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Question regarding speed of light

  1. Jul 5, 2005 #1
    Hello everyone,

    As an amatuer but curious student of physics I am asking this question. If a particle moves at a speed greater than the speed of light, then what happens (if at all anything happens) to the time dimension in consideration to that of the particle.
  2. jcsd
  3. Jul 5, 2005 #2
    I'd imagine if a particle went faster than the speed of light, it would go backward in time. But, you can't go faster than the speed of light so what do I know?
  4. Jul 5, 2005 #3


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    Gold Member

    Hi, pamichel;
    Welcome aboard. The area that you're asking about is entirely theoretical. Relativity firmly shows that no object with mass can reach the speed of light in vacuum. At 'relativistic speeds' (fast enough for the differences to show on an instrument), the objective time will slow just as the mass will increase and the length shorten. From a subjective reference point, nothing changes. So in answer to your question as written, the only particles that could qualify for the test are photons (and possibly gravitons if such exist). Being massless, light speed is the only one that they're capable of.
    Keep in mind, though, that many things can exceed the speed of light in a refractive medium. You could therefore have a highly energetic set of particles such as fast neutrons breaking the speed of light in water or glass or whatever. Their time does not seem to be significantly effected.
  5. Jul 5, 2005 #4
    Nothing can be said though , the mass increases with velocity and at velocity greater than that of light, it would possess infinite mass (which even Universe fails to possess).

    Personally asking , what do you mean by 'zero' mass of photon when it is at rest? , it means it does not exist at rest , similarily inifnite mass is as unusual as the existence of photon at rest.

    As the particle reaches the velocities near to that of velocity of light , it starts becoming a sort of energy , and at velocities greater than 'c' , it would become an 'infinite mass' meaning it would become a form of tremendous energy and will not remain matter.

    Time for that particle would remain the same, but when the particle's time is compared with other's at rest/minimal velocities, its time would appear to be slower , infact slower than minimal possible slowing rate, leading to possibility that it just may be travelling reverse in time.

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