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How long does a ray of light travel for based on ITS time scale

  1. May 8, 2010 #1
    Hi,

    Ive been readin about relativity, im a little confused.

    The faster speed an object has, the faster time passes on the object.

    So how long does say a ray of light take to get from teh sun to the earth? It is ~8.5 of our minutes, but say I were on the ray of light; traveling with it as soon as it left the sun towards . How long would my trip to the earth be?

    thanks
     
  2. jcsd
  3. May 8, 2010 #2

    phyzguy

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    Actually, time passes more slowly in a moving frame by a factor of Gamma=1/sqrt(1-v^2/c^2). Since a light beam travels at c, time does not pass at all. You can't "travel along with the light beam" , because you have mass and it would take an infinite amount of energy to accelerate you to the speed of light. However, if you could travel along with the light beam, you would experience no time passing at all. In other words, the light beam leaving the sun and the light beam arriving at the earth are simultaneous events.
     
  4. May 8, 2010 #3

    haushofer

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    You can't travel along a beam of light; it goes with the speed of light.
     
  5. May 8, 2010 #4

    Fredrik

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    We've been getting this question twice a week lately. Please check out some of the other threads, e.g. this one (which is still only half-way down the first page). The correct answer isn't "zero" as phyzguy is suggesting. It's that the question doesn't make sense. I explained the reasons in several of the other threads.
     
  6. May 8, 2010 #5

    phyzguy

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    While you can say that it is in some sense a meaningless question, since you can't travel along the light beam (as I said in my post), it is clearly a true statement that all events along the light beam are simultaneous in any reference frame.

    So in the simple context in which the questions was asked, I think the correct answer to the OP's question is that "Time stands still along the light beam". I've read some of the other posts on this topic, and IMHO they are simply too pedantic.
     
  7. May 8, 2010 #6

    Fredrik

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    Actually they're not simultaneous in any inertial frame.

    Some of them might be (in particular the ones that point out that photons aren't conscious), but I don't think mine are.
     
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