Regarding the origin of the universe, the mainstream view of the scientific community is that the universe was born in a big bang 13.8 billion years ago. Death is not only a unique phenomenon of life, everything has an end, the sun will die in billions of years, and the universe will die one day.
So how will the universe end? Where will the future fate of the universe go?
Scientists now have a preliminary answer to this question, and it is generally accepted that the ultimate fate of the universe will be one of three ways.
Great collapse, great tearing, great freezing, the universe may end in one of these ways
The ultimate fate of the universe is one of the most important questions in modern physics research, according to the analysis of scientists, the future direction of the universe depends mainly on dark energy and the spatial geometry of the universe, and thus gave birth to three major hypotheses: the great tear, the great freeze and the great collapse.
Regarding the spatial geometry of the universe, scientists believe that there are three possibilities: flat, closed, and open, analogous to the plane, spherical surface, and saddle surface, respectively.
Anyone who has studied general relativity knows that matter with mass can bend space-time and affect the geometry of space-time. The study found that the largest proportion of matter in the universe is not ordinary matter composed of atoms, but dark energy and dark matter. According to the mass-energy equation, mass and energy are essentially indistinguishable, and are different forms of material existence. If calculated by the total amount of mass energy, the current known universe accounts for about 24% of dark matter, dark energy accounts for about 71%, and ordinary matter accounts for about 5%.
Exactly what particles dark matter is made of is not known, but this matter does not participate in electromagnetic interactions, that is, we cannot see it through electromagnetic waves. However, both ordinary matter and dark matter can generate gravitational pull.
As for dark energy, it is even more mysterious, this kind of matter is invisible to the naked eye, but it is evenly distributed in the universe, and it is a matter with negative gravitational properties. Gravity allows two objects to draw closer to each other, and this negative gravitational force has a repulsive property, and the universe is still accelerating and expanding 13.8 billion years after the Big Bang, which is due to the action of dark energy.
Regarding the nature of dark energy, scientists usually use the equation of state of the ratio of pressure to density. At this stage, the equation of state of dark energy under different dark energy models is different, and the equation of state in some models does not change with time, while the equation of state in some models changes with time.
1. The Great Tear Hypothesis
Scientists believe that if the density of dark energy increases with time, it will make the universe expand faster and faster, and eventually all the matter in the universe and even space-time itself will be gradually torn apart, and eventually only unbound elementary particles and radiation will be left.
The reason why the "Great Rift" is in the first place is because the universe is now expanding at an accelerated rate under the influence of dark energy. Data sent back by the probe shows that for every 3.26 million light-years increase in distance, the speed of those distant galaxies in space away from us increases by about "74 kilometers per second."
Before the discovery of dark energy in the 1990s, physicists generally believed that the expansion of the universe due to the Big Bang was slowing or even stopping. But later, through observations of a large number of supernovae, scientists finally discovered that the expansion of the universe was actually accelerating. And, relative to the rate of expansion in the past, the universe is now expanding at a rollercoaster speed. Studies have shown that this accelerated expansion process began about 5 billion years ago.
2, the Great Freeze hypothesis
The Great Freeze is also known as "heat silence", in this state, the temperature of the universe will approach absolute zero (minus 273.15 degrees Celsius), life will cease to exist, everything in the universe will stop functioning, and the entire universe will fall into darkness.
The theory holds that the universe should be an isolated, closed system, and that since entropy (the degree of disorder of the system) in the universe is constantly increasing, the universe will eventually evolve into a state of thermodynamic equilibrium. At this point, the entropy in the universe reaches its maximum. When entropy reaches its maximum, all the energies in the universe will be evenly distributed throughout space, and the temperature of the universe will approach (but not reach) absolute zero. Under such extremely low temperature conditions, the movement of all things tends to be almost static, and life naturally does not exist.
Since the nature of dark energy is unclear, the future of the universe may first undergo a great freeze and then enter a great tear, or enter one of these fates.
3, the great collapse hypothesis
As mentioned earlier, the universe is accelerating and expanding, and some scientists believe that if the density of dark energy decreases with the increase of time, gravity will become the dominant force in the future, then the universe will stop expanding and contracting, eventually causing galaxies and even everything to begin to collapse and shrink to a very small space range.
But what happens after the collapse? Scientists have speculated on one possibility, arguing that as the universe continues to collapse, or even accelerates, it is very likely that the universe will return to its original state and once again have a big bang.
If the universe really ends in this way, then perhaps it is the fulfillment of many people's ideas, that after death, people will return to nature and become nourishment for new life, and the universe will cycle between the "Big Bang" and the "Big Collapse".
However, current observational data do not support the "great collapse" hypothesis.
Other hypotheses
In addition to the three hypotheses mentioned above, the more famous one about the ultimate fate of the universe is the 'Great Devouring' hypothesis.
The theory is that the black hole in the universe will gradually swallow everything in the universe, and the large black hole will continue to swallow the small black hole, and eventually the entire universe will only be left with a large black hole, or the entire universe will become a super black hole.
However, this hypothesis I think is simply impossible. Because the black hole is not a snake, it will not run around in the cosmic space, it will only swallow the matter that falls into its event horizon, and the matter around the black hole will not fall into it as long as it is far enough away from it and moves faster around it. Moreover, black holes are not only in and out, and now the universe is accelerating and expanding, and two black holes that are far apart cannot swallow each other at all, let alone swallow everything.
summary
Having said all this, these are just hypotheses, and we do not have to worry too much about the ultimate fate of the universe, after all, human beings have only been in civilized society for less than 10,000 years, scientific development is still very limited, and the understanding of the universe is also very limited. Even the most likely major tears, scientists are not entirely sure.
For the lifespan of the universe, in 2018, an international team of researchers published a paper saying that after analyzing dark matter and dark energy, it was concluded that the universe may continue to expand, and the lifespan of the universe is at least 140 billion years.
For such a long time, if human development can be sustained, without extinction or regression, what level of scientific and technological civilization can it enter? Simply unimaginable. If there is only one universe, then no matter how human beings develop, they will eventually be unable to resist the general trend. We may not be able to reverse the fate of the universe, but if there really are other universes, perhaps future human beings can reach there through some technical means to continue the fire of human civilization.
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