It’s not completely so—it might become apparent that the universe was finite,
How would this come about? The entire problem of attempting to make observations beyond our lightcone is that there are no interactions beyond that boundary.
If you started seeing earlier versions of the same part of the universe that you now are standing in at an apparently large distance out in space, you pretty much know the universe is finite. Light travelling all the way around the universe and arriving back where it started would be a large clue that the universe was finite.
How would this come about? The entire problem of attempting to make observations beyond our lightcone is that there are no interactions beyond that boundary.
If you started seeing earlier versions of the same part of the universe that you now are standing in at an apparently large distance out in space, you pretty much know the universe is finite. Light travelling all the way around the universe and arriving back where it started would be a large clue that the universe was finite.