WEBVTT - What Was Stephen Hawking's Final Project?

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<v Speaker 1>Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff,

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<v Speaker 1>Lauren voc obam here. Days before his death. On March fourteen, eighteen,

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<v Speaker 1>famed theoretical physicist and cosmologist Stephen Hawking completed what would

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<v Speaker 1>be his final research paper. It has since passed peer

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<v Speaker 1>review and was published online in the Journal of High

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<v Speaker 1>Energy Physics on April. Written with co author Thomas Hertog,

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<v Speaker 1>a theoretical physicist at the University of louisn Belgium, the

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<v Speaker 1>paper adds another facet to our understanding of this universe

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<v Speaker 1>that we live in, and needless to say, it's complicated.

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<v Speaker 1>Titled a Smooth Exit from Eternal Inflation, the publication discusses

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<v Speaker 1>an enigmatic problem facing cosmologists. But before we delve into

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<v Speaker 1>the crux of the study, let's go back to when

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<v Speaker 1>our universe was a baby, some thirteen point eight billion

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<v Speaker 1>years ago. A lot of evidence suggests that our universe

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<v Speaker 1>originated from a singularity, an infinitely dense point from which

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<v Speaker 1>all the universe as we know it was born. We

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<v Speaker 1>call that event the Big Bang. But how the singularity

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<v Speaker 1>came to be and why the Big Bang happened isn't

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<v Speaker 1>of concern right now. We're interested in what happened immediately

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<v Speaker 1>after our universe was spawned, a period known as inflation.

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<v Speaker 1>Cosmologists predict that inflation occurred over a vanishingly small period

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<v Speaker 1>right after the Big Bang, during our universe's very first

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<v Speaker 1>ten to thirty two seconds. During inflation, the universe expanded

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<v Speaker 1>exponentially and much faster than the speed of light. After

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<v Speaker 1>only a second, the energy from this inconceivably gargantuan explosion

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<v Speaker 1>condensed to form sub atomic particles that, over millions of years,

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<v Speaker 1>created the stars, galaxies, planets, and, after another few billion years,

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<v Speaker 1>a life as we know it. Once this inflationary period ended,

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<v Speaker 1>the universe's rate of expansion slowed, but it continues to

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<v Speaker 1>expand to this day. Because inflation powered a faster than

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<v Speaker 1>light speed expansion, The observable uni verse that we see

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<v Speaker 1>today is not the entire universe. Rather, we exist inside

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<v Speaker 1>a region of the cosmos that light has had time

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<v Speaker 1>to reach. It's like dropping a pebble into a calm

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<v Speaker 1>swimming pool. The first circular ripple to propagate from the

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<v Speaker 1>splash travels at a fixed speed across the surface of

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<v Speaker 1>the pool. If we imagine that the limit of our

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<v Speaker 1>observable universe is that ripple traveling across the pool at

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<v Speaker 1>the speed of light. It's not that nothing exists beyond

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<v Speaker 1>that ripple. There's more pool or universe beyond it. We

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<v Speaker 1>just can't see it yet. So the consequence of inflation

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<v Speaker 1>is that there should be a lot more universe beyond

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<v Speaker 1>what we can see, even with our most powerful telescopes,

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<v Speaker 1>and cosmologists have been grappling with the possibility that our

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<v Speaker 1>universe is not the only universe. In fact, we could

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<v Speaker 1>be nothing more than a single bubble in an infinite

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<v Speaker 1>froth the ocean, a concept known as the multiverse. The

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<v Speaker 1>idea here is that inflation didn't happen once, It's always

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<v Speaker 1>happening via some infinitely vast chain reaction known as eternal inflation.

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<v Speaker 1>One universe will appear, and inflation will take over, expanding

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<v Speaker 1>that universe, and that universe will have its own quantum

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<v Speaker 1>instabilities that will spawn more singularities that go on to

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<v Speaker 1>create more universes. It's like blowing up a party balloon

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<v Speaker 1>that itself spawns many other party balloons that are rupped

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<v Speaker 1>from its rubbery surface seemingly at random. If this situation

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<v Speaker 1>sounds chaotic, it is. Proponents of this hypothesis think that

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<v Speaker 1>eternal inflation is unstoppable, vastly complex, and continually generating new universes,

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<v Speaker 1>and the math of this situation suggests that the multiverse

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<v Speaker 1>acts like a fractal, fractals being sets of data that

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<v Speaker 1>contain repeating patterns at every scale. Visually, this means that

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<v Speaker 1>complex shapes look pretty much the same at a wide

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<v Speaker 1>range of scales, like a small piece of it looks

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<v Speaker 1>pretty similar to the whole structure. Think of a head

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<v Speaker 1>of cauliflower. Any given segment will resemble the whole head,

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<v Speaker 1>and if you zoom in further, each clus store of

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<v Speaker 1>buds resembles the larger segments. It's worth noting that in

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<v Speaker 1>this theory, each successive universe and the multiverse doesn't likely

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<v Speaker 1>share the same physics as our universe. One universe might

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<v Speaker 1>not have gravity, another may not support the forces that

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<v Speaker 1>hold matter together. There would be a lot of stillborn

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<v Speaker 1>universes that just don't amount too much. We humans are

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<v Speaker 1>simply lucky to have a universe that has the right

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<v Speaker 1>environment to create what we see. A philosophical argument known

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<v Speaker 1>as the anthropic principle. The problem with eternal inflation is

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<v Speaker 1>that it's messy and infinite, and that the hypothesis is

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<v Speaker 1>ultimately untestable. So what does Hawking and her tog's research

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<v Speaker 1>have to do with this unrelenting multiverse In the multiverse.

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<v Speaker 1>Our universe is merely a pocket universe where inflation has ended,

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<v Speaker 1>and despite the odds, it found enough calm to create

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<v Speaker 1>a bounty of stars and galaxies and a bunch of

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<v Speaker 1>humans living on some random rock pondering the cosmos. What's

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<v Speaker 1>going on beyond our pocket of calm is, however, somewhat different,

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<v Speaker 1>Hawking said in an interview in Tween. The usual theory

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<v Speaker 1>of eternal inflation predicts that globally, our universe is like

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<v Speaker 1>an infinite fractal with a mosaic of different pocket universes

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<v Speaker 1>separated by an inflating ocean. The local laws of physics

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<v Speaker 1>and chemistry can differ from one pocket universe to another,

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<v Speaker 1>which together would form a multiverse. But I have never

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<v Speaker 1>been a fan of the multiverse. If the scale of

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<v Speaker 1>different universes in the multiverse is large or infinite, then

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<v Speaker 1>the theory can't be tested. The problem, according to Hawking

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<v Speaker 1>in Her Dog, allies with the incompatibility of Einstein's general

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<v Speaker 1>relativity that governs the evolution of the universe and quantum

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<v Speaker 1>mechanics that seeds the creation of new universes through quantum fluctuations.

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<v Speaker 1>The eternal inflation model of the multiverse, as her Dog

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<v Speaker 1>said in a press release quote, wipes out separation between

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<v Speaker 1>classical and quantum physics. As a consequence, Einstein's theory breaks

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<v Speaker 1>down in eternal inflation. Their study doesn't go as far

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<v Speaker 1>as reconciling general relativity with quantum physics, a quest that

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<v Speaker 1>has so far been unsuccessful, but they use the math

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<v Speaker 1>of string theory to help simplify the multiverse model. A

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<v Speaker 1>quick recap. String theory predicts that all subtomic particles in

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<v Speaker 1>our universe are in fact composed of one dimensional strings

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<v Speaker 1>that propagate through space. The vibrational state of these strings

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<v Speaker 1>is what gives these particles their quantum state such as charge, spin,

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<v Speaker 1>and mass. But string theory also predicts the existence of

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<v Speaker 1>the hypothetical graviton, a quantum particle that carries the force

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<v Speaker 1>of gravity. The math that suggests that gravitons exist is solid,

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<v Speaker 1>but no one's been able to point to one yet.

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<v Speaker 1>String theory would therefore provide an explanation of how Einstein's

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<v Speaker 1>general relativity gravity jibes with quantum physics using the mathematical

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<v Speaker 1>framework of string theory. This final study from Hawking simplifies

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<v Speaker 1>the multiverse. Hawking and her dog used the string theory

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<v Speaker 1>concept of holography, who reduce our three dimensional universe down

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<v Speaker 1>to a two dimensional surface from which the universe we

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<v Speaker 1>know and love is projected. By doing this, they were

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<v Speaker 1>able to describe eternal inflation without general relativity, creating a

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<v Speaker 1>timeless state. Her dog explained this move in a statement.

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<v Speaker 1>When we trace the evolution of our universe backwards in time,

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<v Speaker 1>at some point we arrive at the threshold of eternal inflation,

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<v Speaker 1>where our familiar notion of time ceases to have any meaning.

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<v Speaker 1>The math is complex, but the result is interesting. The

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<v Speaker 1>calculations have the effect of turning the infinite and fractal

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<v Speaker 1>multiverse into a far simpler and finite situation that eternal

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<v Speaker 1>inflation does predict. Hawking said this about it. We are

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<v Speaker 1>not down to a single unique universe, but our findings

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<v Speaker 1>imply a significant reduction of the multiverse to a much

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<v Speaker 1>smaller range of possible universes. To put it in perspective,

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<v Speaker 1>Hawking's final paper doesn't revolutionize our understanding of how the

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<v Speaker 1>universe and indeed the multiverse works, but it is a

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<v Speaker 1>valuable addition to a huge field of theoretical work. Specifically,

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<v Speaker 1>her TG hopes that this study may help us search

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<v Speaker 1>for ancient gravitational waves that were generated by eternal inflation.

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<v Speaker 1>These ripples in space time are far too weak for

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<v Speaker 1>current gravitational wave detectors to detect. However, we need to

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<v Speaker 1>wait until advanced space based observatories such as the European

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<v Speaker 1>Space Agencies planned LIESA mission are launched. Regardless of whether

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<v Speaker 1>the study leads to groundbreaking discoveries about the cosmos that

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<v Speaker 1>we live in, it's a testament to a great scientist

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<v Speaker 1>who worked tirelessly his entire life to answer some of

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<v Speaker 1>the biggest questions that humanity has pondered, and on Hawking's shoulders,

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<v Speaker 1>other great minds will build on this work to hopefully

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<v Speaker 1>decipher whether our universe is unique or if it's just

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<v Speaker 1>one bubble chaotically floating in the ocean of the multiverse.

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<v Speaker 1>Today's episode was written by Ian O'Neill and produced by

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<v Speaker 1>Tyler Clang with kind engineering assistance from Ramsay Yount. For

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<v Speaker 1>more on this and lots of other eternally expanding topics.

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<v Speaker 1>Visit our home planet, how staff Works dot com