I think it is a statement when philosophy draws its tongue and starts making faces. Technically you cannot prove anything about the universe, because you need

I think it is a statement when philosophy draws its tongue and starts making faces. Technically you cannot prove anything about the universe, because you need some presumptions to start any proof. Like you need to believe your senses for example. Nevertheless we are confident in a lot of things in the universe, because we have some means to distinguish true statements about the universe from false ones. These methods go beyond rules of pure logic and they use a lot of presumtions (oftentimes in an implicit manner), and I'm not sure there are anything true these methods cannot prove. I mean I cannot prove or disprove such a statement. (I always wondered about "I think, therefore I am": how can we talk about "I" before we proved that "I" exists? Maybe it was not Descartes who thought "his" thoughts? Maybe they were induced by aliens? So you need to accept very complex presumptions just to be able to start thinking.) Some downvoted comment above suggested Occam's razor: if we have 2 theories of the universe and the one assuming the universe to be infinite is simplier, then we should believe the universe is infinite. Maybe it doesn't seem as a proof, but if the theory explains all known phenomena, then we have no reason to doubt it. Like with our senses: they work in practice therefore we accept them as a source of truth. I can get to a point from a different direction. If we assume the universe to be infinite, and come with a falsifiable prediction from this assumption, and test it, then it could convince us that universe is infinite. No one can think of such a prediction today, but it doesn't mean that no one will think of one tomorrow.