3 ms·
Nothing can outpace photons (in vacuum, that is - in a medium, cf Cherenkov radiation). However, velocity is a surprisingly tricky concept. While the relative v
by cygx 5y ago
Nothing can outpace photons (in vacuum, that is - in a medium, cf Cherenkov radiation). However, velocity is a surprisingly tricky concept. While the relative velocity of two objects passing each other by is well-defined, velocity at a distance tends to require a clock synchronization convention, which is to some degree arbitrary. In consequence, in special relativity, the speed of light is only isotropic by convention (cf various discussions about the one-way speed of light, which became a topic of online conversations due to Veritasium posting a video about it), and in general relativity, recession velocities (ie change in proper distance at constant cosmological time) of far away, but still observable galaxy can in fact formally be greater than c.