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

[why2everything]

My Opinion

The proponents of this theory may call it "Standard theory", but have no dobut - it is in no way, shape, or form "standard". It's basically yet another crank theory.
I would suggest that you read http://math.ucr.edu/home/baez/physics/Relativity/GR/grav_speed.html"
for what relativity has to say about the speed of gravity.

Thankyou pervect; I am already learning much just by reading this article and your answer. In the article you referred me to, it says:

In general relativity, on the other hand, gravity propagates at the speed of light; that is, the motion of a massive object creates a distortion in the curvature of spacetime that moves outward at light speed.

Now, in my elementary understandings; I thought that if something were to travel at the speed of light, it would require an infinite amount of energy? Where would this energy come from, in the case of gravity? And does light require energy to travel? Where does that energy come from? To me, if it would require this much energy to travel at lightspeed; then relativity must be correct in saying that lightspeed is the fastest thing going. How could anything acquire that much energy on a constant, sustained basis, such as gravity would have to do if it is faster than light? Would we not have to say that it is only possible for something to travel at close to the speed of light? What do you think?

 

[russ_watters]

Now, in my elementary understandings; I thought that if something were to travel at the speed of light, it would require an infinite amount of energy?

That's only true of objects with mass. Light doesn't require an infinite amount of energy to propogate either.

And does light require energy to travel? Where does that energy come from?

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

 

[cd27]

i have read before about exceeding the speed of light. here is a quote from the article i read:

The Time Barrier

During our history there have been many impossibilities and along with those impossibilities came broken records and new limits. First it was to go around the world and prove it wasn’t flat, then it was to fly, then it was to drive a vehicle, control water, make light, control electricity, to communicate with someone on the other side of the world, then to break the sound barrier, then to go into outer space, then to land a man on the moon, and now…now we break the time barrier.

Many scientists have contributed to all of the above accomplishments, each giving a little along the way. But…for each man to contribute his work and get recognized for it, he had to think of the word differently from everyone else. Einstein once said, “The speed of light can never be reached, or even surpassed.” Oh how wrong Einstein was. The entire phrase is a contradiction in itself. If light can reach light speed, then it is a highly possible accomplishment!

Einstein used this formula to base his findings: Time equals time divided by the square root of one minus the velocity squared divided by the speed of light squared, or T=T’/sqrt 1-(V Sq./C Sq). When T=the change in time for the stationary mover, T’=the change in time for the motionary mover, V=velocity, and C=speed of light (186,000 mi./sec.). Now, as long as your velocity never reaches your speed of light, you’re absolutely fine; however, if your velocity reaches or surpasses that speed, well, the speed of light will have to be changed, but since it’s an impossible accomplishment, we won’t go any further…or so said Einstein. You see, 186,000-mi./sec. Divided by 186,000 mi./sec. Equals 1, and 1-1=0. The square root of 0 is a “syntax error” (says my calculator). It cannot be done. Therefore, the speed of light can never be reached.

It is believed (and even proven through mathematical reasoning) that this formula doesn’t work for speeds faster than that of the speed of light or equal to it. Have you ever wondered how fast you’d go in space if you first went 50% the speed of light, then stopped the engines (not the ship, only engines) in mid space and then restarted them at 49% the speed of light? You’d be going 90% the speed of light, right? Wrong, you’d only be going 49% of C (C=the speed of light) because your reference frame had stopped and then continued on 49% of C. In someone else’s reference frame, you are going 99% of C, but in yours you’re only going 49% of C. But if you continually went up to 99% of C in your reference frame, you’d be going precisely that. If you go 100% or above of C, time will no longer exist for you and the formula would no longer work, because you can’t dilate time that doesn’t exist! So there you have it, the time barrier.

i don't know what you guys would think about it, i think it relates to this thread. then again, some may have a completely different view, or may know something i do not, please share it with me if you do.

cd

 

[MichaelW24]

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...?

 

[Severian596]

cd27, this article discusses velocity addition in special relativity. And it does so in a confusing manner! I started wrinkling my brow at all the, "Stop the engines then restart them at 49%, but your frame had stopped, in someone else's reference frame you're going..." Ugh. The last paragraph should really be a series of paragraphs, not just one.

I'm not sure what the point of the article was, but it described how traveling at the speed of light (or above it) results in undefined or imaginary mathematical results (i.e., dividing by 0 or taking the square root of a negative number). Look up "velocity addition relativity" for more info. In short you cannot add velocities in SR or GR like you do in Newtonian physics.

Some links to scratch your itch:
http://en.wikipedia.org/wiki/Velocity-addition_formula
http://math.ucr.edu/home/baez/physics/Relativity/SR/velocity.html
http://hyperphysics.phy-astr.gsu.edu/hbase/relativ/einvel.html
http://patsy.hunter.cuny.edu/CORE/CORE4/LectureNotes/relativity/relativity6.htm

 

[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.

 

[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.