



    And nobody is saying time doesn't exist or isn't required. Just that time isn't on an equal footing with the space dimensions. Because it's a dimension of measure that is derived from motion through space. You can't move through it like you can move through space.

    Quote Originally Posted by SinceYouAsked View Post
    Now far as time travel goes, the PRESENTIST philosophy cannot support it, because only a present ever changing moment ever exists in the space continuum. Per the ETERNALISM philosophy, all moments in time really do exist within the continuum, on equal footing. So per GR, all that's required is that the spacetime medium at 2 remotely separated locations connect via a major curvature of the medium. Then, those 2 distinct moments in (space)time connect, since they coexist in the very first place. No one knows of it's possible, but theory allows for the possibility given the required circumstances exist.
    What I'm saying is that a misunderstanding of the theory says it's possible, when it isn't. And a part of that misunderstanding is a confusion between space and spacetime. The latter is merely an abstract mathematical model. This model works. But spacetime is not what space is. You can move through space, but spacetime is static. It's like the frames of the movie, all stacked up with a red streak in it. The map is not the territory.
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    Quote Originally Posted by Farsight View Post
    I don't think your scenario is correct. Light is moving back and forth inside C's clock, and light moves from C's clock to the A&B point. A and B both see this light, so they agree on the clock reading.
    You are being vague, but what you are really saying is that there is one time and space and that all the effects of special relativity are an illusion caused by the changes to the speed of light relative the to medium that is absolutely still.

    It doesn't. Spacetime is static.
    What definition of "static" do you mean? There are many vague, non-physics meaning and there are a couple of physics meanings. There are many solutions to the Einstein Field Equation that are considered non-static spacetimes, so your words are confusing.
    There's no motion in it. Your worldline is an abstract thing, you don't move along it. Your heart beats, the Earth turns, etc. But all this motion is through space, not spacetime. How can I get this across? Imagine I throw a red ball across the room and you film it with an old-style movie camera. Then you develop the film and cut it into individual frames. Then you form them into a block. There's a red streak in this block. That's like the worldline of the ball. And it depicts the ball at all times. The ball isn't moving up through the block.
    This all seems to be a basic mistake about the nature of spacetime. It is one thing to describe a series of events after they have occurred (or to predict the series as it should go before after they have occurred), it is another to describe a state of affairs at a single moment. General relativity restricts descriptions of affairs at a moment to local descriptions, i.e., descriptions of infinitesimal distances. One can also describe a pseudo-moment of a spacelike-hypersurface that is a decomposition from the spacetime structure. In doing so, one is choosing a system of coordinates in order to decompose the full four dimensional relations of spacetime into three of space and one of time and describing things like that. To do so for one's current state of affairs, "on the fly", so to speak, requires a fair amount of prediction about the state of affairs at any finite distance.

    However, even if one cannot fully describe to oneself the state of affairs all around oneself, that does not change the physics that relates the events that one lives through to the events around one. One can be in a constant state of becoming, of actually experiencing new moments, while at the same time being in one's own local area of becoming cut off from other moments of becoming until they interact with one in the future through the causal structure laid out by general relativity, just as one's current self is being influenced by moments from one's past light cone.

    Facts of the matter about space and time are always put in eternal language, but that does not make the events eternal. Just as the causal structure of Newtonian physics, with its infinite now and no boundary on the speed of cause-and-effect, allows for the now at every place to be developing, so too the causal structure of GR allows for the now of every place to be developing; GR just has different rules for how the events at any place can interact with other events. GR is specifically designed so as to be a patchwork of infinitesimal regions propagating their influence outward, so it certainly doesn't seem to contradict the fundamentals of the theory to allow that every moment experienced is a new, unique moment dependent on influences from without and sending influences out into the world.

    I can't show a mathematical model that explains motion in the absence of time. There is no such mathematical model.
    And this is why we should be suspicious of the idea as physics.
    Mathematics doesn't explain this sort of thing. I can show you motion, and demonstrate that it's empirical. But I can't show you time passing.
    The sad thing is that this seems to be entirely backwards. You can't show someone time passing because it is something that every person experiences for themselves. Everyone who has seriously attempted the physics of motion for the last 500 years has realized that to explain it, one has to be very careful about thinking about space and time and how these are fundamental elements of motion. Since Newton, with more and more clarity, we have realized that whether or not something is moving is not something that can be demonstrated at all, it is a choice. There are constraints on physics that go along with these choices, but it is a choice nonetheless.
    There's no issue with time dilation. But look at your language. You don't actually "feel that passage of time". That's just a figure of speech. Time isn't literally passing, instead things like light and hearts are moving. You experience less local motion when you go fast because the total motion is limited to c.
    Again, to be clear because Farsight is being vague, Farsight is here claiming that there is an absolute reference frame against which motion is "really" compared, even though we cannot use this reference frame and there is no physical sign of its presence.
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    Quote Originally Posted by PhysBang View Post
    You are being vague, but what you are really saying is that there is one time and space and that all the effects of special relativity are an illusion caused by the changes to the speed of light relative the to medium that is absolutely still.
    No, I'm not saying that. There are no changes to the speed of light in the scenario described by SinceYouAsked.

    Quote Originally Posted by PhysBang View Post
    What definition of "static" do you mean? There are many vague, non-physics meaning and there are a couple of physics meanings. There are many solutions to the Einstein Field Equation that are considered non-static spacetimes, so your words are confusing.
    I mean static is in there is no motion in this arena. Because spacetime is a block-universe model that depicts all times at once. It's like the block of movie frames with a red streak running through it.

    Quote Originally Posted by PhysBang View Post
    This all seems to be a basic mistake about the nature of spacetime...
    The basic mistake recurs continually, wherein people think spacetime is space.

    Quote Originally Posted by PhysBang View Post
    And this is why we should be suspicious of the idea as physics.
    I can't show a mathematical model that explains motion in the absence of time, and nor can I show a mathematical model that explains motion in the presence of time. Mathematics just doesn't explain it.

    Quote Originally Posted by PhysBang View Post
    The sad thing is that this seems to be entirely backwards. You can't show someone time passing because it is something that every person experiences for themselves.
    No it isn't. I can hold my hands up a yard apart and I can show you space. I can waggle my hands and I can show you motion. But I can't show you time passing. Nobody can. Because time doesn't pass. Buses pass. Footballers pass. And light moves, hearts beat, and planets turn. But "time passing" is just a figure of speech.

    Quote Originally Posted by PhysBang View Post
    Again, to be clear because Farsight is being vague, Farsight is here claiming that there is an absolute reference frame against which motion is "really" compared, even though we cannot use this reference frame and there is no physical sign of its presence.
    The CMBR rest frame provides a baseline for gauging motion through the universe. It isn't an absolute reference frame in the relativity sense, but the universe is an absolute as it gets.
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    Quote Originally Posted by Farsight View Post
    I mean static is in there is no motion in this arena. Because spacetime is a block-universe model that depicts all times at once. It's like the block of movie frames with a red streak running through it.
    That might make sense if we say that every description of motion is a block-universe model. However, it would be foolish to do so. It is also possible to use spacetime to describe the state of affairs of a system on one spacelike-hypersurface. Using your reasoning, since this is possible, spacetime must be only compatible with presentism!

    Spacetime is merely the prerequisite to describing motion. Before contemporary relativity theory, the intimate connection between spacial geometry and temporal geometry was not realized. But it is clearly possible to accept a metaphysical position on time where each object is becoming rather than eternal and be compatible with GR. There are even papers showing the compatibility of such a position with GR and quantum theory.
    The basic mistake recurs continually, wherein people think spacetime is space.
    You have cherry-picked my statement: you only addressed that I wrote the word "mistake" without actually addressing any of the content that the mistake was about. This is a bad habit.
    I can't show a mathematical model that explains motion in the absence of time, and nor can I show a mathematical model that explains motion in the presence of time. Mathematics just doesn't explain it.
    OK, but why do you completely ignore the actual contents of the relevant theory. That content is partly mathematical in nature because GR is explicitly about certain mathematical relationships between space, time and energy. If you ignore this content, then you can't be said to be saying anything about the theory.
    No it isn't.
    Well, you could take a look at the citation provided by lpetrich discussing the literature on the sense of time that people seem to have. I'm not sure why you write off the entire field of psychology and the empirical research done on human (and animal) time sense.
    I can hold my hands up a yard apart and I can show you space.
    How does this show space? If I cannot conceive of space before you hold your hands apart, how can I conceive of it afterwards?

    If you can use the span of your hands as some sort of accurate measuring device, I might use this to deduce something about objects in space or perhaps about space itself. You have yet to demonstrate how simply showing your hands can teach someone that space exists.
    I can waggle my hands and I can show you motion.
    How does that show motion? I could tell that things are moving relative to one another because they change over time. Do you have some other sense that can distinguish motion without experiencing change over time? If so, have you been studied by psychologists?

    Even if you have such a sense, what use is this to physics, where motion is measured through changes over time? Can you show us how to do physics without this?
    But I can't show you time passing. Nobody can. Because time doesn't pass. Buses pass. Footballers pass. And light moves, hearts beat, and planets turn. But "time passing" is just a figure of speech.
    You seem enamored with your textual analysis of the English language, but less so in physical science or psychological science. I concede that nobody can show me time passing, since I already have a sense of time passing prior to anything being shown to me. (I suspect that you will attempt to cherry-pick that sentence later, but if so, that will be your problem.)
    The CMBR rest frame provides a baseline for gauging motion through the universe. It isn't an absolute reference frame in the relativity sense, but the universe is an absolute as it gets.
    Yes, there is a rough rest frame for the collection of matter that we can see. In the sense of special relativity, not only is this not an absolute reference frame, but it doesn't matter for the motion or behavior of any object. You, on the other hand, with your talk of light slowing down, are telling us that there is some frame that matters, that light is really moving relative to some reference and that corrections within this reference are giving us the illusion of Lorentz invariance and the symmetries of GR.

    I notice that none of the above seems to address the argument that GR is completely compatible with presentism, just with a local presentism, save for the claim that if we describe things using spacetime we might be tempted to describe things over a range of times. This argument seems to be specious since every kind of physics allows us to describe physical systems over a range of times. Unless this aspect of physics implies that the physical universe is simply a block universe, it is unconvincing that the possibility of one type of description necessitates that description is the only metaphysically correct one.
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    Quote Originally Posted by SYA View Post
    OK, so 2 observers (A & B) move relatively and are momentarily co-located on flyby. They both then consider a remotely located observer (C) who moves wrt both of them. A says C's clock then reads 10am. B says C's clock then reads 2pm. The LTs confirm this, and that they are each correct even though they disagree on C's clock reading. Eternalism says that C really does exist at 10am per A, and really does exist at 2pm per B, when A & B are momentarily co-located. All are correct. Now then, how do you explain this using the PRESENTIST philosophy of time, in a way that LT solns are real vs illusionary effect?

    Quote Originally Posted by Farsight View Post
    I don't think your scenario is correct. Light is moving back and forth inside C's clock, and light moves from C's clock to the A&B point. A and B both see this light, so they agree on the clock reading.
    You are mixing up the current time of a remotely located clock, with its time readout per the light-image received at your own location in the present moment. I was of course discussing the former ...

    When A & B consider the current time readout of the remotely located clock C, they do not assume that "it's current time reading" is what photons at their own eyes presently reveal upon receipt. A (and B) must subtract out the light travel time from the C time reading brought to their eyes by the light. Per the LTs, they each measure the distance to the C clock differently ... and since light speed is invariant at c, they measure the traversal time of photons "from the clock to their eyes" differently. That said, they must each deduce "a different current time readout for clock A", and similarly for clock B. Relativity requires it. Therefore, A & B must deduce a different time readout for the remotely located C clock upon the A/B flyby event. OK, so knowing that now, I ask again ...

    A says C's clock then reads 10am. B says C's clock then reads 2pm. The LTs confirm this, and that they are each correct even though they disagree on the remotely located current clock reading of C. ETERNALISM says that C really does exist at 10am per A, and really does exist at 2pm per B, when A & B are momentarily co-located. All are correct. Now then, how do you explain this using the PRESENTIST philosophy of time, in a way that LT solns are real vs illusionary effect?

    Thank You,
    SinceYouAsked
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    Quote Originally Posted by SinceYouAsked View Post
    When A & B consider the current time readout of the remotely located clock C, they do not assume that "it's current time reading" is what photons at their own eyes presently reveal upon receipt. A (and B) must subtract out the light travel time from the C time reading brought to their eyes by the light. Per the LTs, they each measure the distance to the C clock differently ... and since light speed is invariant at c, they measure the traversal time of photons "from the clock to their eyes" differently. That said, they must each deduce "a different current time readout for clock A", and similarly for clock B. Relativity requires it. Therefore, A & B must deduce a different time readout for the remotely located C clock upon the A/B flyby event. OK, so knowing that now, I ask again ...

    A says C's clock then reads 10am. B says C's clock then reads 2pm. The LTs confirm this, and that they are each correct even though they disagree on the remotely located current clock reading of C. ETERNALISM says that C really does exist at 10am per A, and really does exist at 2pm per B, when A & B are momentarily co-located. All are correct. Now then, how do you explain this using the PRESENTIST philosophy of time, in a way that LT solns are real vs illusionary effect?
    A relativistic presentist does not grant that things that are spacelike separated from an event need to be real to that event in some sense other than outlined in their pre-estbalished causal relationship.

    Let's stick to SR alone. In the case of the three people with clocks, we can safely assume that, at the clock times identified for each person, they have past light cones that partially overlap. They can thus use any system of coordinates in which Newtonian mechanics holds to a good approximation in order to calculate the position of these others and when in their own time they might again interact with that person. But these are predictions that the people can make, not facts of the matter. They may later verify what the facts of the matter were, but this verification involves the nature of their shared past light cones, and thus a certain fixed causal structure between events. SR makes demands with regards to things at a distance insofar as they may send a signal or other causal influence to an event; it does not demand anything else.

    A and B can make the claim of what C's clock read "currently" using an infinite number of different determinations of "currently"; SR allows them this freedom and demands that the answers coordinate if A and B are using the same data. It does not demand that, at their present (or at any event), A & B have absolutely correct knowledge about a distant object or event. After the fact, when the past is the past, then everyone has the same set of data about relative events and their relationships and everything matches nicely.

    One way to interpret presentism is to say that for each of the people at those clock times, all that can be said to be mutually real for them is the overlapping past light cones. One can make predictions based on the past light cone, imperfect predictions, but that is all. Things do not become real for an entity until they enter the past light cone of an entity.

    Another way to interpret presentism (not necessarily mutually exclusive with the above) is to consider the present to be the sum total of the presents of all existing entities. These presents interact only through the causal structure of SR. Regardless of what might want to assign as future or past in a system of coordinates, all systems of coordinates agree on cause and effect. So one distinguishes the present as the sum total of all things being caused, the absolute past the events that have been caused and the absolute future the things that (in principle) will be caused. For any being, there will be a large class of events for which they cannot determine the category, but this would be the case for all but the omniscient observer in a Newtonian universe, too.

    I believe that this last interpretation involves a claim that is either frame dependent (the sum total of all presents given some chosen system of coordinates) or that is not, but that cannot be identified with a physical description (i.e., we can talk of the sum total of all entities that ever were and of their presents, but we cannot identify any spacelike-hypersurface that is the particular one that contains all the presents, we cannot identify, even in principle, all the entities that, like us, are currently in the present). I could be wrong on this; I haven't looked at the literature in some time.
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    Quote Originally Posted by PhysBang View Post
    A relativistic presentist does not grant that things that are spacelike separated from an event need to be real to that event in some sense other than outlined in their pre-estbalished causal relationship.
    If not real, then only a mathematical artifact. A philosophy built upon that, is a lesser philosophy IMO, given another philosophy defines all measurements and predictions as real.

    Quote Originally Posted by PhysBang View Post
    Let's stick to SR alone. In the case of the three people with clocks, we can safely assume that, at the clock times identified for each person, they have past light cones that partially overlap. They can thus use any system of coordinates in which Newtonian mechanics holds to a good approximation in order to calculate the position of these others and when in their own time they might again interact with that person. But these are predictions that the people can make, not facts of the matter.
    If the predictions do not match reality, then the predictions are not a good model of reality. If the predictions do match reality, then the predictions are facts of reality.

    Quote Originally Posted by PhysBang View Post
    They may later verify what the facts of the matter were, but this verification involves the nature of their shared past light cones, and thus a certain fixed causal structure between events. SR makes demands with regards to things at a distance insofar as they may send a signal or other causal influence to an event; it does not demand anything else.
    Well, SR assumes the Einstein/Poincare method of time synchronization for inertial bodies ... τ1 = ½(τ0+ τ2). Since SR is an accepted theory in physics, we assume that method is correct, or at least the most likely correct one, and so we use it and assume it correct. If the defined spacetime interval is not timelike, then no cause and effect takes place between the 2 POVs. My scenario here was a timelike interval.

    Quote Originally Posted by PhysBang View Post
    A and B can make the claim of what C's clock read "currently" using an infinite number of different determinations of "currently"; SR allows them this freedom and demands that the answers coordinate if A and B are using the same data. It does not demand that, at their present (or at any event), A & B have absolutely correct knowledge about a distant object or event. After the fact, when the past is the past, then everyone has the same set of data about relative events and their relationships and everything matches nicely.
    SR requires that A & B define "currently" (across the all of space) the same as all inertial observers must, as consistent with the Einstein clock sync method. It's specifically defined. Use any other convention of simultaneity, then it is no longer the accepted theory of SR.

    Quote Originally Posted by PhysBang View Post
    One way to interpret presentism is to say that for each of the people at those clock times, all that can be said to be mutually real for them is the overlapping past light cones. One can make predictions based on the past light cone, imperfect predictions, but that is all. Things do not become real for an entity until they enter the past light cone of an entity.
    What does "for each of the people at those clock times" mean? There are 3 clock carrying observers, A & B, and C. C's clock must then read 10am per A while C's clock must then read 2pm per B, A & B being momentarily co-located upon their own flyby event. A prediction of what a remote clock must read now, based upon what the current receipt of light reveals it to read when it was way back yonder, implies no imperfect prediction if light's speed and inertial velocities do not change over time.

    Quote Originally Posted by PhysBang View Post
    Another way to interpret presentism (not necessarily mutually exclusive with the above) is to consider the present to be the sum total of the presents of all existing entities. These presents interact only through the causal structure of SR. Regardless of what might want to assign as future or past in a system of coordinates, all systems of coordinates agree on cause and effect. So one distinguishes the present as the sum total of all things being caused, the absolute past the events that have been caused and the absolute future the things that (in principle) will be caused. For any being, there will be a large class of events for which they cannot determine the category, but this would be the case for all but the omniscient observer in a Newtonian universe, too.
    Please define ... "the causal structure of SR". As I understand it, locality causes cause and effect, all cause/effects generated by events in spacetime, and the LTs define the location of all events in all spacetime systems ... using the Einstein convention of simultaneity. So I need you to define what you mean be that, because I'm having difficulty making sense of that, and maybe if I have that definition first I may then better understand your point there.

    Quote Originally Posted by PhysBang View Post
    I believe that this last interpretation involves a claim that is either frame dependent (the sum total of all presents given some chosen system of coordinates) or that is not, but that cannot be identified with a physical description (i.e., we can talk of the sum total of all entities that ever were and of their presents, but we cannot identify any spacelike-hypersurface that is the particular one that contains all the presents, we cannot identify, even in principle, all the entities that, like us, are currently in the present). I could be wrong on this; I haven't looked at the literature in some time.
    Hmmm. Well, I must say that I am somewhat confused regarding PRESENTISM, the way you have tried to define it here. I appreciate your first attempt though.

    My understanding, is that PRESENTISM simply assumes that all that exists is an everchanging and real NOW. That future and past are not real, more man made notions. I had long assumed that PRESENTISM was built upon the LET theory (maybe I was mistaken there?), where an absolute aether frame was assumed to exist. If the aether frame were real, then only an observer at rest with it measures what is real ... and all those in motion thru the aether frame measure contracted lengths with contracted rulers, and contracted time intervals with contracted clock rates. Light's speed would measure at invariant c, but only because the relativistic contractions produce that result. The light actually moves slower thru a moving frame, per LET, even though it can never be measured directly as such by any moving observer.

    For PRESENTISM to apply to Einstein's SR, the LT solns cannot represent what is real, IMO. The LT solns must be more a mathematical artifact, similarly as Lorentz's original belief regarding the effect of time dilation. Or, one must assume that while Einstein's simultaneity convention works, that it does not represent what is real, and only the observer at rest in the aether determines that (because only his sense of simultaneity is considered TRUE). Now one may choose to believe that if they so wish, however IMO, ETERNALISM is superior because what you measure is considered real, always. All measurements per either SR or LET can be verified after the fact, but only SR requires the measurements also be true/real. By ETERNALISM, the C clock currently reading 10am per A while also currently reading 2pm per B, when A & B are colocated, represent what is real. Only if all moments in time coexist on equal footing as do inches on a ruler, can both those time predictions be real. Otherwise, all LT solns are unreal, as it would be impossible for the C clock to possess 2 different readings NOW from single point in spacetime, and so they would be mere mathematical artifacts versus real.

    Everything that PRESENTISM requires, is encompassed in the ETERNALISM philosphy. For example, from the POV of a stationary observer, he experiences his own passage thru time (not space), or he may consider himself stationary in space and time passing him by ... its all arbitrary because its all relative. As an observer progresses along his own worldline, from his own POV as stationary, it seems entirely as the PRESENTIST model would require ... because he does not realize he progresses along his own worldline thru time, even though he does. But the ETERNALIST model allows observations that differ per POV, to be equally real and correct. Therein lies the beauty of it, IMO.

    The ETERNALISM philosophy allows for wormholes, and hence time travel (not that it's a known possibility). I don't (yet) see how the PRESENTIST philosophy could.

    Thank You,
    SinceYouAsked
    Last edited by SinceYouAsked; 09-11-2014 at 05:05 AM.
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    Quote Originally Posted by SinceYouAsked View Post
    If not real, then only a mathematical artifact. A philosophy built upon that, is a lesser philosophy IMO, given another philosophy defines all measurements and predictions as real.
    I don't know what that means. It seems that according to SR, there is nothing real about a system of coordinates, just physical rules relating how systems behave. I don't know how to identify particular philosophical theories as greater or lesser in this case.
    If the predictions do not match reality, then the predictions are not a good model of reality. If the predictions do match reality, then the predictions are facts of reality.
    That is a overly simple view of science. But irrelevant to my point.
    Well, SR assumes the Einstein/Poincare method of time synchronization for inertial bodies ... τ1 = ½(τ0+ τ2). Since SR is an accepted theory in physics, we assume that method is correct, or at least the most likely correct one, and so we use it and assume it correct. If the defined spacetime interval is not timelike, then no cause and effect takes place between the 2 POVs. My scenario here was a timelike interval.
    I assumed that your scenario has a spacelike interval, since you identified, "the remotely located clock C". I don't know how to make a remotely located clock such as you described that is not spacelike separated.
    SR requires that A & B define "currently" (across the all of space) the same as all inertial observers must, as consistent with the Einstein clock sync method. It's specifically defined. Use any other convention of simultaneity, then it is no longer the accepted theory of SR.
    People are free to use whatever standard they wish. In order to make a measurement in a specific frame of reference, then certain rules must be followed. I never use my own reference frame when judging the speed of my car. SR does not declare all automobile odometers to be grossly incorrect.

    Too often people fall in love with the "observer" talk of relativity theory. We really should abandon this talk and look at the actual measurements (or rather, the in principle measurements) that one might make.

    What does "for each of the people at those clock times" mean? There are 3 clock carrying observers, A & B, and C. C's clock must then read 10am per A while C's clock must then read 2pm per B, A & B being momentarily co-located upon their own flyby event. A prediction of what a remote clock must read now, based upon what the current receipt of light reveals it to read when it was way back yonder, implies no imperfect prediction if light's speed and inertial velocities do not change over time.
    We identify these people and the readings of the clocks that they carry. Yes, if they maintain a certain speed and direction as indicated in the information from a past light cone, then we can predict their position at a later time. And yes, given the location of a spacetime event in one coordinate system, we can identify the location of that even in another coordinate system. But for a person with a clock, at any given time (identified by the reading of that clock), they cannot guarantee the position of anything outside their past light cone.
    Please define ... "the causal structure of SR". As I understand it, locality causes cause and effect, all cause/effects generated by events in spacetime, and the LTs define the location of all events in all spacetime systems ... using the Einstein convention of simultaneity. So I need you to define what you mean be that, because I'm having difficulty making sense of that, and maybe if I have that definition first I may then better understand your point there.
    The causal structure of spacetime is the limitations on cause and effect put in place by, in this case, SR. E.g., if two events are spacelike separated, one cannot have a causal influence on another. We don't really have to consider simultaneity, except that when we identify spacial distances we are identifying a particular time axis. If we look at the worldline of an object, for any point on that worldline causal influences must all be all in the past light cone of that point. For any time, we can identify a sea of points surrounding that worldline that have no causal influence at that time; everything that is not adjacent to that worldline.
    Hmmm. Well, I must say that I am somewhat confused regarding PRESENTISM, the way you have tried to define it here. I appreciate your first attempt though.
    Truthfully, SR demands that we abandon presentism as usually thought since there can be no one plane of simultaneity. This need not mean that each object does not carry its present with it, so to speak.

    My understanding, is that PRESENTISM simply assumes that all that exists is an everchanging and real NOW. That future and past are not real, more man made notions. I had long assumed that PRESENTISM was built upon the LET theory (maybe I was mistaken there?), where an absolute aether frame was assumed to exist. If the aether frame were real, then only an observer at rest with it measures what is real ... and all those in motion thru the aether frame measure contracted lengths with contracted rulers, and contracted time intervals with contracted clock rates. Light's speed would measure at invariant c, but only because the relativistic contractions produce that result. The light actually moves slower thru a moving frame, per LET, even though it can never be measured directly as such by any moving observer.
    If there is an absolute reference frame, then coordinating these nows seems much easier. But I believe this merely hides the problem, since we can have an abosolute reference frame and an eternalist metaphysics.

    For PRESENTISM to apply to Einstein's SR, the LT solns cannot represent what is real, IMO. The LT solns must be more a mathematical artifact, similarly as Lorentz's original belief regarding the effect of time dilation. Or, one must assume that while Einstein's simultaneity convention works, that it does not represent what is real, and only the observer at rest in the aether determines that. Now one may choose to believe that if they so wish, however IMO, ETERNALISM is superior because what you measure is considered real, always. All measurements per either SR or LET can be verified after the fact, that they existed as such, but only SR requires they also be real. By ETERNALISM, the C clock currently reading 10am per A while also currently reading 2pm per B, when A & B are colocated, represent what is real. Only if all moments in time coexist on equal footing as do inches on a ruler, can both those time predictions be real. Otherwise, all LT solns are unreal, as it would be impossible for the C clock to possess 2 different readings NOW from single point in spacetime, and so they would be mere mathematical artifacts versus real.
    It doesn't matter for any of these actual points that anything at all is happening at a distance. It only matters later, when a causal influence has gone from one to the other. So all a metaphysical picture of time needs to to is ensure that this structure of relationships is preserved, not that every point exists for all time.

    Everything that PRESENTISM requires, is encompassed in the ETERNALISM philosphy. For example, from the POV of a stationary observer, he experiences his own passage thru time (not space), or he may consider himself stationary in space and time passing him by ... its all arbitrary because its all relative. As an observer progresses along his own worldline, from his own POV as stationary, it seems entirely as the PRESENTIST model would require ... because he does not realize he progresses along his own worldline thru time, even though he does. But the ETERNALIST model allows observations that differ per POV, to be equally real and correct. Therein lies the beauty of it, IMO.
    Observations do not differ, except in the sense that observers from different perspectives get to see different things. SR demands that there is always a way for any person who has made an observation to, at least in principle, determine what any other person making an observation would have seen. Choice of frame of reference to use to consider positions is arbitrary (though perhaps suggested by practical concerns), but SR lays out clear fixed objective rules for how to convert from one frame of reference to another. The same events happen regardless of the coordinates to which they are assigned. The worldline, too, is equally arbitrary; behavior along it at any point is determined by the causal influences that reach it at that point. It does not need distant points to exist in any way for it to continue.

    The ETERNALISM philosophy allows for wormholes, and hence time travel (not that it's a known possibility). I don't (yet) see how the PRESENTIST philosophy could.
    Good point. And if we find such a thing, then we will have a fact of the matter about physics for us to consider.
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    Quote Originally Posted by PhysBang
    That might make sense if we say that every description of motion is a block-universe model...
    But that doesn't make sense because the block-universe is static. The red streak in the block of movie frames is not in motion.

    Quote Originally Posted by PhysBang
    However, it would be foolish to do so. It is also possible to use spacetime to describe the state of affairs of a system on one spacelike-hypersurface. Using your reasoning, since this is possible, spacetime must be only compatible with presentism!
    No, observation is only compatible with presentism. Spacetime is a model that works, that's compatible with observation too, provided you don't start thinking space and spacetime are the same thing.

    Quote Originally Posted by PhysBang
    You have cherry-picked my statement: you only addressed that I wrote the word "mistake" without actually addressing any of the content that the mistake was about. This is a bad habit.
    The bad habit is confusing space with spacetime. Even Wheeler did this. And Feynman too, much to my regret.

    Quote Originally Posted by PhysBang
    OK, but why do you completely ignore the actual contents of the relevant theory. That content is partly mathematical in nature because GR is explicitly about certain mathematical relationships between space, time and energy. If you ignore this content, then you can't be said to be saying anything about the theory.
    I don't ignore it. It's just that I can't explain what the mathematics means using mathematics. I cannot describe t using maths, I have to open up a clock and show you that it isn't measuring the flow of proper time, it's accumulating the regular cyclical motion of cogs and gears and showing you a cumulative display that you call the time.

    Quote Originally Posted by PhysBang
    Well, you could take a look at the citation provided by lpetrich discussing the literature on the sense of time that people seem to have. I'm not sure why you write off the entire field of psychology and the empirical research done on human (and animal) time sense.
    Because we have five senses, not six.

    Quote Originally Posted by PhysBang
    How does this show space? If I cannot conceive of space before you hold your hands apart, how can I conceive of it afterwards?
    There's a space between my hands, and you can see that there is.

    Quote Originally Posted by PhysBang
    If you can use the span of your hands as some sort of accurate measuring device, I might use this to deduce something about objects in space or perhaps about space itself. You have yet to demonstrate how simply showing your hands can teach someone that space exists.
    You can see that there's a space between my hands, that's enough.

    Quote Originally Posted by PhysBang
    How does that show motion? I could tell that things are moving relative to one another because they change over time. Do you have some other sense that can distinguish motion without experiencing change over time? If so, have you been studied by psychologists?
    Motion is something I can see happening. I cannot see time, or time flowing, or time passing, or any such thing as "over time". Try to focus on what you can see, on the empirical science rather than abstraction.

    Quote Originally Posted by PhysBang
    Even if you have such a sense, what use is this to physics, where motion is measured through changes over time? Can you show us how to do physics without this?
    Does not parse. We would do physics as now, using t as normal. But we would not think of time as something that literally flows, or of something we can travel through.

    Quote Originally Posted by PhysBang
    You seem enamored with your textual analysis of the English language, but less so in physical science or psychological science. I concede that nobody can show me time passing, since I already have a sense of time passing prior to anything being shown to me. (I suspect that you will attempt to cherry-pick that sentence later, but if so, that will be your problem.)
    It isn't some textual analysis, it's empiricism.

    Quote Originally Posted by PhysBang
    Yes, there is a rough rest frame for the collection of matter that we can see. In the sense of special relativity, not only is this not an absolute reference frame, but it doesn't matter for the motion or behavior of any object. You, on the other hand, with your talk of light slowing down, are telling us that there is some frame that matters, that light is really moving relative to some reference and that corrections within this reference are giving us the illusion of Lorentz invariance and the symmetries of GR.
    Light is really moving. Whether there's anything you might call a rest frame, that light is definitely moving, and the variable speed of light is a different topic.

    Quote Originally Posted by PhysBang
    I notice that none of the above seems to address the argument that GR is completely compatible with presentism, just with a local presentism, save for the claim that if we describe things using spacetime we might be tempted to describe things over a range of times. This argument seems to be specious since every kind of physics allows us to describe physical systems over a range of times. Unless this aspect of physics implies that the physical universe is simply a block universe, it is unconvincing that the possibility of one type of description necessitates that description is the only metaphysically correct one.
    GR gives us the equations of motion. There's no motion in the block universe.

    * * * * * * *

    Quote Originally Posted by SinceYouAsked View Post
    When A & B consider the current time readout of the remotely located clock C, they do not assume that "it's current time reading" is what photons at their own eyes presently reveal upon receipt. A (and B) must subtract out the light travel time from the C time reading brought to their eyes by the light. Per the LTs, they each measure the distance to the C clock differently ... and since light speed is invariant at c, they measure the traversal time of photons "from the clock to their eyes" differently.
    I'm sorry SYA, I'm confident that you have the wrong scenario here. When A and B are at the same location, they see the same set of photons that travelled from C in whatever time it took. Observer A doesn't see the time on C's clock to be 10am while observer B sees the time on C's clock to be 2pm.

    Quote Originally Posted by SinceYouAsked View Post
    A says C's clock then reads 10am. B says C's clock then reads 2pm. The LTs confirm this, and that they are each correct even though they disagree on the remotely located current clock reading of C. ETERNALISM says that C really does exist at 10am per A, and really does exist at 2pm per B, when A & B are momentarily co-located. All are correct. Now then, how do you explain this using the PRESENTIST philosophy of time, in a way that LT solns are real vs illusionary effect?
    I'm sorry, I can only reiterate that you have described the scenario incorrectly. Please reconsider it. Try replacing C with a supernova. Try it out elsewhere and see what other people say.
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    Quote Originally Posted by SinceYouAsked
    ...I had long assumed that PRESENTISM was built upon the LET theory (maybe I was mistaken there?), where an absolute aether frame was assumed to exist.
    Presentism arose in 1908, after Einstein had dispensed with the luminiferous aether. But see this and this and this. Einstein reintroduced an aether for GR. And as described in A World without Time: The Forgotten Legacy of Godel and Einstein he embraced presentism.

    Quote Originally Posted by SinceYouAsked
    If the aether frame were real, then only an observer at rest with it measures what is real ... and all those in motion thru the aether frame measure contracted lengths with contracted rulers, and contracted time intervals with contracted clock rates. Light's speed would measure at invariant c, but only because the relativistic contractions produce that result. The light actually moves slower thru a moving frame, per LET, even though it can never be measured directly as such by any moving observer.
    You need to read this Baez article. Note this:

    "That the speed of light depends on position when measured by a non-inertial observer is a fact routinely used by laser gyroscopes that form the core of some inertial navigation systems. These gyroscopes send light around a closed loop, and if the loop rotates, an observer riding on the loop will measure light to travel more slowly when it traverses the loop in one direction than when it traverses the loop in the opposite direction. The gyroscope does employ such an observer: it is the electronics that sits within the gyro. This electronic observer detects the difference in those light speeds, and attributes that difference to the gyro's not being inertial: it is accelerating within some inertial frame. That measurement of an acceleration allows the body's orientation to be calculated, which keeps it on track and in the right position as it flies."

    Quote Originally Posted by SinceYouAsked
    For PRESENTISM to apply to Einstein's SR, the LT solns cannot represent what is real, IMO. The LT solns must be more a mathematical artifact, similarly as Lorentz's original belief regarding the effect of time dilation. Or, one must assume that while Einstein's simultaneity convention works, that it does not represent what is real, and only the observer at rest in the aether determines that (because only his sense of simultaneity is considered TRUE). Now one may choose to believe that if they so wish, however IMO, ETERNALISM is superior because what you measure is considered real, always.
    It isn't true. Sometimes you change along with the thing you're measuring, and you measure no change. Sometimes you change and the thing you're measuring doesn't, but you measure it as changed.

    Quote Originally Posted by SinceYouAsked
    Everything that PRESENTISM requires, is encompassed in the ETERNALISM philosophy. For example, from the POV of a stationary observer, he experiences his own passage thru time (not space), or he may consider himself stationary in space and time passing him by ... its all arbitrary because its all relative. As an observer progresses along his own worldline, from his own POV as stationary, it seems entirely as the PRESENTIST model would require ... because he does not realize he progresses along his own worldline thru time, even though he does.
    No, he doesn't. A worldline is an abstract thing. It does not exist.

    Quote Originally Posted by SinceYouAsked
    The ETERNALISM philosophy allows for wormholes, and hence time travel (not that it's a known possibility). I don't (yet) see how the PRESENTIST philosophy could.
    It doesn't. That's why it's right. Because time travel is a fantasy. There is no way you can move that undoes the motion of everything else in the universe.
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    (Are rainbows and clouds solid objects?)
    Quote Originally Posted by Farsight View Post
    No. Where do that come from? It isn't relevant. And nor is anything else you've said. Are you trying to derail the thread?
    I was criticizing the simplistic notions of perception that are in your posts on the subject. We *don't* directly perceive objects. Instead, our consciousnesses get ideas that are generated by the perception process, and we interpret these ideas as perceptions of objects. Furthermore, rainbows and clouds are cases where appearances are deceiving. In fact, a lot of premodern beliefs and mythologies feature rainbows and clouds as solid objects. It is not enough to say that those notions are wrong. One must be able to demonstrate that they are wrong.

    Quote Originally Posted by Farsight View Post
    It doesn't hold an equal footing. There's a minus sign on the t term in the spacetime interval expression below:

    A reversed sign. What a teeny teeny tiny difference. Not enough to justify claiming that space is fundamental while time is not.

    Furthermore, that's just one coordinate system. Try cylindrical coordinates or spherical coordinates or light-cone coordinates or Rindler acceleration coordinates and see what you get.
    And nobody is saying time doesn't exist or isn't required. Just that time isn't on an equal footing with the space dimensions. Because it's a dimension of measure that is derived from motion through space. You can't move through it like you can move through space.
    We continually move through time. In fact, we cannot stop moving through time or reverse our direction of motion in time. Our motion through space-time is confined to our forward light-cone interior.

    And a part of that misunderstanding is a confusion between space and spacetime.
    What confusion? Who's doing the confusing?

    Quote Originally Posted by Farsight View Post
    I mean static is in there is no motion in this arena. Because spacetime is a block-universe model that depicts all times at once.
    Except that we are on the inside of it, not on the outside looking in.

    Quote Originally Posted by Farsight View Post
    The bad habit is confusing space with spacetime. Even Wheeler did this. And Feynman too, much to my regret.
    How are they supposed to have done that?

    Motion is something I can see happening. I cannot see time, or time flowing, or time passing, or any such thing as "over time".
    Have you ever seen gravity? Not objects falling down, but gravity itself.

    Try to focus on what you can see, on the empirical science rather than abstraction.
    That argument leads to solipsism. How does one know that everything but one's consciousness is not pure hallucination? Yelling "I know" is not good enough.

    Quote Originally Posted by Farsight View Post
    Einstein reintroduced an aether for GR.
    All based on some quote from his effort to explain GR in nontechnical terms. What book-thumping.

    And as described in A World without Time: The Forgotten Legacy of Godel and Einstein he embraced presentism.
    Except that Einstein was not some inspired prophet and yelling "These are the words of Albert Einstein!" is not a very good argument.

    A worldline is an abstract thing. It does not exist.
    By that argument, neither do coordinate systems. Have you ever seen a coordinate axis?
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    Quote Originally Posted by PhysBang
    Well, you could take a look at the citation provided by lpetrich discussing the literature on the sense of time that people seem to have. I'm not sure why you write off the entire field of psychology and the empirical research done on human (and animal) time sense.
    Quote Originally Posted by Farsight View Post
    Because we have five senses, not six.
    Sense - Wikipedia We have a lot more than the traditional five senses.
    • Mechanical
      • Hearing
      • Pressure
      • Itch
      • Acceleration
      • Rotation
      • Proprioception (joint orientation)
    • Temperature
      • Heat
      • Cold
    • Pain
    • Chemical
      • Smell
      • Taste
      • Internal states, giving feelings of hunger, thirst, asphyxiation, ...
    • Vision
    • Time
    Time perception - Wikipedia goes into more detail about that last one.

    Some species have additional senses:
    • Electric fields
    • Magnetic fields
    Last edited by lpetrich; 09-11-2014 at 01:42 PM. Reason: Added proprioception to the mechanical senses
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    Quote Originally Posted by Farsight View Post
    But that doesn't make sense because the block-universe is static. The red streak in the block of movie frames is not in motion.
    Sadly, I cannot use your strange definition of "static" and I do not recommend that others do either. Like I said, every description of movement uses spacetime, so unless every description of movement implies a block universe, that GR does the same thing as every other form of physics doesn't change anything.
    No, observation is only compatible with presentism.
    That doesn't seem to make any sense.
    Spacetime is a model that works,
    You are making a category mistake. Spacetime is not a model, spacetime is how all physical systems are represented (save perhaps when they are weirdly presented using phase space - this is an interpretation question). There is no mathematical physics that does not use spacetime. Newton used spacetime, he just used a version with particularly nice properties.

    If you don't like the way that GR models spacetime, Farsight, then show that it is wrong. Address the mathematical details, since that's the only difference between GR and any other theory.
    The bad habit is confusing space with spacetime. Even Wheeler did this. And Feynman too, much to my regret.
    Many people make mistakes; Einstein made a ton of mistakes, especially in his popular science speeches. In order for your points to succeed, you have to show that people made these sorts of mistakes in the mathematical physics that people tested, not in their casual discussion.

    Still, you have done exactly the same thing: You have cherry-picked my statement: you only addressed that I wrote the word "mistake" without actually addressing any of the content that the mistake was about. This is a bad habit.
    Because we have five senses, not six.
    So your response to the question, "why do you ignore the science of psychology?" is to respond with a myth about human psychology? It seems from the research that we have more than five senses.
    There's a space between my hands, and you can see that there is.

    You can see that there's a space between my hands, that's enough.
    That doesn't answer my question: If I cannot conceive of space before you hold your hands apart, how can I conceive of it afterwards? Are you just going to dogmatically stick to your position?
    Motion is something I can see happening. I cannot see time, or time flowing, or time passing, or any such thing as "over time". Try to focus on what you can see, on the empirical science rather than abstraction.
    I know that what is see is change in position over time.

    Again I ask: Do you have some other sense that can distinguish motion without experiencing change over time?
    Does not parse. We would do physics as now, using t as normal. But we would not think of time as something that literally flows, or of something we can travel through.
    So you are saying that we would ignore everything that you have to say, do our physics using time, and then pay some sort of homage to you when we weren't doing physics? Seems like you want a nice little religion there.
    It isn't some textual analysis, it's empiricism.
    You literally did nothing but analyze the various uses of the English word "flow". That's textual analysis. We've seen that from you hundreds of time, but never have we seen you look at the details of a physical theory.
    GR gives us the equations of motion. There's no motion in the block universe.
    "Newtonian universal gravity gives us the equations of motion. There's no motion in the block universe."

    See how silly that looks?
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    I recently abandoned the phrase "a clock measures time", since a ruler does not measure distance. It becomes clear if you compare the clock to a metronome, they both establish a standard beat or rhythm. The ruler sets a standard spatial unit of measure. The clock and ruler are tools that allow a human to make measurements. The only difference, the clock is typically active, and accumulates the number of ticks, where the ruler is typically passive. If a clock is adjusted to run faster, we don't have anymore 'time' then before, thus it isn't measuring time. It would only provide more precision when measuring due to shorter periods. The metronome period can be regulated from slow to fast, but the same amount of music is played, and the beat does not cause the music. A clock serves as a standard in the same manner as a metronome or a ruler, and all measurements are made relative to a standard.
    If you are using a light clock, a 'tick' is n light cycles between an emitter and detector, or a finite light distance, equal to 2n *(the space between them).
    Historically 'time' is a finite amount of motion of an object, earth, moon, sand, etc., i.e. 'time' is a pseudonym or alias for 'distance'. On earth, spatial intervals can be measured on the basis of energy required to move from one location to another, eliminating the need for a (traditional) clock. On a space trip at constant speed, the energy consumed by a light source could accomplish the same. These are examples of indirect spatial measurements, but there is no counterpart for measurement of a tangible 'time', unless we recognize its alias. This is why (IMO) the philosophical debate has continued throughout human history.
    Subjective time requires memory, which allows a comparison of a current state to a previous state for any changes, which lends itself to an interpretation of time flowing. Patients with brain damage to specific areas involved in maintaining a personal chronology, lose their ability to estimate elapsed time, short or long term. Consider the fact that people waking from a comatose state, have no memory of how much elapsed time, whether hrs, days, or even years.
    Consider one of the greatest misnomers ever used, 'motion pictures' or 'movies', where a person observes a sequence of still photos and the mind melds them to produce moving objects where there is no motion.

    In the world of quantum physics, suppose a particle can have three states, a, b, and c. Suppose the first three observations record abc, and the second three record cba. Did time 'flow' backward? No, and we have proof, since the 'time' of each observation was recorded. It was just a reversed sequence.
    Flipping a coin is governed by the rules of physics, yet the results are independent of time. The probability of H or T is always 1/2.
    If an object is dropped from a height, next to a vertical measuring stick, and recorded on video, analysis of the video allows a mathematical relation to be formulated between the time stamp of each frame and the height of the object, like (h = h0 -.5gt2). Notice that verification of the experiment requires a clock, since measurement is the modus operandi of science. More importantly notice, gravity, not time, causes the object to fall, and the clock is just a means of ordering the events.
    To bury the idea of time (as we know and use it) as a causal factor, note that the time of an event is assigned after perception of the event.

    Nothing like an objective 'time' has yet been discovered, but that doesn't imply it doesn't or couldn't exist. Consider all the 'fundamental' particles' that were discovered, once the appropriate experiment was designed.

    I would suggest energy as the reason for physical change.
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    Theories of time:
    A-series and B-series - Wikipedia and B-theory of time - Wikipedia list

    So we have a lot of possibilities to argue over.
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    I'm of the opinion that McTaggart was also doing textual analysis and that the A-series/B-series distinction is misleading. It does give one a place to start, however.
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    Relativity causes certain problems with time, because of time being unified with space. To see why, let us consider what we start with.

    Common sense and Newtonian mechanics support Galilean invariance, invariance under translations, reflections, space rotations, and Galilean boosts. For space dimension x and time t, a Galilean boost with velocity v is
    x' = x - v*t
    t' = t

    Its space-time invariants are the time interval, t2 - t1, and with zero time interval, the space interval also, |x2 - x1|.

    Past, present, and future are thus universally defined.

    But in the mid to late 19th cy., it was discovered that electromagnetism is not Galilean-invariant, and Henrik Antoon Lorentz discovered the correct invariance law for it: Lorentz invariance. A Lorentz boost is
    x' = γ*(x - v*t)
    t' = γ*(t - v*x/c2)
    γ = (1 - v2/c2)-1/2

    Einstein showed how to revise momentum and energy to make mechanics Lorentz-invariant, thus yielding special relativity. It has five types of distance-invariant values:
    • Forward timelike
    • Forward null
    • Spacelike
    • Backward null
    • Backward timelike
    The null and timelike directions form cone shapes, with the timelike ones being in the interiors and the null ones being in the surfaces. These are called light cones, and there are both past and future ones.

    So in SR, the only "absolute" past is inside the past light cone, and the only "absolute" future is inside the future light cone. in between the cones is spacelike directions, directions whose time directions are observer-dependent.

    General relativity parallels SR, but one has to mark out the light cones' surfaces with null geodesics. The OP's question can be phrased as asking whether a point can be in its past or future light cones.
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    Pls no one has addressed the comments in the mentioned link,which makes me to repost the link Einstein Strikes Again: One More Discovery From the Great Man | TIME.com
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    Thanx for everyone's comments, regarding presentism vs eternalism. I'm not sure anything is any clearer, as there does seem to be a tendancy to restate those terms without keeping the point at hand in focus. The point IMO, is regarding the LT solns in so far as corresponding to reality, which I believe eternalism supports but that presentism does not (unless there's something about the meaning of presentism I'm missing). I do agree with you PhysBang in that coordinates are man made, but this does not affect my stated point here IMO. I'll submit a spacetime figure at first opportunity (I'm buried at the the moment), which should better keep everyone on the same page specifically regarding my point at hand.

    Thank You,
    SinceYouAsked
    Last edited by SinceYouAsked; 09-13-2014 at 06:25 AM.
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    Examining the simplest Minkowski diagram, the horizontal axis represents the x direction in space, and the vertical axis represents ct, also a distance, but referred to as the 'time' dimension, per Minkowski, in his generalization to a mathematical 4D theory. Einstein, in par 3 of his 1905 paper treated c and t separately, but the composite term has a definite advantage. Using a (t) and (x) axis in seconds and meters, if we plotted a light signal sent at t=1 to the moon and the returned signal at t=3.5, the paths would be horizontal lines that extend off the chart. A practical chart would require scaling of (t) or (x) by c, even without SR theory. So what a straight line plots is x/ct = vt/ct = v/c, or a history of speed. The light line is thus angled at 45º. The chart does not show motion in any form, but a composition of positions corresponding to a sequence of clock events. When viewing the heavens, we see objects at specific locations, but we never see orbits!
    Regarding the loop:
    If an object could accelerate continuously without limit, its speed profile (curve) would transition from vertical to horizontal, indicating instantaneous motion. Since it cannot move any faster, how would it move in the reverse direction, i.e. back in time?
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    Quote Originally Posted by SinceYouAsked
    Well, I would agree in that spacetime coordinates are man made, but this does not change the fact that events in spacetime are measurable, predictable, and thus real, using them.
    I've seen a large number of statements about whether things are real or not in physics. When I was doing my deepest study of general relativity, namely general relativity, I read a lot of Einstein's letters to his friends and colleagues. They were very useful reading because it gives one some insight into the mind of a genius.

    In a letter to Eduard Study dated September 25 1908 he wrote
    Highly esteemed Colleague,

    Many thanks for the amicable letter. I do not yet have your "Kinematics" and would therefore be very pleased to have it. I am supposed to tell you my reservations? ....
    ----------------
    "The physical world is real." This is supposed to be the basics hypothesis. What does "hypothesis" here mean here? For me, a hypothesis is a statement whose truth is temporarily assumed, whose meaning, however, must be beyond all doubt. The above statement seems to be intrinsically senseless though, like when someone says: "The physical world is a cock-a-doodle-doo." It appears to me that "real" is an empty category (drawer) whose immense importance lies only lies only in that I place certain things inside it and not certain others.
    It is true that this classification is not a random one but ........ now I see you grinning and expecting me into falling into pragmatism so that you can bury me alive. However I will do as Mark Twain, by suggesting that you end the horror story yourself, as you please.
    <Real and unreal seem to me to be like right and left.>
    I admit that science deals with the "real" and am nonetheless a "realist." This can be all the same to you, and I also do not feel like your opponent. For I would like to state the proposition:
    If all rubbish is cleared away from the arbitrary "isms." they then become alike.
    That is why you could be mercifully accepted by the priests of all the isms, they then become alike.
    You were accepted because your grace appealed to them.
    Getting back to the notion of real and not real. When people use the term real they use it to mean the same thing as exist

    See Exist - Definition and More from the Free Merriam-Webster Dictionary

    As such people tend to use the term "real" to refer to things that have a material existence. Therefore when people say that something isn't real they are thinking somewhere in the back of their mind that it doesn't have a material existence. I disagree with that kind of thinking and definition.
    Last edited by Physicist; 09-14-2014 at 06:15 AM.
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    Quote Originally Posted by phyti View Post
    Examining the simplest Minkowski diagram, the horizontal axis represents the x direction in space, and the vertical axis represents ct, also a distance, but referred to as the 'time' dimension, per Minkowski, in his generalization to a mathematical 4D theory. Einstein, in par 3 of his 1905 paper treated c and t separately, but the composite term has a definite advantage. Using a (t) and (x) axis in seconds and meters, if we plotted a light signal sent at t=1 to the moon and the returned signal at t=3.5, the paths would be horizontal lines that extend off the chart. A practical chart would require scaling of (t) or (x) by c, even without SR theory. So what a straight line plots is x/ct = vt/ct = v/c, or a history of speed. The light line is thus angled at 45º. The chart does not show motion in any form, but a composition of positions corresponding to a sequence of clock events. When viewing the heavens, we see objects at specific locations, but we never see orbits!
    I would say it this way ... spacetime figures plot the history of events on a static page. The fact that a static page is used, does not in any way lead that time does not flow or exist. One need only envision the advancement of lines-of-simultaneity on the static (which can nowadays be done with animations), ie the passage of time that we always experience. Add, if one cannot show mathematically how change exists in the absence of time, then time will likely never be deleted from the physics.

    In Minkowski figures, setting light speed at unity is arbitrary, and makes only for an easier figure to comprehend at a glance. It doesn't change anything, and models OEMB verbatum. The fusion of space and time was made clearer by Minkowski's geometric model, however it was already inherent in Einstein's 1905 OEMB paper.

    Motion exists given an angular orientation differential between the linear (inertial) worldlines. The experience of motion, requires the passage of time to experience relative change, ie the advancement of lines-of-simultaneity. That, needs imagined on static pages of paper where ink does not move on a page.

    Quote Originally Posted by phyti View Post
    Regarding the loop:

    If an object could accelerate continuously without limit, its speed profile (curve) would transition from vertical to horizontal, indicating instantaneous motion. Since it cannot move any faster, how would it move in the reverse direction, i.e. back in time?
    The relative angular orientation between worldlines would transition from vertical to 45 degrees. At 45, the velocity is c. Light speed plays the role of an infinite velocity in SR. By the LTs, upon attaining light speed, the POV is everywhere at once in known cosmos along its propagation path, assuming it exists at considered locations. That's an anomaly mathematically, and assumed impossible in nature, not to mention infinite mass is required and the cosmos is assumed to possess a finite energy. So, physics doesn't allow for anomalies.

    There is a theory (or theories) that allow for particles to come into existence already >c, and so they do not need to experience the speed c anomaly, eg tachyon theory. For such particles, time goes backwards and mass is imaginary ... although that's per our perspective, as it'd seem perfectly normal to them. No such particle has ever been observed.

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    Quote Originally Posted by Physicist View Post
    I've seen a large number of statements about whether things are real or not in physics. When I was doing my deepest study of general relativity, namely general relativity, I read a lot of Einstein's letters to his friends and colleagues. They were very useful reading because it gives one some insight into the mind of a genius.

    In a letter to Eduard Study dated September 25 1908 he wrote ...
    Yes, I've read that before too, and the point is well received. Yet, physics exists, and it is designed based upon consistent experience. We experience the passage of time and the existence of space (locality). While one may argue that space and change is all that exists, said individual must show mathematically how to model motion in the absence of time. It is insufficient otherwise.

    Now one can argue that we cannot trust our experience, that all experience is a manifestation of pure thought processes. That one cannot know if they are dreaming when dreaming, and so what is then real? Yet, one does not hold their hand on a flame, or step in front of an inbound train ... because deep down, they trust their prior experiences as real. My point, is that while all hypotheses and theories need questioned, this does not lead that we do not have a good definition of what real really is. IMO, we have an existing definition of real, and until a better definition comes along (based upon repeated experience), then we keep the definition we have until then. That defines what is real, today. At one time the world was flat, and that was a great definition of real at the time. Later, we learned better. At one time we thought Newton defined the motion of the heavens and earth, until Einstein extended it for non everyday experience. However, we experience the passage of time everyday, and we cannot model motion without using it. Now, if quantum mechanics can show that time does not exist, and another can show that the macro must be the summation of micro events in a way that explains why uncertainty is lost at non-micro levels, then more may reconsider the definition of time for everyday macro experience.

    Quote Originally Posted by Physicist View Post
    Getting back to the notion of real and not real. When people use the term real they use it to mean the same thing as exist

    See Exist - Definition and More from the Free Merriam-Webster Dictionary

    As such people tend to use the term "real" to refer to things that have a material existence. Therefore when people say that something isn't real they are thinking somewhere in the back of their mind that it doesn't have a material existence. I disagree with that kind of thinking and definition.
    I disagree with that as well Physicist. Real is also that which gives rise to material entity, which would be the medium itself. Material particles do not exist everywhere, because it requires surrounding space and time (gravity wells) for it to exist in the very first place. IMO, it's short sighted to presume that the gravity well that follows particles everywhere (radiating outward at c) is not something, and thus not real. It's all real. Even if one can imagine the medium beyond where any gravitation field has yet formed, that must be real as well. Because if it were not real, then our cosmic birth should never had happened.

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    The truth maybe puzzling.It may take some work to grapple with.It may be counterintuitive.It may contradict deeply held prejudices.It may not be consonant with what we want desperately to be true.But our preferences do not determine what is true. - Carl Sagan.
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