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Thread: How does matter bend space time?

  1. #1 How does matter bend space time? 
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    If gravity is created by the bending of space time caused by objects of matter. Then what causes the matter to bend space time?

    Thank you ahead of time for any info you maybe able to give me.
    Ps. This is my first post so please inform me of any thing I do wrong.
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  2. #2  
    Administrator Markus Hanke's Avatar
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    If gravity is created by the bending of space time caused by objects of matter. Then what causes the matter to bend space time?
    There is no answer to this yet. GR can tell us how the geometry of space-time is connected to sources of energy-momentum, but not why. Perhaps a future theory of quantum gravity will have something to say about this, but that remains to be seen.
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    We live in exciting times!
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    Quote Originally Posted by Markus Hanke View Post
    There is no answer to this yet. GR can tell us how the geometry of space-time is connected to sources of energy-momentum, but not why. Perhaps a future theory of quantum gravity will have something to say about this, but that remains to be seen.
    Thanks all for your answers. I have one more question on this topic. Do u know of any body or any organistaion that is focusing on solving the unanswered questions about gravity yet?
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    Administrator Markus Hanke's Avatar
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    Do u know of any body or any organistaion that is focusing on solving the unanswered questions about gravity yet?
    Quantum gravity is an area of very active and ongoing research, and a lot of physicists and mathematicians are engaged in it. There is no one specific organisation, I'm afraid - it's an international and multidisciplinary effort.
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    It is the fundamental property of space.
    Space time is flexible.
    If a mass occupies space, something has to make way for it.
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    Indeed, no one knows yet.

    However, strings have been argued as superior to point particles, because mathematically, they can eliminate anomalies in calculations that exist if particles are considered as points. Now, you might ask yourself ... why would string form in the first place? Well, a superstring may be nothing more than the folding of the medium of spacetime unto itself, that once in the configuration of string, it becomes locked into that configuration until forced otherwise to return to a pre-string configuration. But again, why would a string form? I would envision it as a "rotation" of spacetime unto itself, along a line element. Likely, a large looped superstring(s) originally, a rotation of spacetime within itself. That energy within the string, comes from somewhere else. Where? From the surrounding medium, or its surrounding density if you prefer. That draw on surrounding medium may produce the gravity well (field), given the string configuration produces the Higgs particle. Just a thought.

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    Quote Originally Posted by docwho View Post
    The space-time is a kind of material. Has a refractive index, which affects the inside spread waves.
    It depends on the refractive index of the vacuum energy content, what includes the Einstein equation.

    Wave is moving in the direction of the Time. This is the Wave of Scrhodinger.
    Spacetime is not a material. The analogy of spacetime curving has unfortunately led many layman to erroneously come to this conclusion.

    Spacetime is a manifold (i.e. set) of points. Each point represents a point in space, i.e. r = (x, y, z) at an instant in time, i.e. t. An event is represented by what is called a 4-position, which I'll give the label X, and is expressed as X = (ct, x, y, z). The "c" in the first slot gives the number "ct" the same dimension as x, y, and z, i.e. a spatial dimension. Spacetime does not have a refractive index either since that'd be meaningless.
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    Quote Originally Posted by Physicist
    Spacetime does not have a refractive index either since that'd be meaningless.
    That's true, and that's false. You cannot dismiss the layman's interpretation, which carefully observe(or is told) that "a region of space" is "bent" in such and such ways that ALL things in it are kind of "refracted" or "pulled".

    The problem, from the layman's perspective, is to understand that space does not exist, it is not some kind of material/subtract/ether. Maybe that basic courses in geometry should insist that the page and their axis you are plotting triangle onto does not exist, that it is a abstraction.

    Anyway, in this 4-position manifold that, for lack of space or patience, I'll call space, you indeed are able to assign value in the "empty part" of not-it, by carefully computing something called a stress-energy tensor, which is only determine by "things" or "event" which are quantities belonging to "things", not to "space".

    The fact that space only exist between thing, is the clue, from my layman's perspective, to understand that space and it properties, are created by the thing and their properties, and not the other way around.

    So matter not only "bend" space, it "create" space
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    Quote Originally Posted by Boing3000
    That's true, and that's false.
    That makes no sense at all. Either something is true or it's false. It can't be both.

    Quote Originally Posted by Boing3000
    You cannot dismiss the layman's interpretation, ...
    I most certainly can dismiss it. Especially since I'm right and he's wrong.

    Quote Originally Posted by Boing3000
    ...which carefully observe(or is told) that "a region of space" is "bent" in such and such ways that ALL things in it are kind of "refracted" or "pulled".
    This most certainly not a subject for debate. Something either exists or it doesn't. When applied to space it's more complicated.

    All of your response is based on a common misconception, one that I'm not interested in exploring or explaining. A friend of mine is an expert on this subject and a superb teacher. I'll ask him the best way to describe this.
    Last edited by Physicist; 10-02-2014 at 08:14 AM.
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  11. #11  
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    Quote Originally Posted by Cyber Space View Post
    what causes the matter to bend space time?
    By presuming that matter actually causes spacetime to bend, you are assuming that matter and bent spacetime are distinct entities. An alternative perspective is to consider that the bent spacetime will appear as matter to observers. As to what causes spacetime to bend, one might consider why it would not be bent in any case.
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    A tensor equation that is valid in any coordinate system is valid in every coordinate system.
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    Quote Originally Posted by KJW View Post
    By presuming that matter actually causes spacetime to bend, you are assuming that matter and bent spacetime are distinct entities. An alternative perspective is to consider that the bent spacetime will appear as matter to observers. As to what causes spacetime to bend, one might consider why it would not be bent in any case.
    Indeed. The assumption would be that nothing exists except the medium itself, and variations/configurations of itself within itself (ie energy of various forms).

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    Quote Originally Posted by Physicist
    Quote Originally Posted by Boing3000
    That's true, and that's false.
    That makes no sense at all. Either something is true or it's false. It can't be both.
    It make perfect sense, if you know how to apply relativity.
    The O.P. is very correct in his Point of View, or FoR. Everything he said is correct from that Layman perpective. He reports very accurately the facts that are described to him. Although it is not space time that is bent, but space. At least it is a very good approximation to explain the trajectory of the moon with local curvature and not instantaneous action at a distance. If another need to associate bending of trajectories with "refraction index", it is also not so bad an approximation. Still better than "spooky action at a distance".
    So no, that is definitely not meaningless, in that frame.

    In your PoV, it is meaningless, that is also an easy fact to observe. Those to events are absolutely not excluding one another and that is why I didn't use an "or" in my statement.

    Quote Originally Posted by Physicist
    I most certainly can dismiss it. Especially since I'm right and he's wrong.
    But you should not. Especially that nobody have said you where wrong, and the quoting you introduce from another dimension (I mean thread), just mention that GR predict how space time behave, and light follow light-like trajectories.

    Quote Originally Posted by Physicist
    This most certainly not a subject for debate. Something that either exists or doesn't.
    That's just the opposite. That's the only subject of debate, and why Physicist got graduated. Not to repeat the same calculus now a century old, but to find that new explanation that does not exist yet (see Markus post #2)


    Quote Originally Posted by Physisict
    A friend of mine is an expert on this subject and a superb teacher. I'll ask him the best way to describe this.
    I'll look forward to read it. Misconceptions are nasty thing. I hope his explanation will not use that kind of old misconception
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    Quote Originally Posted by Boing3000
    It make perfect sense, if you know how to apply relativity.
    I know how to apply relativity to a very high degree of expertise as can be confirmed by my colleagues who are physicists at MIT, some of whom teach the subject, one of which has be proof reading his new text. So please don't post comments so rude as to imply that I don't know how to apply relativity. Especially since my experience with you shows me that I know the subject a great deal better than you do.

    I don't see the point of correcting the errors in your last post since you don't seem to understand what I'm saying so I doubt that rephrasing it will make you understand the subject any better.

    However with that said I'd be glad to explain it all over to someone else who would like me to except for you. Right now I don't see the point of doing anything different.
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  15. #15  
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    Quote Originally Posted by Physicist
    I know how to apply relativity to a very high degree of expertise as can be confirmed by my colleagues who are physicists at MIT
    No. You know how to apply Special relativity or General relativity, not relativity (of point of view)
    Quote Originally Posted by Physicist
    So please don't post comments so rude as to imply that I don't know how to apply relativity
    I do imply in my previous post that you don't know how to apply basic relativity. I am afraid that you refuse to understand what is said to you, in the context of the em-miter.
    That is why you always invent things that does not exist, or put words into my mouth. Also, try to resort to other thing that the argument of authority. It is bad form.
    I don't expect of you to agree with me, I expect at least from you to disagree on something that I have, in fact, said.

    In basic logic, when there are two event (let's say an opinion, in some FoR), which can be false/true, the only conclusion that basic relativity teach you is that there is 4 ways to describe the scene.

    Quote Originally Posted by Physicist
    Especially since my experience with you shows me that I know the subject a great deal better than you do
    That is funny, no matter how much time I will say that I agree we that (especially because my FoR is the layman one), you will still find some way to disagree with me (which is utterly paradoxical)

    Quote Originally Posted by Physicist
    I don't see the point of correcting the errors in your last post since you don't seem to understand what I'm saying so I doubt that rephrasing it will make you understand the subject any better.
    So why bother posting then ?
    My "errors" boils down to quoting wiki, and reminding that is is the best Layman equivalence to 4D tensors-something that Markus describe in his efficient post #2

    I you don't agree with that, I would be perfectly happy to learn that other explanation your friend can provide.
    Don't hesitate to throw math in the mix, I shall pretend to understand them.
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