Crispy said:
Mate, it's fundamental relativity. You even said the word 'relative' in your original explanation. The relative speed of one photon relative to another is the speed of light. The speed of light is
always the speed of light. Time and space dilation are the result.
eg. (god I hope I've got ths right!)
Your two photons are heading in opposite directions
If you hitch a ride on one photon, it will appear as if the other photon is moving at the speeed of light way from you. The distance between the photons is apparently halved
or the time taken is apparently doubled (I forget how you can tell which)
It's a pig to put into language. Try reading
http://en.wikipedia.org/wiki/Principle_of_relativity
If you hitch a ride on one photon, it will appear as if the other photon is moving at the speed of light away from you. I
But it's important to bear in mind that you've mentioned both appearance, and hitching a ride for this thought-experiment.
As far as I remember, and i'm far from an expert on this, then the reason it seems that way is because the faster you get, the more time appears to slow down for the other parties, and so other things would appear to be moving slower, from your frame of reference. Is it true that time and space dilation are the result, or are they perhaps the cause, and how do you decide a question like that?
Summing up the theory of relativity, I wonder if it's a fair approximation to say that the point is that the results of your measurements of something's speed, size, time passing, depend on your frame of reference, in particular on how fast you're moving.
But the normal reference point for considering the case of two photons moving in opposite directions from a "fixed" light source, for example, a star, would be the point of view/frame of reference of the star. From the point of view of whoever lives on the star, the two photons would appear to be moving at twice the speed of light relative to each other. From the point of view of the photons, they would appear to be moving away from each other at the speed of light. This is something I do not quite understand, but I think it's to do with the effect of moving at very fast speeds on time and space.
I found a really good link:
http://www.sysmatrix.net/~kavs/kjs/relrap.html
As far as I can work out, the apparent inconsistency that two photons cannot get away from each other faster than the speed of light, even when moving in opposite directions and even considering the supposition that the speed of light in a vacuum is constant, is actually the result of the fact that the speeds they are moving at shorten distances and make the other's clocks appear to go slow.
Speed after all, is distance/ time, ifwe find that actually, distance and time are not absolute, but depend on your frame of reference, then it is not surprising that from the point of view of the photons things are different than from our point of view, from which I maintain, it is true that they separate at twice the speed of light.
"Scientists assert that no material thing can ever reach or exceed the speed of light. But they're not talking about an object's ABSOLUTE speed, such as relative to a hypothetical macro scale set of x-y-z axes of our universe/space, which is a myth... NO, they mean that no object can move as fast as light as assessed from another object's reference frame. This perhaps is an even greater constraint than the first, because it means that every single object in the world must comply in relation to every other possible citing object! and in relation to any conceivable vantage or trajectory. Another way to phrase this particular rule of Relativity Principle is: no object can OUTRUN being viewed by others. That truth is inviolate and universal."
So, in conclusion, I think on this red herring, I think both laptop and I were correct from different points of view.
Once again, though, I find this truth a great deal more mind-boggling than laptop appears to. mainly because it seems a remarkably intelligent feat for the universe to be able to pull off.