The feeling of time while traveling at the speed of light

[arkay]

So I have been wondering about something, this is completely theoretical obviously you cannot sit on a photon but think about this and let's see what you think...

We have a Photon traveling at the speed of light from one point to another. The origination point, a light source 1000 light years from Earth. Now, let's say a traverler is very tiny and sitting on that photon traveling from the light source to Earth.

A) If the photon is traveling at the speed of light, and time slows down relative to the item in transit, 1000 years will have passed on Earth before the journey is complete, however to the traveler, relatively, no time would have passed. So that leaves two questions: 1) For the traveler, how long would it "feel like", he was sitting on the photon? Was it instant, or was he sitting there for a thousand years? 2) If no time would have passed then the photon, and the traveler on the photon would appear to be in more than one place at a time, in fact would he not be in every place within the path at the same time until the photon slows under the speed of light? Is that a paradox?

B) Now let's take the same scenerio as A except slow the photon down so it is moving just under the speed of light, so the entire trip takes 1001 years now. Does that traveler feel as though he has been sitting on the photon for 1 year or 1001 years?

 

[CompuChip]

So I have been wondering about something, this is completely theoretical obviously you cannot sit on a photon but think about this and let's see what you think...

I think that that in fact, it is not even theoretical, but that it's a pointless exercise.

I have already explained it before here, so - being a lazy physicist/mathematician, I'll just refer you to that thread :-)

 

[Dale]

A) is not possible as mentioned by CompuChip, so I will stick with B).

B) Now let's take the same scenerio as A except slow the photon down so it is moving just under the speed of light, so the entire trip takes 1001 years now. Does that traveler feel as though he has been sitting on the photon for 1 year or 1001 years?

Actually it is 44.7 yrs for the traveller.

 

[arkay]

Interesting that someone else had a very similar thought. Almost worded the scenerio the same as me too. Kinda wierd.

Anyway thanks for the link, that was a very interesting thread.

 

[tunkcart]

In the link, a couple of responders said that, "You can claim 'photons don't age' if you like," and "For photons, the infinitesimal interval is zero, and in this sense, photons experience no time." I think the question both OP's either stated or hinted at what, if it was like something to be a photon, what would it be like? If a photon experienced, what would the experience be like?

If photons "experience no time", then can they experience change? Is change dependent on time?

I'm not sure if the question crosses out of physics and into philosophy, but I'd wondered the same thing myself and might have found an appropriate forum to gain some understanding.

 

[pervect]

The short answer is that assuming photons experience time is like dividing by zero. It leads to contradictions. Other ways of saying this

"Garbage in, Garbage out" (a bit impolite, perhaps, I don't really mean to be perjorative, it's just that if you make an incorrect assumption, incorrect conclusions follow).

"Loaded question". ("A loaded question is a question which contains a controversial assumption such as a presumption of guilt. Or in this case, an assumption that relativity is invalid."). People want to ASSUME that they can travel as fast as light in spite of the fact that it's impossible. Why, I don't know. Some of it might be sloppy thinking, in terms of thinking that is possible to answer questions in a framework where the assumption is inconsistent with said framework without getting nonsense.

 

[NoDoubt]

Actually it is 44.7 yrs for the traveller.

How it can be? Light never slows down, it just takes longer path, so time experienced by the photon rider (If there is any) will still be Zero.

 

[CompuChip]

People want to ASSUME that they can travel as fast as light in spite of the fact that it's impossible. Why, I don't know.

I suspect in this case, with most people naturally having bad intuition for anything involving limits, it feels very natural to assume that v = c is just the limit case of the v < c theory.

 

[Dale]

How it can be? Light never slows down, it just takes longer path, so time experienced by the photon rider (If there is any) will still be Zero.

In case 2 we were explicitly discussing something slightly slower than c, e.g. an observer riding a pulse of light in a dielectric medium. Just use the spacetime interval formula to get the proper time.

 

[NoDoubt]

In case 2 we were explicitly discussing something slightly slower than c, e.g. an observer riding a pulse of light in a dielectric medium. Just use the spacetime interval formula to get the proper time.

Oh.., I see, Now it is "something" slightly slower than c, Then the formula will work perfectly, But I thought I heard "photon moving just under the speed of light". Never heard that before.

 

[Dale]

Did you even read the OP? Take it up with him, it isn't my scenario.

 

[tunkcart]

I suspect in this case, with most people naturally having bad intuition for anything involving limits, it feels very natural to assume that v = c is just the limit case of the v < c theory.

So does that mean that the posters who said that photons don't age were wrong--or at least that they didn't have good justification for claim?

Maybe my hang-up is that I'm familiar with a framework for thinking about time for massive things that travel at less than the speed of light--but then there are these things that travel at the speed of light. Is there a way to think about time for them?

 

[Dale]

You can certainly say that the proper time along the worldline of a pulse of light is 0.

The problem comes when people try to go beyond that and start talking about light's "perspective". In relativity an object's perspective refers specifically to the reference frame where that object is at rest. There is no inertial reference frame where light is at rest, so there is no unambiguous meaning to the term "photon's perspective", just as there is no unambiguous meaning to the "perspective" of a non-inertial object.

In both cases you have to define exactly what coordinate system you mean, and people asking such questions never do that.

 

[tunkcart]

You can certainly say that the proper time along the worldline of a pulse of light is 0.

The problem comes when people try to go beyond that and start talking about light's "perspective". In relativity an object's perspective refers specifically to the reference frame where that object is at rest. There is no inertial reference frame where light is at rest, so there is no unambiguous meaning to the term "photon's perspective", just as there is no unambiguous meaning to the "perspective" of a non-inertial object.

In both cases you have to define exactly what coordinate system you mean, and people asking such questions never do that.

Very interesting. So, if "perspective" in relativity refers to the reference frame of an object at rest, and light is never "at rest", is it true to say that light has no perspective? Or, is talking about a photon's perspective ambigious, but clear and sensical provided that you define a coordinate system?

 

[tunkcart]

I'm referring myself to this thread: https://www.physicsforums.com/showthread.php?t=315122

which I hadn't read yet, and which seems like it might already have explained a lot of what I wonder.