Clearly the universe has a physical aspect of it because we can observe it physically. There is no need to assume that is all there is, but we can't deal with anything else unless we have some evidence and some objective means of studying it.
Well, yes we can. We just deal with it socially or individually, and then some people deny that they do that, because they are special and speak for all humans objectively.
The test if something is objective as per falsifying that, is to test if you can get away with doing it subjectively.
There are 5 main tests -
-Objective as independent of the brain
-Objective as formal thinking in the brain
-Social as shared between brains
-Individual as how to cope as a single human
-What happens when you try to add up the four other ones
There are even more and in Denmark we have 7 kinds of science and not just one.