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Lying just beneath everyday reality
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is a breathtaking world,
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where much of what we perceive about the universe is wrong.
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physicist and best-selling author Brian Greene takes you
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on a journey that bends the rules of human experience.
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BRIAN GBEENE:Why don't we ever see events unfold in reverse order?
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According to the laws of physics, this can happen.
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It's a world that comes to light
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as we probe the most extreme realms of fhe cosmos,
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from black holes to the Big Bang
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to the very heart of matter itself.
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I'm going to have what he's having.
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Here, empty space teems with ferocious activity.
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The three-dimensional world may be just an illusion,
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and there's no distinction
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between past, present and future.
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GREENE: But how could this be?
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How could we be so wrong about something so familiar?
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Does it bother us?
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Absolutely.
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There's no principle
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built into the laws of nature
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that say that theoretical physicists have to be happy.
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It's a game-changing perspective
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that opens up a new world of possibilities.
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Coming up...
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What if new universes were born all the time...
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MAN: In this picture, the Big Bang is not a unique event.
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...and ours was one of numerous parallel realities?
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GREENE: Somewhere there's a duplicate of you and me
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and everyone else.
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Are we in a universe or a multiverse?
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Right now on NOVA.
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Major funding for NOVA is provided by the following:
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And...
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And by the Corporation for Public Broadcasting
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and by contributions to your PBS station from:
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Major funding for "The Fabric of the Cosmos"
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is provided by the National Science Foundation.
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And...
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Supporting original research and public understanding
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at science, technology,engineering and mathematics.
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Additional fundingis provided by...
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And the George D.Smith Fund.
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BRIAN GBEENE: New York City.
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They say there's nowhere else like it--
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home to eight million people, countless structures, monuments
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and landmarks, every one of them unique.
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Or so we think.
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Uniqueness is an idea so familiar,
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we never even question it.
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Experience tells us people and objects are one of a kind.
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Why else would we visit museums and collect great masterpieces?
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Yet a new picture at the cosmos
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is coming to light in which nothing is unique.
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Not that the world's great masterpieces are fakes.
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Instead, I'm talking about something far more profound:
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a new picture of the cosmos
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that challenges the very notion at uniqueness,
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one in which duplicates are inevitable.
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And that's just the beginning.
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There might be duplicates not just of objects,
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but of you and me and everyone else.
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But if this new picture is right,
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where are these duplicates
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and why haven't we ever seen them?
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The answer may lie outside our universe.
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There was a time when the word "universe"
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meant "all there is," everything.
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The notion of more than one universe,
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more than one "everything," seemed impossible.
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But perhaps if we could go beyond our solar system,
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beyond the Milky Way, even beyond other distant galaxies,
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past the end of the observable universe,
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we'll find that there's more, a lot more,
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that our universe is not alone.
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There may be other universes.
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In fact, there might be new ones being born all the time.
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We may actually live
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in an expanding sea of multiplying universes:
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a"multiverse."
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If we could visit these other universes,
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we'd find that some might have basic properties of nature
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so foreign that matter as we know it couldn't exist.
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Others might have galaxies, stars, even a planet
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that looks familiar, but with some surprising differences.
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And if there are an infinite number at universes
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in the multiverse, somewhere there's a place
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where almost everything is identical to ours
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except for the slightest details.
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Like maybe there's another Brian Greene
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who ends up in a different line of work.
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STEVEN WEINBERG: If the multiverse is indeed infinite,
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"then one is going to have to confront a lot of possibilities
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that are very hard to imagine.
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There will be other places where there will be Alan Guths
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who will look and think and act exactly like me,
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as well as many where the Alan Guths look and think
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almost exactly like me, but with some small differences.
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LEONARD SUSSKIND: Is it science?
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Is it a part of metaphysics?
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Is it just philosophy?
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Is it religion?
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Physicists tend not to ask those questions.
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They just say, "Let's follow the logic."
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And the logic seems to lead there.
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GREENE: However unfamiliar and strange the multiverse might seem,
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a growing number of scientists think it may be the final step
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in a long line of radical revisions
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to our picture of the cosmos.
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That is, there was a time when we thought that the Earth
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was at the center of the cosmos
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and that everything else revolved around us.
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Then, along came scientists like Galileo and Copernicus,
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and they showed us
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that it's the sun,not the Earth,
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that's at the center of our solar system.
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And our solar system?
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It's just a little neighborhood
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in the outskirts of a gigantic galaxy.
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And our galaxy?
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It's one of hundreds of billions of galaxies
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that make up our universe.
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Now, all of these ideas sounded outrageous
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when they were first proposed,
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but today, we don't even question them.
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The idea of a multiverse may be similar.
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It simply may require a drastic change
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in our cosmic perspective.
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On the other hand,
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some scientists think that the multiverse
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is nothing but a dead end for physics.
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ANDREAS ALBRECHT: I'm very uncomfortable with the multiverse.
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To become solid science, it's got a lot of growing up to do.
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You know, it exists in the same way that,
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you know, angels might exist.
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We have to make our bets,
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and I think right now the multiverse is a pretty good bet.
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I think there's a good chance that the multiverse is real
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and that a hundred years from now,
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people might be convinced that it's real
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GREENE: So, where did this idea come from,
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and what's the evidence for it?
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Well, several surprising discoveries suggest
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that we really may be part of a multiverse.
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The first of these discoveries
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has to do with the generally accepted theory
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of the origin of our universe: the Big Bang.
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According to this theory,
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our universe began some 14 billion years ago
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in an intensely violent explosion.
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Over billions of years, the universe cooled and coalesced,
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allowing the formation of stars, planets and galaxies.
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As a result of that explosion,
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the universe is still expanding today.
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But if you coud run the history of our universe in reverse,
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all the way back to the beginning,
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you'd find that the Big Bang theory tells us nothing
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about what sent everything hurtling outward
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in the first place.
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GUTH: It's called the Big Bang theory,
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but the one thing that it really says nothing about at all
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is the bang itself.
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It says nothing about what banged,
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why it banged, or what happened before it banged.
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GREENE: So, what fueled that violent explosion?
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What force could have driven everything apart?
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The quest to figure that out would bring scientists
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face to face with the multiverse.
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One physicist whose work
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unexpectedly helped lay the foundation
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for the multiverse idea is Alan Guth.
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Today he's a professor at MIT.
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But back in 1979, Guth and a colleague, Henry Tye,
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were pursuing a new idea about how particles might have formed
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in the early universe.
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GUTH: Henry suggested to me that we should maybe look
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at whether or not this new process that we were thinking of
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would influence the expansion rate of the universe.
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GREENE: Guth and Tye hadn't set out to investigate
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the expansion rate of the universe
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in the first moments after the Big Bang.
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But Henry Tye's question
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caused Guth to review their calculations one more time.
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GUTH: I stayed up quite late that night
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and went over the calculations very cerefully
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trying to make sure everything was correct.
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GREENE: As the night wore on,
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Guth discovered something extraordinary in the equations
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describing how new particles might have formed
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in the early universe.
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GUTH: I came to the shocking conclusion
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that these new-fangled particle theories
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would have a tremendous effect
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on the expansion rate of the universe.
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The kind of process henry and I were talking about
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would drive the universe
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into a period at incredibly rapid exponential expansion.
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GREENE: What Guth found in the math
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was evidence that in the extreme environment
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at the very early universe, gravity can act in reverse.
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Instead of pulling things together,
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this "repulsive gravity" would repel everything around it,
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causing a huge expansion.
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"GUTH: I immediately became very excited about it
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and scribbled out the calculation in my notebook,
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and then at the end I wrote "spectacular realization"
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with a double box around it,
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because I realized that if it was right,
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it could be very important.
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GREENE: By discovering this"repulsive gravity,"
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Alan Guth had unintentionally shed light
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on the very beginning of the Big Bang.
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Described mathematically, this force was so powerful,
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it could take a bit of space as tiny as a molecule
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and blow it up to the size of the Wilky Way galaxy
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in less than a billionth of a billionth of a billionth
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at a blink of an eye.
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After this incredibly short outward burst,
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space would continue to expand more slowly and cool,
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allowing stars and galaxies to form,
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just as they do in the Big Bang theory.
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Guth called this short burst of expansion "inflation,"
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and he believed it explained
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what set the universe expanding in the first place.
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The powerful, repulsive gravity of inflation
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was the "bang" in the the Big Bang.
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But despite having made a momentous breakthrough,
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Alan Guth had an even more pressing concern.
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I had no idea what my employment might be.
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I was really looking for a more permanent job.
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The inflationary universe scenario looks very exciting.
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GUTH: So I went on actually a pretty long trip,
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giving talks about this.
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WEINBERG: Suddenly this idea caught on.
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ALBRECHT: Talks about inflation were packed with people
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from all areas of physics.
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WEINBERG: Lots of astrophysical theorists,
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including me, got very enthusiastic.
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ALBRECHT: It was a very, very exciting time.
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WEINBERG: If you have a really good idea
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that allows other people to move the field forward,
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peope are going to pay attention.
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GUTH: An amazing feeling
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that suddenly I had crossed that gap
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from being an unknown post-doc
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to being one of the major players,
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and it was very hard to absorb, but it certainly felt good.
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GREENE: One reason inflation was so exciting
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was that it made predictions
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that could be tested through observation.
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Scientists realized that if the theory were correct,
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evidence for it should be found in the night sky.
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Imagine that we could shut off the sun
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and take away all the stars.
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If our eyes could detect
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the rest of the energy that's still there,
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we'd see a warm glow everywhere in the cosmos.
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This sea of radiation is called the cosmic microwave background.
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It's the last remnants at heat from the Big Bang itself.
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Theory predicted that the violent expansion of space
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00:15:54,787 --> 00:15:59,531
during inflation would leave an imprint on this radiation.
263
00:15:59,667 --> 00:16:03,159
These telltale "fingerprints" would form a precise pattern
264
00:16:03,254 --> 00:16:05,119
of temperature variations--
265
00:16:05,214 --> 00:16:09,799
slightly hotter spots and slightly colder spots--
266
00:16:09,886 --> 00:16:12,878
that would look something like this.
267
00:16:12,972 --> 00:16:15,088
But it woud be about ten years
268
00:16:15,224 --> 00:16:17,681
before the technology was sensitive enough
269
00:16:17,768 --> 00:16:20,635
to test this prediction.
270
00:16:20,730 --> 00:16:22,311
Then in 1989,
271
00:16:22,398 --> 00:16:26,562
NASA launched the Cosmic Background Explorer satellite,
272
00:16:26,652 --> 00:16:30,941
followed by a second satellite, WMAP, in 200l
273
00:16:31,073 --> 00:16:34,691
that would put inflation to the test.
274
00:16:34,785 --> 00:16:36,491
The missions measured the radiation
275
00:16:36,579 --> 00:16:42,165
with tremendous precision, and the results were stunning.
276
00:16:42,251 --> 00:16:45,163
The temperature variations found in the cosmos
277
00:16:45,254 --> 00:16:46,960
were am almost identical match
278
00:16:47,089 --> 00:16:51,503
with the predictions of the theory of inflation.
279
00:16:51,594 --> 00:16:54,631
It's just a theory, mathematics on the page,
280
00:16:54,764 --> 00:17:00,384
until it makes predictions that are confirmed.
281
00:17:00,478 --> 00:17:03,345
WMAP found what the math of inflation predicted.
282
00:17:03,439 --> 00:17:05,395
That is enormously convincing.
283
00:17:05,483 --> 00:17:09,442
So inflation has had a number of chances now to fail.
284
00:17:09,529 --> 00:17:11,941
It made predictions, data came in,
285
00:17:12,031 --> 00:17:15,649
and inflation has come through with flying colors.
286
00:17:15,785 --> 00:17:19,073
GREENE: Guth's work on inflation, along with that of other physicists,
287
00:17:19,163 --> 00:17:20,949
was hailed as a milestone
288
00:17:21,082 --> 00:17:24,449
toward understanding the origin at the universe.
289
00:17:24,544 --> 00:17:27,126
In the process, its expanse...
290
00:17:27,255 --> 00:17:29,917
GREENE: But soon, two Russian physicists would discover
291
00:17:30,007 --> 00:17:36,503
that the equations of inflation held a shocking secret:
292
00:17:36,639 --> 00:17:40,223
our universe may not be alone.
293
00:17:43,479 --> 00:17:46,141
One of these physicists was Andrei Linde,
294
00:17:46,232 --> 00:17:48,814
who had already made pivotal contributions
295
00:17:48,901 --> 00:17:51,313
to inflationary theory.
296
00:17:51,404 --> 00:17:53,861
The other was Alex Vilenkin,
297
00:17:53,990 --> 00:17:57,733
who happened to attend one at the talks Alan Guth gave
298
00:17:57,827 --> 00:17:59,488
during his road trip.
299
00:17:59,620 --> 00:18:02,362
ALEX VILENKIN: He gave a wonderful talk.
300
00:18:02,498 --> 00:18:04,204
I hadn't met him before,
301
00:18:04,333 --> 00:18:09,453
but what I heard was rather unexpected.
302
00:18:09,547 --> 00:18:12,129
In one shot, inflation explained very well
303
00:18:12,216 --> 00:18:15,128
many features of the Big Bang
304
00:18:15,219 --> 00:18:17,130
and was quite remarkable.
305
00:18:17,221 --> 00:18:21,339
...why the universe is the way it is.
306
00:18:21,475 --> 00:18:23,431
VILENKIN: So I went home greatly impressed.
307
00:18:28,107 --> 00:18:31,019
GREENE: Alex Vilenkin was so impressed that for months afterward,
308
00:18:31,110 --> 00:18:35,444
he couldn't stop thinking about inflation.
309
00:18:35,531 --> 00:18:39,570
VILENKIN: Usually I have my thought of the day in the shower,
310
00:18:39,702 --> 00:18:41,488
which I tend to take long.
311
00:18:43,789 --> 00:18:48,783
GREENE: The more Vilenkin considered the process of inflation,
312
00:18:48,878 --> 00:18:51,711
the more he wondered about what would make it stop.
313
00:18:51,797 --> 00:18:57,042
How would a region of space transition out of inflation?
314
00:18:57,178 --> 00:19:02,514
What exactly would Happen at the moment inflation ends?
315
00:19:02,600 --> 00:19:07,845
VILENKIN: As I thought about it, it turns out that the end of inflation
316
00:19:07,938 --> 00:19:12,056
doesn't happen everywhere at once.
317
00:19:12,151 --> 00:19:13,857
GREENE: Vilenkin suddenly realized
318
00:19:13,944 --> 00:19:17,277
that if inflation doesn't end everywhere at once,
319
00:19:17,406 --> 00:19:19,522
then there's always some part of space
320
00:19:19,617 --> 00:19:21,482
where it's still happening.
321
00:19:21,577 --> 00:19:23,067
VILENKIN: So in this picture,
322
00:19:23,162 --> 00:19:27,906
the Big Bang is not a unique event that happened.
323
00:19:28,042 --> 00:19:31,500
There were multiple bangs that happened before ours,
324
00:19:31,587 --> 00:19:34,078
and there will be countless other bangs
325
00:19:34,173 --> 00:19:36,004
that will happen in the future.
326
00:19:38,094 --> 00:19:40,836
GREEPE: It was a striking and unexpected new picture
327
00:19:40,930 --> 00:19:43,888
in which inflation would stop in some regions,
328
00:19:43,974 --> 00:19:46,636
but always continue somewhere else.
329
00:19:46,769 --> 00:19:49,226
New big bangs are always occurring
330
00:19:49,313 --> 00:19:51,895
and new universes are always being born,
331
00:19:51,982 --> 00:19:56,066
yielding an eternally expanding multiversa.
332
00:19:56,153 --> 00:19:58,018
Linde and Vilenkin in particular
333
00:19:58,114 --> 00:20:01,732
pushed the idea that inflation might never end,
334
00:20:01,826 --> 00:20:03,691
that this ballooning process
335
00:20:03,786 --> 00:20:05,447
could happen over and over again,
336
00:20:05,538 --> 00:20:07,779
giving one universe after another ofter another.
337
00:20:09,959 --> 00:20:12,996
So was this a revolution in science
338
00:20:13,129 --> 00:20:16,713
or a theory that's full of holes?
339
00:20:16,799 --> 00:20:20,007
The idea became known as "eternal inflation,"
340
00:20:20,136 --> 00:20:22,548
and you can picture it something like this.
341
00:20:22,638 --> 00:20:26,972
Imagine that this block at cheese is all of space
342
00:20:27,059 --> 00:20:29,345
before the formation of stars and galaxies.
343
00:20:29,478 --> 00:20:31,139
Now, according to inflation,
344
00:20:31,272 --> 00:20:36,483
space is uniformly filled with a huge amount of energy,
345
00:20:36,610 --> 00:20:41,855
and that energy causes space to expend at an enormous speed.
346
00:20:41,991 --> 00:20:45,449
As it does, here and there the energy discharges,
347
00:20:45,536 --> 00:20:49,495
sort of like a spark of static electricity.
348
00:20:49,623 --> 00:20:54,208
But this is like static electricity on a cosmic scale,
349
00:20:54,336 --> 00:20:56,793
and when it discharges...
350
00:20:59,175 --> 00:21:03,794
...all that energy is rapidly transformed into matter
351
00:21:03,888 --> 00:21:07,005
in the form of tiny particles.
352
00:21:07,099 --> 00:21:11,012
That process is the birth of a new universe,
353
00:21:11,103 --> 00:21:16,689
what we have traditionally called "the Big Bang."
354
00:21:16,776 --> 00:21:18,767
Inside these new universes,
355
00:21:18,861 --> 00:21:21,523
which are like holes in the cheese,
356
00:21:21,655 --> 00:21:26,069
space continues to expand, but much more slowly.
357
00:21:26,202 --> 00:21:30,195
And sometimes, galaxies, stars and planets form,
358
00:21:30,289 --> 00:21:35,124
much as we see in our universe today.
359
00:21:35,211 --> 00:21:38,795
Meanwhile, outside of these new universes,
360
00:21:38,881 --> 00:21:42,715
the rest of space is still full of undischarged energy
361
00:21:42,802 --> 00:21:46,761
and is still expanding at enormous speed.
362
00:21:46,889 --> 00:21:48,379
And more expanding space
363
00:21:48,516 --> 00:21:51,178
means more places where the energy can discharge
364
00:21:51,268 --> 00:21:57,013
into more big bangs and create more new universes.
365
00:21:57,107 --> 00:22:01,726
And that means this process could go on forever.
366
00:22:01,862 --> 00:22:04,194
In other words, when it comes to eternal inflation,
367
00:22:04,281 --> 00:22:07,773
that cheese is more like Swiss cheese,
368
00:22:07,910 --> 00:22:15,328
in which new universes endlessly form, creating e multiverse.
369
00:22:19,421 --> 00:22:23,289
The multiverse-- a profound implication
370
00:22:23,425 --> 00:22:26,963
of eternal inflation.
371
00:22:27,096 --> 00:22:29,553
But, as Alex Vilenkin would soon learn,
372
00:22:29,640 --> 00:22:33,224
one that would not be easily accepted.
373
00:22:33,310 --> 00:22:35,426
VLENKIN: I thought I realized something important
374
00:22:35,521 --> 00:22:37,136
about the universe,
375
00:22:37,273 --> 00:22:42,563
and I wanted to share this with my fellow physicists,
376
00:22:42,653 --> 00:22:46,771
and one at the first, of course, had to be Alan Guth.
377
00:22:46,866 --> 00:22:51,610
Now, we know that quantum fluctuations in the scalar field
378
00:22:51,704 --> 00:22:54,116
are different in different regions in space.
379
00:22:54,248 --> 00:22:56,660
VILENKIN: I thought he would be excited about it.
380
00:22:56,792 --> 00:23:00,250
As a result, in some regions...
381
00:23:00,337 --> 00:23:02,703
But this encounter didn't go as planned.
382
00:23:02,798 --> 00:23:08,919
...inflation will last longer than in others.
383
00:23:09,013 --> 00:23:10,719
The delay of inflatien...
384
00:23:10,806 --> 00:23:16,142
VILENKIN: As I was describing to him my new picture at the universe,
385
00:23:16,228 --> 00:23:17,718
inflating regions and so forth...
386
00:23:18,981 --> 00:23:20,812
...expansion.
387
00:23:20,941 --> 00:23:24,399
VILENKIN: I noticed that Alan is begining
388
00:23:24,486 --> 00:23:26,397
to doze off a little bit.
389
00:23:28,616 --> 00:23:33,952
VILENKIN: Actually I was of course very unhappy about that,
390
00:23:34,038 --> 00:23:36,996
so I thought that I probably should go.
391
00:23:43,839 --> 00:23:46,455
GREENE: One problem with the concept at a multiverse
392
00:23:46,550 --> 00:23:51,544
was that there seemed to be no way to detect it.
393
00:23:51,680 --> 00:23:54,342
Not only is each universe expanding,
394
00:23:54,433 --> 00:23:58,267
but so is the space in between them.
395
00:23:58,354 --> 00:24:00,936
That means that nothing, not even light,
396
00:24:01,023 --> 00:24:05,733
can travel from any of the other universes to reach us.
397
00:24:05,861 --> 00:24:08,568
VILENKIN: Physicists did not really respond very well
398
00:24:08,697 --> 00:24:12,610
to this idea of eternal inflation.
399
00:24:12,701 --> 00:24:15,864
Once I said that I'm going to tell them
400
00:24:15,996 --> 00:24:18,453
something about things beyond our horizon
401
00:24:18,540 --> 00:24:21,577
that cannot in principle be observed,
402
00:24:21,710 --> 00:24:24,873
most ot them just lost interest right there.
403
00:24:25,005 --> 00:24:28,998
GREENE: Alex Vilenkin thought he was on to something big,
404
00:24:29,093 --> 00:24:30,879
but others were skeptical.
405
00:24:31,011 --> 00:24:32,717
So Vilenkin reluctantly tried
406
00:24:32,805 --> 00:24:37,174
to put his work on eternal inflation out of his mind.
407
00:24:37,267 --> 00:24:39,053
ALBRECHT: Who wants to talk about a universe
408
00:24:39,186 --> 00:24:41,552
you're never going to see?
409
00:24:41,689 --> 00:24:45,056
The multiverse can't make predictions, it can't be tested.
410
00:24:45,192 --> 00:24:48,605
You could make the case that it's not really science.
411
00:24:48,737 --> 00:24:51,103
how can you ever be confident of it
412
00:24:51,240 --> 00:24:54,073
when you can't see the other parts of the multiverse?
413
00:24:54,201 --> 00:24:55,987
We can only see our little patch,
414
00:24:56,078 --> 00:24:59,115
our little expanding cloud of galaxies.
415
00:24:59,248 --> 00:25:00,579
How are we ever going to know?
416
00:25:00,666 --> 00:25:03,123
You can't prove the multiverse exists.
417
00:25:03,252 --> 00:25:04,583
It's not wrong.
418
00:25:04,712 --> 00:25:06,327
You can't prove that it doesn't exist.
419
00:25:06,422 --> 00:25:08,128
So why should we believe it?
420
00:25:11,135 --> 00:25:15,094
GREENE: Alex Vilenkin tried to stop thinking about the multiverse.
421
00:25:17,099 --> 00:25:20,011
With no hard evidence to support it,
422
00:25:20,102 --> 00:25:22,058
the idea seemed to have hit a deed end.
423
00:25:23,981 --> 00:25:25,937
VILENKIN: Many people thought that it's just not science
424
00:25:26,066 --> 00:25:28,773
to talk about things that you cannot observe.
425
00:25:28,861 --> 00:25:35,152
So I did not return to the subject for almost ten years.
426
00:25:35,284 --> 00:25:38,868
GREENE: Meanwhile, Vilenkin's Russian colleague Andrei Linde
427
00:25:38,954 --> 00:25:41,411
kept the flame alive.
428
00:25:41,498 --> 00:25:42,988
He had independently come up
429
00:25:43,125 --> 00:25:45,286
with his own version of eternal inflation,
430
00:25:45,419 --> 00:25:48,752
but unlike Vilenkin, he would not be deterred.
431
00:25:48,839 --> 00:25:51,171
ANDREI LINDE: Maybe I am a little bit more arrogant.
432
00:25:51,300 --> 00:25:54,918
When I got the idea for this multiverse,
433
00:25:55,012 --> 00:25:57,469
I understood that this may be the most important thing
434
00:25:57,598 --> 00:25:59,338
which I ever do in my life.
435
00:25:59,475 --> 00:26:01,807
And if somebody doesn't want to hear it,
436
00:26:01,894 --> 00:26:02,724
that's their problem.
437
00:26:04,521 --> 00:26:07,354
GREENE: Linde published more than a dozen papers,
438
00:26:07,483 --> 00:26:10,316
but his work would meet an equally chilly reception.
439
00:26:10,444 --> 00:26:15,655
It seemed no one wanted to hear about the idea of a multiverse.
440
00:26:22,539 --> 00:26:24,996
If the equations of eternal inflation
441
00:26:25,125 --> 00:26:27,741
were the only clues pointing to the multiverse,
442
00:26:27,836 --> 00:26:31,795
that's where the story might have ended.
443
00:26:31,882 --> 00:26:35,374
But the multiverse idea would gain some unexpected support
444
00:26:35,511 --> 00:26:39,550
from two completely unrelated areas at science.
445
00:26:39,681 --> 00:26:43,640
One was an idea called string theory,
446
00:26:43,727 --> 00:26:46,184
designed to explain how the universe works
447
00:26:46,271 --> 00:26:49,138
at the tiniest scales.
448
00:26:49,233 --> 00:26:51,724
The other was an astounding discovery
449
00:26:51,860 --> 00:26:53,851
made by astronomers exploring the universe
450
00:26:53,987 --> 00:26:56,194
on the largest scale,
451
00:26:56,281 --> 00:26:58,146
a discovery thats utterly mysterious
452
00:26:58,242 --> 00:27:00,278
if there's only one universe.
453
00:27:00,369 --> 00:27:03,202
But if we're part of a multiverse,
454
00:27:03,288 --> 00:27:04,698
it's a whole new ballgame.
455
00:27:07,709 --> 00:27:10,166
It has to do with the expansion of the universe,
456
00:27:10,254 --> 00:27:13,041
and its easy to explain using a baseball.
457
00:27:13,173 --> 00:27:15,664
Now, if I toss this ball up in the air,
458
00:27:15,759 --> 00:27:18,045
we all know what will happen.
459
00:27:18,137 --> 00:27:21,925
As it rises, it slows down because of gravity.
460
00:27:23,976 --> 00:27:27,343
Now, astronomers knew that the universe was expanding,
461
00:27:27,437 --> 00:27:30,053
and they assumed that the expansion would slow down
462
00:27:30,190 --> 00:27:33,557
because of the gravitational pull of stars and galaxies,
463
00:27:33,652 --> 00:27:35,734
just as the ball slows down
464
00:27:35,863 --> 00:27:39,105
because of the gravitational pull of the Earth.
465
00:27:39,241 --> 00:27:41,732
But when they actually did the measurements,
466
00:27:41,869 --> 00:27:44,906
they found something astonishing,
467
00:27:44,997 --> 00:27:47,329
something that rocked the foundations of physics.
468
00:27:47,416 --> 00:27:52,251
They found that the expansion is not slowing down.
469
00:27:52,337 --> 00:27:53,952
It's speeding up.
470
00:27:56,425 --> 00:27:59,508
It's as if I took this baseball and when I throw it...
471
00:28:02,097 --> 00:28:08,468
...instead of slowing down as it rush away,it speeds up.
472
00:28:08,604 --> 00:28:11,562
Now, if you saw a ball do that,
473
00:28:11,648 --> 00:28:13,434
you'd assume there's some invisible force
474
00:28:13,567 --> 00:28:16,775
that's counteracting gravity, pushing on the ball,
475
00:28:16,862 --> 00:28:19,399
forcing it to speed away ever more quickly.
476
00:28:19,489 --> 00:28:23,778
Astronomers came to the same conclusion about the universe:
477
00:28:23,911 --> 00:28:26,368
that some kind of energy in space
478
00:28:26,455 --> 00:28:29,288
must be pushing all the galaxies apart,
479
00:28:29,416 --> 00:28:33,125
causing the expansion to speed up.
480
00:28:33,212 --> 00:28:34,793
Because we don't see the energy,
481
00:28:34,922 --> 00:28:39,632
the astronomers called it "dark energy."
482
00:28:39,760 --> 00:28:43,628
It's among the most important experimental discoveries ever
483
00:28:43,722 --> 00:28:45,053
in the history of soience.
484
00:28:45,140 --> 00:28:48,348
It took most of us completely by surprise.
485
00:28:48,477 --> 00:28:51,139
And so, we're still trying to come to grips with that.
486
00:28:52,856 --> 00:28:54,596
GREENE: Discovering that dark energy
487
00:28:54,691 --> 00:28:56,522
is pushing every galaxy in our universe
488
00:28:56,652 --> 00:28:59,860
away from every other at an accelerating rate
489
00:28:59,988 --> 00:29:02,320
was shocking enough.
490
00:29:02,407 --> 00:29:06,650
But even more surprising was the strength of that dark energy.
491
00:29:06,787 --> 00:29:10,496
For over a decade, scientists have been unable to explain
492
00:29:10,624 --> 00:29:15,539
why such a peculiar amount of it exists in empty space.
493
00:29:15,671 --> 00:29:19,380
But that mystery seems easier to resolve
494
00:29:19,508 --> 00:29:22,671
if we're part of a much larger mutiverse.
495
00:29:25,514 --> 00:29:26,754
Now, the idea that space
496
00:29:26,848 --> 00:29:29,510
contains any energy at all sounds strange.
497
00:29:29,601 --> 00:29:34,686
But our theory at small things like molecules and atoms,
498
00:29:34,773 --> 00:29:37,059
the theory called quantum mechanics,
499
00:29:37,192 --> 00:29:39,433
tells us that theres a lot of activity
500
00:29:39,528 --> 00:29:41,359
in the microscopic realm,
501
00:29:41,488 --> 00:29:44,946
activity that can contribute an energy to space.
502
00:29:45,033 --> 00:29:47,240
And according to the math,
503
00:29:47,369 --> 00:29:51,203
the amount of energy generated by that microscopic activity
504
00:29:51,331 --> 00:29:52,867
is enormous.
505
00:29:52,958 --> 00:29:56,542
The problem is, when astronomers measured the amount at energy
506
00:29:56,628 --> 00:29:57,959
thats actually out there,
507
00:29:58,046 --> 00:30:02,085
the amount of energy required to force the galaxies apart
508
00:30:02,217 --> 00:30:04,833
at the accelerating rate that's observed,
509
00:30:04,928 --> 00:30:07,670
they get a numder like this:
510
00:30:07,764 --> 00:30:13,100
a decimal point followed by 122 zeroes, and then a one.
511
00:30:13,228 --> 00:30:16,846
An incredibly tiny amount, very close to zero,
512
00:30:16,940 --> 00:30:19,727
and nothing at all like what the theory predicted.
513
00:30:19,860 --> 00:30:22,647
In fact, it's trillions and trillions
514
00:30:22,738 --> 00:30:25,730
and trillions and trillions of times smaller,
515
00:30:25,824 --> 00:30:27,985
a colossal mismatch.
516
00:30:28,076 --> 00:30:30,738
We have tried everything
517
00:30:30,829 --> 00:30:35,414
to explain why the dark energy is as small as it is.
518
00:30:35,542 --> 00:30:39,160
We have tried everything, and everything fails.
519
00:30:39,254 --> 00:30:40,494
Hopeless!
520
00:30:40,589 --> 00:30:43,080
I once called this the worst failure
521
00:30:43,216 --> 00:30:44,797
of an order of magnitude estimate
522
00:30:44,926 --> 00:30:46,257
in the history of science.
523
00:30:46,386 --> 00:30:47,466
Does it bother us?
524
00:30:47,596 --> 00:30:48,711
Absolutely.
525
00:30:48,805 --> 00:30:51,763
Finding that the amount of energy in space
526
00:30:51,850 --> 00:30:55,217
is so much less than our theory predicts
527
00:30:55,312 --> 00:30:57,849
is not just on academic problem.
528
00:30:57,939 --> 00:31:01,773
The precise strength of that repulsive gravity, well,
529
00:31:01,902 --> 00:31:04,735
that has profound implications for all of us.
530
00:31:04,821 --> 00:31:06,106
For example,
531
00:31:06,198 --> 00:31:08,610
it I were to increase the strength of the darh energy
532
00:31:08,742 --> 00:31:14,829
just a little bit by erasing four or five of these zeroes,
533
00:31:14,956 --> 00:31:17,618
I still have a tiny number,
534
00:31:17,751 --> 00:31:19,992
but the universe would be radically different.
535
00:31:20,128 --> 00:31:23,791
That's because a slightly stronger dark energy
536
00:31:23,924 --> 00:31:28,884
would push everything apart so fast
537
00:31:28,970 --> 00:31:30,585
that stars, planets and galaxies
538
00:31:30,680 --> 00:31:33,012
would never have formed.
539
00:31:33,141 --> 00:31:37,384
And that means we simply would not exist.
540
00:31:37,479 --> 00:31:39,640
And yet here we are.
541
00:31:41,817 --> 00:31:44,229
So, why is the amount of dark energy
542
00:31:44,319 --> 00:31:46,776
so much less than our theory predicts
543
00:31:46,863 --> 00:31:49,650
and also just right to allow the formation
544
00:31:49,783 --> 00:31:52,900
of galaxies, stars, planets and life?
545
00:31:52,994 --> 00:31:55,736
We just don't know.
546
00:31:55,831 --> 00:31:58,163
The mismatch between the theoretical predictions
547
00:31:58,291 --> 00:32:01,203
of dark energy and what astronomers have observed
548
00:32:01,336 --> 00:32:05,500
is one of the great mysteries that science faces today.
549
00:32:06,925 --> 00:32:08,665
But consider this:
550
00:32:08,802 --> 00:32:12,465
If we do live in a multiverse, then the mystery of dark energy
551
00:32:12,556 --> 00:32:17,721
might not be so mysterious after all.
552
00:32:17,853 --> 00:32:20,310
In fact, if we're part at a multiverse,
553
00:32:20,397 --> 00:32:22,479
the value at dark energy we've measured
554
00:32:22,566 --> 00:32:24,978
might actually make total sense.
555
00:32:29,448 --> 00:32:30,403
Hi.
556
00:32:30,532 --> 00:32:31,897
reservation for Greene.
557
00:32:33,618 --> 00:32:37,202
To see how the multiverse might solve the dark energy puzzle,
558
00:32:37,330 --> 00:32:39,241
imagine you're checking into a hotel
559
00:32:39,374 --> 00:32:43,208
and you get a room number like this:
560
00:32:43,295 --> 00:32:45,752
ten million and one.
561
00:32:45,881 --> 00:32:46,745
Hmm
562
00:32:46,882 --> 00:32:48,088
Thanks.
563
00:32:48,216 --> 00:32:49,205
Enjoy your stay.
564
00:32:52,137 --> 00:32:53,468
Ten million and one
565
00:32:53,555 --> 00:32:56,171
would seem like a pretty strange room number,
566
00:32:56,266 --> 00:33:00,054
and getting a room number like this would be surprising,
567
00:33:00,145 --> 00:33:03,137
much as the value of dark energy in our univese
568
00:33:03,231 --> 00:33:05,722
is a number that scientists have found surprising.
569
00:33:05,817 --> 00:33:07,182
But here's the thing:
570
00:33:07,277 --> 00:33:11,065
if this hotel had a huge number of rooms...
571
00:33:16,161 --> 00:33:18,573
say, billions and billions,
572
00:33:18,663 --> 00:33:20,745
then getting room number ten million and one
573
00:33:20,832 --> 00:33:21,992
wouldn't be so surprising.
574
00:33:23,585 --> 00:33:28,420
In a hotel this big, you expect to find a room with that number.
575
00:33:33,637 --> 00:33:36,094
Similarly, if we're part of a multiverse
576
00:33:36,223 --> 00:33:38,259
with a huge number of universes,
577
00:33:38,391 --> 00:33:41,383
each with a different value of the dark energy,
578
00:33:41,478 --> 00:33:43,093
then you'd expect to find one
579
00:33:43,188 --> 00:33:46,180
with the value as small as what we've measured.
580
00:33:46,274 --> 00:33:50,768
If you think of each of these rooms as a universe,
581
00:33:50,862 --> 00:33:53,103
and each universe has a different value
582
00:33:53,198 --> 00:33:54,938
for the dark energy,
583
00:33:55,033 --> 00:33:57,740
then most of these universes won't be hospitable
584
00:33:57,827 --> 00:34:00,068
to life as we know it.
585
00:34:00,163 --> 00:34:03,121
The reason is that the value of the dark energy wouldn't allow
586
00:34:03,250 --> 00:34:06,959
the formation of galaxies, stars and planets.
587
00:34:07,087 --> 00:34:10,830
Universes with much less dark energy than ours
588
00:34:10,966 --> 00:34:13,207
would collapse in on themselves.
589
00:34:15,136 --> 00:34:18,003
And universes with much more dark energy than ours
590
00:34:18,139 --> 00:34:22,257
would expand so fast that matter would never have the chance
591
00:34:22,352 --> 00:34:27,267
to coalesce into clumps and form stars and planets.
592
00:34:27,357 --> 00:34:30,895
So, of course we find ourselves in a universe
593
00:34:30,986 --> 00:34:34,649
where the value of the dark energy is hospitable to life.
594
00:34:34,739 --> 00:34:38,072
Otherwise we woudn't be here to talk about it.
595
00:34:44,165 --> 00:34:46,907
If we're part of a multiverse,
596
00:34:47,002 --> 00:34:50,494
the mystery of dark energy becomes not so mysterious.
597
00:34:52,591 --> 00:34:55,458
But there's a piece of the puzzle missing
598
00:34:55,552 --> 00:34:58,840
How do we know if there's enough diversity within the multiverse
599
00:34:58,972 --> 00:35:01,088
so that every value for dark energy,
600
00:35:01,182 --> 00:35:05,346
including the strange value we observe in our universe,
601
00:35:05,478 --> 00:35:07,343
can be found somewhere?
602
00:35:07,439 --> 00:35:08,724
The answer would emerge
603
00:35:08,857 --> 00:35:13,226
from an entirely different area of physics.
604
00:35:13,361 --> 00:35:15,852
I'm talking about a ground-breaking theory
605
00:35:15,989 --> 00:35:18,696
that comes from investigating the universe
606
00:35:18,825 --> 00:35:20,781
on the tiniest scale.
607
00:35:22,662 --> 00:35:26,325
We know that inside atoms are even tinier bits of matter,
608
00:35:26,416 --> 00:35:27,747
protons and neutrons,
609
00:35:27,876 --> 00:35:32,415
which are made of still smaller particles called quarks.
610
00:35:32,547 --> 00:35:34,959
But physicists realized
611
00:35:35,050 --> 00:35:38,463
that this might not be the end of the line.
612
00:35:38,553 --> 00:35:40,043
These subatomic bits
613
00:35:40,180 --> 00:35:43,593
might actually be made of someting even smaller-
614
00:35:43,725 --> 00:35:50,096
tiny vibrating strands or loops of energy called strings.
615
00:35:50,231 --> 00:35:53,268
This set of ideas, called string theory,
616
00:35:53,401 --> 00:35:56,518
says everythng that exists
617
00:35:56,613 --> 00:35:58,945
is made of this one kind of ingredient.
618
00:36:03,912 --> 00:36:06,403
And just as a single string on a cello
619
00:36:06,539 --> 00:36:09,576
can produce many different notes depending on how it vibrates,
620
00:36:09,668 --> 00:36:12,410
strings can take on different properties
621
00:36:12,545 --> 00:36:14,456
depending on how they vibrate,
622
00:36:14,589 --> 00:36:18,457
creating may kinds of particles.
623
00:36:18,593 --> 00:36:23,553
From this theory came the promise of elegant simplicity:
624
00:36:23,640 --> 00:36:26,882
a single master equation that would explain what we see
625
00:36:26,976 --> 00:36:30,184
in the would around us.
626
00:36:30,271 --> 00:36:33,434
SUSSKND: String theory would be beautiful, it would be elegant,
627
00:36:33,566 --> 00:36:35,852
and calculation from that very simple theory
628
00:36:35,944 --> 00:36:37,900
would produce the world as we know it.
629
00:36:39,781 --> 00:36:44,024
GREENE: But for this beautiful theory to work, there was a catch.
630
00:36:44,119 --> 00:36:45,700
The math of string theory
631
00:36:45,787 --> 00:36:49,405
required something that defies common sense,
632
00:36:49,499 --> 00:36:53,617
a feature that would open the door to the multiverse:
633
00:36:53,753 --> 00:36:56,039
extra dimensions of space.
634
00:36:59,426 --> 00:37:03,089
We're all familiar with three dimensions of space:
635
00:37:03,179 --> 00:37:05,921
height, width and depth.
636
00:37:08,268 --> 00:37:10,304
But the math of string theory
637
00:37:10,395 --> 00:37:13,478
says these aren't the only dimensions.
638
00:37:13,606 --> 00:37:18,817
JOSEPH POLCHINSKI: The mathematics works only if the strings move and vibrate,
639
00:37:18,945 --> 00:37:20,936
not just in the three directions that we see,
640
00:37:21,030 --> 00:37:23,817
but in those and, say, six more-
641
00:37:23,908 --> 00:37:26,024
nine space dimensions in all.
642
00:37:26,161 --> 00:37:29,494
so if string theory is right,
643
00:37:29,622 --> 00:37:32,204
where are these extra dimensions,
644
00:37:32,333 --> 00:37:34,824
and why can't we see them?
645
00:37:34,919 --> 00:37:37,831
Think about the cable supporting a traffic light.
646
00:37:37,964 --> 00:37:41,832
From a distance, it looks like a line, one-dimensional.
647
00:37:41,926 --> 00:37:46,761
But if you could shrink down to,
648
00:37:46,848 --> 00:37:49,180
you'd find another dimension,
649
00:37:49,309 --> 00:37:53,427
a circular dimension that curls around the cable.
650
00:37:53,521 --> 00:37:56,558
And string theory says that if we could shrink down
651
00:37:56,691 --> 00:37:59,774
billions of times smaller than that ant,
652
00:37:59,861 --> 00:38:02,853
we'd find tiny extra dimensions like this
653
00:38:02,989 --> 00:38:06,106
are curled up everywhere in space.
654
00:38:06,201 --> 00:38:08,738
SUSSKIND: At every point of space,
655
00:38:08,870 --> 00:38:11,452
there's extra dimensions of space
656
00:38:11,539 --> 00:38:13,700
that are curled up into little tiny knots
657
00:38:13,792 --> 00:38:16,158
that you can't see because they're too small.
658
00:38:16,252 --> 00:38:19,119
GREENE: And the shape of these extra dimensions
659
00:38:19,214 --> 00:38:23,048
determines the fundamental features of our universe.
660
00:38:23,134 --> 00:38:24,965
Just the way the air streams
661
00:38:25,053 --> 00:38:27,715
that are going through an instrument like a French horn
662
00:38:27,847 --> 00:38:29,337
have vibrational patterns
663
00:38:29,432 --> 00:38:32,720
that are determined by the shape of the instrument,
664
00:38:32,852 --> 00:38:34,058
the shape at the extra dimensions
665
00:38:34,187 --> 00:38:36,223
determins how the little strings vibrate.
666
00:38:36,314 --> 00:38:40,557
Those vibrational patterns determine particle properties,
667
00:38:40,652 --> 00:38:44,144
so all of the fundamental features of our universe
668
00:38:44,239 --> 00:38:48,858
may be determiend by the shape of the extra dimensions.
669
00:38:48,952 --> 00:38:53,571
SUSSKIND: The way those extra dimensions of space are put together
670
00:38:53,665 --> 00:38:59,706
is in many respects like the DNA of the universe.
671
00:38:59,796 --> 00:39:03,505
They determine the way the universe is going to behave,
672
00:39:03,591 --> 00:39:05,377
just exactly the same way
673
00:39:05,468 --> 00:39:08,756
as DNA determines the way an animal is going to look.
674
00:39:08,847 --> 00:39:12,431
GREENE: The problem was, the more string thearists looked,
675
00:39:12,559 --> 00:39:14,925
the more ways they found that extra dimensions
676
00:39:15,019 --> 00:39:16,725
could be curled up.
677
00:39:16,813 --> 00:39:18,599
And the math provided no clues
678
00:39:18,731 --> 00:39:21,063
as to which shape was the right one
679
00:39:21,150 --> 00:39:23,562
corresponding to our universe.
680
00:39:23,653 --> 00:39:25,689
SHAMIT KACHRU: I think the consensus right now
681
00:39:25,780 --> 00:39:28,271
is that that number seems to be astronomical.
682
00:39:28,408 --> 00:39:29,693
There are published papers
683
00:39:29,784 --> 00:39:32,366
suggesting upwards of 10 the 500-
684
00:39:32,453 --> 00:39:36,037
that's 10 followed by 500 zeroes-
685
00:39:36,124 --> 00:39:37,284
different possible shapes.
686
00:39:39,627 --> 00:39:42,289
GREENE: Ten to the 500 different possible shapes
687
00:39:42,422 --> 00:39:48,167
for the extra dimensions, each appearing equally valid.
688
00:39:48,303 --> 00:39:51,966
It seemed preposterous.
689
00:39:52,056 --> 00:39:53,466
Especelly for a theory
690
00:39:53,558 --> 00:39:56,550
that was looking for one, single master equation
691
00:39:56,644 --> 00:39:58,350
to describe our universe.
692
00:40:06,571 --> 00:40:08,903
But then it occurred to some string theorists
693
00:40:08,990 --> 00:40:11,231
that perhaps there was a different way
694
00:40:11,326 --> 00:40:14,489
to look at the problem, and this different perspective
695
00:40:14,621 --> 00:40:19,411
would breathe new life into the idea of a multiverse.
696
00:40:19,500 --> 00:40:22,333
Ten to the 500 different string theories.
697
00:40:22,420 --> 00:40:26,754
This sounded like a complete disaster.
698
00:40:26,841 --> 00:40:28,923
What good is it to have a theory
699
00:40:29,010 --> 00:40:31,877
that has ten to the 500 solutions?
700
00:40:32,013 --> 00:40:34,504
You can't find anything in there.
701
00:40:34,641 --> 00:40:36,848
well, that left string theorists
702
00:40:36,935 --> 00:40:40,519
somewhat unhappy, somewhat depressed.
703
00:40:40,605 --> 00:40:43,017
My own reaction to it at the time is, "This is great.
704
00:40:43,107 --> 00:40:44,392
"This is fantastic.
705
00:40:44,525 --> 00:40:47,642
"This is exactly what the cosmologists are looking for:
706
00:40:47,737 --> 00:40:50,524
"enormous diversity of possibilities.
707
00:40:50,615 --> 00:40:52,651
"Don't be unhappy about this.
708
00:40:52,742 --> 00:40:54,403
"That says that string theory
709
00:40:54,535 --> 00:40:57,402
"fits extremely well with cosmology
710
00:40:57,538 --> 00:41:00,200
and with all the interesting ideas about multiverses."
711
00:41:01,834 --> 00:41:05,418
GREENE: Turning what seemed like a vice into a virtue,
712
00:41:05,546 --> 00:41:08,003
some string theorists became convinced
713
00:41:08,091 --> 00:41:10,548
that the multiple solutions of string theory
714
00:41:10,677 --> 00:41:15,671
might each represent a real and very different universe.
715
00:41:15,765 --> 00:41:20,384
In other words, string theory was describing a multiverse-
716
00:41:20,478 --> 00:41:24,141
and an extremely diverse one at that.
717
00:41:24,232 --> 00:41:27,065
JOHNSON: To everyone's surprise,
718
00:41:27,193 --> 00:41:29,775
string theory was actually quite readily describing
719
00:41:29,904 --> 00:41:33,192
huge numbers of different kinds of solutions,
720
00:41:33,282 --> 00:41:37,400
each of which corresponds to a possible universe.
721
00:41:37,495 --> 00:41:40,362
So we just got this multiverse for free.
722
00:41:40,456 --> 00:41:44,119
DELIA SCHWAETZ-PEELOV: Both from string theory and from inflation,
723
00:41:44,252 --> 00:41:47,415
you have these universes that are produced.
724
00:41:47,547 --> 00:41:50,505
These different univeses would all naturally have
725
00:41:50,591 --> 00:41:53,253
different amounts of dark energy.
726
00:41:53,386 --> 00:41:58,471
GREENE: In fact, according to the math, the amount of dark energy
727
00:41:58,599 --> 00:42:02,763
would span such a wide range of values from universe to universe
728
00:42:02,854 --> 00:42:07,939
that the strange amount we've measured would surely turn up.
729
00:42:08,067 --> 00:42:12,106
String theory, without even trying, solved that problem.
730
00:42:12,238 --> 00:42:16,277
GREENE: So, over a decade after Linde and Vilenkin
731
00:42:16,367 --> 00:42:19,404
had come up with their ideas about eternal inflation,
732
00:42:19,495 --> 00:42:20,951
the multiverse was revived.
733
00:42:24,125 --> 00:42:27,208
Three lines of reasoning were now all pointing
734
00:42:27,295 --> 00:42:30,253
to the same conclusion:
735
00:42:30,339 --> 00:42:36,926
enternal inflation, dark energy and string theory.
736
00:42:37,013 --> 00:42:40,426
Just the way it takes three legs to support a stool,
737
00:42:40,516 --> 00:42:44,304
these three ideas taken together support the argument
738
00:42:44,395 --> 00:42:47,637
that we may live in a multiverse.
739
00:42:47,732 --> 00:42:52,943
When different lines of research all converge on one idea,
740
00:42:53,029 --> 00:42:54,394
that doesn't mean it's right,
741
00:42:54,489 --> 00:42:58,983
but when all the spokes of the wheel are pointing at one idea,
742
00:42:59,118 --> 00:43:01,154
that idea becomes pretty convincing.
743
00:43:02,747 --> 00:43:07,582
Today the multiverse is hotly debated.
744
00:43:07,668 --> 00:43:10,330
Many critics remain.
745
00:43:10,421 --> 00:43:13,879
David Grace is going to tell us, "No, no, no."
746
00:43:14,008 --> 00:43:15,999
GREENE: But mutiverse advocates
747
00:43:16,135 --> 00:43:22,176
like Alex Vilenkin, Alan Guth and Andrei Linde
748
00:43:22,266 --> 00:43:24,382
are no longer alone.
749
00:43:24,519 --> 00:43:26,555
VILENKIN: The tide appears to be turning.
750
00:43:26,687 --> 00:43:30,145
Now these ideas are accepted to a much larger degree.
751
00:43:30,233 --> 00:43:32,349
The genie is out of the bottle.
752
00:43:32,443 --> 00:43:34,604
You cannot put it back.
753
00:43:37,698 --> 00:43:39,939
GREENE: So, what would it be like?
754
00:43:40,034 --> 00:43:42,650
if we could travel to some of these other universes,
755
00:43:42,745 --> 00:43:44,701
what would we see?
756
00:43:47,708 --> 00:43:52,202
Some might be vastly different from our own,
757
00:43:52,338 --> 00:43:54,829
with properties unlike anything we've ever seen.
758
00:43:58,803 --> 00:44:02,887
In fact, some universes in the multiverse
759
00:44:02,974 --> 00:44:07,809
might not have light or matter or anything recognizable at all.
760
00:44:13,234 --> 00:44:16,067
And there might be other universes with features
761
00:44:16,154 --> 00:44:19,362
not unlike the familiar ones we know,
762
00:44:19,448 --> 00:44:22,155
but where life takes a completely different form,
763
00:44:22,243 --> 00:44:25,906
Perhaps communicating in ways we'd find utterly bizarre.
764
00:44:28,749 --> 00:44:30,080
And the math shows
765
00:44:30,209 --> 00:44:33,872
that if we were able to visit enough of these universes,
766
00:44:33,963 --> 00:44:36,454
we might eventually find ones like ours,
767
00:44:36,591 --> 00:44:42,086
with a Miky Way galaxy, a solar system and an Earth.
768
00:44:42,180 --> 00:44:45,013
Except with some slight differences.
769
00:44:45,099 --> 00:44:47,260
In one, maybe the asteroid
770
00:44:47,393 --> 00:44:54,890
that killed off the dinosaurs 65 million years ago missed,
771
00:44:54,984 --> 00:44:57,316
and evolution charted a new course.
772
00:45:04,660 --> 00:45:07,322
In another, there might be an Earth
773
00:45:07,455 --> 00:45:09,320
with people similar to us...
774
00:45:09,457 --> 00:45:11,118
(phone ringing)
775
00:45:11,209 --> 00:45:15,373
...but better at multitasking.
776
00:45:15,463 --> 00:45:19,547
But there's someting even stranger.
777
00:45:19,634 --> 00:45:21,124
Somewhere out there,
778
00:45:21,260 --> 00:45:23,376
we should find exact copies of our universe
779
00:45:23,471 --> 00:45:27,840
with duplicates of everything and everyone.
780
00:45:31,729 --> 00:45:33,640
How could this be?
781
00:45:33,731 --> 00:45:36,689
How could there be exact duplicates of ourselves
782
00:45:36,817 --> 00:45:39,650
out there in the multiverse?
783
00:45:39,737 --> 00:45:43,821
To see how, take this deck of cards.
784
00:45:43,908 --> 00:45:46,945
It's made up of 52 different cards,
785
00:45:47,036 --> 00:45:51,530
and if I deal them, everyone will get a different hand.
786
00:45:51,666 --> 00:45:56,581
But, over the course of many, many rounds,
787
00:45:56,671 --> 00:45:59,333
eventually some of the combinations
788
00:45:59,423 --> 00:46:03,541
will start to repeat.
789
00:46:03,678 --> 00:46:05,339
That's because with 52 cards,
790
00:46:05,471 --> 00:46:08,178
there's a limited number of different hands you can deal.
791
00:46:08,266 --> 00:46:11,474
So if you deal the cards an infinite number of times,
792
00:46:11,560 --> 00:46:14,552
then repeating hands are inevitable.
793
00:46:14,689 --> 00:46:18,477
And in the multiverse, a similar principle applies.
794
00:46:20,319 --> 00:46:23,356
That's because, according to the laws of nature,
795
00:46:23,489 --> 00:46:26,572
the fundamental ingredients of matter, or particles,
796
00:46:26,701 --> 00:46:29,192
are kind of like a deck of cards:
797
00:46:29,287 --> 00:46:32,620
in any region of space, they can only be arranged
798
00:46:32,707 --> 00:46:35,164
in a finite number of different ways.
799
00:46:35,251 --> 00:46:38,038
So if space is infinite,
800
00:46:38,129 --> 00:46:40,791
if there are an infinite number of universes,
801
00:46:40,881 --> 00:46:43,543
then those arrangements are bound to repeat.
802
00:46:43,676 --> 00:46:46,042
And since each one of us
803
00:46:46,137 --> 00:46:49,721
is just a particular arrangement of particles,
804
00:46:49,807 --> 00:46:53,516
somewhere there's a duplicate of you and me
805
00:46:53,602 --> 00:46:56,685
and everyone else.
806
00:46:56,772 --> 00:46:59,354
This can be shocking.
807
00:46:59,442 --> 00:47:00,852
It could be that in another universe
808
00:47:00,943 --> 00:47:03,229
I was a rock star and my life much better.
809
00:47:03,321 --> 00:47:05,733
Or much worse, depending on your opinion of rock stars.
810
00:47:05,865 --> 00:47:08,982
It means all those things that I've never found time to do
811
00:47:09,076 --> 00:47:12,489
are maybe being done by some copy of me somewhere else.
812
00:47:12,580 --> 00:47:15,413
I was rather depressed, actually.
813
00:47:15,499 --> 00:47:17,911
This picture robs us of our uniqueness.
814
00:47:18,044 --> 00:47:19,625
It is a consequence of the ideas,
815
00:47:19,754 --> 00:47:22,291
and the ideas seem very well motivated.
816
00:47:24,759 --> 00:47:26,420
GREENE: Yet critics argue
817
00:47:26,552 --> 00:47:29,419
the multiverse is just too convenient an explanation
818
00:47:29,555 --> 00:47:31,921
for thing we don't understand,
819
00:47:32,058 --> 00:47:34,595
like the tiny value of dark energy in our univese
820
00:47:34,727 --> 00:47:36,843
and the huge number of possible shapes
821
00:47:36,937 --> 00:47:39,929
for the extra dimensions in string theory.
822
00:47:40,066 --> 00:47:41,772
STEINHAEDT: The problem with that kind of reasoning
823
00:47:41,901 --> 00:47:43,266
is that it doesn't explain
824
00:47:43,402 --> 00:47:45,438
why the dark energy is the way it is.
825
00:47:45,571 --> 00:47:47,937
It just says it's random chance.
826
00:47:48,032 --> 00:47:50,114
I don't find that satisfactory.
827
00:47:50,242 --> 00:47:53,234
You can apply this kind of reasoning
828
00:47:53,329 --> 00:47:55,695
any time you don't have a better explanation.
829
00:47:57,541 --> 00:47:59,953
GREENE: On the other hand, supportesrs of the multiverse
830
00:48:00,086 --> 00:48:03,419
point out that sometimes a better or depper explanation
831
00:48:03,506 --> 00:48:08,091
for the way things are simply does not exist.
832
00:48:08,177 --> 00:48:12,011
Take, for example, the Earth's orbit around the Sun.
833
00:48:12,139 --> 00:48:15,802
We find ourselves at a distance of 93 million miles,
834
00:48:15,893 --> 00:48:18,100
perfect for life.
835
00:48:18,187 --> 00:48:20,803
If we were much closer to the Sun,
836
00:48:20,898 --> 00:48:25,767
our planet would be too hot for life as we know it to exist.
837
00:48:28,030 --> 00:48:30,316
And if we were much farther from the Sun,
838
00:48:30,449 --> 00:48:34,943
it would be too cold for life.
839
00:48:35,037 --> 00:48:37,995
So, why are we in this sweet spot?
840
00:48:40,000 --> 00:48:41,831
Well, starting in the late 1500s,
841
00:48:41,919 --> 00:48:47,334
the famous astronomer Jonannes Kepler asked that very question,
842
00:48:47,425 --> 00:48:50,883
and he spent years trying to find a physical reason,
843
00:48:51,011 --> 00:48:53,127
some law of nature
844
00:48:53,222 --> 00:48:58,933
that requires the Earth to be 93 million miles from the Sun.
845
00:48:59,019 --> 00:49:03,513
But Kepler never found it, because it doesn't exist.
846
00:49:03,649 --> 00:49:07,517
There isn't any physical law requiring the Earth to be
847
00:49:07,653 --> 00:49:10,019
93 million miles from the Sun.
848
00:49:10,114 --> 00:49:14,153
It's simply one possibility of the many you'd expect to find
849
00:49:14,243 --> 00:49:18,987
in a universe we know is full of solar systems.
850
00:49:19,081 --> 00:49:21,948
SUSSKIND: You might think it was an extraordinary accident.
851
00:49:22,042 --> 00:49:23,327
It's not.
852
00:49:23,419 --> 00:49:25,751
It's just that there are a lot of planets out there.
853
00:49:25,880 --> 00:49:30,499
GREENE: Similarly, some suggest that the true explanation
854
00:49:30,593 --> 00:49:34,006
for many of the fundamental features of our world
855
00:49:34,096 --> 00:49:38,135
will elude us if we don't consider the possibility
856
00:49:38,225 --> 00:49:41,934
that we live in a multiverse.
857
00:49:42,062 --> 00:49:44,223
GUTH: Clearly if we had a good physical reason,
858
00:49:44,315 --> 00:49:46,351
that would be great and we would understand it.
859
00:49:46,442 --> 00:49:47,397
We'd be much happier.
860
00:49:47,485 --> 00:49:49,066
We may have to live with that.
861
00:49:49,195 --> 00:49:53,234
There's no principle built into the laws of nature
862
00:49:53,324 --> 00:49:57,909
that say that theoretical physicists have to be happy.
863
00:49:58,037 --> 00:50:00,028
It's a hypothesis.
864
00:50:00,122 --> 00:50:01,908
It's the leading hypothesis
865
00:50:01,999 --> 00:50:04,741
because nobody has another hypothesis
866
00:50:04,877 --> 00:50:06,162
which makes as much sense.
867
00:50:09,507 --> 00:50:14,092
GREENE: The multiverse, a tantalizing possibility.
868
00:50:14,178 --> 00:50:18,467
But with no experimental evidence, should you belivee it?
869
00:50:18,599 --> 00:50:20,590
We can't believe in anything
870
00:50:20,726 --> 00:50:23,968
until there's observational or experimental support.
871
00:50:24,104 --> 00:50:27,312
But what we have found over the last few centuries
872
00:50:27,441 --> 00:50:31,104
is that mathematics provides a sure-footed guide
873
00:50:31,237 --> 00:50:32,943
to the nature of things
874
00:50:33,030 --> 00:50:36,648
that we haven't yet been able to see, observe or experiment with.
875
00:50:36,784 --> 00:50:40,743
Math predicted things like black holes
876
00:50:40,829 --> 00:50:42,865
and certain subatomic particles
877
00:50:42,957 --> 00:50:46,165
long before we ever observed them.
878
00:50:46,293 --> 00:50:48,204
And math is suggesting
879
00:50:48,295 --> 00:50:50,877
that there may be these other universes.
880
00:50:50,965 --> 00:50:54,799
That doesn't mean it's right, but often it's leading you
881
00:50:54,927 --> 00:50:57,919
to a deeper understanding of reality.
882
00:50:58,013 --> 00:51:00,800
If you choose not to believe it, that's perfectly fine,
883
00:51:00,933 --> 00:51:03,800
because we have not given you any evidence yet,
884
00:51:03,936 --> 00:51:06,678
and one of the wonderful things about science
885
00:51:06,814 --> 00:51:09,430
is it's about evidence; it's not about belief.
886
00:51:09,525 --> 00:51:13,985
GREENE: And some scientists now think we might just be able
887
00:51:14,071 --> 00:51:16,312
to find that evidence.
888
00:51:16,407 --> 00:51:18,864
They propose that if our universe and another
889
00:51:18,993 --> 00:51:20,858
were born close together,
890
00:51:20,995 --> 00:51:23,452
the two might have collided.
891
00:51:26,417 --> 00:51:29,909
That collision could have left its own telltale sign
892
00:51:30,004 --> 00:51:32,746
in the form of a pattern of temperature differences
893
00:51:32,840 --> 00:51:36,833
that we might detect in the cosmic background radiation,
894
00:51:36,927 --> 00:51:41,170
the heat left over from the Big Bang.
895
00:51:41,265 --> 00:51:42,880
My guess is yes, that in 100 years
896
00:51:43,017 --> 00:51:45,929
we will know one way or another whether these ideas are right.
897
00:51:46,020 --> 00:51:47,510
A hundred years from now
898
00:51:47,605 --> 00:51:50,187
it may be an amusing historical episode.
899
00:51:50,274 --> 00:51:51,639
We don't know.
900
00:51:53,068 --> 00:51:54,683
But if you only work on the things
901
00:51:54,820 --> 00:51:56,435
that are already well established,
902
00:51:56,530 --> 00:51:59,738
you're not going to be part of the next big excitement.
903
00:52:01,493 --> 00:52:05,361
GREENE: If we do verify the multiverse, it would change our perspective
904
00:52:05,456 --> 00:52:09,870
much as Copernicus did 500 years ago when he showed
905
00:52:10,002 --> 00:52:13,460
that the Earth is not the center of the cosmos.
906
00:52:13,547 --> 00:52:17,881
And some might say that if our universe is just one of many
907
00:52:18,010 --> 00:52:22,344
our descent from the center would be complete.
908
00:52:22,431 --> 00:52:24,387
SCHWARTZ-PERLOV: Regardless, I think it's more important
909
00:52:24,475 --> 00:52:28,684
just that we're so lucky that we can understand the universe.
910
00:52:28,771 --> 00:52:30,727
I think it's a great ride,
911
00:52:30,814 --> 00:52:32,520
and I think it's really good for physics
912
00:52:32,608 --> 00:52:34,018
that we have this tension.
913
00:52:34,109 --> 00:52:36,065
I don't know where we're going to end up.
914
00:52:39,573 --> 00:52:43,031
GREENE: So, what does this all mean?
915
00:52:43,118 --> 00:52:45,109
Are there infinite duplicates
916
00:52:45,245 --> 00:52:49,705
of you and me and everything existing right now
917
00:52:49,792 --> 00:52:52,579
in an infinite number of other universes?
918
00:52:55,422 --> 00:52:59,085
Is the multiverse the next Copernican revolution?
919
00:52:59,218 --> 00:53:02,631
We don't know at least not yet.
920
00:53:02,763 --> 00:53:06,347
But if the idea that we live in a multiverse proves true,
921
00:53:06,433 --> 00:53:08,674
we'd be witnessing one of the most exciting
922
00:53:08,769 --> 00:53:10,475
and dramatic upheavals
923
00:53:10,604 --> 00:53:14,267
to our understanding of the fabric of the cosmos.
924
00:53:26,370 --> 00:53:28,861
Major funding for NOVA is provided by:
925
00:53:31,291 --> 00:53:32,656
And...
926
00:53:43,470 --> 00:53:46,837
And by the Corporation for Public Broadcasting
927
00:53:46,974 --> 00:53:51,138
and by contributions to you PBS station from:
928
00:53:57,776 --> 00:54:00,358
Major funding for "The Fabric of the Cosmos"
929
00:54:00,487 --> 00:54:03,149
is provided by the National Science Foundation.
930
00:54:10,914 --> 00:54:12,450
And...
931
00:54:15,502 --> 00:54:18,335
Supporting original research and public understanding
932
00:54:18,422 --> 00:54:24,292
of science, technology, engineering and mathematics.
933
00:54:24,386 --> 00:54:26,297
Additional funding is provided by...
934
00:54:38,192 --> 00:54:40,183
And the George D. Smith Fund.
935
00:54:43,155 --> 00:54:45,862
Captioned by Media Access Group at WGBH access.wgbh.org
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