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Thread: NExt: Through a key hole....?

  1. #1 NExt: Through a key hole....? 
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    OK. In the former post I have learnt that I will receive a chromatic shift in colors. I didnt recieve an answer - anyhow, not an answer that fits my lame capabilities, sorry and thanks for the effort.... - about the angle of reflection.

    So I have deviced another setup:

    Again, I am standing in front of a mirror train.
    But in this setup, inbetween me (the source of light) and the mirror train there is an opaque wall.

    In the wall there is a very-very-very small hole which from light can escape both ways. In a pictureque fashion only a thin ray of light. (Laser perhaps...?)

    IF the mirror on the other side is stationary I expect the light that comes in to bounce straight back to the hole. Correct?


    And the question:

    Therotically speaking - When the mirror-train starts rollig, will the light bounce back to the hole or will it be shifted and be absorbed in the inner side of the wall etc?


    I THANK YOU ALL FOR YOUR WISE ANSWERS!
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    In reply to chaimc, re: your #1 post.

    I believe you describing a "camera obscura" scenario. You should be able to easily find out about this w/ any search engine. I would be happy to describe more, but my posts are being

    monitored and everything I write is being derided in one way or another. I am tired of personal attacks and insults for which I try to defend myself...but no "luck".

    ......

    Stay w/Physicist and Jilan, they are both very skilled, or the "mods" will help you understand light (you must realize this is a HUGE topic you are asking questions about, and you will

    never receive simple answers because there are none. You must understand basics first, in order to be able to know what the replies mean...you can find basic theory published in

    every major language using search engines, and tutor yourself!


    (Thanks for reading!)
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    Chaimc, you need to apply the same logic as to the last problem. I.e. Switch it around and think what it looks like in the mirror frame. The oberver and hole are both moving at the same speed. By the time the light passes through the hole the first time the hole has moved with respect to the mirror so it lets the let through at exactly the correct angle that allows it to be reflected and pass through the hole a second time on its way back to the source.
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    Quote Originally Posted by Gerry Nightingale View Post
    In reply to chaimc, re: your #1 post.

    I believe you describing a "camera obscura" scenario. You should be able to easily find out about this w/ any search engine. I would be happy to describe more, but my posts are being

    monitored and everything I write is being derided in one way or another. I am tired of personal attacks and insults for which I try to defend myself...but no "luck".

    ......

    Stay w/Physicist and Jilan, they are both very skilled, or the "mods" will help you understand light (you must realize this is a HUGE topic you are asking questions about, and you will

    never receive simple answers because there are none. You must understand basics first, in order to be able to know what the replies mean...you can find basic theory published in

    every major language using search engines, and tutor yourself!


    (Thanks for reading!)
    **********************

    Gerry thanks for the advices and for your patience with me.

    I should have thought about camera obscura.... But what I am after is not really that. Maybe i should have insisted on laser light as I want to single out only a very fine thread of light . All I am intersed in is whether the beam of (laser...?) light will return in the same path/trajectory on the way back from the mirror as on the way forth ("me" and the hole are stationary, the mirror is rolling)?

    Thanks again
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    Gerry thanks for the advices and for your patience with me.

    I should have thought about camera obscura.... But what I am after is not really that. Maybe i should have insisted on laser light as I want to single out only a very fine thread of light . All I am intersed in is whether the beam of (laser...?) light will return in the same path/trajectory on the way back from the mirror as on the way forth ("me" and the hole are stationary, the mirror is rolling)?

    Thanks again
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    Hi Jilan

    Something went wrong in your phrasing "...or so it lets the let through...".

    I want to make sure i understood: The mirror's motion will not affext the trajectory of the light.

    See what i wrote to Gerry.

    Thanks.
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  7. #7  
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    Quote Originally Posted by chaimc View Post
    Hi Jilan

    Something went wrong in your phrasing "...or so it lets the let through...".

    I want to make sure i understood: The mirror's motion will not affext the trajectory of the light.

    See what i wrote to Gerry.

    Thanks.
    Sorry that should read, ... So it lets the light through...
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    I understand that I have recahed the point that everyone is fed up with me.... I am in a quest after somethig that i thought will be much simpler.


    What affect will a motion of a mirror will be in the angle of the reflection on a beam of light - let it be a laser. I didnt get a straight foeward answer, yet....


    So to make it easier for a "goodbye" please answer with a YES or a NO:

    If I shoot a laser beam vertically on a moving mirror, and the laser beam leaves an inaginary trace on the its way to the moving mirror, will it return on these traces?


    Can I put it in a simpler fashion?

    I thank you very much - YES or NO?
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    Yes
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    In reply to chaimc, re: your post #8.

    I am not encouraged to see you say "good-bye" merely because of my own perceptions. There is much to be "learned" here regarding physics theory...but you must realize there are

    many different aspects to a simple "yes or no" regarding physics theory. You will realize this as you gain more knowledge of "how things MAY work". Even Einstein himself did not know

    every aspect of light, or Newton, or anyone else. There are deep fundaments involved w/such energies, so deep it is hard to imagine them, never mind being able to define what they are.

    I encourage you to stay here, and keep asking questions! There are a few here that will help you if they can...but you must realize things are nowhere near as simple as they may seem to be.

    What our minds are capable of seeing is NOT the "real truth" of light, chaimc. The aspects of light are not so simple as that, just "face value" and nothing more.


    (Thanks for reading!)
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    Quote Originally Posted by Gerry Nightingale View Post
    In reply to chaimc, re: your post #8.

    I am not encouraged to see you say "good-bye" merely because of my own perceptions. There is much to be "learned" here regarding physics theory...but you must realize there are

    many different aspects to a simple "yes or no" regarding physics theory. You will realize this as you gain more knowledge of "how things MAY work". Even Einstein himself did not know

    every aspect of light, or Newton, or anyone else. There are deep fundaments involved w/such energies, so deep it is hard to imagine them, never mind being able to define what they are.

    I encourage you to stay here, and keep asking questions! There are a few here that will help you if they can...but you must realize things are nowhere near as simple as they may seem to be.

    What our minds are capable of seeing is NOT the "real truth" of light, chaimc. The aspects of light are not so simple as that, just "face value" and nothing more.


    (Thanks for reading!)

    Gerry, thanks for the encouragements! I meant goodbye for this topic, but though I stiil think that the question is answerable with a yes or no conclusion. See Jilan's reply.

    Can you you give at this point a yes or a no?

    Thanks again!
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    Thanks!
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    The answer is yes...but you must remember this a "static" frame-of-reference, no influences can be introduced or any changes made.
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    Quote Originally Posted by Gerry Nightingale View Post
    The answer is yes...but you must remember this a "static" frame-of-reference, no influences can be introduced or any changes made.
    Gerry can you explain pls "no influences can be introduced or any changes made"?

    Thx
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    Will A vertical laser beam will bounce verticaly (from a moving mirror)?

    YEs or NO before you explain pls.
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    Quote Originally Posted by chaimc View Post


    And the question:

    Therotically speaking - When the mirror-train starts rollig, will the light bounce back to the hole or will it be shifted and be absorbed in the inner side of the wall etc?
    The key to your answer is in the part "When the mirror-train starts rolling". Since "starts rolling" means acceleration, then the answer is "NO", the light will not come back to the hole. You have just devised a laser beam accelerometer (a detector for accelerated motion). The light beam will miss the keyhole.

    On the other hand, if you did your experiment in a train that is in UNIFORM motion, the light beam WILL bounce back to the keyhole. Relativity is very tricky, you need to think really hard about the setup of your exercises.
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    Quote Originally Posted by x0x View Post
    The key to your answer is in the part "When the mirror-train starts rolling". Since "starts rolling" means acceleration, then the answer is "NO", the light will not come back to the hole. You have just devised a laser beam accelerometer (a detector for accelerated motion). The light beam will miss the keyhole.

    On the other hand, if you did your experiment in a train that is in UNIFORM motion, the light beam WILL bounce back to the keyhole. Relativity is very tricky, you need to think really hard about the setup of your exercises.

    x0x : I am doing the best I can. ..

    MAy I ask why....? If the laser beam is very-very-very short (is it correct to say "single photon" in this instance?) will it still be accelaration dependant?
    I mean that what is important is the minute of collision between the ray of light (or photon?) and the mirror. As this incident is very close to timeless , is it really significant whther it is a uniform motion or accelaration of the moving mirror?

    Thanks again.
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    Hello chaimc. Last try
    Have you taken the suggestion form Jilan and invert the problem ? That's the correct way to understand x0X post #16

    You can even replace the light by a tennis ball if you want. From the mirror FoR the ball is coming at an angle, but both key-hole and balls are always vertical to each other in the whole trajectory.
    But if the key_hole changes speed (accelerate/decelerate) the ball is no more under the hole and will fail to return trough. You have devised an accelerometer.

    Two problem though.
    -Any tennis ball do NOT bounce back at the same angle, a part of the momentum is exchange with the floor. If you picture yourself standing above a rolling floor, dropping a ball and waiting for it to bounce back, you get the feeling it won't exactly.
    -My problem to understand this with light is that I thought there is also a momentum exchange between light and mirror. But apparently only in the vertical axis, that means the angle won't change for light even at relativistic speed. What is still true, is that acceleration is changing the angle (kind of logic if constant-speed does NOT)
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    Quote Originally Posted by Boing3000 View Post
    -My problem to understand this with light is that I thought there is also a momentum exchange between light and mirror. But apparently only in the vertical axis, that means the angle won't change for light even at relativistic speed.
    What is still true, is that acceleration is changing the angle (kind of logic if constant-speed does NOT)

    The angle of reflection is NOT equal to the angle of incidence for accelerated mirrors. Images will be reflected distorted by an accelerated mirror. The distance between two points will increase progressively with each light reflection.
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    Quote Originally Posted by me
    Quote Originally Posted by x0x
    The angle of reflection is NOT equal to the angle for accelerated mirrors
    What is still true, is that acceleration is changing the angle (kind of logic if constant-speed does NOT)
    I really hope that you've understand that I agree with you on that point. Maybe you can try to explain to me why in the case of un-accelerated mirror the "parallel" to the mirror dirction component of the momentum is NOT exchanged/interacted.

    Please throw as many math as you'd care to. I really want to understand chaimc setup (non-accelerating setup). I cannot understand even using SR (the key-hole would be length contracted (in the width dimension (X) the movement of the mirror or observer) and kind of zoom-in (the z-dimension) but zero-length contacted (so as the classic Pythagorean observed speed of C is c (the angle speed of light in the mirror FoR)) in Y dimensions (the up-down of the mirror).
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    Quote Originally Posted by Boing3000 View Post
    I really hope that you've understand that I agree with you on that point. Maybe you can try to explain to me why in the case of un-accelerated mirror the "parallel" to the mirror dirction component of the momentum is NOT exchanged/interacted.
    It is not "exchanged" in the frame of the mirror. For obvious reasons, the ray is perpendicular on the mirrior, so there is no parallel component.
    It is surely exchanged in the frame of the platform, where the light of ray makes an (aberration) angle with the mirror, so there are non-null components in BOTH perpendicular AND parallel direction.

    Please throw as many math as you'd care to. I really want to understand chaimc setup (non-accelerating setup).
    chaimc setup IS accelerated. All his setup are accelerated (see the "mirror on the train"). This is what makes his setups so much more interesting.

    I cannot understand even using SR (the key-hole would be length contracted (in the width dimension (X) the movement of the mirror or observer) and kind of zoom-in (the z-dimension) but zero-length contacted (so as the classic Pythagorean observed speed of C is c (the angle speed of light in the mirror FoR)) in Y dimensions (the up-down of the mirror).
    I have no idea what you are talking about, you are coming across as totally muddled. Clear your thought and ask again.
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    OK. I think I got it by now. You have answered what I wanted, even though did not know how to ask....

    The Statement (as I copied fron BOING):" there is also a momentum exchange between light and mirror. But apparently only in the vertical axis, that means the angle won't change for light even at relativistic speed is true".
    In my words : A perpindicular photon/light sent to a non accelerating mirror will bounce perpincular regardeless of the mirror's motion. That I believe is agreed by all so far.


    QUESTION: How do you reconcile this with Einstein's light clock???

    If the above is true then the whole concept of the light clock experiment is iligitimate!! isnt it....?

    What I see is this: we have two parallel mirrors moving unformicaly and a "photon" is bouncing from one mirror the other. The photon will keep bouncing on the same imaginary track, the whole appratus will keep moving and eventually the photon will escape from the apparatus and will be left behind.



    Thanks for your wise answers!
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    Quote Originally Posted by chaimc View Post

    What I see is this: we have two parallel mirrors moving unformicaly and a "photon" is bouncing from one mirror the other. The photon will keep bouncing on the same imaginary track, the whole appratus will keep moving and eventually the photon will escape from the apparatus and will be left behind.
    No, the light will continue to bounce off between the mirrors if the motion of the apparatus is inertial.
    If the motion is accelerated, the apparatus will function as an accelerometer, doing what accelerometers do: detecting the acceleration. The "light clock" in this case will stop functioning after a long, long time.
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    Quote Originally Posted by x0x View Post
    No, the light will continue to bounce off between the mirrors if the motion of the apparatus is inertial.
    If the motion is accelerated, the apparatus will function as an accelerometer, doing what accelerometers do: detecting the acceleration. The "light clock" in this case will stop functioning after a long, long time.
    Hi XoX

    pls. is the statement i quoted from BOING in my last post correct or not?
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    Quote Originally Posted by chaimc View Post
    In my words : A perpindicular photon/light sent to a non accelerating mirror will bounce perpincular regardeless of the mirror's motion. That I believe is agreed by all so far.
    I already answered that: in the frame of the mirror, the statement is true. In a frame in motion wrt. the mirror, the statement is not true, light gets aberrated REGARDLESS of whether the motion is inertial or not.
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    didnt you sya before that only when the mirror accelerates it will abberate?
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    Quote Originally Posted by chaimc View Post
    didnt you sya before that only when the mirror accelerates it will abberate?
    No, I did not say that. Please go back and read carefully what I posted.
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    again, the light is bouncing up and down on the same and exact track. aal the time. as if it independant of anything else. including "frames".
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    i wiil have to look for it but as i recall yoy have agreed with someone (Boing?) who said it... maybe i was wrong.
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    Quote Originally Posted by chaimc View Post
    again, the light is bouncing up and down on the same and exact track. aal the time. as if it independant of anything else. including "frames".
    You can't have that.
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    again, I have never set foot in university for my regret so my questions are ... what ever they are... sorry.

    BUT On what grounds do you stand when you answer in such confidence? Is there an experimental evidence to that ?

    (just dont say relativity...)

    Thx, really!
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  32. #32  
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    Quote Originally Posted by chaimc View Post
    again, I have never set foot in university for my regret so my questions are ... what ever they are... sorry.
    This appears to be your problem. It is not too late to go and study. I suggest that you do so.

    BUT On what grounds do you stand when you answer in such confidence? Is there an experimental evidence to that ?

    (just dont say relativity...)

    Thx, really!
    Why not "say relativity"? Do you have a problem with that? Are you yet another of those that hopes to disprove it?
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    hahaha.... maybe I am . no' really, it is way out of my league.

    But you did not answer my question: On what ground etc`?
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    Quote Originally Posted by chaimc View Post
    hahaha.... maybe I am . no' really, it is way out of my league.

    But you did not answer my question: On what ground etc`?
    Relativity teaches you that, you should try learning it.
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    Quote Originally Posted by x0x View Post
    Relativity teaches you that, you should try learning it.


    I can not say I have studied it, not formally any how.

    But we have the above statement that say one thing and in one hand and a set of postulations and believes on the other hand.
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    Quote Originally Posted by chaimc View Post
    I can not say I have studied it, not formally any how.

    But we have the above statement that say one thing and in one hand and a set of postulations and believes on the other hand.
    So, you haven't studied relativity, you do not know relativity, and yet , you try to pass judgement? So, as I guessed, you are an anti-relativistic crank. Bye!
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    Quote Originally Posted by x0x View Post
    So, you haven't studied relativity, you do not know relativity, and yet , you try to pass judgement? So, as I guessed, you are an anti-relativistic crank. Bye!
    C'mon.. dont go. i enjoy talking to you. (-:

    I did not study relativity FORMALLY but bymyself. It is problematic, trust me, I know.


    Sears Zimansky & Young in their monumental book say that "you must learn how to mistrust intuition" if you want to understand relativity.
    What the hell does it mean? Its phylosophy, maybe even psychology, not physics.

    It is all about that, isn't it? It is all about walking the extra mile beyond the zone of intuition. No?
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    Quote Originally Posted by x0x
    I have no idea what you are talking about, you are coming across as totally muddled. Clear your thought and ask again.
    Sorry, I have made a picture

    I have represented the key-hole has seen from front at 3 different moment in the trajectory (the rest a the picture is seen from above)
    So in the mirror frame, A-C distance must be the same as A-B distance in the key hole frame (same constant multiple of the speed of light).
    So the solution is that the mirror see the Key-hole closer/zoom'ed-in (A-B is shorter) and squeezed (B-C shorter). The up down dimension squeezed too (not shown here) (and time also, which I won't even try to think about)

    Please let's simplify by speaking only about non-accelerating setup. What I understand from trying to apply SR, is that all along its passing-by path, the apparent contraction changes, because B-C distances changes. When zero at middle giving a rounder object (sorry I haven't try to represent the key-home deformed like a "hour-glass).
    That picture is more like a hunch, red lines are also curved I think.

    My point being: If I had my Feynman right, mirror do not invert left and right. But front from rear. Thus the image deformed at the left is received by something deformed in another way at the right. So in the mirror frame, I think aberration is predicted at the key-hole.
    That is how a drop out like me would have explain to another drop-out like chaimc.
    Is it a valid explanation ? Or the time distortion and the fact the all different light paths must be added (ray-tracing) cancel-out OR increase the aberrations ?

    My other personal question is I cannot quite understand how light could bounce without changing momentum along the B-C axis (missing the keyhole even without acceleration involved (like a tennis ball))
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    Quote Originally Posted by Boing3000 View Post
    Sorry, I have made a picture

    I have represented the key-hole has seen from front at 3 different moment in the trajectory (the rest a the picture is seen from above)
    So in the mirror frame, A-C distance must be the same as A-B distance in the key hole frame (same constant multiple of the speed of light).
    So the solution is that the mirror see the Key-hole closer/zoom'ed-in (A-B is shorter) and squeezed (B-C shorter). The up down dimension squeezed too (not shown here) (and time also, which I won't even try to think about)

    Please let's simplify by speaking only about non-accelerating setup. What I understand from trying to apply SR, is that all along its passing-by path, the apparent contraction changes, because B-C distances changes. When zero at middle giving a rounder object (sorry I haven't try to represent the key-home deformed like a "hour-glass).
    That picture is more like a hunch, red lines are also curved I think.

    My point being: If I had my Feynman right, mirror do not invert left and right. But front from rear. Thus the image deformed at the left is received by something deformed in another way at the right. So in the mirror frame, I think aberration is predicted at the key-hole.
    That is how a drop out like me would have explain to another drop-out like chaimc.
    Is it a valid explanation ? Or the time distortion and the fact the all different light paths must be added (ray-tracing) cancel-out OR increase the aberrations ?

    My other personal question is I cannot quite understand how light could bounce without changing momentum along the B-C axis (missing the keyhole even without acceleration involved (like a tennis ball))

    You will not be able to understand what is going on with the aberration and conservation of momentum if you cannot follow the math describing the phenomena, so I will give you a different kind of explanation that does not discuss either aberration or momentum conservation.

    In the frame of the train, the light ray returns to the keyhole, no matter how small the keyhole. ALWAYS.
    This means that , in ANY other INERTIAL frame, the light ray will return to the keyhole, ALWAYS. You do not have to worry about any time dilation, length contraction, etc. All you need to remember that the outcome of the experiment is the same in all (inertial) frames.
    If the train accelerates, then the light beam will NOT return to the keyhole, it will "fall behind". The explanation is complicated and it requires math. Suffice to say that , if you throw a ball up in the air in an accelerating vehicle, the ball will end up somewhere behind you.
    To learn physics you will NEED to learn the math behind the physics, there is no other way around.
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    Quote Originally Posted by x0x
    To learn physics you will NEED to learn the math behind the physics, there is no other way around.
    Fair enough. I'll return to the other closed thread and try again do dig out the math.

    Thanks for you patience.
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  41. #41  
    x0x
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    Quote Originally Posted by Boing3000 View Post
    Fair enough. I'll return to the other closed thread and try again do dig out the math.

    Thanks for you patience.
    A much better option would be to re-enroll in school and finish your studies.
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  42. #42  
    Senior Member Boing3000's Avatar
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    Quote Originally Posted by x0x
    A much better option would be to re-enroll in school and finish your studies.
    Well, I have studied other things, and have a full time job some lawn to repay, some other activities, like any normal person.
    So maybe when I retire, and got to much time on my hand. We'll see that in 25 year
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  43. #43  
    KJW
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    Quote Originally Posted by chaimc View Post
    Again, I am standing in front of a mirror train.
    But in this setup, inbetween me (the source of light) and the mirror train there is an opaque wall.

    In the wall there is a very-very-very small hole which from light can escape both ways. In a pictureque fashion only a thin ray of light. (Laser perhaps...?)

    IF the mirror on the other side is stationary I expect the light that comes in to bounce straight back to the hole. Correct?


    And the question:

    Therotically speaking - When the mirror-train starts rollig, will the light bounce back to the hole or will it be shifted and be absorbed in the inner side of the wall etc?
    Let's assume that all motion (velocity and acceleration) is parallel to the surface of the mirror (so that I don't have to keep repeating this). Also, in case it is not clear, the motion of the wall includes the motion of the light source.

    If the mirror and wall are both inertial and moving at arbitrary velocity relative to each other, then the light will return through the hole.
    If the mirror is accelerating and the wall is inertial, then the light will return through the hole.
    If the wall is accelerating and the mirror is either inertial or accelerating, then the light will not return through the hole.

    Generally speaking, a mirror that is invariant with respect to its motion will be indistinguishable in terms of its reflection properties from the mirror at rest.
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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 KJM
    Generally speaking, a mirror that is invariant with respect to its motion will be indistinguishable in terms of its reflection properties from the mirror at rest.
    Of course, that argument can be understood.

    What I can't, however, it understand how "reflection", which is an interaction between and electromagnetic waves and a bunch of atom with special properties called "a mirror", could not be influenced by the motion of the atoms (inertial or accelerated, parallel to the surface, or not).

    But then there a many things I don't understand. So I'll take your word for that.
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  45. #45  
    KJW
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    Quote Originally Posted by Boing3000 View Post
    parallel to the surface, or not
    Parallel to the surface is an important qualification because motion of a mirror normal to its surface does affect the reflected light.
    A tensor equation that is valid in any coordinate system is valid in every coordinate system.
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  46. #46  
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    Quote Originally Posted by KJM
    because motion of a mirror normal to its surface does affect the reflected light
    I cannot reconcile that with basic relativity. For example when I am moving and the mirror is not.

    It would be like saying you could define an absolute movement of the mirror by looking at some reflected light. But I am running in circle. I am going to brood over this a year or two.
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  47. #47  
    KJW
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    Quote Originally Posted by Boing3000 View Post
    Quote Originally Posted by KJM
    Generally speaking, a mirror that is invariant with respect to its motion will be indistinguishable in terms of its reflection properties from the mirror at rest.
    Of course, that argument can be understood.

    What I can't, however, it understand how "reflection", which is an interaction between and electromagnetic waves and a bunch of atom with special properties called "a mirror", could not be influenced by the motion of the atoms (inertial or accelerated, parallel to the surface, or not).

    But then there a many things I don't understand. So I'll take your word for that.
    Don't take my word for it. First note that in the What will I see if the mirror will move very fast? thread, I made no assumptions about the nature of a mirror beyond what you can see for yourself. From this, you can deduce how a moving mirror will behave by applying the principle of special relativity. In the case of an accelerated mirror, note that the reflection of a very short pulse of light takes place at more-or-less an instant in time, too short an interval for any change in the velocity to have any effect, especially given that the reflection is independent of the velocity anyway. The case of the accelerated wall is different because the angle of the emitted light beam depends on the velocity at the instant it was emitted, and if the velocity subsequently changes while the light is in-flight, then the hole in the wall will be at a different location for the returning light. It should be noted that unlike velocity, acceleration is absolute, so it does matter whether it is the mirror or the wall that is accelerating.


    [Btw, it is KJW, not KJM.]
    A tensor equation that is valid in any coordinate system is valid in every coordinate system.
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  48. #48  
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    Quote Originally Posted by Boing3000 View Post
    I cannot reconcile that with basic relativity. For example when I am moving and the mirror is not.
    If you move towards a mirror, the light you emit is blue-shifted in the stationary mirror frame. This is reflected unchanged, but because you are moving towards the reflected light, that light is again blue-shifted. Note that the image you see of your reflection is moving towards you at nearly double the speed of the mirror (hence the double application of the blue-shift).


    Quote Originally Posted by Boing3000 View Post
    It would be like saying you could define an absolute movement of the mirror by looking at some reflected light.
    No. In fact, my argument (for motion parallel to the surface) is based on the principle that you can't.
    A tensor equation that is valid in any coordinate system is valid in every coordinate system.
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