• This paper was submitted for review about 10 days before Hawking passed away
  • The theory that there are infinite parallel universes that were created as a result of the big bang is wrong, says the new paper
  • Parallel universes are finite, can be detected, and follow the same physical laws that this one follows, argue Hawking and Hertog 
  • There is no way to travel between these universes

Professor Stephen Hawking's final paper that he co-authored with Professor Thomas Hertog has finally been published. It is a new theory that explores the possibilities of multiverses, the big bang, as well as the origin of the entire universe. The paper was submitted just ten days before Hawking died.

The theory, in short, explains that the universe is a lot more simple and finite when compared to what many existing theories on the big bang say, notes a report by the University of Cambridge. The new paper argues that the concept eternal inflation to explain the events that followed the big bang is just wrong.

To understand what the professors mean when they say eternal inflation, consider what one existing theory on the big bang is. The Cambridge report mentions that modern theories on the big bang predict how the universe came to be with a "brief burst of inflation" that happened a fraction of a second after the bang itself which in turn kicked off the exponential expansion of the universe. The belief is that once this process started, it never really stopped. Quantum effects can simply keep this inflation going forever in some parts of the universe, making inflation eternal in the overall picture. However, there exist certain pockets like the one where our observable universe is and it just so happens to be a hospitable one where inflation has ended and stars, galaxies, and worlds formed.

Stephen Hawking
Stephen Hawking pictured during one of his speechesReuters

"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," said Hertog.

"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.

"We predict that our universe, on the largest scales, is reasonably smooth and globally finite. So it is not a fractal structure," said Hawking.

The new theory that Hawking and Hertog propose is based on string theory, notes a BBC report. The theory explains that there can only be a finite number of universes and that there can only be universes that have and follow the same physics as the one we are in now. This also means that this universe is typical and so the observations made from here will be significant in developing ideas of how other universes exist.

Hertog says that this approach could help physicists in future to work on developing a complete theory that explains the entire universe and how it really came to be.

"The laws of physics that we test in our labs did not exist forever. They crystallised after the Big Bang when the universe expanded and cooled. The kind of laws that emerge depends very much on the physical conditions at the Big Bang. By studying these we aim to get a deeper understanding of where our physical theories come from, how they arise, and whether they are unique."

One of the implications in this new paper is that, according to Hertog, it could be possible to detect the presence of other universes by looking at the microwave radiation left over from the big bang. He also noted that traveling between the parallel universes might not be possible.

The paper has been published in the Journal of High Energy Physics.