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Why is our universe fine-tuned for life? | Brian Greene

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http://www.ted.com At the heart of modern cosmology is a mystery: Why does our universe appear so exquisitely tuned to create the conditions necessary for life? In this tour de force tour of some of science's biggest new discoveries, Brian Greene shows how the mind-boggling idea of a multiverse may hold the answer to the riddle.

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Brian Greene: Is our universe the only universe?

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Is there more than one universe? In this visually rich, action-packed talk, Brian Greene shows how the unanswered questions of physics (starting with a big one: What caused the Big Bang?) have led to the theory that our own universe is just one of many in the "multiverse."

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Parallel universes are no longer just a feature of a good sci-fi story. There are now some scientific theories that support the idea of parallel universes beyond our own. However, the multiverse theory remains one of the most controversial theories in science.

Our universe is unimaginably big. Hundreds of billions, if not trillions, of galaxies spin through space, each containing billions or trillions of stars. Some researchers studying models of the universe speculate that the universe's diameter could be 7 billion light-years across. Others think it could be infinite.

But is it all that's out there? Science fiction loves the idea of a parallel universe, and the thought that we might be living just one of an infinite number of possible lives. Multiverses aren't reserved for "Star Trek," "Spiderman" and "Doctor Who," though. Real scientific theory explores, and in some cases supports, the case for universes outside, parallel to, or distant from but mirroring our own.

Multiverses and parallel worlds are often argued in the context of other major scientific concepts like the Big Bang, string theory and quantum mechanics.

Eternal inflation, the Big Bang theory and parallel universes

Around 13.7 billion years ago, everything we know of was an infinitesimal singularity. Then, according to the Big Bang theory, it burst into action, inflating faster than the speed of light in all directions for a tiny fraction of a second. Before 10^-32 seconds had passed, the universe had exploded outward to 10^26 times its original size in a process called cosmic inflation. And that's all before the actual expansion of matter that we usually think of as the Big Bang itself, which was a consequence of all this inflation: As the inflation slowed, a flood of matter and radiation appeared, creating the classic Big Bang fireball, and began to form the atoms, molecules, stars and galaxies that populate the vastness of space that surrounds us.

Related: How an inflating universe could create a multiverse

That mysterious process of inflation and the Big Bang have convinced some researchers that multiple universes are possible, or even very likely. According to theoretical physicist Alexander Vilenkin of Tufts University in Massachusetts, inflation didn't end everywhere at the same time. While it ended for everything that we can detect from Earth 13.8 billion years ago, cosmic inflation in fact continues in other places. This is called the theory of eternal inflation. And as inflation ends in a particular place, a new bubble universe forms, Vilenkin wrote for Scientific American in 2011.

Those bubble universes can't contact each other because they continue to expand indefinitely. If we were to set off for the edge of our bubble, where it might butt up against the next bubble universe over, we'd never reach it because the edge is zipping away from us faster than the speed of light, and faster than we could ever travel.

Related: How many stars are in the universe?

But even if we could reach the next bubble, according to eternal inflation (combined with string theory), our familiar universe with its physical constants and habitable conditions could be totally different from the hypothetical bubble universe next to our own.

"This picture of the universe, or multiverse, as it is called, explains the long-standing mystery of why the constants of nature appear to be fine-tuned for the emergence of life," Vilenkin wrote. "The reason is that intelligent observers exist only in those rare bubbles in which, by pure chance, the constants happen to be just right for life to evolve. The rest of the multiverse remains barren, but no one is there to complain about that."

Vilenkin's explanation implies that in some of the infinite bubble universes outside our own, there could be other intelligent observers. But in every instant that passes, we get farther away from them, and we will never intersect.

Quantum mechanics and parallel universes

Some researchers base their ideas of parallel universes on quantum mechanics, the mathematical description of subatomic particles. In quantum mechanics, multiple states of existence for tiny particles are all possible at the same time - a "wave function" encapsulates all of those possibilities. However, when we actually look, we only ever observe one of the possibilities. According to the Copenhagen interpretation of quantum mechanics as described by the Stanford Encyclopedia of Philosophy, we observe an outcome when the wave function "collapses" into a single reality.

But the many-worlds theory proposes instead that every time one state, or outcome, is observed, there is another "world" in which a different quantum outcome becomes reality. This is a branching arrangement, in which instant by instant, our perceived universe branches into near-infinite alternatives. Those alternate universes are completely separate and unable to intersect, so while there may be uncountable versions of you living a life that's slightly - or wildly - different from your life in this world, you'd never know it.

Related: Black holes, aliens, multiverse & Mars: Space TED talks you need to watch

The many-worlds theory is the most "courageous" take on the quandary of quantum mechanics, physicist Sean Carroll wrote in his book, " Something Deeply Hidden: Quantum Worlds and the Emergence of Spacetime" (Dutton, 2019). He also argued that it is the most straightforward theory, although not without wrinkles.

One of those wrinkles is that the many-worlds idea is not really falsifiable. This is an important component of scientific thought and is the way the scientific community develops ideas that can be explored with observation and experimentation. If there's no opportunity to find evidence against a theory, that's bad for science as a whole, science journalist John Horgan argued in a blog post for Scientific American.

Infinite space, infinite universes?

(Image credit: Weerakarn Satitniramai via Getty Images)

Some physicists believe in a flatter version of multiple universes. That is, if the universe that we live in goes on forever, there are only so many ways that the building blocks of matter can arrange themselves as they assemble across infinite space. Eventually, any finite number of particle types must repeat a particular arrangement. Hypothetically, in a big enough space, those particles must repeat arrangements as large as entire solar systems and galaxies.

So, your entire life might be repeated elsewhere in the universe, down to what you ate for breakfast yesterday. At least, that's the theory.

But if the universe began at a finite point, as nearly every physicist agrees that it did, an alternate version of you likely doesn't exist, according to astrophysicist Ethan Siegel's 2015 Medium article.

According to Siegel, "the number of possible outcomes from particles in any Universe interacting with one another tends towards infinity faster than the number of possible Universes increases due to inflation."

"So what does this mean for you?" Siegel wrote. "It means it's up to you to make this Universe count."

The mirror-image universe

(Image credit: NASA / WMAP Science Team)

In a relatively recent addition to the pantheon of multiverse theories, researchers from the Perimeter Institute for Theoretical Physics in Waterloo, Ontario, have proposed that the universe began at the Big Bang - and on the opposite side of the Big Bang timeline, stretching backwards in time, a universe once existed that was the exact mirror image of our own.

"Instead of saying there was a different universe before the bang, we're saying that the universe before the bang is actually, in some sense, an image of the universe after the bang," Neil Turok, a Perimeter Institute researcher, told Space.com sister site Live Science.

That means everything - protons, electrons, even actions like cracking an egg - would be reversed. Antiprotons and positively charged electrons would make up atoms, while eggs would un-crack and make their way back inside chickens. Eventually, that universe would shrink down, presumably to a singularity, before expanding out into our own universe.

Seen another way, both universes were created at the Big Bang and exploded simultaneously backward and forward in time.

Multiverse: Arguments for and against

Arguments for the multiverse theory
Cosmic inflation
Our universe grew exponentially in the first moments of its existence, but was this expansion uniform? If not, it suggests different regions of space grew at different rates - and may be isolated from one another.
Mathematical constants
How are the laws of the universe so exact? Some propose that this happened only by chance - we are the one universe out of many that happened to get the numbers right.
The observable universe
What is beyond the edge of the observable space around us? No one knows for sure, and until we do (which could be never), the thought that ou universe extends indefinitely is an interesting one.

Arguments against the multiverse theory
Falsifiability
There is no way for us to ever test theories of the multiverse. We will never see beyond the observable universe, so if there is no way to disprove the theories, should they even be given credence?
Occam's razor
Sometimes, the simplest ideas are the best. Some physicists argue that we don't need the multiverse theory at all. It doesn't solve any paradoxes, and only creates complications.
No evidence
Not only can we not disprove any multiverse theory, we can't prove them either. We currently have no evidence that multiverses exists, and everything we can see suggests there is just one universe - our own.

Parallel universes in fiction

(Image credit: Marvel.com)

Countless works of myth and fiction draw from ideas of parallel universes and the multiverse. Overlapping worlds make appearances in Norse mythology as well as Buddhist and Hindu cosmology. The idea of multiple universes coming into contact showed up in print as early as Edwin A. Abbott's novella "Flatland: A Romance of Many Dimensions" (Seeley & Co., 1884), and can still be seen in recent movies such as the 2016 Marvel film "Doctor Strange." An entire genre of Japanese graphic novels, called isekai, deals with characters transported to parallel worlds, as described by the New York Public Library.

Nearly every "Star Trek" series incorporates some form of mirror universe, and the 2009 reboot film starring Chris Pine and Zachary Quinto took subsequent "Star Trek" movies into an entirely new timeline that explicitly branches off from the original series.

And comics, as well as their corresponding movies, delve deeply into the idea of parallel worlds. Recent Marvel Comics' storylines (both film and in print), DC's Flashpoint arc and 2018's "Into the Spider-Verse" all explore multiple universes and the intersections between them.

This is an incomplete list of some appearances of multiverses, split-timeline universes and parallel universes in fiction:

Movies

Into the Spider-Verse (2018)

Terminator Genisys (2015)

Phineas and Ferb the Movie: Across the Second Dimension (2011)

Star Trek (2009)

Donnie Darko (2001)

Run Lola Run (1998)

Sliding Doors (1998)

Back to the Future 1-3 (1985, 1989, 1990)

The Adventures of Buckaroo Banzai Across the 8th Dimension (1984)

Television

Star Trek: Discovery, multiple episodes

Star Trek: Enterprise, multiple episodes

Star Trek: Deep Space Nine, multiple episodes

Star Trek: The Next Generation, "Parallels" (Episode 11, Season 7) (1993)

Star Trek: The Original Series, "Mirror, Mirror", (Episode 4, Season 2) (1967)

Doctor Who, multiple episodes

Sliders, entire series

Community, "Remedial Chaos Theory" (Episode 4, Season 3) (2011)

Rick and Morty, multiple episodes

Futurama, multiple episodes

Eureka, multiple episodes

Agents of Shield, multiple episodes

Print

"The Chronicles of Narnia" series (Geoffrey Bles, 1950-56) by C. S. Lewis

"His Dark Materials" series (Scholastic, 1995-2000) by Phillip Pullman

The "Discworld" series (HarperCollins, 1983-2015) by Terry Pratchett

"Men Like Gods" (Macmillan, 1923) by H. G. Wells

"The Dark Tower" series (Donald M. Grant, 1982-2012) by Stephen King

Video games

BioShock Infinite, 2013

Kingdom Hearts, 2002-2020

Chrono Cross, 1999

Half-Life, 1998-2020

Metroid Prime 2: Echoes, 2004

Zero Escape, 2009-2016

This article was adapted in part from previous work by Space.com contributor Elizabeth Howell.

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Parallel universes are not just for science fiction. Scientific theories can sometimes support the case for universes outside or parallel to our own.

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The Higgs Boson Simplified Through Animation

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There are hundreds of known cosmic events that could obliterate the life on our planet. High energy solar flares, cataclysmic impact events, gamma ray bursts, a nearby supernova, and on and on. However, the chances of Earth suffering a life-ending global catastrophe are actually rather slim.

But we know that it is coming. According to astronomers, the Sun's luminosity increases by about 6% every billion years. While 6% might not seem like much, it's enough to render our planet inhospitable to life as we know it in 1.1 billion years.

The end of everything else, though, is a little bit more difficult to predict, but that hasn't stopped scientists from speculating and theorizing.

Notably, the ultimate fate of the universe depends on three things: the universe's overall shape, its density, and the amount of dark energy that exists. The first two scenarios hinge upon the universe existing in a "flat" or "open" system (one that is negatively curved, similar to the surface of a saddle).

The Big Rip

Our universe is expanding. It happens because of a mysterious form of energy know as " dark energy." We don't know what it is but, each year, this dark energy causes the rate of expansion to increase.

One theory of our ultimate end relies on the assumption that this expansion will continue indefinitely - until the galaxies, stars, planets, and matter (even the subatomic building blocks that comprise all matter) can no longer hold themselves together. At which point, they rip apart.

This theory is called (surprise!) the Big Rip.

Whether or not this actually happens depends on critical density (the boundary value between open models that expand forever and closed models that re-collapse),

According to Robert Caldwell, a theoretical physicist from Dartmouth College, if the Big Rip won out over all of the apocalyptic scenarios put forth in this piece, the event would occur in some 22 billion years, when the Sun has already transitioned from a main-sequence star to a red-giant (incinerating Earth as a result) and then into a white dwarf.

If Earth did manage to survive intact (spoiler alert: it won't), the planet would explode about 30 minutes before the grand finale.

The Big Freeze

Another popular scenario for the end of the universe that relies on deciphering the true nature of dark energy is the Big Freeze (also referred to as Heat Death or the Big Chill).

In this scenario, the universe continues to expand at an ever-increasing speed. As this happens, the heat is dispersed throughout space while galaxies, stars, and planets are all pulled farther and farther from one another. In the very distant future, intelligent civilizations will look into the sky and think they are alone. Everything will be so far away that the light from distant stars and galaxies can never reach them.

Eventually, planets, stars, and galaxies would be pulled so far apart that the stars would eventually lose access to raw material needed for star formation And thus, the lights would inevitably go out for good.

It will continue to get colder and colder until the temperature throughout the universe reaches absolute zero. At absolute zero, all movement stops. Nothing can exist in such a place, as there is literally no energy. At all. Anywhere.

This is the point at which the universe would reach a maximum state of entropy. Instead of fiery cradles, galaxies would become coffins filled with the remnants of dead stars.

Many scientists (astronomers and physicists alike) believe this is one of the most probable scenarios.

The Big Crunch

The Big Crunch is thought to be the direct consequence of the Big Bang. In this model, the expansion of the universe doesn't continue forever.

After an undetermined amount of time (possibly trillions of years), if the average density of the universe was enough to stop the expansion, the universe would begin the process of collapsing in on itself. Eventually, all of the matter and particles in existence would be pulled together into a super dense state (perhaps even into a black hole-like singularity).

Such an event might have already happened before. Some scientists have theorized that the universe we see is the result of a cyclic repetition of the Big Bang, where the first cosmological event came about after the collapse of a previous universe. This is something called conformal cyclic cosmology.

Unlike the first two scenarios, this model relies on the geometry of the universe being "closed" (like the surface of a sphere). An event like this would be like a single breath: the universe would "breathe out" the Big Bang, and "breathe in" the Big Crunch.

This could also happen if we see a reversal of dark energy's current expansion effect.

Similar to this theory (and the Big Bang) is the Big Bounce. A sort of symmetry is proposed here: the universe is in a continuous cycle of expanding out and then collapsing onto itself. Effectively, we could be one of many iterations of the universe. Perhaps even more eerie to think about is the idea that maybe each time the universe resets, it plays out the same way. Perhaps the you that is currently reading this article right now is just one you out of 10^googleplex versions that existed before.

Ultimately, the universe may be like the mythical phoenix: its death is actually a fiery rebirth.

The Big Slurp

This theory surfaced just a few years ago, after revelations were released about the true nature of the Higgs Boson, which is the particle that plays a role in granting mass to elementary particles.

In this model, if the Higgs Boson particle weighs in at a certain mass, it could indicate that the vacuum of our universe may be inherently unstable, perhaps existing in a perpetual " metastable' state - something that has been discussed at length many times before.

If this were the case, our universe might experience a catastrophic event when a "bubble" from another alternate universe appears in ours. If this bubble exists in a lower-energy state than our bubble. the universe could be completely annihilated.

In essence, it would cause all the protons in all matter in our universe to decay. By proxy, so would we. If that doesn't sound unpleasant enough, this sort of a vacuum metastability event could happen at virtually any moment, anywhere in our universe. The bubble could pop over and start expanding at light-speed until it swallowed us entirely.

Truly, none of these scenarios sound very fun.

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How Will Our Universe End? Here Are The Top Four Theories

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There are hundreds of known cosmic events that could obliterate the life on our planet. High energy solar flares, cataclysmic impact events, gamma ray bursts, a nearby supernova, and on and on. However, the chances of Earth suffering a life-ending global catastrophe are actually rather slim. But we know that it is coming.

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Venus Keus: Three ways the universe could end

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We know about our universe's past: the Big Bang theory predicts that all matter, time and space began about 14 billion years ago. And we know about the present: scientists' observations of galaxies tell us that the universe is expanding at an accelerated rate. But what about the future?

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No they are just predictions, the universe could have been created in ways we could have never imagined but these theories are the most logical ones to date

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The daughter universe theory also known as the many worlds theory is what we would think of as a parallel universe, it would mean that in each universe we would make different decisions than we did in our universe.

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The bubble universe theory is the theory that each universe is in its own bubble and when bubbles interact scenarios such as the big slurp can happen.

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The infinite multiverse theory is the theory that an infinite amount of universes all lie on a flat plane of existence that goes on forever.

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The higgs boson particle field is everywhere in our universe and it is made up of higgs boson particles and this field determines the mass of all other particles in our universe.

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We may be alone in space but if scientists are correct then there may be other universes besides our own. There are many theories on what these other universes would be like but the main 3 theories are Infinite, Bubble, and Daughter.

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The big slurp theory comes into play if our universe becomes unstable, which we can detect if there is a change in the higgs boson's mass. If it does change then our universe could collide into another universe and if that other universe exists at a lower energy state then our universe will be destroyed via the decay of all protons.

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The big crunch theory is that if gravity gets so strong, it pulls everything in our universe to its center, destroying it. This could also cause a recreation of the big bang which would reset our universe via the big bounce theory in which the universe can "reset" itself through the big crunch.

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The big rip theory is when dark energy gets so strong that it rips apart every atom in the universe, destroying everything. This is possible to happen after the big freeze.

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The big freeze theory also known as the heat death of the universe. Due to scientific data it is the most likely theory to become the real end of the universe. This would happen when the universe expands so much that dark energy pushes everything into distant space where all suns and eventually even black holes would die

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There are many ways that our universe could die but the 4 most likely of them are:
The big rip
The big freeze
The big crunch
And the big slurp

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We know how the universe was created via the big bang but the big bang was, due to scientific data, it was likely created by a massive fuel source traveling throughout the multiverse creating an almost infinite amount of big bangs as it travels, therefore creating an almost infinite amount of universes