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Non-locality and relativity

  1. Sep 16, 2014 #1
    It is my understanding (perhaps I am wrong) that relativity implies that all frames of reference are equal. For example, if there are two uniformly (no acceleration ) moving objects ( and no others, an empty universe) then one can say object "A" is moving and "B" is still. It is equally true to say that "B" is moving and "A" is still.
    A photon is a uniformly moving object. Therefore one can say it is still and the universe is rushing past it. For the photon the universe has zero volume, no distance. To me this fits in with QM's non-locality.
    Physics is not my area of expertise, so be kind!
     
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  3. Sep 16, 2014 #2

    PeterDonis

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    No, it isn't; at least, not in the sense required here. The term "uniformly moving" is misleading in this respect; it seems to mean "unaccelerated", which a photon is; but it really means (i.e., the math that underlies these English words really means) "unaccelerated, and moving slower than the speed of light". Things moving at the speed of light are fundamentally different, in relativity, from things that move slower than light. There is a forum FAQ on this:

    https://www.physicsforums.com/showthread.php?t=511170
     
  4. Sep 16, 2014 #3

    phinds

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    You are making the completely understandable and very common beginners mistake of thinking that you can assign an IRF (Inertial Reference Frame) to a photon, but you can't. The math gives physically impossible answers when you try to do that so it's considered a meaningless concept.
     
  5. Sep 16, 2014 #4

    Nugatory

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    You cannot. The problem is that there is no frame in which light travels at any speed other than ##c##. We have a FAQ for this question: https://www.physicsforums.com/showthread.php?t=511170
     
  6. Sep 16, 2014 #5

    ghwellsjr

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    More precisely, all Inertial Reference Frames (IRF's) are equally valid and part of the definition of an IRF is that light travels at c in it.

    More precisely, object "A" is moving according to a particular IRF and "B" is at rest in the same IRF.

    More precisely, object "B" is moving according to a different IRF and "A" is at rest in that IRF.

    As I said before, light is defined to move at c in each and every IRF.

    No, you can't say that light is at rest in any IRF. As I said before, light is defined to move at c in each and every IRF so you can never say it is still in an IRF.

    There are IRF's where the universe is rushing at near the speed of light but not including the speed of light.

    I hope I have been kind.
     
  7. Sep 17, 2014 #6
    Thanks for your answers. Why is the speed of light 186282 mps? I know that that speed has been empirically validated. What I am asking, is why 186282 mps is so special. If photons traveled at 186181 mps would that mean that the Lorenz transformation equations would yield different results? If photons did not exist would 186282 mps still give accurate results via the Lorenz equations? Why is 186282 mps the exact speed required to get accurate results (of relativistic effects, such as time dilation etc) from the Lorenz equations?
     
    Last edited: Sep 17, 2014
  8. Sep 17, 2014 #7

    Nugatory

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    If the speed of light were something other than 186282 m/s, then that different speed is the constant that would appear in the Lorentz transforms. The transforms are derived from the assumption that the speed of light, whatever it is, is the same in all frames.

    As for why that speed is what it is? Light is electromagnetic waves, and the speed at which these waves propagate is determined by and can be calculated from the laws of electricity and magnetism which James Maxwell discovered in 1861 (google for "Maxwell's equations").

    [as an aside.... except when you are studying the quantum mechanical properties of light, you should avoid thinking in terms of photons. They aren't what you think they are].
     
  9. Sep 17, 2014 #8

    ghwellsjr

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    Actually, 186282 mps is not the exact speed of light. It's more like 186282.397051221 mps but even that is not exact. The exact speed of light is 299792458 meters per second. You may be wondering how the exact speed of light came out to be an integer. Well, that's not a measured value or an empirically validated value, that's a defined value and it was defined to be that value before it was possible to validate it. It could have been defined to be some other value. But now we define the meter by how far light travels during a certain interval of time. So if some other value were used, it would change the physical length of what we call a meter.

    I'm sure if scientists could rule the world and start over with a more consistent set of units, they probably would have defined the exact value of the speed of light to be some power of ten and use another unit of length more closely to a foot. In a lot of my diagrams I use the speed of light to be 1 foot per nanosecond which is close but not exact to the defined value but good enough to make the distance and time be in terms that most people can relate to. Can anyone relate to how far a light-second is?
     
  10. Sep 17, 2014 #9

    PeroK

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    It's most of the way to or from the moon! Which is about 1.3 light-seconds away.
     
  11. Sep 17, 2014 #10

    Nugatory

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    In other words.... Not the tape measure that I want to be using to frame a house, or build a road, or just about anything else that I might need to measure here on earth. :smile:

    (This is, of course, the point that ghwellsjr was making - I'm pretty sure that was a rhetorical question).
     
  12. Sep 17, 2014 #11

    ghwellsjr

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    I'll remember that next time on the way to or from the moon!

    Off the top of your head, can you say approximately how far away the moon is in feet?
     
  13. Sep 17, 2014 #12

    PeroK

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    It's about 400,000 km.

    I can picture light travelling to the moon in 1.3 seconds. I can't picture light travelling from my heel to my toe in 1 nanosecond!
     
  14. Sep 17, 2014 #13

    ghwellsjr

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    I asked about feet not km.

    If you know that light travels 1 foot per nanosecond then it's pretty easy to determine that if it takes 1.3 seconds for the light to get from the earth to the moon, then the moon is 1.3 billion feet away from the earth.

    With our electronics instruments capable of measuring sub nanosecond intervals, it's easy for me to picture an experiment that shows light taking 1 nanosecond to propagate 1 foot.

    Anyway, this is all just a bunch of side track just for fun.
     
  15. Sep 17, 2014 #14

    Nugatory

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    and we've just hijacked wittgenstein's thread... So let's give it back to him now :smile:
     
  16. Sep 17, 2014 #15

    PeroK

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    Yes, so to say something constructive re the OP. If you think classically, you would imagine that distance and time are the fundamentals of the universe and speed would be derived from that. But, as it turns out, the speed of electro-magnetic radiation (which can propagate itself through free, empty space) is fundamental to the universe, and time and distance are, in a way, derived from that.

    So, the speed of light itself (however you measure it, whatever units you use or how fast it actually is) is not the point. It's that the speed of light is a fundamental property of our universe and, in a sense, trumps our classical notions of time and distance.
     
  17. Sep 17, 2014 #16
    I was not precise enough in my question (post 6). I meant to ask,
    1. Why is 186282 mps the only number that yields accurate results in the Lorenz equations and/or E=MC2?
    2. If any number works (depending on the speed of light) then if light speed is 5 mph, I am 6 feet tall and am going 4/5 of 5 mph then I will be 3.6 feet tall. That does not seem right! *
    So 186282 mps is more than just how fast light travels.
    Why does light travel at the only speed (186282 mps) that works in the equations?
    * If that is true, ( that light's distance per second is arbitrary and not linked to another physical principle ) how does the speed of a photon influence how tall I will be? If I am in a totaly dark part of the universe (no light) how can a distant photon make me smaller when I am going faster?
     
    Last edited: Sep 17, 2014
  18. Sep 17, 2014 #17

    Dale

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    Don't get hung up on the number. It is purely an artifact of the choice of units. You can make it have any number you want by picking the units.

    The key points are that it is finite and frame invariant.
     
  19. Sep 17, 2014 #18
    My point is not what units we use ( miles per second , inches per hour etc), its that if light traveled much slower, say 5 miles per hour, why would I be 3.6 feet tall, if I am 6 feet tall (when stationary ) and going 4/5 of 5 miles per hour?
    1. If the speed of light is arbitrary and not linked to another physical principle, then a single photon can determine my size. Nothing other than the photon (there is no connection to any other physical principle) determines my size. That does not seem right!
    2. Therefore 186282 mps * is not arbitrary. Why is the speed of light 186282 mps, the only number that gives accurate results for E=MC2?
    * You can convert that to any unit you wish, miles per hour, inches per 24 hours etc. The speed is what counts not how you measure that speed.
     
    Last edited: Sep 17, 2014
  20. Sep 17, 2014 #19

    Nugatory

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    Light is electromagnetic waves. The speed at which these waves propagate is determined by the laws of electricity and magnetism. The only way that ##c## could have a different value that it does would be if the laws of E&M were different from what they are - for example, if the force between two charged particles were different than what we've observed it to be.
     
  21. Sep 17, 2014 #20
    If the laws of electricity and magnetism were different in a particular way that made the speed of light 5 mph then I would be 3.6 feet tall (if I was 6 feet when stationary ) if I was going 4/5 of 5 mph ?
    In other words it is not my relation to the speed of light *that explains why I am 3.6 feet but rather the principle ( laws of electricity and magnetism ) linked to the velocity of light that explains why I am 3.6 feet tall? In other words particular laws of electricity and magnetism explain why the speed of light is what it is and why I would be 3.6 feet tall ( if the speed of light was 5 mph, I'm 6' and going 4/5 of 5 mph)?
    Is that what you are saying? That makes sense to me.
    * The relation of my speed to the speed of light is not the explanation. The relationship between the speed of light and my size is a correlation not an explanation.
    For example, there is a correlation between crime and ice cream sales. When ice cream sales go up, crime goes up. However, ice cream sales go up in summer (as does crime) and go down in winter (as does crime). Ice cream sales and crime are linked but one does not explain the other. Summer is the explanation. Similarly, my relationship with the speed of light is a correlation but not an explanation as to why my size is different at different velocities? The laws of electricity and magnetism is the explanation?
    PS: My degree is in philosophy (hence my name Wittgenstein). Physics is not my field of expertise. Thank you for past help and please help me more!
     
    Last edited: Sep 17, 2014
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