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## Main Question or Discussion Point

If when you're moving at the speed of light time freezes, why then does it take light 8 minutes to reach the earth from the sun?

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If when you're moving at the speed of light time freezes, why then does it take light 8 minutes to reach the earth from the sun?

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ghwellsjr

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Do you think maybe it's because you're not moving at the speed of light?If when you're moving at the speed of light time freezes, why then does it take light 8 minutes to reach the earth from the sun?

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What do you mean?

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Pauli's exclusion principal???

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Dale

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How could that possibly be relevant?Pauli's exclusion principal???

You may want to read the FAQ on the rest frame of a photon:

https://www.physicsforums.com/showthread.php?t=511170

Basically your opening statement "when you're moving at the speed of light time freezes" is fundamentally invalid.

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As has already been pointed out, you CAN'T move at the speed of light. However, light can, so the second part of your question is meaningful.

Do you understand the concept of distance = rate x time ? Rewritten as time = distance/rate, you could use this to figure out how long it would take you to go 1 mile if you are going 60 miles an hour. How about you apply this to light traveling from the sun to the earth.

EDIT: Do you understand that all I've done here is expand post #2 ?

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So far we know that because an axiom of the theory of special relativity is that light moves at c, we cannot use that theory to describe time dilation for a photon. One might still ask, DO we have a theory that suggests the meaning of time for a photon? I am still curious.

Or maybe I have misunderstood something?

Edit:

In the FAQ the last bit is "The concept doesn't make sense."

I guess I'm asking if in some other theoretical framework it does make sense?

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Dale

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Not that I am aware of.One might still ask, DO we have a theory that suggests the meaning of time for a photon?

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No. There is a sort of geometry that describes photon's worldlines, and one's ability to make "equally spaced" marks along them, even though one cannot assign a non-zero value to the spacing of the marks.One might still ask, DO we have a theory that suggests the meaning of time for a photon? I am still curious.

THis sort of geometry is called an "affine geometry".

It's an interesting topic, but it's a mistake to think of it as having all the properties of "time". That tends to lead only to self contradictions and confusion.

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russ_watters

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Your question started:What do you mean?

But you'reIf when you're moving at the speed of light...

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You have some a notion of time, and you assume that light must have some sense of it too. And this idea is wrong.

Time is something that can be measured, and assigned values. This gives geometry a metric structure. We can say "the interval between point A and point B is C seconds".

The geometry of light has an affine nature - it doesn't have measurable "time intervals" at all. We can order A, B, and C, but we can't assign any meaningful numerical intervals to the "distance" between them.

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You've been a great help, but from the last paragraph I only understood that time doesn't have measurable time intervals! But why?The geometry of light has an affine nature - it doesn't have measurable "time intervals" at all. We can order A, B, and C, but we can't assign any meaningful numerical intervals to the "distance" between them.

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Suppose you have a nice standard plane polarized radio wave.You've been a great help, but from the last paragraph I only understood that time doesn't have measurable time intervals! But why?

If you calculate the invariant time interval, also known as the "proper time" between any two points on the light wave according to relativity, the number you get will be zero.

However, any given observer can mark points along the wave at which the E-field is zero at any given time. And he'll find these points will be evenly spaced. This "even spacing" property happens in spite of the fact that all the proper time intervals are zero.

The distance from A to B, from A to C, and from B to C, measured using the invarinat interval, will all be zero. However, there is a unique point C such that AB and BC are "evenly spaced". This is the affine geometry of the light wave.

The exact spacing depends on the ight wave and the observer. One observer might see an AM radio wave with a 300 meter wavelength - a relativistically travelling observer might see it as much shorter, or longer, due to the doppler effect,

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Dale

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Thank you all, you have been a great help.

Last post puts it straight and simple.

Last post puts it straight and simple.

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the lorentz transformation is singular for the speed of light i.e. Not defined

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The time dilation formula is according to http://en.wikipedia.org/wiki/Time_dilation

T‘ = T * sqrt (1-v

Set v=c, the proper time of light T’ will always be 0. The lorentz transformation is not defined for the speed of light, but the time dilation formula above is.

However, time is not frozen, the proper life time of a photon is zero.

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ghwellsjr

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Here's a thread you should read:

The time dilation formula is according to http://en.wikipedia.org/wiki/Time_dilation

T‘ = T * sqrt (1-v^{2}/c^{2}).

Set v=c, the proper time of light T’ will always be 0. The lorentz transformation is not defined for the speed of light, but the time dilation formula above is.

However, time is not frozen, the proper life time of a photon is zero.

https://www.physicsforums.com/showthread.php?t=661429

Last edited:

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(1)

The question shows a more basic misunderstanding of frames of reference. Suppose the OP had asked instead:

(2) "If when you're moving close to the speed of light time freezes, why then does it take neutrinos 8 minutes to reach the earth from the sun?"

The answer is that when we talk about the time taken for something to reach the earth from the sun, we're implicitly talking about the time as measured in the frame of the earth. But relativistic time dilation would relate the 8 minutes to the much longer time taken in the frame of the neutrino.

A question that didn't involve this misconception would be:

(3) If when you're moving close to the speed of light time freezes, does that mean that only a very short time passes in the frame of a neutrino that, in the earth's frane, takes 8 minutes to reach the earth?

The answer would be yes.

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Thanks, great answer!