The Washington Post

One of Stephen Hawking’s final scientific acts: Tackling the multiverse

Ten days earlier than he died, Stephen Hawking despatched yet one more written perception out into the cosmos — a paper, co-written with physicist Thomas Hertog of the Catholic University of Leuven in Belgium, tackling the drawback of a multiverse.

The paper had beforehand been posted on a pre-print website, the place scientists share drafts of papers earlier than they’re revealed in peer-reviewed journals. It impressed so much of breathless experiences that he had predicted the end of the world and provided a solution to detect alternate universes.

The precise research, published in the Journal of High Energy Physics, is not fairly so sensational. It offers with a paradox that the physicist himself helped increase: If the large bang created infinite universes with an inexhaustible quantity of variations on the legal guidelines of physics, then how can scientists hope to reply elementary questions on why our universe appears to be like the method it does?

Hawking, who died March 14 at age 76, overcame a devastating neurological illness to publish groundbreaking insights into black holes and different mysteries of the cosmos.

“It’s very Stephen,” Michael Turner, a cosmologist at the University of Chicago, mentioned of the new analysis. “To the very end, he was not afraid to take on the toughest problems, and the problem he’s taking on is the one that gives me a headache.”

Scientists imagine that proper when the universe started, some 13.eight billion years in the past, it underwent a course of known as inflation — exponential growth in a really brief quantity of time. Over the course of that speedy growth, tiny quantum fluctuations in house have been magnified to cosmic measurement, creating the seeds of the constructions that may turn out to be galaxies and light-weight up the universe.

Some of the architects of inflation principle, together with Stanford University physicist Andrei Linde, have proposed a parallel concept: Quantum fluctuations throughout inflation gave rise not solely to galaxies however to complete universes. Weirder but, Linde suggests that inflation continues to be taking place. In an interview Wednesday, he in contrast the cosmos to an ever-expanding block of Swiss cheese. The holes are “pocket universes,” locations the place inflation has stopped domestically, permitting matter to condense and stars and galaxies to kind. We might effectively stay in a single of these pockets, encased in dense dairy product, disconnected from and blissfully unaware of the infinite alternate universes that exist round us.   

If that concept has you elevating your eyebrows, you are not alone. Some cosmologists are cautious of “eternal inflation” — and the multiverse that may stem from it. For one factor, if the numerous pocket universes are disconnected, how will we ever confirm that they’re there? For one other, an infinite multiverse would defy mathematical evaluation, making it exhausting to make use of the mannequin to grasp how the cosmos ought to work.

In their new paper, Hawking and Hertog “give the multiverse a haircut,” Turner mentioned. To accomplish that, they draw on Hawking’s “no boundary” theory — an concept developed in the 1980s to clarify how the universe arose — and an idea often called the “holographic universe,” which means that the universe may be seen as a hologram and three-dimensional actuality may be mathematically collapsed into solely two dimensions to make calculations simpler.

As a consequence, they have been in a position to carry some measure of order to the sprawling, incomprehensible multiverse. Pocket universes on this mannequin would be much less quite a few, and they’d share sure elementary qualities, making them simpler to research.

“We are not down to a single, unique universe, but our findings imply a significant reduction of the multiverse to a much smaller range of possible universes,” Hawking mentioned in an interview with Cambridge University final fall.

The proposed mannequin is not absolutely developed, mentioned Katie Mack, a cosmologist at North Carolina State University. “It’s extra like a simplified model of one thing simply to see what occurs,” depending on ideas that aren’t but broadly accepted and mathematical instruments which can be nonetheless new. 

She additionally identified that Hawking and Hertog don’t provide any quantifiable predictions of their paper, making it exhausting to check the concept.

“It’s not 42,” Turner agreed — referencing a joke from the novel “A Hitchhiker’s Guide to the Galaxy,” during which the quantity is “the Answer to the Ultimate Question of Life, the Universe, and Everything.”

But for scientists, it is one thing simply nearly as good: Not an answer to all the issues in the universe, however an intriguing — if considerably wacky-sounding — concept. A possible path to observe, although they do not know the place it would lead.

In that, it is a becoming legacy for the physicist.

“Stephen Hawking was a human being,” Linde mentioned. “He was not a genius who mentioned all appropriate issues day by day of the week. He was struggling by way of the identical scientific issues by way of which all of us are struggling” — albeit amid larger adversity and with sharper perception than most folks can hope to realize. 

With this paper — which Cambridge University says is his “final theory on the origin of the universe” — Hawking has given his colleagues yet one more factor to consider as they deal with the issues of “life, the universe and everything.”

“But it is very sad that Stephen is not here to talk about it with us,” Linde mentioned.

Read extra:

Stephen Hawking, physicist who came to symbolize the power of the human mind, dies at 76

Scientists detect signal from ‘cosmic dawn,’ when stars first lit up the universe

What made Hawking’s ‘A Brief History of Time’ so immensely popular?

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