Physics Van 3-site Navigational Menu

Physics Van Navigational Menu

Q & A: relative speed of photons

Learn more physics!

Most recent answer: 02/19/2013
Q:
two photons emitted from the same source, at the same time, in the same straight line with opposite velocities (+ C and -C) deviate from one another at what speed?
- joao carlos leal cunha (age 60)
salvador bahia brazil
A:
If you stay along the line between the photons, in your frame their relative speed is just 2c, c in each direction. If you're moving relative to that line, in your frame they each travel at c but not in opposite directions, so their relative speed is less than 2c. If you are heading away from that line with speed v then you see their relative speed as 2c(1-v2/c2)1/2.

Mike W.

(published on 02/19/2013)

Follow-up on this answer.