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Is SOL infinite? (from its own point of view)

  1. Nov 14, 2011 #1
    I wondered if just stating that the speed of light is 300,000 km/s in all reference frames does not give the whole picture.

    I heard Penrose say that time for light is 0. Wouldn't that mean from its point of view it goes everywhere instantly and thus has infinite speed?
     
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  3. Nov 14, 2011 #2

    ghwellsjr

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    If you're going to say that time for light is zero, then you must also say that distance for light is also zero, and since zero divided by zero is indeterminate, you have to figure out the problem some other way. You cannot jump to the conclusion that it is infinite any more than that it is zero or any other value.
     
    Last edited: Nov 14, 2011
  4. Nov 14, 2011 #3
    Why is distance zero for light? I know it stems from the equation but clearly light travels so assuming physical laws are everywhere the same, that contradicts that light travels for me but not for itself.

    EDIT: Sticking to the math, if 0/0 could be any number this at face value seems to say distance that light travel is any value and it is omnipotent.
     
    Last edited: Nov 14, 2011
  5. Nov 14, 2011 #4

    ghwellsjr

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    Any line of reasoning that leads to the idea that time for light is zero also leads to the idea that distance for light is also zero.

    How do you get that distance is any value from 0/0? The zero on the top is distance. The result of the division is speed and you cannot draw any conclusion from doing this calculation.

    And I'm not saying that time or distance for light is zero. I'm saying that the whole idea does not lead to anything conclusive.
     
  6. Nov 14, 2011 #5
    Yes, the speed is 0/0. But that means it can be any speed because 0*x=0.

    So we don't know its speed, it can be anything, and we know its speed to be 300,000 km/s. Where is the mistake here?

    a) Relativity: light speed is finite
    b) Penrose: "clock" of light is at all times zero.

    ?

    EDIT: Was Penrose saying the "clock" of light never moves for us?
     
    Last edited: Nov 14, 2011
  7. Nov 14, 2011 #6

    ghwellsjr

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    Did Penrose put quotes around clock? That means he is trying to illustrate that the idea of a clock for light is meaningless and the idea of time for light is meaningless. Can you provide a fuller quote so we can see the context of what Penrose is saying, or a link where we can see it for ourselves?
     
  8. Nov 14, 2011 #7
    No, I put the quotes to show an analogy for time - he said just time in a video in an explicit way. As soon as I find it I will post the link.
     
  9. Nov 14, 2011 #8

    ghwellsjr

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    OK, but I would suggest that you listen carefully to what he says before and after that short sound bite and see if you can figure it out on your own. I'm sure Penrose would never try to convince anyone the light can have a clock or that it can keep track of time. He's probably trying to point out the ridiculousness of the concept.
     
  10. Nov 14, 2011 #9
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  11. Nov 14, 2011 #10

    ghwellsjr

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    Start listening at 9:05. He says:

    If you wanted to build a clock, you have to have massive entities in it and you have to have particles with mass but in this view everything with mass in it finally decays away; radiates away and there is no way of building any entity which keeps time, and so, although the universe goes on expanding to eternity...eternity to these things in the universe isn't all that long in a sense. If you were a photon, eternity is no time at all.​

    So he is pointing out that a photon, since it is massless, has no concept of time, not that eternity is an infinite time or a long time or a short time or zero time or any time at all.

    So he did not say "that time for light is 0", as you misquoted him. He said time does not apply to a photon. So my prediction was exactly correct:
     
  12. Nov 14, 2011 #11
    How so, I think that depends on how you measure distance.

    An observer traveling near light speed between A and B can measure distance by using light, and in that case he will find it is smaller, however if he were to use a surveyor's wheel on a road between A and B he would not find it smaller.
     
  13. Nov 14, 2011 #12

    ghwellsjr

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    The topic of this thread is about how light could measure its own speed, not how an observer traveling near light speed would measure anything.
     
  14. Nov 14, 2011 #13

    ghwellsjr

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    Just to clear up one other point of confusion: an answer that is indeterminate doesn't mean that the answer is anything, it just means we have to solve the problem some other way as I stated earlier:
    So there is no mistake because 0*300,000=0, correct?
     
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