Stephen Hawking’s paper cuts ‘multiverse’ theory down to size

The British cosmologist’s report, co-authored with Thomas Hertog, was posthumously published this week

With a science paper published after his death, Stephen Hawking has revived debate on a deeply divisive question for cosmologists: is the universe just one of many in an infinite, ever-expanding “multiverse”?

According to one school of thought, the cosmos started expanding exponentially after the Big Bang.

In most parts, this expansion or “inflation” continues eternally, except for a few pockets where it stops. These pockets are where universes like ours are formed — multitudes of them that are often likened to “bubbles” in an ever-expanding ocean dubbed the multiverse.

Many scientists don’t like the idea, including Hawking, who said in an interview last year: “I have never been a fan of the multiverse.”

If we do live in an ever-inflating multiverse, it would mean the laws of physics and chemistry can differ from one universe to another, a concept that scientists struggle to accept. In his last contribution to cosmology, Hawking — with co-author Thomas Hertog from the KU Leuven university in Belgium — does not dismiss the multiverse concept, but proposes dramatically scaling it down.

“We are not down to a single, unique universe,” the University of Cambridge quoted Hawking as saying of the paper submitted before his death on March 14 and published this week in the Journal of High Energy Physics.

The British cosmologist died at the age of 76 after a lifelong battle against motor neurone disease, which paralysed him and left him unable to speak.

However, “our findings simply a significant reduction of the multiverse, to a much smaller range of possible universes.”

The new hypothesis relies on a branch of theoretical physics known as string theory, and concludes that the cosmos is “clearly finite”, Mr. Hertog said.

“It is a debate that touches on the very foundations of cosmology. The underlying question is whether we can achieve a deeper understanding of where the laws of nature come from, and whether they are unique,” Mr. Hertog added.