My recurring "what if" deep thought.... what if our solar system is just an atom and our galaxy just a giant collection of molecules in some huge universe above the one we know?
Reminds me a little of something I read once while studying some Neo-Confucianism philosophy; that nothing exists outside of our own minds.
But the way that the philosophy looks at it is not that nothing else is real, just that each individual and their individual mind has their own unique universe.
For example, I can tell you all about the beautiful lilac bush out in my back yard. I can tell you how it gets dozens of beautiful, deep purple blooms almost covering it just about every spring. How the smell of lilac will waft in through the nearby windows and make the whole house smell of it. But...none of that exists in your world. Only my description of it would exist in your world. Because you have never seen the bush, smelled the bush, touched the bush, etc..etc... it doesn't exist in YOUR world. Only my description of it does.