Is Flash a ghost?

He is not a ghost, he only takes into account the "theory of relativity" which states that "when

a body travels at the speed of light its dimensions change so that when it returns to an initial

speed it returns to its natural shape, as long as the body resists that speed" (hence the composition of his suit).

When a body travels at a speed greater than the theory of relativity, it can cross dimensions, but it must be careful with combustion, which is why the Flash suit is designed not to generate combustion while traveling in space, as NASA's SoFIe technology does with its suits.

This in turn has to do with Klein's paradox and the theory of relativity. These two, when traveling thousands of light years Flash does not deform and this is because it uses vortex space-time. The same thing that happens with the movie "Guardians of the Galaxy".