The fact that we don't know what's going on within the Planck length doesn't demonstrate that spacetime is discretized; I don't even think it strongly indicates

The fact that we don't know what's going on within the Planck length doesn't demonstrate that spacetime is discretized; I don't even think it strongly indicates it, unless you're already predisposed to think that way. Anyway, that seems to have no bearing on whether the universe is infinite.