It is impossible (I think) to know if there is a world outside of what we experience, or if this is all just for me and no-one else experiences what I experience.
All our experiences suggest a world and universe beyond, yet we die and everything we used to experience this dies with our body (or does it?).
We always assume we live just one life. It is possible that everything is possible and every fork is explored yet we are only aware of one path.
This is a philosophical stuff.
