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We see light?

  1. May 11, 2004 #1
    hello, ive always been wondering why do people say that nothing can travel faster than light? is it because we just dont have anything to push to a speed faster than light or is it actually impossible??
     
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  3. May 11, 2004 #2

    chroot

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    According to currently accepted scientific theory, it is impossible for anything with mass to go the speed of light, and anything without mass to go any speed other than the speed of light. It has nothing to do with our technology.

    - Warren
     
  4. May 11, 2004 #3

    ShawnD

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  5. May 12, 2004 #4
    What do you mean by that statement???
     
  6. May 12, 2004 #5

    russ_watters

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    You can apply a force to an object forever and it will never reach the speed of light.
     
  7. May 13, 2004 #6

    Phobos

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    That simple question could start a huge debate in this forum (mass vs. relativistic mass....feel free to look through some of the older threads).

    Sufficed to say, it is in the very nature of spacetime (the "fabric" of the universe) to resist the acceleration of any mass to the speed of light. You can keep accelerating to get closer and closer....0.9c...0.99c....0.999c....but spacetime won't let you get that last bit. It's as if your mass increases so that it gets harder and harder to accelerate any more.

    You affect spacetime and spacetime affects you. Travelling through space also has an effect on spacetime. At our normal Earthly speeds, it's not noticeable, but as you start getting near the speed of light, spacetime starts behaving in weird ways.

    Stick around this forum for all the juicy details.
     
  8. May 13, 2004 #7
    light, although fairly simply defined, is something that I can't ever seem to make up my mind on. It's the visible part of the electromagnetic spectrium, and in essence is nothing more than waves. It has no mass, so it can't be pushed. It'd be like trying to push a giant mass of vaccumed space...there's nothing to push against.

    However, isn't it common theory that mass and energy are one in the same?

    meh.....*goes back to eating lasagna*





    Jeff
     
  9. May 13, 2004 #8
    as to all of the light stuff.

    plenty of well documented research shows that light can be treated as a wave and a particle. it definately shows properties of both.

    as for mass and energy, they are. and a high energy photon collision can actually create new particles. however this requires a lot of energy in the photon!

    according to modern physics, it would take an infinate amount of work to move any mass to the speed of light.
     
  10. May 14, 2004 #9
    so right now we could change energy to mass but not mass to energy? i always thought that all physical changes could be reversed but this is the only thing that i came across that cant be done. that sort of bothers me a bit :grumpy:
     
  11. May 15, 2004 #10
    Isn't mass changed to energy in the sun through the process of fusion? Or a nuclear reactor? Or is that all that something different?
     
  12. May 17, 2004 #11

    Phobos

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    Actually, it includes the entire EM spectrum.
     
  13. May 17, 2004 #12

    Phobos

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    We can change mass to energy...like Amphi said. Another example...fission bombs.
     
  14. May 18, 2004 #13
    I thought that just turns the bonds between protons and neutrons to energy???
     
  15. May 21, 2004 #14
    I remember that, actually, Einstein's theory was saying that it is impossible to accelerate a massive body up to speed of light, however it says nothing about the objects already moving faster than light - e.i. such objects can exsist. Is it "accepted" in current theory?
     
  16. May 21, 2004 #15
    That's a solution to the equations, if you have imaginary mass. But such objects would never be able to travel slower than c, and I don't know how imaginary mass would manifest itself, or if we could detect or interact with it.
     
  17. May 21, 2004 #16

    Chronos

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    experiments with particle accelerators have confirmed the light speed limit and relatavistic effects [increasing resistance to acceleration as particle velocities approach c] with extreme accuracy. we can safely predict that all tardyons [mass possessing bodies with sub light velocities] are forever confined to sub-light velocities in our space time dimension. the existence of tachyons [particles traveling faster than light] is still [at least last i heard] a theoretical possibility. these bodies are, however, forbidden to travel slower than light! it is speculated that if two tachyons with the same momentum collided head on, they would set off an e=mc^2 fireworks display visible in our universe.

    just to much matters up further, lorentzian relativity does not prohibit faster than light speeds and has not yet been entirely refuted. as a matter of fact, it offers a more satisfactory explanation than GR for some relatavistic effects that have been observed: e.g., atomic clocks traveling at the same speed but in opposite directions relative the the rotation of the earth do not tick at the same rate! this is easily explained by LR. it is possible to explain by GR, but is very complicated. it was once thought that the michelson-morley experiment doomed LR, but, that conclusion was hasty and incorrect.
     
    Last edited: May 21, 2004
  18. May 22, 2004 #17
    What's so complicated about it? All you have to do is use an inertial observer as a comparison point for all of the clocks, as was done by Hafele and Keating (Science 177, IIRC).
     
  19. May 23, 2004 #18

    Chronos

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    you are correct. 'very complicated' overstates the case. 'more complicated' is better. LR and GR make the same predictions in most cases. Lorentz eventually conceded that GR was a simpler explanation in most cases. the main difference between LR and GR is that LR assumes a 'preferred' reference frame [aether]. GR asserts a preferred reference frame is not necessary. the differences are fairly subtle, but, make testably different predictions. some interesting experiments are planned [gravitational probe comes first to mind] that should help clarify which is the case. i can envision ways the results could still be inconclusive, but, they should be fascinating regardless.
     
  20. May 23, 2004 #19

    Haelfix

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    Actually in GR, its perfectly ok for things to move faster than light speed relative to an observer in a *sense*. However, it requires the metric to be expanding, as well as coupled with a peculiar set of initial conditions.

    Richard Gott came up with just such a solution in the 90s (anything that is locally causal and travels faster than c, must basically be a time machine), so he basically discovered a time travelling device, his solution involved two cosmic strings interacting antiparralel.

    There are serious problems though, and technical reasons (both in GR and quantum mechanics) why these sort of things must be excluded in a sensible universe (beyond the obvious grandfather problem).

    It was interesting though for mathematical reasons, and as a test of our limitations.

    Incidentally, there are reference frames in inflation scenarios that display this sort of behaviour (parts of the universe becoming invisible as time progresses). Though there is no causality problem there.
     
  21. Jul 9, 2004 #20
    I'm no expert on atomic bombs so I'm not entirely sure, however I believe some of the mass is converted into energy. The point is, matter CAN be turned into energy and energy can be turned into matter. Why? They're the same thing!
    e=mc^2
    With the right mechanism to do so, you can convert between matter and energy since they are just different manifestations of the same stuff.
     
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