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