What Would Remain If the Entire Universe Were Rolled into a Single Clump? From a Clump of Humanity to Black Hole Cosmology

In its introduction, the video first notes that Earth itself began as a small collection of dust, which grew over a mind-boggling span of time by sweeping up gas, rock, and asteroids in space until it became a planet harboring countless forms of life. The video's starting point is to overlay this cosmic process, in which gravity draws matter together, onto Katamari Damacy's gameplay of "rolling things up to make the clump bigger."

The first thing to roll up is people. Taking the population as of 2026 to be about 8.3 billion and assuming an average body weight of 50 kg, all of humanity weighs about 415 million tons. Since the density of the human body is roughly the same as water, the video calculates that packing everyone into a sphere with no gaps would give a diameter of about 930 meters. That is large enough to roll up not only Tokyo Tower but also the Tokyo Skytree. Whether this seems big or small will vary from person to person, the video adds.

However, even this clump cannot defy Earth's gravity. If people were stacked 930 meters high, those at the very bottom would be under about 90 atmospheres of pressure, the same as on a seabed 930 meters deep. That works out to a weight of about 93 kg on every square centimeter.

So can bones withstand this weight? According to the video, the strongest bone in the human body is the femur in the thigh, which is strong against forces pressing along its length, and there is data showing it can withstand up to about 1,000 atmospheres. Its strength drops when pressed from the side, but even so, bone tissue can reportedly withstand compression equivalent to about 400 atmospheres. Therefore, about 90 atmospheres alone would not break bones. Still, the video cautions that some bones would likely break if the force were concentrated in one spot or applied in a way that bends the bone.

The problem lies with softer tissues. Muscle, fat, and internal organs would all deform easily under this much pressure. Meanwhile, water, which makes up most of the human body, barely compresses at all when squeezed. If something incompressible is forcibly pressed down from above, the body, with nowhere else to go, has no choice but to spread sideways. As a result, the video depicts the clump of all humanity flowing out in every direction as the largest "flesh tsunami" in history. That said, flesh tsunamis apparently don't happen in the world of Katamari Damacy, so the story moves on to using this clump to roll up even more.

Next, everything on the surface gets rolled up. Gathering all the things humanity has made—buildings, roads, machines, plastics, and so on—excluding waste and counting only what is in use, comes to about 1.1 trillion tons as of 2020. Made into a sphere with the same density as concrete (2.4 g per cubic centimeter), it would be about 9.6 km in diameter.

Interestingly, all living things on Earth, including humans, are also estimated to weigh about 1.1 trillion tons in dry weight, with water removed. In other words, the total mass of artificial objects and the dry weight of living things are nearly the same. Including water, living things weigh about 2.2 trillion tons, which would make a clump about 16 km in diameter. Gathering all the water on Earth would produce a clump of about 1.35 quintillion tons, more than 1,300 km in diameter.

So what about Earth after removing artificial objects, life, and water? A clump about 12,800 km in diameter still remains. In terms of mass, the clump gathered from the surface amounts to less than 0.1% of Earth. Adding the Moon would help a little, but the difference in "play time"—4.6 billion years—is simply too great, as the video puts it. In the end, no matter how much of the surface you regather, the conclusion is that what you end up with is the familiar Earth itself.

Next, the entire solar system gets rolled up. But here, too, something similar to the Earth case happens. The Sun accounts for about 99.85% of the solar system's mass, and about 70% of the remainder is Jupiter, which corresponds to about 0.1% of the whole solar system. Earth, for its part, is only about 1/300 of Jupiter. In other words, even if the whole solar system were combined into one, its mass would be almost no different from the current Sun.

However, the video says the process of rolling things up would offer some violent spectacles. For example, when Jupiter merges with the Sun, the energy released by gravity alone would reach about 870 megatons of TNT equivalent—enough, it says, to shatter the Earth clump made earlier more than a million times over.

Moreover, whatever gets rolled up cannot keep its original form. The Sun is not a solid but a plasma, with a surface temperature of about 5,500 degrees and an interior reaching 15 million degrees. Humanity, oceans, and planets would all melt inside it—indeed, they would break apart into atomic nuclei and electrons, until it became impossible to tell what had been what.

Leaving the solar system, the next step is to gather the entire Milky Way galaxy. Here the video changes scale, shrinking the clump made from the solar system down to 5 cm in diameter. Even at this scale, the distance to Proxima Centauri, the star closest to the Sun, is about 1,400 km. The center of the Milky Way is about 8.8 million km away, and even that is less than half the width of the whole galaxy. Rolling from one end to the other would require traveling about 34 million km.

The galaxy contains countless stars, but they are separated from one another by distances like these. To roll them all up, the video explains, you have no choice but to keep rolling through space that seems to contain nothing at all.

So what would the clump look like once the Milky Way has been combined into one? Matter is pulled together by gravity, but when it is compressed, a pressure arises that resists it. If these two forces balance, the clump collapses no further, and as long as the balance holds while stars are gathered, it simply becomes an ever-heavier star.

But there is a limit to that, too. Stars with masses exceeding around 100,000 times that of the Sun are thought to be unable to support their own gravity and to become black holes directly. They collapse relatively quietly, without a supernova explosion. What is born this way is called a "direct-collapse black hole."

The mass of the Milky Way is said to be about 1.5 trillion times that of the Sun. Therefore, the video states, long before the whole galaxy has been gathered, the clump would become a black hole, no longer letting even approaching light escape.

Furthermore, galaxies contain many black holes from the start; the Milky Way alone is said to have around 100 million of them. Foremost among them is Sagittarius A* at the center of the galaxy, estimated to have a mass of about 4 million times that of the Sun. Black holes also attract one another through gravity and eventually merge. The clump grows as it rolls up these black holes as well, and in such mergers, ripples in spacetime propagate as gravitational waves, carrying away enormous amounts of energy.

Intense light is also emitted as matter is rolled up. Why would a black hole, from which not even light should be able to escape, shine? According to the video's explanation, what emits the light is the accretion disk that forms around the black hole. Matter approaching a black hole is pulled in by gravity and falls inward, but along the way it orbits at high speed and forms a disk. Within the disk, matter is heated by friction and other effects, becoming a plasma split into atomic nuclei and electrons, from which intense electromagnetic radiation is emitted.

Objects in which the surroundings of a supermassive black hole shine brilliantly in this way are called quasars. When the universe was still young, there was a great deal of gas around supermassive black holes, so they are thought to have shone actively. Quasars are said to be the brightest objects discovered in this universe.

The video emphasizes that this mechanism is an extremely efficient way of converting mass into energy. In theory, depending on conditions, it could potentially convert more than 40% of mass into energy. By comparison, nuclear fusion, the Sun's energy source, converts about 0.7%, so the difference is striking.

As a concrete estimate, the video sets the total mass of the Milky Way's stars at 50 billion times that of the Sun and the efficiency of conversion to energy at 10%. The energy released when all the stars in the galaxy are rolled up then totals 2×10^41 tons of TNT equivalent. Even if this energy were used to destroy one Earth every second, it would take more than 10 years to use it all up.

However, this brilliance does not last forever. Light also exerts pressure, and if it becomes too strong, it can push infalling matter back outward. In addition, the larger a black hole grows, the more matter from the accretion disk it consumes. Eventually, once everything has been rolled up, the clump falls silent again, and the place that once brilliantly lit up the entire galaxy is left with nothing but the stillness of complete night, the video describes.

What would happen if you tried to roll up the entire universe with the ultra-massive black hole made from the Milky Way? This time, the video shrinks the 100,000-light-year-wide Milky Way down to 5 cm. The neighboring Andromeda galaxy is then about 125 cm away. The group of several dozen galaxies including these two is the Local Group, which measures about 5 meters from end to end.

Measured relative to their own sizes, galaxies are much closer to one another than the stars within a galaxy are. You might think that if you managed to gather one galaxy, gathering the whole universe would be surprisingly easy, the video says.

But the universe is expanding. Because of cosmic expansion, the more distant an object is, the faster it recedes, and beyond a certain distance that speed exceeds the speed of light. The distance to that boundary is called the Hubble radius. Depending on the observational results, it is about 13.7 billion light-years, which corresponds to about 7 km in the world where the galaxy has been shrunk to 5 cm.

The video examines the clump formed by rolling up everything within this range as follows. A black hole has a boundary called the event horizon, from inside of which no information can travel outward. If all the matter, dark matter, and dark energy within the Hubble radius are converted into mass, and that mass is used to calculate the event horizon of a non-rotating black hole, the radius comes out to about 13.7 billion light-years—the same value as the original Hubble radius.

In other words, if you gather the matter and energy in this region of the universe and do the calculation, you get a black hole the same size as the original region. If this region could be viewed from outside, wouldn't it look like a black hole? Such a question naturally arises, the video says. The hypothesis connected to this idea is "black hole cosmology," which proposes that the universe we live in may be the interior of a black hole within an even larger universe. The video presents the idea that, while it may sound outlandish, it is mathematically possible to form a universe in which we exist inside a black hole.

On the other hand, the video states clearly that no observational evidence supporting this hypothesis has been found so far. It further explains that there is a reason the two radii match. What is involved is the curvature of the universe. General relativity explains gravity as the warping of spacetime, but the curvature referred to here is distinct from the warping of spacetime around individual celestial bodies; it describes how space is curved when the universe as a whole is viewed on a large scale. According to observations, the curvature of this universe is zero, or extremely close to zero. Taking this as a premise and using the current expansion rate of the universe determines the average density of matter and energy. Because the calculation is based on that density, the Hubble radius and the event horizon radius match, the video says. In other words, this match is framed not as evidence that the universe is the interior of a black hole, but as something that follows from the premises of the calculation.

The universe does not end at the Hubble radius; it extends even beyond the region that recedes at the speed of light due to expansion. There are various estimates of the universe's true size, and the video notes that, because its curvature is extremely close to zero, some physicists have estimated a radius of 7 trillion light-years or more.

So what would happen if everything within a radius of 7 trillion light-years were rolled up? Calculating the radius of the resulting black hole gives about 1.8 quintillion light-years, far larger than the range that was gathered. Applying this calculation at face value, the clump would exceed the size of the universe before everything had been gathered, swallowing the entire universe.

However, the video says the more mainstream view today is that the universe extends infinitely. If so, the answer is simple: no matter how far you roll, it never ends. However large the clump becomes, an infinite universe always stretches out beyond it. Moreover, the video continues, if the universe is infinite, there would also be countless universes exactly identical to the place we live, and somewhere along the way of rolling on and on, you might see the exact same scene.

In closing, the video states that even at this very moment, clumps are being formed by gravity throughout the universe. Dust gathers, rocks collide, and galaxies are drawn together—processes that continue even now, 13.8 billion years after the birth of the universe. And if the universe is infinite, there is no end to what can be rolled up. The video's conclusion is that this process of "rolling, sweeping up, and growing bigger," which began 13.8 billion years ago, is still only just beginning.