Only one thing can be known for sure. Direct experience, pure, raw, unconceptualized experience. Nothing else. Not one single thing.
Philosophers and physicists alike have tried to nail down reality for ages, starting with the external world. But we have zero direct information about the external world. There seems to be some experience to which we apply all kinds of concepts and then we reason (tell made-up stories) about those concepts. We look for patterns and describe them, with words or mathematics.
But we disregard the huge step that we have taken by doing so. The step from subjective, internal experience to some external, material, physical, real, actual world. We have no evidence for such a world. And we certainly have no evidence for that world being somehow primary over the subjective experience in consciousness that it appears as.
All we know for sure is: ‘experience in consciousness’ or ‘consciousness and its content’. That experience or that content has no dimensions, no matter, no stuff. In fact it also has no me or you or anything else. To go even further yet, consciousness and its content can’t be separated. They aren’t two separate things, they are one and the same, they are inseparable.
That’s atman. God. The one. That’s you. Except that the ‘you’ part is made up. Everything is made up. There is experience and just experience. All concepts are nonsense. You are a concept.
Happily, there is nothing for you to do because you don’t exist. So, that’s the good news I guess. You were done before you started because you didn’t exist when you started and you don’t exist now. So there is no you to do anything.
Big success!
Atman in this post should have been Brahman but I want to leave it the way I wrote it so I’m not going to change it in the text.