3 ms·
That's not the "same" spot, though. It doesn't consist of the same photons; the spot in the "new" position consists of photons which have been traveling in a
by mewse 5y ago
That's not the "same" spot, though.
It doesn't consist of the same photons; the spot in the "new" position consists of photons which have been traveling in a straight line from your flash light at (assuming vacuum) a constant rate of C (and then reflected back to reach your eye again, also at a constant rate of C); they haven't traveled to or from the previous "spot" position at all, much less exceeded the speed of light at any point in the process of reaching the new position.
Right?
- hyperman1 5y agoThat's correct in both the superluminal and the subluminal case, and more or less the point of the example. The spot moves superluminal, but the particles creating it don't. This makes it impossible to use it for superluminal information transfer. AFAIK Expansion of the universe is comparable. It pushes things away not by speed but by putting extra 'new' space between things. Your sibling comment makes a variant of the same point:c is the maximal speed of information or causality. Light in a vacuum is just one of the things capable of reaching it.