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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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- Thread starter Lukas_23
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- #1

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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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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.

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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.

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.

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ghwellsjr

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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.

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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*?

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

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ghwellsjr

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ghwellsjr

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Here it is: http://www.youtube.com/watch?v=pEIj9zcLzp0"

09:30

"If you're a photon, eternity is no time at all."

09:30

"If you're a photon, eternity is no time at all."

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ghwellsjr

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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:

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How so, I think that depends on how you measure distance.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.

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.

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ghwellsjr

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How so, I think that depends on how you measure distance.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.

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.

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.

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ghwellsjr

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Just to clear up one other point of confusion: an answer that is indeterminate doesn't mean that the answerYes, 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?

So there is no mistake because 0*300,000=0, correct?...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.

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