How is that just the lab expoeriments on earth will verify everything that going on in black holes and other galaxies? What if there is a parallel universe, or a negative of this universe where things. I guess these are just my philoshopical question. (damn it, we do not have a ophilosophy forum yet.😞 )[/b]
For most practical physics (and we all know that other sciences are just fluffier versions of physics 😉, there is the assumption that the universe is homogenous, and that's called the Cosmological Principle:
It's a reasonable basis to explore things on. The local universe seems to behave in predictable ways, as does the observable distant universe, within limits.
However, there are also a lot of people working on other theories that assume the Cosmological Principle is wrong. The trick is creating theories that are testable in some fashion. If you can't test it, it's just waffling 😉 Still, it's very interesting.
Some links, if you are into this sort of thing: