- #1
granpa
- 2,268
- 7
if an orbiting electron positron pair is moving through space with net momentum p and the 2 particles then annihilate each other producing 2 photons then where did the momentum go?
granpa said:if an orbiting electron positron pair is moving through space with net momentum p and the 2 particles then annihilate each other producing 2 photons then where did the momentum go?
granpa said:well, there's nowhere else for it to go. but I can't really say that I understand it.
What specifically do you not understand?
granpa said:then where does the net momentum of the pair go? (see post #1)
granpa said:then where does the net momentum of the pair go? (see post #1)
The electron and positron have very tiny masses. Since p=mv, we can say (9.109 x 10^-31) x velocity (let's just say 200,000,000 m/s) = the momentum of an electron. So an electron and a positron pair should have a net momentum of around 2 x (the above stated) = 3.6436 x 10^-22 kg m/s in this example. This is a very small momentum. It should be easy for the photons emitted to carry this momentum.
granpa said:small is a relative term.
But I gave you an exact number to compensate for that.
yes. its about the reverse processVanadium 50 said:That thread is about a completely different process.
granpa said:I don't know what you are referring to but I was referring to a pair moving through space with an arbitrary net momentum p (which could be as large as you want)
granpa said:I don't know what you are referring to but I was referring to a pair moving through space with an arbitrary net momentum p (which could be as large as you want)
protonchain said:Satisfied?
Nick89 said:That is, assuming only one photon is created. Why is it not possible that 114 photons with an energy of approx. 1 GeV are created?
Erm, no they can't. Ever heard of special relativity? Ever heard of protonchain's post 'bout 5 inches up?granpa said:excuse me? the momentum can be increased virtually without limit simply by nicreasing the velocity. ever hear of the 'oh my God' particle?
protonchain said:From what I understood from my lectures, 2 particles go into the mix, 2 photons go out.
granpa said:excuse me? the momentum can be increased virtually without limit simply by nicreasing the velocity. ever hear of the 'oh my God' particle?
v must be less that c but gamma increases without limit so momentum increases without limit
granpa said:p=gamma * m * v increases without limit because gamma increases without limit
granpa said:if an orbiting electron positron pair is moving through space with net momentum p and the 2 particles then annihilate each other producing 2 photons then where did the momentum go?
Nick89 said:Gamma does not stop increasing when v = c. Gamma is undefined when v = c. And when v > c, gamma is imaginary so you can no longer speak of increasing, since complex numbers have no 'order'. You cannot say (a + bi) > (c + di).
Of course, v must always be less than c. But you can make it go as near to c as you want (theoretically of course). In fact, the closer you get to c, the larger the momentum increase becomes.
granpa said:gamma increases without limit as v approaches c