As part of our joint project with FQXi called Science fiction, science fact, we asked you what question on the frontiers of physics you'd like to have answered. The question that topped our first poll was 'What is time?'.
We went to ask Paul Davies, a theoretical physicist and cosmologist at Arizona State University and Director of BEYOND: Centre for Fundamental Concepts in Science and here is his answer.
You can also read the accompanying article.
And don't forget to vote for the next question you'd like us to put to an expert!