How Does a Photon Experience Time During Its Journey Across the Universe?

[maximiliano]

Time in the "eye" of a photon

Dumb question...but thought I'd throw it out there.

So, ever since I was a little kid of 6 or so, I loved to look up at the sky. I knew all those stars were just suns. I also knew I was looking back in time, many thousands to millions of years, since all the light from those stars would have taken that long to reach me. For all I knew, everything I see doesn't even exist anymore...but I'd never know it.

Okay...to my question, since time, at the speed of light, moves very very very slowly (or not at all?) relative to the observer...IF you were a photon, how long would it seem to you that your journey from a sun, 1 million light years from Earth, took?

 

[phinds]

This is a question that comes up here often and the answer is ... there IS no answer because a photon has no frame of reference from which to make the question meaningful.

By the way, with your naked eye you can only see object up to something like 20 or 30 thousand light years away, so you can't see anything millions of years old. That would be outside the Milky Way, which is only 100,000 light years across.

EDIT: Hm ... I think maybe I once saw that the Andromeda Galaxy is sometimes visible to the naked eye and it's something like 4 million LY away, so maybe the statement above was a bit too strong.

 

[rcgldr]

The closest thing to a "clock" for a photon is it's frequency, and a fixed number of cycles will occur when a photon moves from one point to another, regardless of the observer's frame of reference. However, a new set of rules would be needed for observations made from a photons frame of reference, as it's not clear what time means to an object that only moves at light speed.

 

[jtbell]

Glancing down at the bottom of this page at the list of "Related Discussions," I see a couple of threads on this topic:

Time in the "reference frame" of the photon […]

time "stopped" for a photon traveling at the speed of light?

 

[Nugatory]

Glancing down at the bottom of this page at the list of "Related Discussions," I see a couple of threads on this topic:

also there's a FAQ in teh relativity forum: https://www.physicsforums.com/showthread.php?t=511170

 

[Oldfart]

EDIT: Hm ... I think maybe I once saw that the Andromeda Galaxy is sometimes visible to the naked eye and it's something like 4 million LY away, so maybe the statement above was a bit too strong.

Andromeda is not "sometimes visible" but rather is easily visible in clear dark skys if you know where to look. You'll see a faint fuzzy patch of light.

 

[dauto]

EDIT: Hm ... I think maybe I once saw that the Andromeda Galaxy is sometimes visible to the naked eye and it's something like 4 million LY away, so maybe the statement above was a bit too strong.

I think I remember reading some claims that in extremely favorable sky conditions it is also possible to see Bode's galaxy at 12 million light-years distance.

 

[phinds]

Andromeda is not "sometimes visible" but rather is easily visible in clear dark skys if you know where to look. You'll see a faint fuzzy patch of light.

Thanks for that correction. Clearly, I remembered wrong.

 

[bcrowell]

I have a discussion of this in section 3.4 of my SR book, http://www.lightandmatter.com/sr/ .

 

[TungstenX]

So, am I to understand that a photon can not be an observer, or have an observer? (https://www.physicsforums.com/showthread.php?t=511170)

 

[phinds]

So, am I to understand that a photon can not be an observer, or have an observer? (https://www.physicsforums.com/showthread.php?t=511170)

Yes, it is correct to say a photon cannot be an observer, but I don't know what you mean by "have an observer". Every time we see ANYTHING we are observing photons, if that's what you mean.

 

[TungstenX]

Nope, more like an observer "riding" a photon. Or an observer traveling at the speed of light, theoretically.

 

[Dale]

Correct, that is not possible.

 

[phinds]

Nope, more like an observer "riding" a photon. Or an observer traveling at the speed of light, theoretically.

Ah, I get it now.

As Dale said, this is not possible. Such a question boils down to "if the laws of physics didn't apply, what would the laws of physics say about ... <anything!>".