First of all, I think most people think about those things at least occasionally, it's totally normal and part of the curious nature of humans and many other mammals.
You mention "I can't ever just stop thinking and relax. My brain is so fucked." which indicates that this is a real problem affecting your mental health. I think you could benefit from going to therapy specifically about anxiety, or at least start with implementing some of the basic principles.
Worrying about things you can't control, or can't influence, while completely normal, can be quite destructive. Try to reframe these in your head. Don't be anxious because you might never know the answer, let yourself be freed by the fact that you don't have to do anything about it. All those things you mentioned are really awe inspiring. Things to wonder and imagine. That could be a positive thing in your life, part of the great mysteries of humanity, not something to be upset about.
Focus on the things in your life that you can control. You can study, practice music, write stories, etc. So many many things you can control, so don't be upset about what you can't. Be happy with what you can.
Maybe you could directly transform your anxiety into creativity here. If you're so consumed by these things, write a short sci-fi story about if the world was a simulation, etc. There's a reason why people with anxiety or ADHD tend to be creative. Just an idea.
StoryGraph