Complexity of our universe is beyond our imagination, we still have to find a lot about nature of time, understand quantum mechanics and see order behind chaos; gravity is another great mystery worth exploring.
Perhaps M-theory can reveal all the secrets once we will manage to complete it. It suggests existence of eleven dimensions, understanding these dimensions is a key to understanding universe itself.
We, humans are able to move only in three dimensions, we can also clearly understand fourth dimension – time, but we still are not able to move through time. If we could navigate in four dimensions, visiting past and future times would be same as for example walking across the road.
Now everything above the four dimensions is extremely hard to imagine and understand, because it is beyond our consciousness, however following video below can clarify some interesting moments which can give you a headache, but I promise it is really interesting.