What surprises us most in the universe is how little we know about it. And just like we want to know what happens to our death, science asks the question of what happens at the end of the universe. The scientific community has produced many theories - and some are truly impressive.
Big Compression
The most compelling theory for how the universe began is the Big Bang, when all matter was first in the form of a singularity, an infinitely dense point in the abyss of nothing. Because something caused the explosion. Matter expanded at an incredible rate and ultimately shaped the universe we see today.
The Big Squeeze, as you might guess, is the opposite of the Big Bang. All matter expands outward towards the edges of the universe under the influence of our universe's gravity. According to this theory, gravity will eventually slow down and begin to contract. This contraction will bring all matter (planets, stars, galaxies, black holes - everything) back to the center from which it all began, and squeeze into a singularity. We will find ourselves in the same conditions in which the universe was before the Big Bang - all matter in the universe will be compressed into an infinitesimal point - the infinitesimal.
However, this is unlikely to happen, according to the knowledge that we now have, as the universe is expanding at an ever faster pace.
The inevitable heat death of the universe
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Think of heat death as the exact opposite of the Big Shrink. Gravity will not be able to overcome the expansion, so the universe will simply expand exponentially. The galaxies will drift apart like unhappy lovers, and the night between them will grow wider and wider.
The universe lives by the same rules as any thermodynamic system, and they all ultimately end up the same: when the heat is evenly distributed. Roughly speaking, the wind will carry heat throughout the universe, and it will become cold, dark and dull. All the stars that we know will darken one by one, and one day there will not be enough energy to ignite new ones. The whole universe will be extinguished. Matter will be, but in the form of particles, and their movement will be completely random. The universe will be in a state of equilibrium and these particles will bounce off each other without exchanging energy. We will remain “a crumpled butt, a spit, in the shade under the bench, where the angle will not allow the ray to penetrate. And we stick together in an embrace with the mud, counting the days, in humus, in sediment, in a cultural layer."
Heat death due to black holes
According to popular theory, most of the matter in the universe revolves around black holes. Just look at galaxies, which contain almost everything, and supermassive black holes at their centers. Black holes eat up stars and entire galaxies that cross the event horizon.
In a finite universe, these black holes will eventually consume most of the matter, leaving us alone with the dark universe. From time to time there will be a flash of light, almost like lightning, when the object gets close enough to the black hole to emit energy, and everything will plunge into darkness again. Ultimately, only gravity wells will remain nowhere. Massive black holes will swallow smaller ones and grow even larger. This will be the final state of the universe. Over time, black holes evaporate (lose their mass), emitting so-called Hawking radiation. So when the last black hole dies, we are left with evenly distributed subatomic particles of Hawking radiation.
End of time
If there is anything eternal, it is time. Regardless of whether the universe exists or not, time goes on as usual. Otherwise, there would be no way to distinguish one moment from the next (although there is a theory that time is just a sequence of events). But what if time just froze? What if there are no more moments? Just the same minute in time, forever.
Suppose we live in a universe when it never ends. With an infinite amount of time, anything that can happen will happen with a 100 percent chance (according to Poincaré's theory). The same paradox will happen if you live forever. You live an infinite time, so any event is guaranteed to happen (and will happen an infinite number of times). Therefore, if you live forever, the chance that you will freeze in time is 100 percent. Because this assumption has confused many calculations that have tried to predict the end of our universe, scientists have suggested something else: time itself must stop one day.
Let's say you are alive to experience this (billions of years after the end of the Earth), but you cannot understand that something went wrong. Time will just stop and everything will freeze, like a snapshot, like a cast, forever. But it won't be forever, because time simply won't move forward. It will just be one moment in time. You will never die or grow old. This is a kind of pseudo-immortality, but you will never know about it.
Big Rebound
The Big Rebound is similar to the Big Squeeze, but much more optimistic. Imagine the same scenario: gravity slows down the expansion of the universe and condenses everything into one point. According to the theory, this compression could be enough to start another explosion, and the universe will begin again. Nothing is destroyed, but redistributed.
Physicists do not like this explanation, so some scientists believe that the universe simply will not revert back to the singularity. Rather, it will get very close to this state and bounce off, just like a ball bounces off the floor. The Big Bounce is very similar to the Big Bang in this regard and could theoretically spawn a new universe. In this oscillating cycle, our universe could become the first universe in a series, or four hundred. Nobody will know about it.
The Great Divide
Regardless of how everything ends up, scientists need to use the word “big” to describe this end. According to this theory, an invisible force called "dark energy" is accelerating the expansion of the observable universe. Eventually, the expansion will accelerate as fast as the Enterprise, with a warp factor of nine, that the universe will have no choice but to burst into nothingness.
The scariest part of this theory is that while most of these scenarios happen after the stars have burned out, the Big Rip should occur, according to early estimates, in 16 billion years. At this stage, the universe, planets, and theoretically life will still exist. This cataclysm can burn her alive, tear her away from all that exists and feed the space lions that live between the universes. It is not known what will happen. But this death is clearly more brutal than the slow heat death.
Vacuum metastability event
This theory hinges on the idea that the universe exists in a fundamentally unstable state. If you look at the meanings of quantum particles, it's not hard to guess why some believe that our universe is balancing on the brink of stability. Some scientists suggest that billions of years later, the Universe will simply fall off this edge. When this happens, at some point in time, a bubble will appear in the universe. This bubble will expand in all directions at the speed of light and destroy everything it touches. Eventually, this bubble will destroy everything in the universe.
But don't worry: the universe will still be there. The laws of physics will be different, and possibly a different life. But there will be nothing in the universe that we cannot understand.
Time barrier
If we try to compute probabilities in the multiverse (which has an infinite number of universes), we will return to the problem outlined above: anything can happen with 100 percent probability. To get around this problem, scientists simply take a piece of the universe and calculate the probabilities for it. It works, but the boundaries they delineate inevitably cut an area off the rest of the world.
Since the laws of physics do not make sense in an infinite universe, the only conclusion that can be drawn is that there is a physical boundary, a boundary that cannot be exceeded. And if physicists are to be believed, in the next 3.7 billion years we will cross this time barrier and the universe will end for us. Although it is much more likely that we simply cannot understand and describe this principle with our physical terminology.
It won't be (since we live in the multiverse)
According to the scenario of a multiverse with an infinite number of universes, these universes can arise even during our existence. They could even begin to arise with the Big Bang. One universe will end up with a Big Compression, another with heat death, a third with a Big Rip, and so on. But that doesn't matter: in the multiverse, our universe is just one of many others. And even if our world crumbles like a rainbow in the void between the universes, the big "universe" will remain. And since there will be a different universe and existence and life in it, nothing threatens us.
The number of new universes will always be greater than the old ones, so in theory the number of universes is increasing.
Eternal universe
For a long time it was believed that the universe was, is and always will be. This is one of the first concepts that people created about the nature of the Universe, but recently this theory has received a new impetus, already seriously supported from the point of view of physics.
So, the countdown of time did not begin with the Big Bang singularity, time could have existed earlier (infinity before that), and the singularity and the resulting explosion could be the result of the collision of two branes (space-time structures of a higher level of being). In this model, the universe is cyclical and will continue to expand and contract forever.
By the way, we can figure it out in the next 20 years - we have the Planck satellite, which has been exploring space in search of patterns of the microwave background that will tell us something about the origin of the universe. This is a long process, but it will provide us with knowledge of how our Universe began, and possibly tell us how it will end.
Ilya Khel