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Don't get this

  1. Feb 2, 2006 #1
    Don't get this....

    OK, I know it is impossible to reach the speed of light, but, yeah, so, ummm...

    If one could reach the speed of light time stopps,but then light always travels at the speed of light. If time stops for something at the speed of light, then wouldn't it stop for light, maaking light go a distance over 0 time, giving it infinte velocity? Even though it is like 300,000,000m/s and that is a big number, it isn't infinite so how can time come to a complete stop if one was to reach the speed of light?

    I don't get that so someone please inject some brains into my ears so I will understand that lol.
  2. jcsd
  3. Feb 2, 2006 #2


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    The proper time concept is really irrelevant to light because it is the time experienced in a rest frame and light has no rest frame. The photon just doesn't experience time; a photon that left a distant galaxy a billion years ago, by OUR time, and just now entered your retina has not experienced any time at all on its flight. Not even, really, zero time.
  4. Feb 3, 2006 #3
    Try to synchronize a clock comoving with the photon
  5. Feb 3, 2006 #4


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    Yes, you could say that.

    But time stopping for the light doesn't mean an infinite speed from an external observer's point of view, it means infinite from an internal observer's point of view.

    Light (photons) do not experience time at all. They "see" the entire universe in one instant - as if they really are travelling at infinite speed - in their own frame of reference, that is.

    (Caveat: as many posts are likely about to tell you, it is meaningless to speak about photons "seeing" anything, or even a frame of reference moving at c. This is true, but as a fellow layperson, I understand how it can help to loosen the rules to make a leap of understanding. Keep in mind though, that faulty analogies (such as mine, and the clock Bernhard mentions) will eventually steer you awry.)
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