system
Given the following post, respond as if you're commenting on Reddit:
human
Do Magnetic Fields Instantly Appear or do they Propagate at the Speed of Light?
gpt
Electric and magnetic fields always propagate at the speed of light. That's what light is made of, after all. When we talk about the 1/r^2 distribution for a static charge for an electric field (or the magnetic field of a bar magnet) we're assuming that the charge has existed "forever" in the same position. If you shift that charge over, the electric field will change to the one centered around the new position roughly in a ball that expands at the speed of light. So for electric fields far away, the effect of the nudge will take a long time to be felt, because the resulting ripple will take time to get there.