Speaker 1: Welcome to brain Stuff from How Stuff Works, Hey, brain Stuff,
Speaker 1: Lauren voc obam here. Days before his death. On March fourteen, eighteen,
Speaker 1: famed theoretical physicist and cosmologist Stephen Hawking completed what would
Speaker 1: be his final research paper. It has since passed peer
Speaker 1: review and was published online in the Journal of High
Speaker 1: Energy Physics on April. Written with co author Thomas Hertog,
Speaker 1: a theoretical physicist at the University of louisn Belgium, the
Speaker 1: paper adds another facet to our understanding of this universe
Speaker 1: that we live in, and needless to say, it's complicated.
Speaker 1: Titled a Smooth Exit from Eternal Inflation, the publication discusses
Speaker 1: an enigmatic problem facing cosmologists. But before we delve into
Speaker 1: the crux of the study, let's go back to when
Speaker 1: our universe was a baby, some thirteen point eight billion
Speaker 1: years ago. A lot of evidence suggests that our universe
Speaker 1: originated from a singularity, an infinitely dense point from which
Speaker 1: all the universe as we know it was born. We
Speaker 1: call that event the Big Bang. But how the singularity
Speaker 1: came to be and why the Big Bang happened isn't
Speaker 1: of concern right now. We're interested in what happened immediately
Speaker 1: after our universe was spawned, a period known as inflation.
Speaker 1: Cosmologists predict that inflation occurred over a vanishingly small period
Speaker 1: right after the Big Bang, during our universe's very first
Speaker 1: ten to thirty two seconds. During inflation, the universe expanded
Speaker 1: exponentially and much faster than the speed of light. After
Speaker 1: only a second, the energy from this inconceivably gargantuan explosion
Speaker 1: condensed to form sub atomic particles that, over millions of years,
Speaker 1: created the stars, galaxies, planets, and, after another few billion years,
Speaker 1: a life as we know it. Once this inflationary period ended,
Speaker 1: the universe's rate of expansion slowed, but it continues to
Speaker 1: expand to this day. Because inflation powered a faster than
Speaker 1: light speed expansion, The observable uni verse that we see
Speaker 1: today is not the entire universe. Rather, we exist inside
Speaker 1: a region of the cosmos that light has had time
Speaker 1: to reach. It's like dropping a pebble into a calm
Speaker 1: swimming pool. The first circular ripple to propagate from the
Speaker 1: splash travels at a fixed speed across the surface of
Speaker 1: the pool. If we imagine that the limit of our
Speaker 1: observable universe is that ripple traveling across the pool at
Speaker 1: the speed of light. It's not that nothing exists beyond
Speaker 1: that ripple. There's more pool or universe beyond it. We
Speaker 1: just can't see it yet. So the consequence of inflation
Speaker 1: is that there should be a lot more universe beyond
Speaker 1: what we can see, even with our most powerful telescopes,
Speaker 1: and cosmologists have been grappling with the possibility that our
Speaker 1: universe is not the only universe. In fact, we could
Speaker 1: be nothing more than a single bubble in an infinite
Speaker 1: froth the ocean, a concept known as the multiverse. The
Speaker 1: idea here is that inflation didn't happen once, It's always
Speaker 1: happening via some infinitely vast chain reaction known as eternal inflation.
Speaker 1: One universe will appear, and inflation will take over, expanding
Speaker 1: that universe, and that universe will have its own quantum
Speaker 1: instabilities that will spawn more singularities that go on to
Speaker 1: create more universes. It's like blowing up a party balloon
Speaker 1: that itself spawns many other party balloons that are rupped
Speaker 1: from its rubbery surface seemingly at random. If this situation
Speaker 1: sounds chaotic, it is. Proponents of this hypothesis think that
Speaker 1: eternal inflation is unstoppable, vastly complex, and continually generating new universes,
Speaker 1: and the math of this situation suggests that the multiverse
Speaker 1: acts like a fractal, fractals being sets of data that
Speaker 1: contain repeating patterns at every scale. Visually, this means that
Speaker 1: complex shapes look pretty much the same at a wide
Speaker 1: range of scales, like a small piece of it looks
Speaker 1: pretty similar to the whole structure. Think of a head
Speaker 1: of cauliflower. Any given segment will resemble the whole head,
Speaker 1: and if you zoom in further, each clus store of
Speaker 1: buds resembles the larger segments. It's worth noting that in
Speaker 1: this theory, each successive universe and the multiverse doesn't likely
Speaker 1: share the same physics as our universe. One universe might
Speaker 1: not have gravity, another may not support the forces that
Speaker 1: hold matter together. There would be a lot of stillborn
Speaker 1: universes that just don't amount too much. We humans are
Speaker 1: simply lucky to have a universe that has the right
Speaker 1: environment to create what we see. A philosophical argument known
Speaker 1: as the anthropic principle. The problem with eternal inflation is
Speaker 1: that it's messy and infinite, and that the hypothesis is
Speaker 1: ultimately untestable. So what does Hawking and her tog's research
Speaker 1: have to do with this unrelenting multiverse In the multiverse.
Speaker 1: Our universe is merely a pocket universe where inflation has ended,
Speaker 1: and despite the odds, it found enough calm to create
Speaker 1: a bounty of stars and galaxies and a bunch of
Speaker 1: humans living on some random rock pondering the cosmos. What's
Speaker 1: going on beyond our pocket of calm is, however, somewhat different,
Speaker 1: Hawking said in an interview in Tween. The usual theory
Speaker 1: of eternal inflation predicts that globally, our universe is like
Speaker 1: an infinite fractal with a mosaic of different pocket universes
Speaker 1: separated by an inflating ocean. The local laws of physics
Speaker 1: and chemistry can differ from one pocket universe to another,
Speaker 1: which together would form a multiverse. But I have never
Speaker 1: been a fan of the multiverse. If the scale of
Speaker 1: different universes in the multiverse is large or infinite, then
Speaker 1: the theory can't be tested. The problem, according to Hawking
Speaker 1: in Her Dog, allies with the incompatibility of Einstein's general
Speaker 1: relativity that governs the evolution of the universe and quantum
Speaker 1: mechanics that seeds the creation of new universes through quantum fluctuations.
Speaker 1: The eternal inflation model of the multiverse, as her Dog
Speaker 1: said in a press release quote, wipes out separation between
Speaker 1: classical and quantum physics. As a consequence, Einstein's theory breaks
Speaker 1: down in eternal inflation. Their study doesn't go as far
Speaker 1: as reconciling general relativity with quantum physics, a quest that
Speaker 1: has so far been unsuccessful, but they use the math
Speaker 1: of string theory to help simplify the multiverse model. A
Speaker 1: quick recap. String theory predicts that all subtomic particles in
Speaker 1: our universe are in fact composed of one dimensional strings
Speaker 1: that propagate through space. The vibrational state of these strings
Speaker 1: is what gives these particles their quantum state such as charge, spin,
Speaker 1: and mass. But string theory also predicts the existence of
Speaker 1: the hypothetical graviton, a quantum particle that carries the force
Speaker 1: of gravity. The math that suggests that gravitons exist is solid,
Speaker 1: but no one's been able to point to one yet.
Speaker 1: String theory would therefore provide an explanation of how Einstein's
Speaker 1: general relativity gravity jibes with quantum physics using the mathematical
Speaker 1: framework of string theory. This final study from Hawking simplifies
Speaker 1: the multiverse. Hawking and her dog used the string theory
Speaker 1: concept of holography, who reduce our three dimensional universe down
Speaker 1: to a two dimensional surface from which the universe we
Speaker 1: know and love is projected. By doing this, they were
Speaker 1: able to describe eternal inflation without general relativity, creating a
Speaker 1: timeless state. Her dog explained this move in a statement.
Speaker 1: When we trace the evolution of our universe backwards in time,
Speaker 1: at some point we arrive at the threshold of eternal inflation,
Speaker 1: where our familiar notion of time ceases to have any meaning.
Speaker 1: The math is complex, but the result is interesting. The
Speaker 1: calculations have the effect of turning the infinite and fractal
Speaker 1: multiverse into a far simpler and finite situation that eternal
Speaker 1: inflation does predict. Hawking said this about it. We are
Speaker 1: not down to a single unique universe, but our findings
Speaker 1: imply a significant reduction of the multiverse to a much
Speaker 1: smaller range of possible universes. To put it in perspective,
Speaker 1: Hawking's final paper doesn't revolutionize our understanding of how the
Speaker 1: universe and indeed the multiverse works, but it is a
Speaker 1: valuable addition to a huge field of theoretical work. Specifically,
Speaker 1: her TG hopes that this study may help us search
Speaker 1: for ancient gravitational waves that were generated by eternal inflation.
Speaker 1: These ripples in space time are far too weak for
Speaker 1: current gravitational wave detectors to detect. However, we need to
Speaker 1: wait until advanced space based observatories such as the European
Speaker 1: Space Agencies planned LIESA mission are launched. Regardless of whether
Speaker 1: the study leads to groundbreaking discoveries about the cosmos that
Speaker 1: we live in, it's a testament to a great scientist
Speaker 1: who worked tirelessly his entire life to answer some of
Speaker 1: the biggest questions that humanity has pondered, and on Hawking's shoulders,
Speaker 1: other great minds will build on this work to hopefully
Speaker 1: decipher whether our universe is unique or if it's just
Speaker 1: one bubble chaotically floating in the ocean of the multiverse.
Speaker 1: Today's episode was written by Ian O'Neill and produced by
Speaker 1: Tyler Clang with kind engineering assistance from Ramsay Yount. For
Speaker 1: more on this and lots of other eternally expanding topics.
Speaker 1: Visit our home planet, how staff Works dot com