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Speed of Light

  1. Jan 31, 2004 #1
    Firstly, just a high to everyone, (first post, aye).

    Now, everyone has been saying that FTL Travel (Faster than Light) and even the speed of light is impossible. (dammit... ) than how is it that light can go at the speed of light.

    Now, for some touching back on the SOL theory. As you approach the SOL time gets slower and the energy needed for the speed gets higher. AT the SOL energy is infinite and time is held. (e.g 12:00 forever: never even hitting 1 ms later)

    Now, if the energy required is infinite than how can Light itself go that fast.

    Is the secret hidden in Light??!
     
  2. jcsd
  3. Feb 1, 2004 #2

    russ_watters

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    The secret is that light has no mass.
     
  4. Feb 1, 2004 #3
    AS he said light has no mass. It is an electromagnetic fluctuation. think of light as an increase in the electromagnetic field that moves throuhg space. This fluctuation can only propagate at the speed of light. It has no mass so the rules about accelerating to that speed are irrelevant. Also there is no known reason why it travels at that speed, it just does.
     
  5. Feb 1, 2004 #4
    oh ok. i didn't really know that... well a day in which you learn something isn't a day wasted...

    thanx guys
     
  6. Feb 1, 2004 #5
    There is a common misunderstanding about the speed of light being the limit of all physical speed. The actual limit is the the speed that a mass can be accelerated relative to the accelerating energy source. Since electromagnetic waves (light) is the fastest means of transferring energy it appears to the energy source as if the mass is increasing without bound as speed approaches light speed. Actually if some energy source is already travelling near the speed of light relative to some other object it can still accelerate another mass in the same direction producing greater than light speed relative to the first object. As a result the only limit on the speed of a rocket is the limited energy (and ejectable mass) it carries with it.
     
  7. Feb 1, 2004 #6

    selfAdjoint

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    Actually if some energy source is already travelling near the speed of light relative to some other object it can still accelerate another mass in the same direction producing greater than light speed relative to the first object. As a result the only limit on the speed of a rocket is the limited energy (and ejectable mass) it carries with it.

    Absolutely wrong, and often refuted on these boards. Learn relativity.
     
  8. Feb 2, 2004 #7

    Phobos

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    - - moving this to the Relativity forum - -
     
  9. Feb 2, 2004 #8

    Umm...yeah. You can't jsut add velocities straight like that. The correct formula for adding velocities ( don't recall off hand) does not allow for the sum to exceed the speed of light. Just as the speed of light in a vacuum is a constant irrelevant of the motion of the observer, at the same time the sum of two velocities is limited to the speed of light irrelavant of the speed of the observer. This is dictated by the Lorentz transformations which are in turn dictated by the minkowski metric which describes spacetime in the absence of gravity (Special Relativity).
     
  10. Feb 4, 2004 #9
    I gave a physical process for why the mass increase is only apparent. How about you giving a physical process for why velocities can't be added (not just a mathematical speculation). [:>)]
     
  11. Feb 4, 2004 #10

    turin

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    How about 100 years of experimentation in electromagnetics?
     
  12. Feb 4, 2004 #11
    How about it? [:>)]
     
  13. Feb 5, 2004 #12

    russ_watters

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    A good example is a particle accelerator. They put tons and tons of energy into a proton (or other small particle) and only get it asymptotically closer to C. Einstein's relativity is not just "mathematical speculation."
     
  14. Feb 5, 2004 #13
    You didn't read my first post. Remember that in the accelerated particles rest frame its mass is still rest mass. Where is the increased mass. It only looks to the accelerator (or any observer at rest relative to the accelerator) as if the mass has increased because the particle is tending to outrun the means of energy transfer (or information transfer).
     
  15. Feb 5, 2004 #14

    turin

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    Electromagnetic energy propagates at speed c away from its source. This is true regardless of how fast the source is moving or how fast the observer is moving.
     
  16. Feb 6, 2004 #15
    Tha manner of that statement shows, beyond any shadow of doubt, that you don't have a clue. The idea of relativity is just that. RELATIVE. {;>)] ~
     
  17. Feb 9, 2004 #16

    turin

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    By all means, enlighten me. Which part of my last statement of incorrect? I will admit that I have not performed exhaustive experimentation to validate my last statement, but the experiments I have done have demonstrated it. I have also been taught the same thing in all of my academic education. So, I would certainly like to hear why you think that it is incorrect. Has there been an experiment that falsifies the invariance of Maxwell's equations under a Lorentz transformation?
     
  18. Feb 9, 2004 #17
    Electromagnetic energie propagates at speed c in every inertial system.
    When the source is moving with a speed v in te observers systems, lights propagate at speed c for the observer, but the relative velocity between the light and the source isn't c, but c-v (if v is small). The observer who travels with the source, sees that the light is going away from the source with light speed.
     
  19. Feb 9, 2004 #18
    I think we are getting a definite maybe on this subject.

    Maybe some light shift would help:

    Take two observers, one on Earth and one on Earth'. They are two billion light years apart. Exactly halfway between the two planets is a galaxy (8C1435+635). It is .93C red shifted to Earth and blue shifted a like amount to Earth' indicating a movement away from Earth and toward Earth'. Strictly from the perspective of the observers on Earth and Earth', and these observers only, take a simultaneous emission of a beam/wave/photon leaving the exact center of 8C1435+635 at the same instant moving toward these planets. From a number of discussions it appears the .93C red shifted light will arrive at Earth in the same instant the blue shifted light will arrive at Earth'.

    No other observers are allowed. We don't care about an observer on 8C1435+635. Assume ideal vacuum along both paths with no intervening mass. Is there general consensus the arrival times would differ or arrival times would be identical?
     
  20. Feb 9, 2004 #19
    If they did arrive at the same instant, should the red and blue shift be so pronounced?
     
  21. Feb 10, 2004 #20
    Where does the doppler shift occur, at the source, at the observer, half at the source and half at the observer or gradually along the way?
     
  22. Feb 10, 2004 #21
    I don' t think the dopler effect is essential in this question. It only says that the galaxy is moving towards earth'.
    Sinds there are only two observers, there are two answers
    Observer 1 on earth detect the redschited beam first and after (a long) time he see that the other beam reaches earth'(because the reflection of the hit has to travel from earth' to earth.
    The observer on eart'see it the other way around.
    simultaneous doesn't exist in special relativity. It always depend from the observer which events take place together.
     
  23. Feb 10, 2004 #22
    ______________________________________________________________
    Take two observers, one on Earth and one on Earth'. They are two billion light years apart. Exactly halfway between the two planets is a galaxy (8C1435+635). It is .93C red shifted to Earth and blue shifted a like amount to Earth' indicating a movement away from Earth and toward Earth'. Strictly from the perspective of the observers on Earth and Earth', and these observers only, take a simultaneous emission of a beam/wave/photon leaving the exact center of 8C1435+635 at the same instant moving toward these planets. From a number of discussions it appears the .93C red shifted light will arrive at Earth in the same instant the blue shifted light will arrive at Earth'.
    ________________________________________________________________

    Alrighty then, let’s take a little different spin. The light is emitted at the point source (galaxy 8C1435+635) at wavelength X. Let the "frequency" shift in the wavelength of the light receding/approaching at .93C be Y. So the Frequency of light on Earth would be X - Y and Earth' X + Y. How is the drastic alteration in properties of the original light source accounted for? Does it mean the photon arrives at exactly the same instant on both Earth and Earth' but parts of the receding (Earth') photon arrive later and parts of the approaching (Earth') photon arrive a little sooner?
     
  24. Feb 10, 2004 #23

    turin

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    Speak for yourself (and other people of like mind). In this discussion, all three perspectives are valid.




    Simultaneity exists just as much as spatial distance, temporal time, or 3-velocity in SR.

    Actually, a better analogy would be, if you can't say "simultaneous" in SR then you can't say "at rest" in SR either.
     
    Last edited: Feb 10, 2004
  25. Feb 10, 2004 #24

    selfAdjoint

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    Sure you can say at rest in SR. Every inertial observer can cll herself at rest. And her frame (in the small limit) is Galilian.
     
  26. Feb 10, 2004 #25
    quote:
    ----------------------------------------------------------------------Originally posted by meddyn
    We don't care about an observer on 8C1435+635.
    ----------------------------------------------------------------------

    Speak for yourself (and other people of like mind). In this discussion, all three perspectives are valid.

    _______________________________________________________________

    Thank you for your response. That shed a great deal of light on the subject and helped clarify technical points.
     
    Last edited: Feb 10, 2004
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