From the Voids to the Birth of the Universe: 13 Journeys to the Extremes of Space and Time

The universe has a hierarchical structure. Earth belongs to the solar system, the solar system to the Milky Way, the Milky Way to the Virgo Cluster, and the Virgo Cluster to the Laniakea Supercluster. Superclusters in turn gather into thread- and wall-like shapes to form galaxy filaments. Between these filaments are thought to lie "voids," where galaxies are extremely scarce. The narrator compared this to galaxies gathering in the films of soap bubbles floating on water.

The following figures were given for scale. The Milky Way is about 100,000 light-years across, the Laniakea Supercluster about 500 million light-years, and the galaxy filament that contains it about 1.6 billion light-years long. Many voids are roughly spherical, mostly around 30 million to 300 million light-years in diameter, though some approaching 1 billion light-years have been found.

The emptiness of voids was explained in terms of the density of matter. Even an "empty glass" on Earth contains about 2.5×10²⁵ air molecules per cubic meter. Between the stars within a galaxy there are roughly 100,000 to 1 million atoms per cubic meter, and outside galaxies the figure is estimated at one or fewer. Within galaxy filaments, the average distance between galaxies is said to be about 1 million light-years, whereas the interior of a void is far sparser. For example, in the Boötes Void, 250 million light-years across, only 60 galaxies have been found. Around the Milky Way, there are more than 20 galaxies within a region 3 million light-years across; applying that density to the size of the Boötes Void, one would expect about 10,000. A 2014 study estimated that voids occupy 77% of the universe's volume but account for only about 15% of its mass.

So what would the sky look like from the center of a void? The narrator's answer was "very likely pitch black." Most of the stars visible to the naked eye are relatively nearby stars within the Milky Way, and even the combined light of an entire galaxy can only be seen with the naked eye up to a limited distance. The Andromeda Galaxy (about 2.5 million light-years away) can be seen with the naked eye under good conditions, but the next nearest, the Triangulum Galaxy (about 3 million light-years away), is close to the limit of naked-eye visibility. From this, the narrator estimates that galaxies visible to the naked eye lie within a few million light-years at most. From the center of a void more than 30 million light-years across, there may not be a single point of light visible; with luck, one might faintly see a few nearby galaxies.

The narrator added that the boundaries of voids are not clear-cut. A void is defined as "a region where the density of galaxies is lower than its surroundings," but since there are galaxies inside them, each announcement of a newly discovered void often sparks debate over whether it should really be called a void. There is also research claiming that the Milky Way itself sits near the center of a giant void 2 billion light-years across. It was named the "KBC Void" after the initials of the three researchers who proposed it. There are opposing views, but the narrator remarked that voids may be closer to home than one might think.

The second journey heads beyond the solar system. The energy needed to break free of the Sun's gravity is expressed as a speed, called the escape velocity. Escaping Earth from its surface requires 11.2 km per second, and escaping the solar system from Earth's orbit requires 42.1 km per second. Taking into account factors such as Earth's orbital speed, the energy required from the surface is equivalent to 16.7 km per second. Real spacecraft use "swing-bys" (gravity assists), which exploit the gravity of celestial bodies to accelerate without using fuel. Voyager 1 and 2 used the gravity of Jupiter and Saturn to gain the energy to escape the solar system. As of 2021, Voyager 1 was about 23 billion km (about 150 astronomical units) from the Sun and Voyager 2 about 19 billion km (about 130 astronomical units), and they are expected to keep traveling even after humanity is gone.

The journey begins at Neptune's orbit (about 30 astronomical units). Here the Sun is dim enough to look at directly without glare, yet it is still more than 4,000 times brighter than the full Moon as seen from Earth. The surface temperature is below minus 200 degrees. Beyond it lies the Kuiper Belt, where more than 1 trillion objects are distributed in a disk, and comets with orbital periods of 200 years or less are thought to come from here.

Pluto's distance from the Sun varies greatly, from 30 astronomical units at its closest to 49 at its farthest, and its orbit is steeply inclined. The narrator explained that this is typical of Kuiper Belt objects. Makemake, 1,400 km in diameter, orbits between 38 and 53 astronomical units, while Eris, about 2,400 km in diameter—nearly the same as Pluto—orbits between 38 and 98 astronomical units. If Pluto were defined as a planet, many other objects would have to be called planets too, which is said to be one of the reasons Pluto was removed from the list of planets. On the other hand, despite the many objects, there is little danger of collision. Even New Horizons, which observed Pluto in 2015, found no object it could approach by adjusting its course after the flyby.

At about 50 astronomical units, the number of objects drops off sharply. This is called the "Kuiper Cliff." Its cause is unknown, but some scientists think it is due to an undiscovered planet. At about 120 astronomical units, one reaches the heliopause, where the solar wind collides and mixes with interstellar matter and the galactic magnetic field. Beyond this point, the protection from cosmic rays provided by the solar wind disappears.

However, the Sun's gravity still reaches this far. From around 2,000 astronomical units to around 100,000 astronomical units, there is thought to be the "Oort Cloud," a shell of objects surrounding the Sun. It has never been directly observed, but the existence of comets with extremely long periods of hundreds of thousands of years makes it considered a certainty. Past it, at about 100,000 astronomical units—roughly 1.6 light-years—the Sun's gravitational influence becomes diluted as it mixes with other gravitational forces in the galaxy, and the Sun appears only slightly brighter than Sirius. The narrator made this the end point of the escape from the solar system.

Light travels about 30 cm in a billionth of a second. As a result, everything we see is how it looked in the past. We see the Sun as it was 8 minutes ago, Alpha Centauri as it was 4 years ago, and the Andromeda Galaxy as it was 2.5 million years ago. We can now observe light that has taken about 13.8 billion years to reach us, and this is "the edge of the universe observable from Earth."

However, the present distance to that place is not 13.8 billion light-years but about 46.5 billion light-years. This is because the universe itself is expanding, and while the light was traveling, the place that emitted it kept receding. The detailed cause of the expansion is still unknown. This 13.8-billion-year-old light is called the cosmic microwave background radiation and is thought to have been emitted about 370,000 years after the Big Bang. Before that, temperatures were so high that light was blocked by protons and electrons and could barely travel.

So what would you see if you went 46.5 billion light-years away? The narrator's answer was "not much different." There would be galaxies similar to the Milky Way, and looking farther out, the view would be indistinguishable from that seen from Earth. The edge of the observable universe is simply the place from which light that left 13.8 billion years ago is just now reaching Earth; from the perspective of the universe as a whole, it is an utterly unremarkable place.

Then could you reach an edge by continuing in one direction? According to the current prevailing view, the universe has no edge. The key is curvature, which describes how much space is curved. If the curvature is 0, space is like a flat sheet of paper; if it is less than 0, it is shaped like a saddle; both extend infinitely. If it is greater than 0, space is finite like the surface of a sphere, but if you keep going you return to where you started. In none of these cases is there an edge.

Actual observations put the curvature at nearly 0. The sizes of the hotter and colder regions seen in the cosmic microwave background can be theoretically calculated from the state of the universe 370,000 years after the Big Bang. If space were curved, light would bend too, and the apparent sizes would deviate from the theoretical values. Yet the observations matched the theoretical values almost exactly. The narrator stated that why the curvature is nearly 0 has not been explained.

The journey into the future begins at 100 million years from now. The premise is that while it is hard to predict what society will be like 10 years from now, many things about events on Earth and in space can be known with certainty.

In 1,000 years, the Moon's gravity will have slowed Earth's rotation, making the day slightly longer. Even adding a leap second every month will not keep up, making it difficult to synchronize time around the world. Reportedly, even experts have no good solution. In 15,000 years, the precession of Earth's rotational axis will reverse the Sun's distance in summer and winter compared with today. Seasonal differences in the Northern Hemisphere will become more extreme, and it is estimated that the Sahara Desert will become a green savanna, as it was about 10,000 years ago. In 20,000 years, radiation across the entire area contaminated by the 1986 Chernobyl nuclear accident is estimated to fall to harmless levels. On the other hand, a 2017 study was also introduced suggesting that supereruptions capable of collapsing civilization have occurred on a cycle of 5,200 to 48,000 years. An ice age is predicted to arrive in 50,000 years, but one estimate suggests it will be delayed by another 50,000 years due to carbon dioxide emissions. In about 64,000 years, Sirius will become the south pole star.

Dangerous astronomical phenomena were also covered. Betelgeuse and Antares are considered certain to explode as supernovae in 10,000 to 1 million years. For several months they would be as bright as the full Moon and might be visible even during the day. Effects on life are said to occur within about 30 light-years, and both stars are several hundred light-years away. However, the gamma-ray bursts that occur in some supernovae can destroy the ozone layer even from thousands of light-years away. It has been suggested that WR 104, 8,400 light-years away, could explode within 1 million years and that its gamma-ray burst could hit Earth directly. The narrator cautioned that the mechanism behind such bursts is not well understood and that the probability of being hit is low. It is also estimated that in about 1.29 million years, the star Gliese 710 will approach within 0.17 light-years of the solar system. It could disturb the orbits of tens of millions to 100 million comets in the Oort Cloud, some of which might plunge inward and collide with Earth.

As for continental movement, in 10 million years the Red Sea is expected to flood and split the African continent in two. Beyond that, prediction becomes difficult and there are many models. Even the well-known claim that "Japan and Hawaii will collide in 50 million years" is hard to state definitively because plate motion could reverse. In one model, Europe and Africa collide in 50 million years, the Mediterranean disappears, and a Himalaya-like mountain range stretches all the way to the Persian Gulf. In the same model, the Antarctic and Greenland ice sheets melt, raising sea levels by about 90 m; the present-day Hawaiian Islands sink beneath the sea in 80 million years; and in 250 million years the continents gather toward the supercontinent Pangaea Ultima.

The Sun's luminosity increases by about 1% every 110 million years, because helium accumulating in the core expands the region where nuclear fusion occurs. In 200 million years, tidal friction with the Moon will make the day 25 hours long. In 300 million years, Saturn's rings are expected to disappear completely, based on data from the Saturn probe Cassini's final mission, the "Grand Finale" (which found that ring material is being lost at 400 to 2,800 kg per second).

Supercontinents have formed and broken apart on a cycle of 500 to 700 million years. Even so, there is a reason it is called the "last Pangaea." The heat source driving the mantle convection that moves the continents is Earth's cooling core, and plate tectonics will eventually stop. The prevailing prediction is that this will happen after 1 billion years, but at the earliest it could be 500 to 800 million years from now. After Pangaea Ultima breaks up, a supercontinent may never form again.

The Moon is receding from Earth by about 4 cm per year. As a result, Earth's last total solar eclipse will occur in 600 million years, after which only annular eclipses will be visible. However, the narrator points out that by then there will be far more serious problems. Because of the carbon-silicate cycle, in which rocks absorb atmospheric carbon dioxide more readily at higher temperatures, carbon dioxide levels will drop drastically in about 600 million years, when the Sun's luminosity has increased by more than 5%. C3 photosynthesis, used by most plants, cannot function below about 150 ppm, leading to a mass extinction of plants including rice, wheat, potatoes and soybeans. C4 and CAM plants will also be unable to survive once levels fall below 10 ppm in 800 million years, and multicellular life will disappear. In 1.1 billion years, luminosity will have increased by 10% and the average temperature will reach 47 degrees. Water vapor reaching the stratosphere will be broken down by ultraviolet light, hydrogen will escape into space, and most of the oceans will be lost.

What remains in 1.1 billion years is thought to be microbes feeding on hydrogen sulfide and methane in small polar seas, and microbes underground. According to one prediction, in 2.8 billion years surface temperatures even at the poles will approach 200 degrees, and no living thing will survive. In 3 billion years, they will exceed 900 degrees.

Even so, traces of humanity will remain in the form of spacecraft. Voyager 1 and 2, launched in 1977, were traveling at about 17 km and about 15 km per second relative to the Sun as of 2024, and carry records documenting the life and culture of Earth. The spacecraft will gradually be worn away by collisions with cosmic dust, but the records themselves are expected to easily last 5 billion years. By then, Voyager 1 is calculated to be about 280,000 light-years from the Sun.

The Andromeda Galaxy is approaching at about 110 km per second. According to one study, the two galaxies will collide and pass through each other in 4 billion years, and in 6 billion years their supermassive black holes will merge to form the "Milkomeda" galaxy. Collisions between stars will be almost nonexistent, but it has been suggested that during the collision in 4 billion years, the Sun could be temporarily captured by Andromeda.

In 5.4 to 6 billion years, the Sun will exhaust the hydrogen in its core and begin to become a red giant. As it approaches Earth's orbit, helium fusion will begin, triggering a "helium flash" that releases in one burst about 200 million years' worth of the present Sun's energy. As a result, the Sun will shrink considerably over a short period of about 10,000 years and remain in that state for about 100 million years. According to one study, during this period the moons of Jupiter and Saturn will come close to the habitable zone and could potentially be inhabited by humans. Afterward, the Sun will expand again beyond Earth's orbit, and possibly beyond Mars's orbit, shedding its outer layers and losing about half its mass. In 8 billion years, it will become a white dwarf about the size of Earth.

Further ahead, hydrogen, the fuel of stars, will run out across the universe. One prediction holds that the energy emitted by the Milkomeda galaxy will begin to decline in 800 billion years. Eventually, the cosmic microwave background will become undetectable, and a little later, galaxies other than one's own are expected to become unobservable as well. Civilizations born then will have no way of knowing about the existence of other galaxies or the evidence for the Big Bang. From this, the narrator remarked that the present, 13.8 billion years after the birth of the universe, may be just the right era for unraveling the origins of the universe.

The episode on time introduced the modern physics view that the passage of time differs depending on the observer. Humans have long defined time by the movements of the Sun and stars, and with the spread of mechanical clocks came to think of time as absolutely constant. Overturning this view was the special theory of relativity, published by Einstein in 1905. A few years later, the concept of Minkowski space was proposed, unifying time into "spacetime" as a dimension on par with the spatial dimensions of forward-backward, left-right and up-down.

In special relativity, the faster you move, the slower time passes. The narrator explained this with the example of a train. When "Mr. VAIENCE" drops an apple inside the train, to him it appears to fall straight down. To you, watching from outside, the apple appears to travel a longer distance, by as much as the train has moved. In classical physics, this can be explained as a difference in the apple's speed. But if what is dropped is replaced with light, the principle of the constancy of the speed of light requires its speed to be the same for both. If the speed is the same but the distance differs, the only conclusion is that time passes differently. Time passes more slowly for the moving Mr. VAIENCE.

In general relativity, time passes more slowly where gravity is stronger. Using the equivalence principle—that free fall and weightlessness cannot be distinguished—the narrator explained, from the standpoint that "you standing on the floor are continuously accelerating upward in curved spacetime," why time slows closer to the ground. In daily life this is a negligible difference, but the clocks on GPS satellites (at an altitude of about 20,000 km) run about 38 microseconds per day faster as seen from the ground, so GPS would not function without correcting for this.

Finally, going beyond relativity, an extended theory claiming that time runs backward when exceeding the speed of light was introduced. According to one calculation, making a round trip at 30 times the speed of light to a planet 10 light-years away that is receding at 0.1 times the speed of light would return you to Earth about four months in the past. From there, the narrator touched on the grandfather paradox (here, the paradox of killing one's parent) and closed by asking, "What do you think time is?"

The Second Muroto Typhoon of 1961 recorded a maximum wind speed of 75 m per second. By contrast, Jupiter's Great Red Spot is larger than Earth in diameter, has maximum wind speeds exceeding 180 m per second, and has been blowing for at least 150 years. A spot on Jupiter was recorded in 1664 or 1665, but it is unknown whether it is the same as the present Great Red Spot. In 1831, a phenomenon thought to be the present Great Red Spot was observed. One reason for its longevity is that Jupiter has no ground, so the storm loses little energy to surface irregularities. However, some scientists think this alone would only allow it to last a few decades, and the reason it persists has not been explained.

The long axis of the Great Red Spot has shrunk from about 56,000 km at the end of the 19th century to about half that by 1979, and to about 16,000 km by 2017. This has led to more reports that its disappearance is imminent. However, the narrator says it may be more natural to see it as an ellipse becoming more circular. Given also that wind speeds at its edge increased by an average of 8% between 2009 and 2020, the narrator's position is that no one knows whether it is truly weakening.

During the descent, you first pass through the thermosphere. At an altitude of 1,000 km, the temperature exceeds 600 degrees and the pressure is around one hundred-millionth of an atmosphere—extremely thin. The air above the Great Red Spot is several hundred degrees hotter still and is said to be the hottest part of Jupiter's atmosphere. The cause is thought to be atmospheric vibrations transmitted from the Great Red Spot. There are various theories about what causes its reddish-brown color, with the leading one being that it is ammonium hydrosulfide altered by radiation. In the outer 2,000 km, wind speeds constantly exceed 100 m per second and sometimes exceed 180 m per second. The Great Red Spot is an anticyclone, and it was reported that between 2018 and 2020 it collided with smaller surrounding anticyclones, increasing its wind speeds. Wind speeds at the center are relatively calm at about 20 to 30 m per second, but on Earth that would be too strong for a person to stand. Once you pass through the clouds of ammonia, ammonium hydrosulfide and water, almost no visible light reaches you. The Great Red Spot extends to a depth of about 500 km, and its deepest part is thought to be about 230 degrees.

The journey into the past begins 100 million years ago, in the Cretaceous period (about 145 million to 66 million years ago). If Earth's history were compressed into one year, 100 million years ago would correspond to December 23. Oxygen levels were about the same as today's roughly 21% or slightly higher, and carbon dioxide is estimated at several hundred to 1,000 ppm, so breathing would pose no major problem. The breakup of Pangaea was progressing: South America and Africa were beginning to separate, India was an island, and Australia and Antarctica were connected. Antarctica was not locked in ice, and there is a theory that sea levels were as much as 200 m higher than today. A shallow sea was forming in the middle of the North American continent. Some extreme predictions put the average temperature at around 30 degrees, and volcanic activity was also intense.

Tyrannosaurus and Triceratops had not yet appeared, and Stegosaurus had already gone extinct. Instead, there were Spinosaurus, 14 m long with a 1.5 m sail on its back; Giganotosaurus, possibly larger than Tyrannosaurus; Carcharodontosaurus, with shark-like teeth; and Argentinosaurus, 30 to 35 m long. Also introduced were the pterosaur Pterodaustro, with a curved beak lined with around a thousand fine teeth; Stomatosuchus, a 10 m crocodilian whose lower jaw swelled like a pelican's; bivalves 1 m in diameter; sharks with wing-like fins; Nigersaurus, with a mouth like a nail clipper; snakes with remnants of hind legs; and bipedal crocodiles.

Among plants, angiosperms, which appeared about 130 million years ago, were beginning to spread with pollination by bees and butterflies. Today they make up about 90% of plants, but at the time gymnosperms were still dominant, and since there were no grasses there were no grasslands; the ground is thought to have been covered with mosses and ferns. About 60% of the world's oil is said to have formed during the Cretaceous, and the name "Cretaceous" (hakua in Japanese) refers to chalk.

Going further back: the mass extinction about 201 million years ago is attributed to massive volcanic activity near the present-day boundary between the Americas and Africa, accompanying the breakup of Pangaea. One estimate puts the total volume of lava at more than 3 million cubic km. Compared with the Aso eruption about 90,000 years ago (1,000 to 2,000 cubic km), which is said to have devastated Kyushu, the scale becomes clear. The released carbon dioxide more than doubled concentrations from about 1,000 ppm to 2,000–2,500 ppm, and climate change and ocean acidification wiped out about 80% of all life. About 252 million years ago, a massive eruption in Siberia drove more than 80% of life to extinction, and trilobites, which had lived in the seas for about 270 million years, disappeared.

About 300 million years ago was an era when oxygen levels are said to have reached as high as 35%. Almost no organisms could break down lignin, the substance that forms trees, so fallen trees remained without rotting, reducing carbon dioxide and allowing oxygen to accumulate. Insects, which breathe through spiracles, are thought to have a maximum size determined by oxygen levels, and creatures such as Meganeura, with a 71 cm wingspan, and Arthropleura, a millipede relative that may have exceeded 2 m in length, appeared. About 390 million years ago, oxygen reached the deep sea and bony fish flourished, with relatives of the coelacanth living in the shallows. About 460 to 480 million years ago, algae and fungi moved onto land. The ozone layer began to stabilize about 600 million years ago.

In the Cambrian explosion about 540 million years ago, strange animals appeared, such as Anomalocaris; Hallucigenia, whose reconstructions once got both its front and back and its top and bottom wrong; and Opabinia, with five eyes and a claw-like mouth at the tip of a trunk on its head. About 700 million years ago came Snowball Earth, when ice covered the planet all the way to the equator. The leading theory is that newly formed rock from volcanic activity absorbed carbon dioxide, and that the lack of plants and exposed bare rock accelerated this. Food became precious, and the cold increased the viscosity of the seas, making it harder for nutrients to reach organisms, which may have favored organisms made of many cells gathered together that could swim toward prey. The narrator introduced a recent theory that the multicellular organisms born at this time may be humanity's ancestors. And 1 billion years ago falls in the middle of the "Boring Billion," from 1.8 billion to 800 million years ago. Though there was little visible change, it is said to have been an era when eukaryotes, the same type of organism as humans, were diversifying.

Opening with the photo of a dot-like Earth taken by Voyager 1 from about 6 billion km away in 1990, the video recounted the birth of the solar system. About 4.6 billion years ago, at a location about 27,000 light-years from the center of the Milky Way, a supernova exploded at a distance estimated to be possibly within 1 light-year, and its shock wave caused gas and dust to begin gathering. In less than 1 million years a protostar was born, and from the surrounding protoplanetary disk, rocky protoplanets formed close in while gas and ice protoplanets formed farther out. About 10 million years later, Jupiter and Saturn formed, and the Sun became a main-sequence star, blowing away the lighter gases with its strong solar wind.

In the Grand Tack model, the leading hypothesis, Jupiter moved closer to the Sun as it grew. According to one study, it began migrating 70,000 years after its formation and by 100,000 years had reached roughly the present distance of Mars. During that time, many protoplanets fell into the Sun or were ejected. Eventually Saturn approached, an orbital resonance occurred, and the two planets moved back outward. At 500,000 years, Jupiter settled at about 5.2 astronomical units, nearly its present position, and by 600,000 years Saturn, Uranus and Neptune were also in nearly their present orbits. There is no direct evidence, but because it can explain the absence of super-Earths and hot Jupiters in the solar system and the unnaturally small size of Mars, it is considered broadly correct. Jupiter's migration also had the effect of delivering water-carrying asteroids and comets from the outer solar system to Earth.

As for the Moon, the giant impact hypothesis—that about 4.5 billion years ago the Mars-sized Theia struck the proto-Earth in a glancing blow, and the scattered material formed the Moon within a few hours—was presented as the most likely. Oceans may have formed within about 10 million years after the Moon formed. There is also a theory that under a 100-atmosphere atmosphere composed mainly of carbon dioxide, liquid oceans existed even at 230 degrees. By 4.3 billion years ago, the environment was such that life could plausibly have arisen, and genetic analysis suggests that the last universal common ancestor of all life lived 4.1 to 4.3 billion years ago.

Earth 3.5 billion years ago had almost no oxygen. Carbon dioxide was 10 to 50 times present levels and methane tens to hundreds of times, and the sky may have been covered in an orange haze like that of Saturn's moon Titan. The Sun was about 75% as bright as today, and colonies of bacteria resembling cyanobacteria are thought to have lived in shallow hot springs. The layered rocks formed by these bacteria survive as stromatolites. Because multiple species of bacteria already existed, life is thought to have originated even earlier.

About 5 billion years ago, the expansion of the universe, which had been decelerating, switched to accelerating. This is said to be because expansion lowered the density of matter, allowing dark energy—thought to be a property of space itself—to become dominant. About 8 billion years ago, successive generations of stars and supernova explosions had increased the amount of heavy elements, creating the conditions for many rocky planets to form. Applying the criteria of being a moderate distance from the galactic center and in a place where supernovae do not occur frequently, it is estimated that about 75% of star systems meeting those conditions are older than the solar system.

And 10 billion years ago was "cosmic noon," when star formation across the entire universe peaked. Dark matter (more than 80% of the matter in the universe), which is not affected by electromagnetism, formed the skeleton of large-scale structure from early on, and gas poured into galaxies in large quantities along the filaments. As a result, stars formed at about 10 times the current rate, and one theory holds that nearly half the stellar mass of galaxies was created during this period. About 30% of the mass growth of large galaxies came from mergers with galaxies of similar size, and the Milky Way also collided with Gaia-Enceladus around this time. Black holes grew dramatically as well, and many quasars were shining. If 3C 273, the first quasar to be observed, were at the center of the Milky Way, it would appear about as bright as the full Moon from Earth, 26,000 light-years away. By 11.2 billion years ago, Kepler-444, with five rocky planets, already existed, and water and organic compounds were abundant more than 12 billion years ago. The narrator stated that the possibility that a civilization gazed upon this scene at the time is not zero.

The final installment is about the origin of the universe. Even Einstein wrote a paper in 1917 premised on a static, eternal universe, but in 1929 Hubble demonstrated through observation that the universe is expanding. The Big Bang theory holds that going back in time, the universe becomes extremely hot and extremely dense, and observations put the age of the universe at about 13.8 billion years.

However, the moment of birth itself is completely unknown to modern science. The narrator gave as an example the mistake of extrapolating backward from the height changes of a growing child to conclude that "people are born from nothing." It is unknown whether general relativity and the Standard Model of particle physics apply unchanged to the past. Therefore, everything before about 10⁻⁴³ seconds after the beginning of the universe is unknown, and many scientists think new laws are needed.

The subsequent history was described in the following stages. The grand unification epoch, when the three forces other than gravity were one. The inflationary epoch, when the universe expanded in an instant by a factor of at least 10²⁶—by one account 10⁴⁰—and the portion corresponding to the observable universe became about 10 cm across. The electroweak epoch, when electromagnetism and the weak force were unified. The quark epoch, when the four forces became independent and quarks and electrons were born. At this stage, matter and antimatter should have been created in equal amounts, but for some reason matter outnumbered antimatter by about 1 in 2 billion, and that difference is said to have created the present universe. Next came the hadron epoch, in which protons and neutrons were in place by about 1 second, and the lepton epoch, which ended at about 3 minutes. When the temperature fell to about 1 billion degrees, hydrogen and helium nuclei formed, and about 20 minutes in, when it dropped below 10 million degrees, nuclear fusion stopped. This is said to be why elements other than hydrogen and helium are scarce today.

About 380,000 years later, when the temperature reached about 3,000 degrees, nuclei and electrons combined and light could travel in straight lines—the "recombination" or "clearing" of the universe. The extreme uniformity of the temperature of the cosmic background radiation emitted at this time in every direction is considered one of the strongest pieces of evidence that inflation occurred. There followed the Dark Ages, when nothing emitted visible light. Between 10 million and 17 million years after the birth of the universe, its temperature was 0 to 100 degrees, and the narrator also touched on the panspermia hypothesis that traces of life born around this time reached Earth. Between 100 million and 500 million years after the birth, the first stars and galaxies were born along the web of dark matter. The first stars were hundreds of times the size of the Sun and became supernovae within a few million years. The Sun is thought to be a later third-generation star, born about 9 billion years after the birth of the universe. From around that time, the expansion of the universe accelerated, and humanity devised dark energy to explain it, but its nature remains a mystery.

As for the future of the universe, the leading scenario is the "Big Freeze," in which accelerating expansion isolates galaxies, stars burn out, the universe heads toward heat death in 1 trillion to 100 trillion years, and by 10¹⁰⁰ years from now only dark matter and small amounts of electrons and the like are left flying about. On the other hand, there are also the possibilities of the "Big Rip," in which expansion becomes so fast that everything is torn apart, and the "Big Crunch," in which the universe turns to contraction and returns to an extremely hot, extremely dense state. Which one occurs depends on dark matter and dark energy, which humanity does not yet understand, and on the laws surrounding them, the narrator said. The video concludes that the quest to answer how we and this world came to be, and where we are headed, continues.