Why don't photons experience time?

A.T.

By "invalid reference frames" I meant something like "the rest frame of a photon". SR doesn't make any statements about the rest frame of a photon. For all other frames it states that the proper time of a photon is zero.

PeterDonis

I'm not sure I agree; I would say that SR says there is no such thing as "the rest frame of a photon", not that it says nothing at all about it.

Once again, this presumes that the zero interval associated with a photon's worldline is appropriately described as "proper time", which is precisely the thing that causes so much confusion about the "time experienced by a photon". I think the term "proper time" should be reserved for timelike intervals only.

WannabeNewton

I would also agree because one tends to use proper time as an affine parameter along time - like geodesics because we can without running into contradictions but for light - like paths this is not possible and since we can't even use proper time to parametrize the path of light I wouldn't say it holds any physical meaning in the way proper time holds meaning along world lines of massive particles.

Naty1

Quote by andrien

The individual photons DO travel at c; but as they progress thru the material, delays are encountered so the overall, effective transmission rate is slower than c:

From the wiki reference above:

WannabeNewton

I was talking about light as a wave traveling through the medium. If you want to talk about the individual photons then it is much more subtle than that. This is not related to the thread so for now take a look at: http://physics.stackexchange.com/que...-through-glass

Naty1

La6ki: Short answer: yes, that apparently works.....

there have been discussions in these forums about it...search if you want more.
I had not seen such before the discussions here and found the concepts worthwhile.

Check out here: http://en.wikipedia.org/wiki/Relativ...ectromagnetism


I searched...and got sidetracked......found BenCrowell posted about a text he likes on the subject here:

http://www.physicsforums.com/showthr...ectromagnetism

A.T.

It simply doesn't make any predictions about physics in the rest frame of a photon.

PeterDonis

I hate to keep nit-picking about language, but the way this is phrased implies (at least, I expect it will imply to a lot of newbies) that there *is* something called "the rest frame of the photon", when the whole point is that there isn't. SR says there is no such thing as "the rest frame of the photon". IMO that's the way to phrase it.

Naty1

la6ki:
In case you haven't seen it, there are some closely related perspectives here:

Light doesn't travel through time?
http://www.physicsforums.com/showthr...ht=photon+time

where you should check the posts from Fredrik and Dalespam...and follow the few links provided.

Naty1

Can somebody tell me what "CTC"s are [from post #26]:

Quote by Naty1
BCrowell:

Fredrik

CTC = Closed Timelike Curve.

If there's a CTC in spacetime, you could in principle move as described by it and meet a younger version of yourself. BCrowell was joking. It got a LOL out of me, so the joke works on some nerds at least. I wouldn't try it as a pick-up line though.

dm4b

It was my understanding that the logic (put in laymen's terms, perhaps) that the reason a neutrino cannot be massless is because it can undergo neutrino oscillations, which was the solution to the solar neutrino problem. Neutrino Oscillations are a time-dependent phenomenon and since a massless particle does not experience the passage of time, it would not be able to experience these oscillations. Since it has been shown neutrinos do undergo the oscillations they therefore cannot be massless.

There was a show on the science channel that said as much too.

Also, when you analyze the time dilation formula in the limit of v=c, while the equations are still valid, as you get infinitesimally close to v=c, deltaT moves infinitesimally close to zero.

Naty1

Minor Notes:
1]Closed Timelike Curve....haven't seen that one in a long time!

2]It is a lot more relaxing to read you experts picking each other apart than reading when you pick ME apart!!!!

3] la6ki: You lucked out getting all these experts to offer perspectives!! Great discussion.


la6ki: I hope after reading the posts from a number of the most knowledgeable people here you have a perspective now on WHY I posted early on:

Now I have been in these forums enough to know better....I should have known THAT wording would get some riled up...far better had I said something like "I hope eventually some part of the FAQ can be revised as a result of new discoveries."

Some of the ways the experts phrase it in this discussion:

"....there are no inertial coordinate systems that are comoving with a massless particle"

You can decide for yourself if you think those are conclusive answers to your original question about time for a photon. Such answers, which I think ARE completely accurate within GR, make me SUSPECT we have more to learn. They just seem inadequate to me. I say "we can do better.' Now if quantum theory offered more precise answers I'd be more comfortable...but that is another bag of worms worse than this one!!

Another way to express my concern is that I think most of these posters would agree QM and GR have some problems at what we call singularities, apparent infinities....like the center of a black hole and at the big bang. Most probably don't think we have the full answers at those points; my question is whether we should consider that maybe we don't have a full understanding at v = c.

You can decide for yourself what you make of all this.

PeterDonis

I'm not sure exactly what aspects of QM you're referring to, but the singularities at the center of a black hole and at the Big Bang have nothing to do with any understanding (or lack thereof) at "v = c".

IMO we understand perfectly well what happens at v = c; the behavior of null curves, and how it differs from the behavior of timelike curves, is well understood. The fact that it's difficult to describe this behavior to lay people in English is because English is not well suited to describing physics, not because the physics is not well understood.

PeterDonis

Exactly: that's the point. Putting things in laymen's terms distorts them.

Which show? I'd be interested to see if it is on the list of "usual suspects" that tend to generate these PF threads.

The Lorentz transformation is *not* valid at v = c; the factor that goes to zero is in the denominator, and you can't divide by zero.

Naty1

not yet! [I have high hopes!!]

You seem to think relativity is more complete than I..you may be right. We haven't any experimental evidence I can think of at either [the 'infinities', nor at v= c] yet, so a discussion seems moot,maybe that's your point, and that's ok by me....

Perhaps I have an inflated hope for science?

PeterDonis

I think my comments were more in the nature of clarifying exactly where the incompleteness is.

True.

Here I disagree: we've studied the behavior of light in great detail. That counts as evidence of "v = c".