What happens when two photons travel at the speed of light?

[Severian596]

well I'm not too good at this stuff yet, but that seems to say basically:
"well now we can break the time barrier... blah blah blah some special relativity... blah blah... so there you have it, the time barrier"
He seems to have proven himself wrong...?

Yes, strike the last two sentences especially. Actually, just strike the article and read some of the other articles out there instead.

:tongue:

 

[why2everything]

That's only true of objects with mass. Light doesn't require an infinite amount of energy to propogate either. I don't think it's useful to think of light as requiring energy to travel, so much as simply carrying energy with it.

What you are saying here makes sense; as far as I can understand all this stuff; I guess I am thinking that light does carry energy with it atleast; but wondering where that energy comes from & what kind of "energy" would that be? Also, I see it as you do, regarding objects with mass - How can they possibly travel as fast as light if to reach that velocity would require infinite energy? It would be impossible to acquire or sustain such velocity...now I am wondering too though...what is there, that does not have "mass" and could possibly attain lightspeed or greater velocity?

 

[cd27]

thank you for those links, i will most definitely read them. i am just beginning in this field, and i only know bits and pieces. I've been looking for all kinds of stuff to study, but i have no internet at home, a 60 year old encyclopedia, and absolutely no books or people i can talk to about it, so i must do it here at school and come on forum sites to get what i need.

i will study this in depth, the above article was a simple thought, nothing really huge.

cd

 

[why2everything]

Is Light "Entropy?"

You stated:

I don't think it's useful to think of light as requiring energy to travel, so much as simply carrying energy with it.

Do we then, class light as some kind of entropy?

 

[RogerAshford]

In a sense, there's no point in trying to figure out what anyone will observe when they are traveling at the speed of light, because from their frame of reference, Lorentz contraction will have made the size of the universe (in the direction of their travel) zero: the universe will be, to them, an exceedingly thin pancake. They will take zero time to travel from one end of the universe to the other, and so will therefore have no time in which to measure how fast anything else seems to be traveling relative to themselves.

I have sometimes wondered whether this is how certain aspects of quantum indeterminacy: if a proton takes zero time (self-measured) to move from A to B via possible alternative paths, perhaps it can wait until it is observed before it "decides" which path it has taken (decoherence) because, to the photon, the start and end of its journey are one instant? (I guess this belongs in another forum).

 

[JesseM]

In a sense, there's no point in trying to figure out what anyone will observe when they are traveling at the speed of light, because from their frame of reference, Lorentz contraction will have made the size of the universe (in the direction of their travel) zero: the universe will be, to them, an exceedingly thin pancake. They will take zero time to travel from one end of the universe to the other, and so will therefore have no time in which to measure how fast anything else seems to be traveling relative to themselves.

Like I said on the "more light questions" thread, light can't have its own reference frame. You can talk about what the limit would be as an object's speed approached c relative to some other frame, like the galaxy's rest frame; it is true that in this limit, the length of the galaxy along the direction it's moving relative to the object would approach zero, and therefore the time required for the object to cross it would approach zero as well. But some quantities don't have a well-defined limit as you approach c, like the velocity of a second object whose velocity approaches c as your own velocity approaches c; if you take the limit by letting the second object's velocity be fixed at c while yours approaches c, you'll conclude the second object's velocity is c in this limit, but if you let the other object be at rest relative to you and have both your velocities approach c, then you'll conclude the second object's velocity is 0 in the limit. So there's no way to meaningfully answer the question of what the velocity of one photon would be as seen by another photon, even if you're just talking about a limit rather than a genuine reference frame.