NARRATOR: Humans are natural-ham explorers.
We charge into uncharted territory and seek out the unknown.
We've mapped nearly every inch of Mother Earth...
...and left tracks on the moon.
But to set foot on another planet...
...to travel beyond our solar system...
...that is a dream for the future.
A dream that comes to life in the feature film Interstellar.
BRAND: We must think not as individuals but as a species.
We must confront the reality of interstellar travel.
NARRATOR: The film Interstellar deals with the quest for new worlds and the fate of humanity.
Sound like the stuff of science fiction?
Maybe.
But the foundations of this film are rooted in real science...
...thanks to the involvement of renowned astrophysicist Kip Thorne.
In Interstellar, one of the most important features...
...is the way that the science is totally embedded in the film.
There are some wild things in here.
NARRATOR: Beyond fantasy and fiction, this is the real science of Interstellar.
Space travel has been a staple of the movies from the very beginning...
...but the feature film Interstellar has a unique pedigree.
It was inspired in part by the work of Kip Thorne...
...an authority on astrophysics, gravitational waves...
...and the warping of space-time.
He's also an executive producer on the film.
In Interstellar, real science was built into the fabric of the film from the outset.
The other major players in this film, they all respected the science...
...and they worked with me to see that the science was well incorporated.
Can you tell me what the easiest definition of what a singularity is?
Kip and myself meshed well in terms of trying to use current thinking...
...current scientific understanding to drive the narrative.
The language we use...
...is it's a place where the curvature of space and time gets infinitely high.
So we're good, okay.
And we just hope that the research we've done and the conversations I'd had with Kip...
...and that Chris had had with Kip informed the narrative...
...and that the audience would feel that.
NOLAN: Why simply imagine, fantasize...
...about things that might happen in space or on an interstellar journey?
Why not actually look at, uh, the real science there?
It's an Indian surveillance drone.
NARRATOR: Interstellar takes place in a future...
...where living conditions on Earth threaten the survival of humanity.
BRAND: Your daughter's generation will be the last to survive on Earth.
COOPER: Now you need to tell me what your plan is to save the world.
BRAND: We're not meant to save the world, we're meant to leave it.
One of the things that the film explores is, do we belong on Earth...
...and should we be staying on Earth...
...and if there is anything else out there, should we be exploring that?
Here we go.
NARRATOR: In the film, the crew seeks a new place to call home.
A planet that can sustain life.
Human life.
- I'm not gonna make it! - Yes, you are.
It's an exciting concept that there may be other worlds out there.
Well, what are those worlds and what could they be...
...and is there a place for us out there?
NARRATOR: The search for another Earth...
...sounds like a job for the explorers of tomorrow...
...but it's happening right now.
Astrophysicist Natalie Batalha is a passionate planet hunter.
BATALHA: I think the only way that we're going to really understand our place in the galaxy...
...is by looking at this broad picture and understanding the diversity of all planets.
Twenty or 30 years ago, we didn't know...
...of any other planets orbiting normal stars like our own sun.
NARRATOR: Natalie has helped rewrite that story as mission scientist...
...for NASA's Kepler space telescope.
BATALHA: Kepler's objective is very simple.
It's to determine the fraction of stars in our galaxy...
...that harbor potentially habitable Earth-size planets.
NARRATOR: And what makes a planet potentially habitable?
The one ingredient that we think is common to all life forms...
...is this requirement of liquid water.
So that's why we look for planets that have rocky surfaces...
...where water could pool...
...and that are receiving the right amount of energy from the star...
...where the water wouldn't be locked up in a frozen state because the planet is so cold...
...nor would it be evaporated away because the planet is too hot.
We call it the Goldilocks Zone, where liquid water could potentially exist.
NARRATOR: Launched in 2009, Kepler stared...
...at one small patch of the Milky Way for four years straight.
Compared to stars, planets are too tiny for Kepler to spot...
...but it can detect their shadows.
BATALHA: Every planet orbiting a luminous object is casting a shadow out into space.
The Kepler spacecraft makes use of that fact...
...waiting for a planet in its orbit about the star...
...to pass directly between the disc of the star and the spacecraft...
...and the telescope perceives that as a dimming of light.
NARRATOR: This simple method has revealed thousands of exoplanets.
Planets orbiting other stars in our galaxy.
What we've learned so far...
...is that literally every star in the galaxy has at least one planet.
There's an amazing diversity of exoplanets out there...
...and we've found very exotic worlds.
Two hundred light-years away, there is a Saturn-size planet orbiting...
...not one, but two stars.
So if you were living on a world like Kepler-16b...
...you would see in the sky two stars rising in the east, setting in the west...
...continuously changing position as they orbit one another.
This is an artist's rendition of the planet Kepler-10b.
It's orbiting 23 times closer to its parent star than Mercury is to our own sun.
So this star-facing side is just being blasted by stellar radiation...
...creating temperatures in excess of that required to melt iron.
The planet has an entire hemisphere larger than the Pacific Ocean...
...which is an ocean, but it's not an ocean of water.
It's an ocean of molten lava.
NARRATOR: Not an attractive destination.
But Kepler recently found us a possible second home.
This is an artist's concept of the Kepler-186 planetary system.
Five planets orbiting this M-type star...
...and the outermost planet is Kepler-186f.
Our first discovery of an Earth-size planet in the habitable zone of a normal star.
When I think about Kepler-186f, I try to imagine it as a real place...
...because it is a real place.
We know that it could be rocky, it's the same size as Earth...
...so I do imagine a rocky surface.
We don't know that it has a liquid ocean, but we can certainly imagine one.
And then, all of a sudden in your imagination...
...you internalize the existence of this world out there...
...that there is a place that could be very, very much like Earth.
NARRATOR: So when do we set sail for these distant shores?
Reality check.
Kepler-186f is nearly 3 quadrillion miles from Earth.
Otherwise put, 500 light-years away.
That's a journey of 500 years at the speed of light.
But no thing can travel as fast as light.
At best, our spacecrafts are thousands of times slower.
Even the spaceships in Interstellar don't come close.
BRAND: We need the bravest humans to find us a new home.
COOPER: But the nearest star is over a thousand years away.
- Hence the bravery. - Okay.
NARRATOR: So how do they reach new worlds beyond our solar system?
They take a walk on the warp side of space and time.
You have no idea when you're coming back.
AMELIA: Couldn't you have told her you were going to save the world?
No.
I'm coming back.
NARRATOR: When we journey to a far-off place, we travel not just in space but also in time...
...as we move into the future.
Until about a century ago, scientists believed that space and time were entirely separate.
Theoretical physicist Sean Carroll explains how Albert Einstein overturned that idea.
CARROLL: One of Einstein's great insights...
...was that space and time were related to each other...
...where you have space and you have time.
Einstein says, "There's only one thing which we call space-time."
And then he says, "This space-time thing...
...it's not just the stage on which all the action plays out.
It's an actor itself."
Space-time can change, it can move, it can bend, and it can warp.
NARRATOR: Einstein's theory of relativity states that space-time is like a flexible fabric.
The objects embedded in it: The sun, planets, even us, warp that fabric.
And the consequence of that warping is what we call gravity.
The more massive the object, the more space-time is warped...
...and the greater the gravity.
We feel gravity.
The flexibility of space-time is harder to grasp on a gut level...
...but its effects are measurable.
As Sean demonstrates, the greater the gravity, the more slowly time flows.
CARROLL: For example, if I were on the ground floor with a clock...
...a super accurate atomic clock...
...and a twin of mine was up on the top floor of a building...
...with an equally accurate atomic clock...
...if we later on compared them, mine would have ticked off fewer seconds.
NARRATOR: On the ground floor, Sean experiences slightly more gravity...
...than his twin on the top floor.
He also experiences slightly less time than his twin.
The difference is tiny, but real.
And there are practical applications.
CARROLL: For example, the GPS system, the Global Positioning System...
...that is a very, very precise set of clocks...
...on satellites orbiting around the Earth...
...and that orbit is in a slightly different gravitational field than we are in down here.
So the fact that time moves differently here on the surface of the Earth...
...than in the satellite orbit, is very, very important...
...to getting the GPS to work correctly.
NARRATOR: Time on a GPS satellite clock advances faster than a clock on Earth...
...by about 38 microseconds per day...
...so the system's computers correct for that.
Motion also affects our experience of space-time.
CARROLL: The best way to say it is just staying still...
...means that you experience the most time that you can.
Moving around and doing things means you experience less time.
NARRATOR: Let's revisit Sean at the wheel of his car and his twin on a park bench.
If you move out on your car, and then you come back...
...compared to the person who stayed behind...
...your clock that you took with you on that journey...
...will have experienced a little bit less time than the one who stayed behind.
NARRATOR: We normally move too slowly to notice the effect.
But if Sean could drive near the speed of light...
...he could race across the United States and back again a million times...
...and experience less than a second of time...
...while the twin he left behind...
...would endure hours of waiting for Sean's return.
In other words, Sean would've traveled into the future compared to his twin.
This means space travel may get tricky in years to come.
The faster our spaceships, the greater the gravity fields we encounter...
...the further out of sync we may become with those we leave behind.
COOPER: So if we find a home, then what?
Every hour is seven years back on Earth.
NARRATOR: The relativity of time is the source of hardship and heartbreak in Interstellar.
The theory of relativity is fascinating all by itself...
...but it immediately becomes something very emotional...
...when you talk about the distances between people.
You know, we all spend time away from our families.
I just thought, what if you could take that to its logical and very bittersweet extreme?
NOLAN: For me, it was very exciting to be able to examine the concept...
...of the subjective experience of time.
It's really the first time I've had an objective structure...
...around the film saying that time literally is relative...
...that we all experience time differently depending on where we are in the universe.
NARRATOR: But the warping of space-time may also provide shortcuts...
...that could make interstellar travel a snap.
Wormholes.
They're a staple of science fiction...
...but they're based on real science.
Einstein's relativistic laws govern the warping of space and time...
...and they say that wormholes might exist, they could exist.
So this dates all the way back to 1916.
CARROLL: A wormhole is a particular way that space and time can be curved.
It's like adding a little tube that connects two parts of space.
The basic idea is that if you're an ant and you live on the surface of the apple...
...the surface of the apple is your entire universe.
You can go around the outside through the universe itself...
...or you can go through the wormhole.
NARRATOR: But Einstein's equations also predict that if wormholes do form in nature...
...they may be subatomic in size...
...and exist for only fractions of a second before closing off.
Theoretically, what would it take to keep a wormhole open...
...and make it big enough to accommodate a spaceship?
THORNE: It turns out that in order to hold a wormhole open...
...so it doesn't crunch off and kill you when you try to go through...
...that you have to have the wormhole threaded by a negative mass or negative energy.
Einstein says mass and energy are equivalent.
NARRATOR: Almost all the forms of matter we know have positive mass and exert gravity.
Negative mass would exert antigravity...
...and repel the walls of a wormhole to keep it open.
Strangely, it is true that negative energy can exist...
...and it's been created in the laboratory, but only in very tiny amounts.
NARRATOR: It would take vast quantities...
...to prop open a wormhole large enough for a spaceship.
But just maybe, in the future...
...engineers will devise advanced technologies to do just that.
Today it's an educated guess, maybe I should say a half-educated guess...
...that wormholes cannot exist in our universe...
...but we're far from sure of that.
CARROLL: The truth is, we just don't know right now.
We don't understand the laws of physics well enough to say for sure...
...whether or not wormholes are possible.
NARRATOR: But since they're not impossible, they're fair game for a filmmaker.
I was very excited about the idea of focusing on a family...
...who would be the pioneers...
...who would experience some of the extraordinary features of astrophysics...
...particularly the idea of a wormhole that would allow us to travel to distant stars.
NARRATOR: To create a wormhole based on real science...
...Visual Effects supervisor Paul Franklin turned to Kip Thorne.
FRANKLIN: The popular image of what a wormhole might look like...
...is literally just a hole in space.
It sits on an invisible surface, you see stuff sliding down the sides...
...and disappearing down the drain, as it were.
And right in that first conversation, Kip showed me an image...
...of that kind of classical fantasy image of these things...
...and said, "This is all wrong." Ha, ha. "This is not how it is."
NARRATOR: Kip worked out the scientific equations that define the wormhole...
...and sent them to Paul's animators back in London.
THORNE: And so for the movie, I built a mathematical model wormhole...
...based on Einstein's relativity equations.
Paul, Kip and myself, we discussed, "Okay, we'll visualize the thing.
We'll simulate the thing exactly as the calculations say."
And Paul Franklin and his team, they were thrilled to get algorithms...
...that were the absolute latest, most interesting and up-to-the-minute.
MAN: Now we can go to the other one.
The wormhole is a three-dimensional hole in space.
What do you get if you take a Circle and sweep it out in three dimensions?
You get a sphere.
So the wormhole almost feels like a crystal ball hanging in space.
THORNE: I don't think anybody had ever really done this kind of visualization before.
This is really unique.
Uh, first time for me, as well as for you and the audience.
Absolutely, yes.
NARRATOR: In Interstellar, crew members take a giant leap of faith...
...When they plunge into a wormhole.
DOYLE: You can't think about your family. You have to think bigger.
COOPER: I am thinking about my family and millions of other families.
AMELIA: You might have to decide between seeing your children again...
...and the future of the human race.
NARRATOR: Beyond the wormhole, the crew Will face a far greater challenge:
To navigate the perils of a black hole.
For a filmmaker, that threat is full of dramatic possibilities.
NOLAN: When you venture out into a story about a man against the elements...
...visualizing the threat against our protagonist become very much more exotic.
Deep, deep space gives you a very, very fresh approach.
NARRATOR: Black holes were predicted by Einstein's equations...
...but physicists questioned whether they could really exist.
THORNE: A black hole is a strange beast.
If this were a black hole, then instead of a rubber surface...
...it would have a surface that is made of absolutely nothing...
...except warped space and time.
It's a place where gravity is so strong...
...that if anything falls into the black hole, it can never get back out.
If you fall in, you can't send signals back out.
Light can't get out from the interior.
CARROLL: So you might ask, how would that ever happen?
In outer space, you can get so much mass together, like in a super-massive star...
...that the gravity just becomes stronger and stronger and stronger...
...and eventually the pressure that matter exerts on itself can't keep up.
And everything collapses, there's a big explosion.
Some of the stuff is blown away, but the rest of it collapses into a black hole.
NARRATOR: A black hole that spins on its axis drags the very space around it...
...into a whirling motion that pulls stars and planets into orbit.
Closer in, gravity increases like a riptide.
At a boundary called the event horizon, gravity becomes so extreme...
...that nothing can escape being pulled into the heart of the beast...
...and lost forever.
GHEZ: Black holes are simple, and yet they have a lot of character.
It's almost like they can take on personalities.
Um, they can be picky eaters, urn, they can be energetic.
And what you're seeing and describing...
...is really how the black hole interacts with the environment.
NARRATOR: UCLA astronomer Andrea Ghez...
Looks like this is Sagi's star.
NARRATOR: ...is an expert on black hole detection.
- Must be this one, right? - I think it's that one.
NARRATOR: She played a key role investigating what had long been a scientific hunch.
That a huge black hole lives at the center of the Milky Way.
It's looking good.
NARRATOR: Astronomers knew the heart of our galaxy was buzzing...
...with gas, dust and millions of stars.
Some powerful force appeared to be driving this hubbub.
Could it be a black hole?
Ground telescopes just couldn't produce sharp images of the region...
...then a technique called adaptive optics vastly improved the view.
This is what it looks like before you use advanced technology.
It's a blurry mess...
...and now you can see the individual stars with adaptive optics turned on.
So each point of light here is associated with an individual star.
NARRATOR: Andrea put that technique to work at the Keck Observatory in Hawaii.
GHEZ: This is a road map.
NARRATOR: And she and her team began to track the stars at the center of the Milky Way.
GHEZ: And that's the center of our galaxy.
The very first year that we took the data was in 1995.
Then we go back to the telescope in '96, then we take our second image...
...and you have two pictures, and you can compare them.
NARRATOR: Andrea wanted to see if the stars were orbiting a single source of gravity...
...but stars can take years to complete an orbit.
GHEZ: And so it was really important that we kept going...
...and by 2000 we finally started to see the star's curve.
In other words, the gravitational influence of the black hole, um...
...had made those stars go from straight lines to starting to bend.
Precise enough to see that curvature.
NARRATOR: Year by year, Andrea and her team built their case.
This animation represents, uh, 20 years of work...
...and it tells you that there is a black hole, and exactly how massive it is.
NARRATOR: Andrea's painstaking project revealed a monster...
...with more than 4 million times the mass of our sun...
...at the center of our Milky Way.
Today, scientists are hunting black holes with new tools.
Caltech astrophysicist Fiona Harrison scans the skies with NuSTAR...
...a telescope that looks at the universe in high-energy x-rays.
HARRISON: The black hole itself doesn't emit light...
...but dust and gas falls onto the black holes...
...and in doing so, it heats up, and it emits x-rays.
NARRATOR: NuSTAR captures black holes in the process of feasting on matter...
...and the telescope is spotting them all over the place.
HARRISON: It's really only 10, 20 years ago that we thought black holes were rare.
We now know that every galaxy, like our Milky Way...
...has a massive black hole at its heart.
80 rather than just being curiosities, they're actually fundamentally important...
...to why the universe is the way it is.
NARRATOR: So is the Earth at risk of getting swallowed by a black hole?
HARRISON: Even though we have black holes sprinkled throughout the galaxy...
...we're in absolutely no danger.
It's a common misconception that black holes might suck the Earth.
Well, there's no sucking going on, it's just normal gravity.
It's just when you get very close to it...
...that there's a region from which light can't even escape...
...and Earth is not gonna do that.
NARRATOR: But in Interstellar...
...crew members have a precariously close encounter with a black hole.
COOPER: Oh, we are not prepared for this.
NARRATOR: What would the beast look like to them?
One of the things that Kip was very insistent on...
...is that the black hole, it's spherical, but it's absolutely black.
It has no surface detail.
Doesn't give shadows or highlights or anything.
But then early on, we were talking about accretion disks.
And that gave us a way to define the spherical shape of the thing.
NARRATOR: A black hole's accretion disk is made up of gas and dust and magnetic fields...
...that spin at high speeds...
...radiating heat and light.
The black hole's gravity would actually bend that light like a camera lens...
...in ways that Kip would calculate.
THORNE: I worked out the equations for tracing light rays traveling around the black hole...
...to see what the disk would look like if you were in a spacecraft looking at it up close.
NARRATOR: And Paul's team brought the mathematics to life.
We were really able to use a very, very accurate representation...
...of the gravitational lens and the effects of gravity and light around the black hole.
Uh, because what the algorithms gave us was extremely spectacular.
NARRATOR: Even Kip was surprised.
You see the disk in front...
...and then when it goes around...
...you see the disk wrap up around the top of the black hole...
...and wrap around the bottom of the black hole.
I had guessed it would look more or less like this...
...but knowing it intellectually is different than feeling it...
...than absorbing it, than seeing it.
It just blew me away.
NARRATOR: But this brilliant depiction...
...still can't tell us what happens in the heart of a black hole...
...beyond the event horizon.
What would happen to an astronaut daring or crazy enough to dive in feet-first?
THORNE: In the simplest descriptions of this...
...the descriptions that you will find in most books that you read...
...you're simply stretched from head to foot...
...and squeezed from the side by tidal forces, "spaghettified" is what it often says.
You're spaghettified as you fall in and you're destroyed.
That's the standard story.
NARRATOR: The truth is, all the laws of physics that we know...
...break down in the heart of a black hole.
Physicists are still working on exactly what happens there.
That's the gravity well, though, isn't it?
When we talk to non-physicists, we will often say it's the gravity well.
So you've been lying to us all these years.
You know how these things go, there are lies and there are "lies."
I know, but now...
The movie Interstellar deals with physics that is well-understood, well-established.
It deals with physics where we make educated guesses...
...and we're almost sure, but not 100 percent sure of our guesses.
And it deals with physics at the frontiers of human understanding...
...where we have to speculate...
...and when you get beyond those frontiers...
...Interstellar works hard to align itself...
...with the best speculations a scientist could imagine.
We're struggling very hard as filmmakers to try and explain, uh...
...these scientific concepts, these sort of abstract ideas...
...in a subjective way and a way that you can actually experience and feel something about.
NARRATOR: Interstellar mines that gray area where new ideas percolate...
...and taps deep into questions about the nature of the universe.
In Interstellar, telescopes on Earth first detect the presence of a wormhole.
It shows up as a gravitational anomaly that distorts the view of space.
We made the wormhole not have all that strong a gravity.
But why the wormhole?
Because then you have a reason for your trip around it.
I feel uncomfortable with the wormhole having that much gravity.
THORNE: When I first began working with Christopher Nolan...
...he wanted a wormhole that had rather gentle gravity...
...so we discussed how big the wormhole should be...
...and agreed that it should be just barely big enough...
...that it could be seen from Earth...
...through the bending of light around the wormhole...
...by the wormhole's warped space.
NARRATOR: Kip Thorne worked out just the right gravity for Interstellar's wormhole...
...using equations based on Einstein's theory of general relativity.
As we've learned, that theory states that objects warp space-time, creating gravity.
It also predicts that when objects move, they generate a pulse...
...that propagates through space-time, a bit like waves through water.
These gravitational waves have never been directly observed.
They would be small and hard to detect...
...unless they were generated by a massively violent motion.
Like the birth of the universe.
Physicists developed their big bang theory...
...in part by observing that today the universe is expanding.
Galaxies are moving away from each other like raisins in a rising loaf of bread...
...which suggests that in the distant past, the universe must have been much smaller.
CARROLL: If you wind the movie backwards, in the past, everything was closer together...
...and you plug that idea into the equations that Einstein gives us.
And there's a moment, which we now know was about 14 billion years ago...
...when everything was on top of everything else...
...when the density of stuff in the universe was apparently infinitely big.
NARRATOR: Then a powerful force triggered an expansion of space itself.
Faster than the speed of light, a theory called cosmic inflation.
And the theory said that this inflation should've taken fluctuations in the shape of space...
...and amplified them so they got much stronger.
And they become gravitational waves...
...producing ripples in the fabric of space and time.
NARRATOR: If we could detect those ripples today...
...it would help us understand how the big bang banged.
BOOK: The trick was always how were we going to measure such a thing.
And that led us to propose and develop...
...this very specialized experiment, um...
...which one of my colleagues referred to gleefully as a wild-goose chase.
NARRATOR: Caltech physicist Jamie Bock works in experimental cosmology.
BOCK: Experimental cosmology is building experiments...
...trying to get back to the dawn of time.
You need a hand with that?
NARRATOR: The focus of his latest experiment...
...Was the oldest light in the universe.
The faint afterglow of the big bang.
Physicists have mapped this cosmic microwave background...
...across the universe.
If the birth of the universe produced gravitational waves...
...they would've warped this primordial light...
...and caused it to be polarized or curled in a specific direction.
BOCK: If one could measure the polarization...
...and then not only measure it but look at its pattern...
...there might be kind of a swirly pattern...
...that would be an indicator of gravitational waves.
NARRATOR: Jamie and his team designed a series of small super-sensitive telescopes...
...that they installed where the skies are crystal clear.
At the South Pole.
BOOK: The South Pole is the closest we can get to outer space...
...to make our measurements.
NARRATOR: For eight years, the team's telescopes scanned a patch in the sky...
...measuring minute differences in the temperature...
...of the cosmic microwave background...
...and a pattern emerged.
BOCK: Our results reported that we see this swirly pattern of polarization...
...that's consistent with, uh, what you expect from gravitational waves.
THORNE: So they didn't really see the gravitational waves from the early universe...
...but they saw this polarization pattern that was precisely what was predicted...
...except that it was stronger than expected.
Tells us what went on immediately after the big bang...
...when the universe was a trillionth of a trillionth of a trillionth of a second old.
So it's seeing almost the creation of the universe.
NARRATOR: The finding must be confirmed by other experiments.
If it holds up, this first evidence for the detection of gravitational waves...
...will deepen our understanding of the birth of the universe.
And that, by extension, may help us answer an enduring question:
Can we time travel?
CARROLL: You know, it's very easy to travel in time.
Yesterday, I've moved forward 24 hours and here I am.
But that's the only way that it's easy. It's easy to go into the future.
In fact, it's not just easy, it's inevitable. We all move into the future over time.
NARRATOR: But traveling to the past is a different story...
...because space and time have profoundly different properties.
In space, you can go up, down, left, right, forward, backward.
NARRATOR: We move freely through the three dimensions of space.
In time, we experience its one dimension and a lot less freedom.
CARROLL: Because time has a direction and space does not.
In time, there's a huge difference...
...between one direction, the future, and the other direction, the past.
For example, you remember the past, but you don't remember the future.
You were younger in the past, we were all younger in the past.
We will all be older. It's all universal to us.
This arrow of time is a little bit mysterious.
We understand the basic underpinnings...
...in a concept called entropy, the disorderliness of the universe.
NARRATOR: Entropy is the measure of the disorder in a system.
The more ordered a system, the lower its entropy.
The more disordered a system, the higher its entropy.
A classic example of entropy increasing is just mixing cream into coffee.
When the cream and the coffee are separate, that's low entropy.
They're organized. There's the cream, the coffee.
You pour them together, you let them mix together.
Entropy just goes up. Things become more and more disorderly.
And this goes all the way back 14 billion years to the big bang.
NARRATOR: Back then, all the matter in the universe would have been on top of itself.
Density would have been infinite.
It was the epitome of low entropy.
But entropy has been on the rise ever since the big bang.
CARROLL: We think, but we haven't absolutely established...
...that this general tendency to go from order to disorder...
...is the single reason why the past is different from the future.
We can't discount in principle the possibility of visiting the past...
...but all of these weird puzzles that sort of rub us the wrong way...
...about if I go back into the past and I give myself a really good idea...
...and then I grow up and become rich off that idea, where did the idea come from?
These kinds of puzzles would evaporate...
...if we just said, "Well, the laws of physics don't allow you to visit the past."
So that's probably true.
NARRATOR: To contemplate the mysteries of space, time and the universe...
...can make a person feel mighty small.
Maybe it's best to lower our sights, hunker down and focus on planet Earth.
But that's not really an option for humanity in the long run.
Interstellar depicts a future where living conditions on Earth are grim.
Our mission does not work if the people on Earth are dead by the time we pull it off.
NARRATOR: Failing crops.
Clouds of dust.
Roads clogged with refugees.
Sound familiar?
That's because we've lived through this scenario before.
In the 19308, the Great Plains were hit by extreme drought.
Farmers had plowed up native grasslands.
When crops failed, unprotected topsoil billowed into clouds that darkened the sky for days.
Some 400,000 people lost nearly everything during the dust bowl.
One of America's worst man-made ecological disasters.
It was the model for the calamity depicted in Interstellar.
NOLAN: I really wanted to try and bring the audiences' attention...
...to the idea that this sort of thing really can happen.
And it struck me that the imagery that you can find...
...was so much more extraordinary than anything you see in a science fiction film.
And, indeed, in our portrayal of it, we had to frankly water it down.
NARRATOR: But we'd never let a dust bowl happen again, would we?
In recent years, cities in the American Southwest, especially Texas...
...have been battered by huge dust storms.
They've caused fatal traffic accidents and damaged infrastructure.
The causes are frighteningly familiar to UCLA geographer Greg Okin...
...an expert on the dynamics of wind and dust.
OKIN: We have wind-erodible soil.
We have agriculture that's disturbed the native vegetation.
We have bare ground because crops fail.
And we have windy conditions.
So all of the same things that happened in the dust bowl are happening now.
NARRATOR: Models of climate change predict higher global temperatures.
That probably means more droughts.
Economic pressures may lead to increased farming of wildlands.
If crops fail due to drought, that could mean more dust.
OKIN: It could happen in China.
It could happen in Africa.
Any of these factors, when they're in place, could cause what we have called the dust bowl.
NARRATOR: And to make matters worse...
...dust is much dirtier today than it was in the 19303.
OKIN: The dust that is interacting with clouds of pollution from Cities...
...in urban and industrial activities, um...
...that actually does appear to also be more noxious than regular dust.
NARRATOR: Winds blow dust across oceans and continents and into our lungs.
Dust, particularly for kids with asthma, is a really big problem.
There's actually quite good evidence...
...for dust being correlated with pediatric hospital admissions.
That's where the really clear evidence is.
NARRATOR: No one predicted the dust bowl of the 19308.
Today, we should know better.
OKIN: We learned the important lesson that poorly-planned human activity...
...plus unexpected climate variability can lead to disaster.
There's a lot to worry about.
NARRATOR: Sadly, we don't have a great track record taking care of Mother Earth.
But the planet is also threatened by forces far beyond our control.
February 15th, 2013...
...a meteor shining brighter than the sun streaks across Siberia.
It's a rock 65 feet in diameter...
...and when it explodes in midair, it releases more than 20 times the energy...
...of the bomb dropped on Hiroshima.
[SCREAMING]
No one was killed, but more than a thousand people were injured.
Asteroids have struck Earth before.
Some 65 million years ago...
...a monster 6 miles wide may have wiped out half the species on Earth.
Remember the dinosaurs?
A similar impact, or worse, could happen any time...
...and turn our blue marble into a lifeless rock.
And the bottom line?
Earth cannot sustain us forever.
In a few billion years, our sun will expand as it begins to die...
...and our planet will be toast.
But there's good news.
Unlike the dinosaurs...
MAN: Flight crew, close and lock your visors. Time to fly.
NARRATOR: we can leave Earth.
MAN: T-minus-10, nine...
Ignition sequence start.
Six, five, four, three, two, one.
Zero.
Zero and liftoff of space shuttle Atlantis.
NARRATOR: Today, nearly 600 people have traveled to space.
During the shuttle era, Marsha Ivins made the trip five times.
In order to record all of this, um, we have created this, uh, wiring nightmare here.
NARRATOR: At Kennedy Space Center Visitor Complex, she checks in on an old friend.
IVINS: I look at Atlantis hanging here, it's a surreal kind of experience to think...
...I flew that into space.
It's still something that I have a hard time believing.
- Hi. - My name is Tanya.
PHOTOGRAPHER: One, two, three.
And it makes me feel good that people still have a wonder...
...and an amazement and a pure joy...
...for the fact that we did fly this vehicle into space.
NARRATOR: For Marsha, each mission was as breathtaking as her first.
IVINS I looked up overhead...
...and here was this black sky and this blue Earth.
All hits you at that point, "I am not on the planet anymore."
And every astronaut who has flown has come back and said the same thing.
As you circle the Earth...
...you do not see natural borders and boundaries that separate the countries.
And all of the wars and the angst and the strife that tear this planet apart...
...seem so insignificant from that view.
NOLAN: To me...
...space travel, space exploration has always represented the ultimate frontier.
It's of the absolute extremities of what human experience is...
...and it's all about trying to, in some way, define our place in the universe.
MAN: Forty seconds away from the Apollo 11 liftoff.
JONATHAN: I remember growing up as a kid...
...and we were both fascinated by this impulse to flight.
This impulse to build unimaginable machines and use them to blast off into space.
MAN: Having fired the imagination of a generation, pulls into port for the last time.
NARRATOR: The space shuttles were retired in 2011...
...after traveling more than a half billion miles.
Space exploration demands enormous resources.
The kind that government agencies like NASA can marshal.
Recently, some new players entered the fray.
MUSK: I do think we're at the dawn of a new space era...
...and it's one where commercial companies play a stronger role.
NASA'S not out of the picture.
They're very much in the picture, but it's not all a NASA-designed system.
NARRATOR: In 2002, Elon Musk started his own rocket company.
A decade later, under contract to NASA...
...SpaceX became the first private company in history to carry supplies...
...to and from the International Space Station.
Now SpaceX is tackling an even greater challenge.
MUSK: I started SpaceX with the idea of trying to revolutionize space transport.
And critical to that is full and rapid reusability of the rocket.
The big issue with rocketry today is you get one use out of the rocket...
...and then it smashes down into the ocean or into the plains of Siberia, um...
...and you can't use it again.
If you can, in fact, land the rocket safely...
...and then reuse it with a minimal amount of effort...
...then you can dramatically reduce the cost of space transport.
NARRATOR: SpaceX is currently developing a fully and rapidly reusable launch system.
And that will take Elon closer to a more ambitious goal:
To help send crews to establish a colony on Mars.
Not a mission for the fainthearted.
MUSK: Anyone who wants to go to Mars...
...their desire for adventure would have to overcome their desire for comfort and safety.
NARRATOR: The colony on Mars could be the next giant leap for humankind.
NOLAN: It's such a fundamental idea when you think about it.
It's just a decision that has to be made in terms of how you view the-
The human race's place in the universe.
We either stay here on Earth or we leave and we journey through the galaxy.
NARRATOR: To create the look of the space technology in Interstellar...
...Christopher Nolan took a clear design approach.
NOLAN: We didn't wanna have anything that felt purely decorative.
We wanted to approach it from a more functional point of view...
...just be as convincing as possible...
...looking at the NASA technology that exists today...
...the International Space Station, these kind of things as our influences.
NARRATOR: There's no telling how space technology Will evolve in the years to come.
We may be decades away or longer from establishing a colony on Mars...
...or a permanent habitat in orbit around the Earth.
But people around the world are dreaming of that next step.
At a recent space conference...
...NASA and the National Space Society...
...handed out awards to dozens of forward-looking designs.
A self-sustaining settlement for 20,000 people.
A moon base that mines minerals from lunar soil.
A fleet of robots that clean up space junk.
But, of course, this is hard because we're burning fuel...
NARRATOR: There's not a single PhD among the prize-Winning designers.
[SINGING IN SPANISH]
NARRATOR: These are middle and high school students from around the world.
What first inspired me was the sky, the stars, the moon, the planets.
Thinking about going to space is really exhilarating.
I've always wanted to know, like, what's next? And for me, space is next.
What we can do is beyond our imagination.
For the survival of the human race, really, the only option is to go into space.
It should be something that... A first step we should take as a world.
NARRATOR: One of these kids may stand on Mars someday...
...or make a breakthrough in propulsion systems...
...or start a revolution in astrophysics.
To inspire their kind of enthusiasm is the hope of the Interstellar team.
THOMAS: I would love for kids to watch Interstellar...
...and get excited about possibilities of space travel and exploration.
I would hope that this film introduces many people to science...
...who might not have gotten curious about this kind of science in any other way.
I think it would be really thrilling if people got some sense from this film...
...that, uh, these ideas are worth thinking about.
NARRATOR: The interplay between science and science fiction...
...springs from a deep-seated creative drive.
To make sense of the unknown.
To engineer new worlds.
To dream up a better future.
We'll find answers where we always have:
Just beyond the next horizon.