This year marks the 30th anniversary of Stephen Hawking’s A History of Time, the popular science book that drove the Big Bang theory into the mainstream. In the time since, Hawking has arguably been the voice of the theory in the scientific world – and now he says he knows what the universe looked like before the Big Bang.

The smartest man in the world recently visited Neil DeGrasse Tyson’s webseries, Star Talk, and the two obviously started talking about their shared passion: science. Tyson asked what he thought was around before the bang that started our universe, and Hawking’s first reply was deceptively simple: nothing.

“According to Einstein’s general theory of relativity, space and time come together for a space-time continuum…which is not flat but curved by the matter and energy in it,” continued Hawking, then talking about the Euclidean approach to quantum gravity. “In the Euclidean approach, the history of the universe in imaginary time is a four-dimensional curved surface like the surface of the Earth, but with two more dimensions.”

That’s six dimensions he’s talking about, right there.

Ultimately, the superstar physicist believes the universe to be entirely without boundaries. The Euclidean space-time continuum would then be a closed surface without end, much like the surface of our planet. For Hawking and scientist Jim Hartle, the “boundary condition of the universe is that it has no boundary,” which by extension means that there was nothing before the Big Bang – not even time.

If there’s one person in our planet that could get closer to answering the mysteries of the universe, it’s Hawking, a world-renowned expert on time.

It’s a fascinating approach to the literal beginning of times, and a tough concept to truly grasp. Thankfully, if there’s one thing professor Hawking does well, it’s explaining dense scientific concepts in layman’s terms. Then again, his interviewer and talk show host, Tyson, is certainly no layman.

You can watch Hawking’s example-filled explanation on the video below.