Well it depends on what you're describing, if you mean infinite as a math concept, then you don't need to prove it, in the same way you don't need to prove a "1" is actually a "1", you just say it's a "1" and use it in a problem.
If you mean infinite in our physical reality, like space being "infinite," the laws of physics don't allow that.
We can say it is, but we can never prove it. That's the paradox.
Well it depends on what you're describing, if you mean infinite as a math concept, then you don't need to prove it, in the same way you don't need to prove a "1" is actually a "1", you just say it's a "1" and use it in a problem.
If you mean infinite in our physical reality, like space being "infinite," the laws of physics don't allow that.