Merely? The curving of light rays is a direct measure upon the effects of mass on spacetime.
Actually, you cannot have a supposed discrete 'universe' unless space IS closed, unless you make the assumption that our universe is the ONLY universe in an open-ended matrix of preexisting spacetime already there to just expand out into, but every indication is that our universe is but one of innumerable universes, therefore space must be closed, if only at some higher dimension not immediately obvious to us.