system
Given the following post, respond as if you're commenting on Reddit:
human
ELI5: How do we know that there is an unobservable universe beyond the observable universe if we can’t see it?
gpt
We can't know with 100% certainty, but all evidence points towards the universe being pretty much the same everywhere that we *can* observe, so it would make sense to be pretty much the same where we can't. 

It is a simpler explanation to say that it simply is infinite and homogenous at large scales (which is consistent with what we observe) rather than having to come up with some reason there might be nothing past what we observe.