Hawking paper cuts down ‘multiverse’ theory

PARIS: With a science paper published after his death, Stephen Hawking has revived debate on a deeply divisive question for cosmologists: Is our Universe just one of many in an infinite, everexpanding “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 everexpanding 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 everinflating 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 coauthor 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.

However, “our findings imply 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”, Hertog said, though still composed of numerous universes.

“It is a debate that touches on the very foundations of cosmology,” Hertog said.

“The underlying question is whether we can achieve a deeper understanding of where the laws of nature come from, and whether they are unique.”

Not everyone likes the new theory. “The idea that we live in a ‘multiverse’ is a fringe idea in a small part of a subfield of the physics community,” said theoretical physicist Sabine Hossenfelder of the Frankfurt Institute for Advanced Studies.

The main problem, Hossenfelder explains, is that any multiverse theory is “underdetermined” and “doesn’t contain enough information to make calculations”.

It is a debate that touches on the very foundations of cosmology. Thomas Hertog