Q:

Is distance always 0 relative to an object moving at speed of light $c$?

As I understand it, when an object is traveling at the speed of light, relative to itself all travel is instantaneous and the distance is zero. If a photon traveling from the sun was aligned with the Earth and Mars is the trip to Mars literally the same as the trip to Earth. I'm trying to picture how that works - are Earth and Mars and the rest of the universe for that matter condensed to a single point relative to the photon?

A:

You are asking us for the distance of the trip in the rest frame of the photon. The problem with asking that is that there is no rest frame of a photon. A photon can never be at rest, so it has no rest frame. This is like asking what a bowl of petunias thinks about its existence as it falls to the surface. A bowl of petunias doesn't think, therefore we can't tell you what its existential thoughts are. Similarly, a photon has no rest frame, therefore we can't tell you what distances become relative to it

