Where did the universe come from? Where is it heading? Are we just living in one of many possible realities?
These are the sorts of questions that Brian Greene, a professor of physics and mathematics at Columbia University, has spent his lifetime trying to answer.
In between, he has also found time to write several best-selling books on the subject. His latest, The Hidden Reality, explores the possibility that our universe is not the only universe.
He tells BBC Future how pushing the boundaries of scientific exploration will shape our future.