How the Universe Works - S05E01 - Most Amazing Discoveries
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00:00Join us on a journey to infinity and beyond, to a place where the rules of physics collapse.
00:14Imagine a place surrounded by trillions of icy rocks.
00:20Unlock the secrets of Earth's first oceans, and we'll unlock the secrets of alien life.
00:28And the magnetic fields that help stars ignite, they shape entire galaxies.
00:38And what's going on in its outer reaches determines whether we live or die.
00:57The first second of the universe has barely begun.
01:01And the shortest possible units of time, Planck times, are flying by in their millions.
01:07The universe is a super-hot ball of radiation, billions of times smaller than an atom and dense beyond imagination.
01:21Gravity has begun shaping the future of the cosmos.
01:25But as the universe expands, temperature drops, another force arrives on the scene, the strong force.
01:38Without the strong nuclear force, the nuclei of the atoms themselves would all disintegrate.
01:48Three forces, gravity, the strong force, and the fractured super-force, rule the universe as it hurdles towards its next milestone.
01:58An event that sets out the blueprint for the galaxies that fill the cosmos today.
02:06We think this event happened because it explains a long-standing mystery.
02:12Everywhere we've looked in the universe, its billions of galaxies are spread evenly, the same number in every direction.
02:22Nobody could explain why.
02:25All of these parts of the universe must have at one point been in contact with each other.
02:30It's kind of like having two people who live on opposite sides of a country, getting up at the same time, eating the same breakfast, dressing the same way, even when they don't talk to each other.
02:38There must be something common in their past that links them.
02:42This problem needed a solution.
02:45And in 1979, a young cosmologist named Alan Guth proposed one.
02:52He called it inflation.
02:57It was very exciting. I suddenly realized that this might be the key to a very important secret of the universe.
03:03But at the same time, I was, of course, very nervous because it was all new and I was shaky about whether or not it was right.
03:13Guth speculated that the infant universe went through a phenomenal growth spurt.
03:19Cosmic inflation was a moment in the history, the very early history of the universe, when the expansion suddenly accelerated.
03:25It got huge for the briefest moments of time.
03:30Just 10 million plank times after the Big Bang, a tiny volume of space suddenly starts to expand much more quickly than before.
03:39This inflation is so rapid that it turns chaos into order, spreading the constituents of our universe evenly throughout space and fixing their positions within it.
03:54As the universe cooled down in those earliest moments, it increased in volume by a factor of 10 to the 90th in a millionth of a billionth of a billionth of a second.
04:06It's like a grain of sand swelling to larger than the sun, faster than the speed of light.
04:13Well, have we violated Einstein's laws? Nothing can go faster than the speed of light.
04:17And here's one of the real subtle points about the Big Bang.
04:20Space can expand so much that two objects appear to move apart faster than the speed of light, but they're not moving.
04:27It's the space in between them that's growing.
04:31Guth's audacious idea, the inflationary universe, could push the limit of our understanding back to the very first moments of the very first second.
04:42But how could we ever test it? How could we peer into the birth of creation?
04:50TV static holds a clue.
04:55One percent of the static on this screen comes from light from the Big Bang.
05:03In 1964, astronomers Arno Penzias and Robert Wilson were listening to radio signals from space.
05:12But in every direction, they were picking up a background hum.
05:17Puzzled by the hum, they suspected they knew the culprit and swept the entire receiver free of pigeon droppings, but to no avail.
05:28What Penzias and Wilson had stumbled upon was the afterglow of the fireball created by the Big Bang.
05:37As the universe expanded, it cooled. After a few hundred thousand years, it was just protons and electrons flying around.
05:43But at some point, the universe cooled enough that when an electron and proton got together all over the universe, essentially all at once, the universe became transparent.
05:53Think of a gigantic fog that suddenly lifts. Before the fog lifts, you can only see a few feet in front of you.
06:01Then suddenly, everything becomes clear.
06:05That's what happened 380,000 years after the Big Bang.
06:11Ever since that moment, 380,000 years after the Big Bang, this light has traveled uninterrupted through space.
06:23Scientists call it the cosmic microwave background.
06:29If you were to write down a handful of the greatest scientific discoveries of all time, one of them might be the discovery of DNA.
06:38Another one might be the discovery of the cosmic microwave background.
06:42That's how big this discovery was.
06:50We once believed creating a star was easy.
06:54Take a huge cloud of gas, add some gravity, and stand back as the gravity crushes the gas down to a hot ball of plasma.
07:08Temperatures and pressures rise until fusion sparks and a star is born.
07:16Now, scientists think gravity alone is not enough.
07:21To construct a star, you also need magnetism.
07:26The primary mover when you're forming a star is gravity.
07:30The material condenses in the center to form a star.
07:33And as that star forms, there's material swirling around it, attracted to that central mass by its gravity.
07:39But there's a problem.
07:40This stuff has what's called angular momentum.
07:45Angular momentum is the force of rotation that keeps the clouds of gas spinning around the center of the forming star.
07:55It works against gravity, smearing the gas into a thin disk.
08:04Young stars, or protostars, can only ignite if the central gas cloud reaches a super hot, dense state.
08:13But the disk spins around the center too fast for gravity to do its work.
08:21Scientists now understand that a third force is at play here.
08:26That's where magnetism can play a role.
08:28The magnetism of the protostar, the forming star, can actually affect the disk and slow it down...
08:33...and actually let it drop in and help the star itself form.
08:39The swirling gas in the forming star and its surrounding disk generate powerful magnetic fields.
08:48These fields grab at the fast-moving particles, slowing them down.
08:54Magnetism works like a cosmic brake.
08:56It slows down a little bit and eventually spirals into the center.
08:59Gravity starts to win. Gravity beats out that angular momentum and star formation happens.
09:07Gravity drags the slowing disk inwards, crushing it until the gas gets so dense it ignites.
09:16A star bursts into life.
09:20This is our universe as it looked 12 billion years ago.
09:26The gassy cosmos is filled with flashes as gravity and magnetism crush clouds of hydrogen gas to create stars.
09:38Some of the largest of these stars burn through their hydrogen fuel quickly.
09:42Without the power of fusion, there's nothing to fight against gravity.
09:47Sometimes this leads to a violent magnetic death when the star collapses and implodes in a supernova.
10:02The gassy outer layers of the star blow out into space.
10:06And the core of the star crushes inward, supercharging its magnetism.
10:13If you look at stars, just about all stars have strong magnetic fields at their surface.
10:18What happens is that if a star dies and it collapses, the same amount of magnetic field must still be present.
10:24So if the surface area of the star is decreased by a factor of 10, the magnetic field is still present.
10:32So if the surface area of the star is decreased by a factor of 1,000 or 10,000,
10:37then that means that the magnetic field intensity must increase by that same amount.
10:44As the supernova's core collapses, the magnetic field strength keeps building.
10:50At the end of all this, you get a ball 12 miles wide called a magnetar.
10:58These dense balls have very, very strong magnetic fields.
11:01In fact, the strongest magnetic fields in the universe.
11:06The magnetic field can be more than a trillion times stronger than the Earth's field.
11:12If you got very, very close to a magnetar, that strong magnetic field might possibly rip you apart.
11:18Because your atoms just can't stay together in the vicinity of such a strong magnetic field.
11:25Giant stars with the potential to form magnetars still exist within our universe.
11:32Some of the strongest magnetic fields in the universe are still present.
11:36Giant stars with the potential to form magnetars still exist within our universe.
11:41Scientists know of 23 magnetars within our galaxy today.
11:47And one of these, SGR 180620, located 50,000 light years from Earth,
11:55is the same magnetic monster that unleashed an assault on the Earth in 2004.
12:07The blast was triggered by a starquake.
12:14That's like an earthquake, but it's on a star.
12:16And the crust of the star slipped about this much, literally about a centimeter, the width of your finger.
12:22But this was far larger than any earthquake this planet has ever seen.
12:26Millions of times stronger.
12:28And the magnetic field is coupled with the matter in it.
12:31So when the crust slipped, so did the magnetic field.
12:34And it launched a blast of energy so powerful that 50,000 light years away,
12:40it physically affected our planet.
12:50Happily, this occurred halfway across the galaxy.
12:58If this thing had been a lot closer, the effect on us would have been huge.
13:05NASA Jet Propulsion Laboratory, California Institute of Technology
13:19A magnetar a couple of light years from Earth would devastate our planet.
13:27There could be a burst of radiation that could literally strip away our atmosphere.
13:32Without an atmosphere, there's no air to breathe.
13:35Animal life would die.
13:38Without air pressure, the seas would boil away.
13:42Earth would be left as a lifeless ball of rock spinning through space.
13:52Everywhere we look in the universe, we see the same stuff following the same rules.
13:59The universe is only made up of a handful of basic ingredients.
14:04Hydrogen, helium, lithium, carbon, and so on.
14:07All of these chemicals in different proportions are what make us up.
14:11And these same chemicals in different proportions make up everything.
14:17The same chemicals that form galaxies and stars do something amazing on Earth.
14:23Perhaps even unique.
14:26They become living things, organisms that can grow, reproduce, and think.
14:34We are bits of the universe made conscious.
14:37I think it's a biological miracle.
14:40You look out into the sky and you know you're connected to that somehow.
14:43It's pretty fantastic.
14:48So when does the story of life on Earth begin?
14:52Actually, it begins long before Earth existed.
15:03After the Big Bang, the universe is little more than a vast cloud of hydrogen gas.
15:13Then, pockets of the gas cloud collapse to form stars.
15:17And only stars can turn hydrogen into the more complex molecules that will become planets and people.
15:30Deep inside the cores of these early stars,
15:33heat and pressure crush hydrogen atoms together so powerfully they fuse,
15:39creating helium atoms and releasing a burst of energy.
15:44Over time, helium atoms fuse together too,
15:48creating carbon, nitrogen, oxygen, and even heavier atoms.
15:55Over hundreds of millions of years,
15:57ancient stars build up all the elements that make up our solar system today,
16:02including the atoms in your body.
16:06But in doing so, these stars pay a catastrophic price.
16:12Drained of energy, the ancient stars collapse and then explode in a supernova,
16:17spreading their chemically rich stardust across space.
16:23The iron in your blood, the calcium in your teeth and your bones,
16:26these were created in a supernova explosion,
16:30probably different stars that blew up billions of years ago,
16:34seeding the space around them with this stuff.
16:42Blasted through space,
16:44these complex atoms now pepper the clouds of gas that are nurseries of new stars.
16:51And 4.6 billion years ago,
16:54one particular cloud begins to collapse under its own gravity,
16:59and our sun ignites.
17:02Much of the ancient stardust is sucked into the sun, never to be seen again.
17:08But the leftovers clump together to form comets, asteroids, planets,
17:14and eventually, life.
17:18I actually think of myself as a very complicated rock.
17:21I am made of things like iron and copper and manganese.
17:24When you sit down on a mountainside and you're there with a rock,
17:27those are your cousins too.
17:30Thanks to ancient supernovas,
17:32the Earth forms with all the atoms needed to create both rocks and life.
17:38But what is it that distinguishes us from a piece of granite?
17:46Three things.
17:47A power source, a protective sack,
17:50and the plans for making more protected power sources.
17:55DNA is the plan.
17:57It's a long molecule built up from small units called nucleotides.
18:02DNA contains the instructions for how to build the cell's protein engine
18:07using small molecules called amino acids.
18:11DNA also tells the cell how to make lipids,
18:15a fatty molecule that forms a perfect protective sack.
18:19And that's all there is to it.
18:21You have the basic form of life, a cell.
18:25The chemistry set for life is actually quite simple.
18:28It's 20 amino acids.
18:30It's a few nucleotide bases for making DNA and RNA,
18:34a few lipids, and that's it.
18:38Think of it as like a Lego kit.
18:51A few billion years ago, when you looked in our solar system,
18:54you might have seen two Earths.
18:56Well, a few billion years from now, in the future,
18:59you might look at our solar system and see two Venuses.
19:05So we can look to Venus's past and see our future.
19:10We know the temperature skyrocketed,
19:13and the scarred surface hints at why.
19:19Hawaii's volcanic lava fields look like Venus in miniature.
19:23Both produce the same kind of runny lava,
19:26building flat, shield-like volcanoes.
19:31The big difference is there are only five active volcanoes on Hawaii.
19:40Venus is covered in them.
19:44One thing that really jumps out all around the planet
19:47is the number and variety of volcanoes.
19:50I mean, Venus could almost be nicknamed Volcano World.
19:53Venus has tens of thousands of volcanoes all over the planet.
20:02But it's not the erupting lava that turns up the heat.
20:06It's what comes out with it.
20:13Up close on the surface, Janie can see the origin of the gases.
20:18If we look behind us, we can see volcanic gases gushing out of steam vents.
20:23We've got carbon dioxide being delivered to the atmosphere.
20:26It's exactly like what has happened on Venus.
20:31Carbon dioxide has been delivered out of volcanoes
20:34over and over and over again throughout its history.
20:38So that now we have just a tremendously thick, dense atmosphere.
20:42The net result of all of these volcanic gases pouring out of volcanoes,
20:46major greenhouse gases,
20:48is that they've been absorbing heat for the billions of years of the history of Venus.
20:52The temperature has been gradually creeping up
20:55until today, the surface of Venus is 900 degrees.
21:01It's hard to imagine such extreme temperatures.
21:06But probes orbiting the planet revealed just how insanely hot it is.
21:14Scientists studying the images noticed something strange on the planet's mountains.
21:21It looks like on the mountains that there's apparently snow-like structures.
21:25But this is not like any snow found on Earth.
21:30So if you look at the white peak mountains of Venus,
21:33you would think that it was snow,
21:35but it's actually metals that have rained down and deposited on the top of those mountains.
21:42Metals like bismuth and lead have been deposited on the top of the mountains.
21:48And there's a lot of snow on the top of the mountains.
21:52Metals like bismuth and lead melt.
21:57Then they evaporate into the atmosphere.
22:04As they rise, they cool until they finally fall like snow on the mountaintops.
22:12I'm not sure even the imagination of science fiction authors
22:15would have come up with something as weird as Venus.
22:17I mean, just think about that.
22:18You have possibly metal frost on the top of mountains.
22:21I mean, how weird is that?
22:23It's pretty insane.
22:24Raining metals.
22:25Where would you ever think about that existing on Venus?
22:33In the future, metallic snow is forecast for Earth, too.
22:38And our scorching mountain caps will glitter like Venus.
22:49This is the Earth half a billion years after the crust cooled.
22:57The climate is warm and wet,
22:59and the asteroids that delivered the building blocks for life are a distant memory.
23:06Some simple life may have already taken hold.
23:10But this may not be the life we've been waiting for.
23:15But this may not be the life that turned into us.
23:22Because the Earth is about to be pummeled by a second wave of asteroids.
23:27And a radical theory called panspermia suggests some of these space rocks are filled with alien life.
23:37So panspermia is the idea that life rose on some other planetary body or other environment
23:43and came to Earth and was delivered by falling debris.
23:53The panspermia argument begins with a game of cosmic pinball 4.1 billion years ago.
24:00The outer planets of the solar system haven't yet settled into stable orbits.
24:05They jostle for position.
24:07The gravitational fallout sends a hail of giant asteroids towards the Earth.
24:14It's called the late heavy bombardment.
24:18We're just orbiting the Sun, happy as can be.
24:20And the outer planets are throwing these gigantic objects at us.
24:24And they just kept coming in and kept coming in and kept coming in.
24:31If delicate organisms had developed in the early oceans,
24:34the late heavy bombardment would have wiped them out.
24:38But the Earth wasn't the only planet in the firing line.
24:42Asteroids also hit Mars.
24:44And back then, Mars was a very different planet.
24:51With an evolutionary head start,
24:53Mars could have developed hardy bacterial life by this stage.
24:58Perhaps living deep within the surface rock.
25:01We've seen life on Earth that are cryptoendolithic.
25:05So they hide in the rocks and they survive the radiation and the harsh environment...
25:10...by hiding and thriving inside of that surface.
25:18A giant impact on the surface of early Mars...
25:22...could have thrown rocks filled with bacteria...
25:26...high in the atmosphere,
25:28filled with bacteria,
25:30high into space.
25:32These are organisms pre-packaged, ready to fly.
25:35You can imagine some of them trapped in a rock,
25:37kicked off a planet,
25:39flying through space thousands of years later,
25:41landing on another world,
25:43popping open and being able to reproduce and grow.
25:50So, did a Martian rock seed the Earth with life...
25:54...toward the end of the late heavy bombardment?
25:58It's an incredible possibility.
26:01But, how could the Mars bugs have survived the long journey through space?
26:10Certain bacteria on Earth, when they experience a stressful environment,
26:14they start forming what we call spores.
26:17And spores, if you imagine a seed,
26:20has all of the genetic information in the middle,
26:22and it's protected by numerous layers of defense.
26:25They really seal themselves up in little spaceships,
26:28and that would allow them to survive in space.
26:31You could take a spore, put it in space,
26:33bring it back, and it would still be viable.
26:39Spores also allow bacteria to stay alive in a dormant state
26:43for incredible lengths of time.
26:45The record on Earth is a spore that formed before the age of the dinosaurs,
26:50and was recently resurrected after a 250 million year nap.
26:56You know that spores can survive in theory for millions and millions of years,
27:00but to actually see evidence of a spore being revived is pretty fantastic.
27:10The final hurdle for panspermia
27:13is the fiery touchdown on the surface of the Earth.
27:17Planetary scientists simulate violent impact events
27:21with high-speed guns to see if Martian bacteria could have survived.
27:27Not every bit of the projectile is destroyed and highly shocked in an impact.
27:31When we do these experiments, we often find little bits of the projectile
27:34left over in the impact chamber.
27:38If there are bacteria living in that portion of that rock,
27:41they could potentially survive the impact back onto the planet.
27:44The science shows us that panspermia is possible,
27:48but does it take us any closer to understanding the origins of life?
27:55The fundamental problem with panspermia is that it's just removing
27:58one step of the problem and putting it someplace else.
28:01We don't know how life originated on Earth,
28:03now it's going to originate on Mars,
28:05but we don't know how it originated on Mars,
28:07so you still have this basic problem, and that is, how did life start?
28:12Did our ancestors arrive from space,
28:15or did they rise up from the oceans of the Earth?
28:26Pushing atoms together so strongly they stick is called nuclear fusion.
28:33It's the first step for turning a universe full of gas
28:36into one filled with the ingredients for planets, people, and cars.
28:43So how do you get two atoms to fuse?
28:47This guy's been doing it in his garage since he was 14.
28:53Tanner Wilson is obsessed with nuclear fusion.
28:59Yeah, the neighbors know about the radioactive stuff that's in the garage,
29:03and so does the government.
29:05It's all relatively low level.
29:08It's my watch going off.
29:10I think I'm the only person I've ever met with a Geiger counter watch.
29:16The centerpiece of Taylor's nuclear man cave
29:19is this precision-engineered fusion reactor,
29:23which he built when he was still in high school.
29:26Okay, I'll let in some gas now.
29:28The first ingredient? Hydrogen gas.
29:31And it will be flowed into the chamber
29:33through this very precise sapphire leak valve.
29:37The next ingredient? High-voltage electricity.
29:43Taylor passes a high voltage through a small spherical cage
29:47that sits inside the reactor.
29:49The negatively charged cage quickly draws the hydrogen ions inside it.
29:55So it's taking all those ions and sucking them towards the center.
29:58As they fly in, they get confined,
30:00and hopefully they collide with each other and fuse.
30:03The temperature of the atoms inside the cage is now so great
30:07that hydrogen atoms are fusing together,
30:10creating heavier helium atoms
30:12and a burst of energy hotter than the surface of the sun.
30:16It's that little tiny blob of plasma inside those grid wires.
30:21That's kind of like a star in a jar.
30:31Thirteen billion years ago,
30:33the universe uses gravity to fuse atoms
30:36instead of an electrical cage.
30:42Across the cosmos,
30:44vast clouds of hydrogen gas collapse under their own gravity.
30:50Pressure and temperature build
30:52as more and more gas gets sucked in.
30:55Eventually, fusion sparks deep in the core of these giant balls of gas,
31:00and the first stars start to manufacture
31:03many of the heavy elements that make up your car today.
31:21Deep in the outer reaches of the solar system,
31:23far beyond the last gasps of the sun's atmosphere,
31:27we are blind.
31:29We simply can't see that far.
31:31But sometimes we get messengers from beyond,
31:35potentially life-ending messengers.
31:38Comets.
31:49There's basically two kinds of comets.
31:51One is called short-period comets,
31:53and the other kind is called long-period comets.
31:56Short-period comets come from the Kuiper belt,
31:59the disk of space junk just beyond the planets.
32:02They travel around the solar system in relatively small circuits,
32:06returning at regular intervals of 200 years or less.
32:14Long-period comets are a bit more mysterious.
32:19The long-period comets can come back around
32:22something like every 1,000 years or even a million years.
32:25And unlike the short-period comets that come in on sort of circles,
32:28the long-period ones come in on really plunging orbits,
32:31and they can come in from all over the place in all different directions.
32:36And that tells us they come from somewhere different.
32:44The long-period comets, we think, are coming from someplace
32:47much, much farther away, and it's more like a spherical cloud
32:51of very distant things that are now plunging down into the sun
32:55every now and again.
32:57When a comet comes in, the sun heats it up,
33:00the ice turns into a gas, and the comet loses mass.
33:03Over time, these comets will disappear, and yet they keep coming.
33:07That means that there must be a reservoir of them out there.
33:12But where is there? Where are they coming from?
33:15One of the first explanations for these strange comets
33:18is maybe they're not from our solar system.
33:21Maybe the galaxy is full of these icy chunks that occasionally rain down on us.
33:25But then we thought, maybe they come from another part of the solar system.
33:30Maybe our whole solar system was surrounded by a ball of junk
33:34left over from the very first days of its creation, the Oort cloud.
33:40It was theorized that there must be a reservoir of them,
33:43a giant cloud surrounding the solar system with millions, billions,
33:47maybe even trillions of these icy bodies.
33:50But we've never actually seen it.
33:53So this Oort cloud, this theorized population of comets,
33:57is that. It's theoretical. It's never been directly observed.
34:00The objects in the Oort cloud are so far away and so small and dark
34:04that we've never observed something actually out in the Oort cloud.
34:08Something has to fall in.
34:10So you see things falling in from all of these different angles.
34:13From there, you can deduce what must be out there.
34:17A fun way to think of the Oort cloud
34:19is that these are pieces of planets that never got used.
34:22They really are leftovers.
34:24The Oort cloud actually didn't come with the original package, if you will.
34:28The Oort cloud formed when they tried but miserably failed
34:31to join the party and become those giant planets
34:34and instead got thrown all different directions,
34:37and they now exist halfway to the next star.
34:39They're a big, giant spherical distribution.
34:424.6 billion years ago, our sun ignites.
34:47A cloud of dust and gas circles the infant star.
34:51Then gravity gets to work, sucking in gas, dust, ice, and rocks
34:57to form the infant planets.
34:59The planets formed out of building blocks, smaller chunks of material,
35:04rock, ice, stuff that came together over time.
35:10The frenzy of swirling, colliding matter leaves behind debris
35:14as rocky rubble in the asteroid belt and ice in the Kuiper belt.
35:20Then Neptune and Uranus got in on the act, scattering the debris out further.
35:26Most of them got thrown out of the solar system forever,
35:29but the ones that didn't go on these big, long, million-year looping orbits,
35:33and that's the Oort Cloud.
35:35Billions of icy rocks were thrown out in all directions
35:39until a ball of debris formed around the whole solar system.
35:44The Oort Cloud comets are dinosaur bones of solar system formation.
35:48Contained in them are the ingredients that went up to make our planets.
35:52Most of the Oort Cloud objects will stay in this icy cloud forever,
35:56orbiting the distant sun, but a few get nudged loose
36:01and the sun's gravity pulls them inwards like moths to a flame.
36:06And such a comet can sneak up on you and you won't even know it's there.
36:19These comets can be many miles across, and they're moving extremely rapidly,
36:23sometimes as much as 100 miles per second.
36:26This makes them pretty dangerous.
36:28How dangerous? Ask a dinosaur.
36:32Some people think that the massive impact that killed off the dinosaurs
36:36may have been caused by a huge Oort Cloud comet.
36:43They can be every bit as dangerous
36:46as the asteroids usually blamed for extinctions on Earth.
36:53We'd have little or no warning
36:55because we have no idea what is hurling stuff out of the Oort Cloud at us.
37:18For over 4 billion years, the Earth and the Moon
37:21have traced a delicate dance around the sun.
37:26But our celestial partner is gradually slipping away.
37:34Sometimes when we talk about things that are reliable,
37:37we say there's nothing as reliable as the rising of the sun, right?
37:40We can think of the Moon in the same way.
37:42It goes through its phases, it's there, night after night, year after year.
37:46But it turns out the Moon is actually moving away from the Earth,
37:50and that's due to the interaction of the Moon and the Earth's tidal bulge.
37:56The bulge of water pulled up by gravity sits slightly ahead of the Moon
38:01because the Earth spins faster than the Moon orbits.
38:05The Moon pulls by gravity on that bulge and slows the Earth's rotation.
38:11Over billions of years, that has slowed the Earth's rotation a lot.
38:14We used to be spinning a lot more rapidly,
38:16probably more than twice as fast as we do now.
38:20But, like a gravitational whipline,
38:22the Moon's attraction to the bulge also speeds up its orbit.
38:27This speed makes the Moon's orbit wider, pushing it farther and farther away.
38:36It's a very small amount, so it's only about 3.8 centimeters,
38:39which is about an inch and a half a year.
38:42Over billions of years, the Moon will shrink to a dot in the night sky,
38:48and the Earth's spin will become so slow
38:50that the Moon will appear to freeze above our heads.
38:55There will come a time where the Earth is actually locked.
38:58One side of the Earth faces one side of the Moon,
39:01and the two of them will go around in lockstep.
39:06So there'll be one place on Earth where you can see the Moon.
39:09So you might imagine you'd have to go on some kind of vacation
39:12to actually see the Moon at that point in time.
39:15But that's going to be a long time from now.
39:17So, you know, I wouldn't start booking your tickets quite yet.
39:24Is this the long-term future of our Moon?
39:27Some scientists envision a more dramatic ending.
39:33A death by fire that will destroy the Moon and, quite possibly, all life on Earth.
39:39The process begins with the expansion of the Sun.
39:43The actual future history of the Earth-Moon system will depend upon the Sun.
39:48And it could produce remarkable effects.
39:52As the Sun gets older, it expands,
39:55filling the inner solar system with a denser solar wind.
39:59This wind will impede the Moon.
40:03So as the Moon orbits around the Earth, there'll be drag.
40:06There'll just be more stuff in space for the Moon to push against.
40:09So the Moon has been moving away from the Earth for billions of years.
40:12Maybe at that point, it'll start coming back.
40:16This new inward trajectory is a death spiral.
40:21The Moon eventually is going to spiral closer and closer.
40:25And then because of the gravitational forces, the tidal forces are going to be so strong,
40:29it's going to essentially explode.
40:33The Moon, 11,000 miles above the surface of the Earth,
40:37reaches a point of no return.
40:39The gravitational pull of the Earth finally overwhelms it.
40:47The fractured remains of the Moon create a Saturn-like ring of rocky debris.
40:54Having a ring around the Earth would be a phenomenal sight.
40:59I would love to see that.
41:02You would look up, and you would be able to see the ring.
41:05It would be at an angle to the Earth.
41:07If you were at the right place on the Earth,
41:09you'd be able to see it broad, stretching across the sky.
41:13I don't know if you'd be able to see it during the day,
41:15but at night it would be one of the most spectacular sights I can imagine.
41:21But the beauty soon turns to terror as pieces of the ring rain down on Earth.
41:29I mean, it's going to be an awesome sight, a terrifying sight.
41:33I mean, the whole sky is going to be filled with raining meteors
41:38just showering through the sky, and they're going to be huge.
41:50Eventually, all of that material will be incorporated into the Earth,
41:53and now, these two sides of the ring are going to collide.
41:57And now, these two siblings, separated at birth,
42:00now are finally again one body.
42:07More than nine billion years after the Big Bang,
42:11our sun and our planet, Earth, is born.
42:18Slowly, we're piecing together the complex connections
42:22that bind it to our lives and to the universe beyond.