That'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.
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.