How do we know space is not infinite?

Imax

It depends on whether or not we can identify ghost images. If space is compact, then light from a distant galaxy can travel in two directions, towards us or it can circumnavigate the universe and appear somewhere else as a ghost image.

Imax	It depends on whether or not we can identify ghost images. If space is compact, then light from a distant galaxy can travel in two directions, towards us or it can circumnavigate the universe and appear somewhere else as a ghost image.