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Faster than the speed of light?

  1. Aug 14, 2007 #1
    Faster than the speed of light??

    As I understand it, according to GR, E is directly proportional to M. Therefore hypothetically speaking, if one did have an unlimited supply of E to enable matter to travel as fast as C, M would become infinite, and travel would not be possible.

    However if one wanted to isolate M from the E=MC2 equation, would it not be re-written as M = C2\E, thus making M infinitely small? Please correct me if I am wrong here!

    Also, what experiments have been carried out to support GR and exactly how fast has matter travelled to date?

    Finally, again hypothetically speaking, with an unlimited energy supply available, would one be able to transport space around the matter so theoretically the matter would be stationary and the space around it would be travelling as fast as C.
  2. jcsd
  3. Aug 14, 2007 #2
    First, your algebra is simply wrong. E = mc^2 implies m = E/c^2. When we speak of the mass of an electron as 511 keV, we really mean 511 keV/c^2, but GR folk (and particle physicists) take the value of c to be unity so that m = E = 511 keV.

    I can't speak to how fast matter has travelled, but I would imagine it's really close to c in high energy electron accelerators.
  4. Aug 15, 2007 #3


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    As far as tests of relativity go, I would suggest http://math.ucr.edu/home/baez/physics/Relativity/SR/experiments.html

    The OP would be well advised to forget about asking "what happens if you travel at the speed of light". It can't happen according to relativity, and speculating about it is as fruitless as dividing by zero in mathematics.

    A relevant faq on this frequently asked question is:


    which I'll quote in part:

  5. Aug 16, 2007 #4


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  6. Aug 17, 2007 #5
    That article is true and not true at the same time, reminds me as QM statement :P.

    What we know so far is that "locally" nothing can violate Special Relativity statement that nothing can travel faster than the speed of light in vacuum.

    But the deal comes with physics on "non locality", the idea of velocity or speed as a measure of the displacement rate from place to another loses all its concepts.

    You can imagine a quantum entaglement as a pair of particles or waves that have a mutual past, and if you somehow modified those particles the "information about quantum states" goes "instantly" to the other particle or wave.

    So the false statement is the thing they call "faster" i think that is just bias for making attention on that site :P, since there is no concept like that for non locality.

    Well there are so many tests of General relativity and the most traditional that everyone has done in class is the seconds of arc of Mercury perihelion.

    One more thing, i think GR is best looked by its principles rather than that result of equation, as analogy is like saying all newtonian dynamics are just f=ma and we forgot everything else....., at leaft we need the 3 laws and action or lagrangian or hamiltonian for that.

    I better think GR is well described as "matter curves spacetime and spacetime deforms matter"
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