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Jun
12
answered What is the physical importance of current density?
May
8
comment Chasing a photon
@brightmagus This seems to have spurred an interesting discussion, but to reply to your original comment: I never claimed this was a proof. Velocity addition was originally derived from the assumption that c=const, so it had better work that way. Marco Prins asked whether or not a photons velocity would still be c if one were trying to chase it at high speeds, and what the equation to calculate such a scenario is. I provided him with what he asked for. Of course, you can't "prove" that c=const must be true simply via theory - this is something that must be confirmed by experiment.
May
6
awarded  Nice Answer
May
6
revised Chasing a photon
added 78 characters in body
May
6
answered Chasing a photon
Feb
10
awarded  Yearling
Jan
17
comment Why don't positive charges move?
They can move, but tend not to because they are held in place by other atoms.
Dec
28
answered What does this summation mean in relativity?
Aug
26
comment How can we deduce the relation $m = \frac{m_0}{\sqrt{1-\frac{v^2}{c^2}}}$ between relativistic mass and rest mass in special relativity?
I remember Feynman did something involving analyzing collisions of masses in different reference frames, and concluding that, while $mv$ is not a conserved quantity, $\gamma mv$ is. It's therefore natural to modify either the definition of momentum or mass in order to maintain momentum conservation in relativity.
Aug
15
answered Why is there a factor of $4\pi$ in certain force equations?
Jul
18
awarded  Nice Answer
Jun
5
comment What's the basic premise of General Relativity?
The Doppler factor (1+v^2/2c^2) that follows after "for our purposes" is an approximation that comes from a Taylor expansion of the exact factor. And Taylor expansion comes from calculus.
Jun
4
awarded  Revival
May
27
answered Can one of Newton's Laws of motion be derived from other Newton's Laws of motion?
May
25
comment What force is responsible for anti-gravity?
The triangle lifter you're referring to works by ionizing air and forcing it downward, producing lift. The Mythbusters crew tested it in a vacuum and it didn't work, so it's clearly not anti-gravity. It's just a highly inefficient way of obtaining lift.
May
20
awarded  Fanatic
May
11
awarded  Citizen Patrol
May
5
comment QED photon propagator to one-loop order gets different answers
Well that's not really what you asked for. How about this: 152.78.192.50/hepwww/staff/D.Ross/qft/aqft3.pdf ?
May
5
answered QED photon propagator to one-loop order gets different answers
Apr
20
comment Transforming an equation to the co-vector version
You're right. I've changed my answer to reflect this.