# I How does a photon view the universe?

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1. Mar 22, 2016

### Al X

This question has been bugging me quite some time now. I'll start presenting my background for the problem:

Fact:
Photons are time-dependent oscillations of electric and magnetic fields as described by Maxwell's equations.

Now, I've heard a lot of people, including professors saying that a photon experiences no time and no distance due to time dilation and length contraction. Also, I've heard a professor say that if you could travel alongside the photon (this seems weird per the postulates of SR), you would see frozen electric and magnetic fields. My questions are:

1. Can we use the word photon about something that's frozen in time? Or is the photon description only valid when we have a time-dependent oscillation.

2. If the answer above is that we can, then I assume it has something to do with photons being a quanta of light. This is especially used when talking about absorption and emission of photons. What about radiowaves that can have a wavelength of several km? Can we speak of an immidiate absorbtion and emission? Does the photon definition collapse?

3. If we apply SR to the photons, they shouldn't exist. Since the distance between two points are infinitely contracted. Also, on the flipside of this effect, the photon uses an infinitely small time to cross the distance due to time dilation. This seems to me to be in contradiction of us knowing electromagnetic waves exist, and that we can measure a wavelength and frequency.

4. How can a professor say that the infinite contraction and dilation, and frozen fields are well defined? I don't ask this to bash the guy, I just simply don't get it. Especially since another professor I've had is saying this is unsatisfactionary and that SR shouldn't be applied to light in this way.

5. Finally, entangled photons. Now say that it is true that photons don't experience distance, nor time, but we can experience the time and distance they've travelled. Could the entanglement be due to the fact that we're basically manipulating the same photon?

Let's discuss!

2. Mar 22, 2016

### Staff: Mentor

Photons aren't what you're thinking they are, but if we substitute the words "flash of light" for "photon" throughout we'll get through #1-#4.

Basically, any discussion of the point of view of something moving at the speed of light is inconsistent with SR (so you're right to have been dubious). You'll hear this bit about time stopping and lengths contracting to zero a lot in the popular press, but it's basically bogus. We even have a FAQ on this, because it comes up so often.

#5 doesn't work because massive particles which move at speeds less than that of light can also be entangled.

3. Mar 23, 2016

### haushofer

4. Mar 23, 2016

### PeroK

This sums up the issue. The second professor is right. There is nothing in SR about infinite contraction and dilation and there is no frame of reference for a photon.

If you look at the mathematics, then it may be tempting to interpret an undefined quantity (such as $1/0$) as "infinite". But, mathematically, that is unsound. $1/0$ is undefined.

It's a shame if this question has been bugging you, as it is not really a valid question or valid issue at all.

5. Mar 23, 2016

### Al X

Thanks guys! That helped a lot!

6. Mar 23, 2016

### Ibix

One of the postulates of special relativity is that light travels at the same speed in all inertial frames of reference. A frame of reference moving along with a pulse of light would be an inertial frame (in the sense that it is moving at constant speed viewed from another inertial frame). So light would have to be moving at light speed. But it would also have to be stationary because that's what moving along with something means.

That's how fundamental the problem with "the perspective of light" is. The notion is self-contradictory in relativity. You were right to be suspicious.