h2g2 The Hitchhiker's Guide to the Galaxy: Earth Edition

.....Then why does the light from a distant star take so bloody long to get here?

It doesn't. To the light itself, it probably arrives in the blink of an eye.

It only takes a long time to us because we're going very very slowly ...

So your assumption is that time has stopped for the photon contained with the light from distant star?

*IF* that were true, then why would the light *ever* get here?

*If* it were true, presumably time only stops for the photon, not for the observer. To the photon, it would arrive at the exact moment it was created. I've heard that a bloke falling into a black hole would experience this. To an outside observer, the bloke would be frozen in time forever, to the bloke it happens instantly.

http://www.math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/headlights.html

Rough summary: it's a bit meaningless to consider what a photon experiences.

Won't that give the photon a bit of a negativity complex?

B

Or is it only electrons that have those?

B

I actually think light exists outside of time and we're talking dimensionally. It's very close to all photons being the exact same photon but I suspect we are just existing on one corner of a very complex shape indeed.

But I might as well be a goldfish in a bowl wondering what a firework is. Damn my pesky monkey-brain!

Balato: I can´t say I understand what you were saying with that last post of yours. However as has been mentioned, time slows down only for the object actually moving fast. So if you asked the photon, it would probably think no time at all had passed going from Alpha Centauri to here. Same with a spaceship heading to Alpha Centauri and back at near-light speed. They would tell you the flight had taken 5 minutes, but you would have been standing on Earth waiting for 8 years.

Yes that's a good point. So the logical conclusion then, from the point of view of a photon which is travelling at light speed and therefore has zero time... is that a photon in any particular "position" in the universe has been there forever and will be there forever.....as well as moving? Because movement is a function of time, that's difficult to comprehend.

It doesn't really make sense to ask what "time" the photon experiences. Are you really asking "what time would I experience if I could ride along with the photon at light speed"?

Time does pass for the photon - you can observe their generation and absorbtion quite routinely

how can time pass for something travelling at light speed? as far as I am aware, it can't. isn't that the point of relativity?

I believe that time slowing down is also related to the increase in mass. As photons doesn´t have a mass, things might be different for them.

Also the movement of the photon will be measured with distance/time of the outside reference frame, not the time of the photon itself.

I think Xanatic has hit upon a key point. Re-write the time dilation in terms of the mass effect. The photon is not infinitely massive, despite traveling at the speed of light.

The real problem is that we're trying to analyze the "words" used by scientists to describe the math, rather than the underlying math.

photons as a wave don't have a mass, but they are particles sometimes too aren't they? My head hurts.

Wether they are waves or particles shouldn´t change their mass.

Right again Xanatic. Electrons, photons - anything - are both wavelike and particle like, whether you are observing wavelike or particlelike behavior, the mass is the same.

but doesn't the very term particle require a mass? unlike a wave. I'm out of my depth on that one!

Haven't I read of a scheme to propel a large 'sail' in space, using the 'solar wind'? Or, is that wind particles (neutrons...)?

Light possesses no mass but paradoxically it *does* possess momentum.

Besides which, as you say there are plenty of other particles in the solar wind that are not photons.

Didn't I read recently that they had now measured a (tiny) mass for photons or was it neutrinos?