BrainStuff Classics: What Was Stephen Hawking's Final Project?

his final research paper. It has since passed peer review and was published online in the Journal of High Energy Physics on April. Written with co author Thomas Hertog, a theoretical physicist at the University of louisn Belgium, the paper adds another facet to our understanding of this universe that we live in, and needless to say, it's complicated. Titled a Smooth Exit from Eternal Inflation, the publication discusses an

enigmatic problem facing cosmologists. But before we delve into the crux of the study, let's go back to when our universe was a baby, some thirteen point eight billion years ago. A lot of evidence suggests that our universe originated from a singularity, an infinitely dense point from which all the universe as we know it was born. We call that event the Big Bang. But how the Singularity came to be and why the Big Bang happened isn't of concern

right now. We're interested in what happened immediately after our universe was spawned, a period known as inflation. Cosmologists predict that inflation occurred over a vanishingly small period right after the Big Bang, during our universe's very first ten to thirty two seconds. During inflation, the universe expanded exponentially and

much faster than the speed of light. After only a second, the energy from this inconceivably gargantuan explosion condensed to form sub atomic particles that, over millions of years, created the stars, galaxies, planets, and, after another few years, a life as we know it. Once this inflationary period ended, the universe's rate of expansion slowed, but it continues to expand to this day. Because inflation powered a faster than light speed expansion, the observable universe

that we see today is not the entire universe. Rather, we exist inside a region of the cosmos that light has had time to reach. It's like dropping a pebble into a calm swimming pool, The first circular ripple to propagate from the splash travels at a fixed speed across the surface of the pool. If we imagine that the limit of our observable universe is that ripple traveling across the pool at the speed of light, it's not that nothing exists beyond that ripple. There's more pool or universe

beyond it. We just can't see it yet. So the consequence of inflation is that there should be a lot more universe beyond what we can see, even with our most powerful telescopes. And cosmologists have been grappling with the possibility that our universe is not the only universe. In fact, we could be nothing more than a single bubble in an infinite, frothy ocean, a concept known as the multiverse.

The idea here is that inflation didn't happen once, It's always happening via some infinitely vast chain reaction known as eternal inflation. One universe will appear, and inflation will take over, expanding that universe, and that universe will have its own quantum instabilities that will spawn more singularities that go on to create more universes. It's like blowing up a party balloon that itself spawns many other party balloons that are

rupped from its rubbery surface, seemingly at random. If this situation sounds chaotic, it is. Proponents of this hypothesis think that eternal inflation is unstoppable, vastly complex, and continually generating new universes, and the math of this situation suggests that the multiverse acts like a fractal, fractals being sets of data that contain repeating patterns at every scale. Visually, this means that complex shapes look pretty much the same at a wide range of scales, like a small piece of

it looks pretty similar to the whole structure. Think of a head of cauliflower. Any given segment will resemble the whole head, and if you zoom in further, each cluster of buds resembles the larger segments. It's worth noting that in this theory, each success of universe and the multiverse doesn't likely share the same physics as our universe. One universe might not have gravity, another may not support the forces that hold matter together. There would be a lot

of stillborn universes that just don't amount too much. We humans are simply lucky to have a universe that has the right environment to create what we see, a philosophical argument known as the anthropic principle. The problem with eternal inflation is that it's messy and infinite, and that the hypothesis is ultimately untestable. So what does Hawking and her Tog's research have to do with this unrelenting multiverse In

the multiverse? Are you? Niverse is merely a pocket universe where inflation has ended, and despite the odds, it found enough calm to create a bounty of stars and galaxies and a bunch of humans living on some random rock pondering the cosmos. What's going on beyond our pocket of calm is, however, somewhat different, Hawking said in an interview. In 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. 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, then the theory can't be tested. The problem, according to Hawking in her Dog, allies with the incompatibility of Einstein's general relativity that governs the evolution of the universe and quantum mechanics that seeds the creation of new universes through quantum fluctuations. The eternal inflation model of the multiverse, as her Tog said in a press release quote, wipes out separation between classical and quantum physics. As a consequence,

Einstein's theory breaks down in eternal inflation. Their study doesn't go as far as reconciling general relativity with quantum physics, a quest that has so far been unsuccessful, but they use the math of string theory to help simplify the multiverse model. A quick recap. String theory predicts that all subtomic particles in our universe are in fact composed of

one dimensional strings that propagate through space. The vibrational state of these strings is what gives these particles their quantum state such as charge, spin, and mass. But string theory also predicts the existence of the hypothetical graviton, a quantum particle that carries the force of gravity. The math that suggests that gravitons exist is solid, but no one's been

able to point to one yet. String theory would therefore provide an explanation of how einstein general relativity gravity jibes with quantum physics using the mathematical framework of string theory. This final study from Hawking simplifies the multiverse. Hawking and her dog used the string theory concept of holography to reduce our three dimensional universe down to a two dimensional surface from which the universe we know and love is projected.

By doing this, they were able to describe eternal inflation without general relativity, creating a timeless state. Her dog explained this move in a statement. When we trace the evolution of our universe backwards in time, at some point we arrive at the threshold of eternal inflation, where our familiar notion of time ceases to have any meaning. The math

is complex, but the result is interesting. The calculations have the effect of turning the infinite and fractal multiverse into a far simpler and finite situation that eternal inflation does predict. Hawking said this about it. 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. To put it in perspective, Hawking's final paper doesn't revolutionize our understanding of how the universe and indeed the multiverse works, but it is a valuable addition to a huge field of theoretical work. Specifically, her Tug hopes that this study may help a search for ancient gravitational waves that were generated by eternal inflation. These ripples in space time are far too weak for current gravitational wave

detectors to detect. However, we need to wait until advanced space based observatories such as the European Space Agencies planned

LIESA mission are launched. Regardless of whether the study leads to groundbreaking discoveries about the cosmos that we live in, it's a testament to a great scientist who worked tirelessly his entire life to answer some of the biggest questions that humanity has pondered, and on Hawking's shoulders, other great minds will build on this work to hopefully decipher whether our universe is unique or if it's just one bubble

chaotically floating in the ocean of the multiverse. Today's episode is based on the article Stephen Hawking's Last Paper Takes on the Multiverse on Housetofworks dot com, written by Ian O'Neill. Brain Stuff is production of I Heart Radio in partnership with housetfworks dot com and it's produced by Tyler clang Or more podcasts my heart Radio, visit the I heart Radio app, Apple Podcasts, or wherever you listen to your favorite shows.