About 13.7 billion years ago, our Universe was born in a extremely dense point of heat and energy, no bigger than an atom. This subatomic ball, known as a singularity, was not inside the Universe, it was the Universe. But what was there before?

In a new episode of Star Talk, the famous British physicist Stephen Hawking spoke with host Neil deGrasse Tyson to talk about what existed before Big Bang, this conceptual line only “visible” by calculation, which is impossible to cross. Hawking’s answer? Nothing, he explained.

Hawking relied on the shape of the Earth as analogy to the curved shape of the space-time continuum: “According to Einsteinâ€™s General Theory of Relativity, space and time come together form a space-time continuum or manifold which is not flat but curved by the matter and energy in it.”

To go a step further, Hawking relies on the Euclidean approach of quantum gravity. In the Euclidean approach, ordinary real time is replaced by imaginary time, which behaves like a fourth dimension. “I adopt a Euclidian approach to quantum gravity to describe the beginning of the universe, in this, ordinary real time is replaced by imaginary time, which behaves like a fourth direction of space,” he said.

“In the Euclidian 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,” he added.

So, six dimensions in total. But what does that mean exactly? This means that the Universe, according to Hawking, has no boundaries. In other words, the Euclidean space-time continuum is an endless closed surface, much like the surface of the Earth. Just as it is possible to travel all around the Earth’s surface without encountering any edge, the Big Bang would not be the beginning of space-time anymore than on Earth the North Pole would represent the beginning of the surface of the earth.

“We can consider ordinary and real time as starting at the South Pole, which is a smooth point of space-time where the natural laws of physics hold,” he explains. “There is nothing south of the South Pole, so there was nothing around before the Big Bang.” Just as there is nothing south of a southernmost point, time can not exist before the Big Bang. Instead, time and space extend from this singular point in time, like the degrees of latitude on the planet Earth.