Stephen Hawking's Final Theory About Our Universe Will Melt Your Brain

The universe is finite and far simpler than many current theories about the "big bang" - that's according to the late Professor Stephen Hawking's final work on how it all began 13.8 billion years ago.

The famed cosmologist's theory, which he worked on in collaboration with Professor Thomas Hertog of Belgium's KU Leuven, has been published few months after his death and nearly a year after it was first announced.

Modern theories of the big bang predict that our local universe came into existence with a brief burst of inflation - in other words, a tiny fraction of a second after the big bang itself, the universe expanded at an exponential rate.

It is widely believed, however, that once inflation starts, there are regions where it never stops.

It is thought that quantum effects can keep inflation going forever in some regions of the universe so that globally, inflation is eternal.

The observable part of our universe would then be just a hospitable pocket universe, a region in which inflation has ended and stars and galaxies formed.

"The usual theory of eternal inflation predicts that globally our universe is like an infinite fractal, with a mosaic of different pocket universes, separated by an inflating ocean," Hawking explained in one of his last interviews.

"The local laws of physics and chemistry can differ from one pocket universe to another, which together would form a multiverse.

"But I have never been a fan of the multiverse. If the scale of different universes in the multiverse is large or infinite the theory can't be tested."

In their new paper, Hawking and Hertog say this account of eternal inflation as a theory of the big bang is wrong.

"The problem with the usual account of eternal inflation is that it assumes an existing background universe that evolves according to Einstein's theory of general relativity and treats the quantum effects as small fluctuations around this," Hertog said.

"However, the dynamics of eternal inflation wipes out the separation between classical and quantum physics.

As a consequence, Einstein's theory breaks down in eternal inflation.

The two scientists thus predicted that our universe, on the largest scales, was reasonably smooth and globally finite, and not a fractal structure.

Hertog now planned to study the implications of the new theory on smaller scales that were within reach of our space telescopes.

He believed that primordial gravitational waves - or ripples in spacetime - generated at the exit from eternal inflation offered the most promising "smoking gun" to test the model.