In October last year, a theoretical physics group gathered in Madrid to discuss two topics in the esoteric world of string theory: "alien landscape phenomena" and the "anthropic principle." The former means that the string theory equations can lead to the existence of a large number of possible universes. The latter attempts to explain why various properties of our universe, including various fundamental natural constants, exist as they do now. The problem that experts cannot avoid here is the parallel universe (multiverse).

According to a report in the January issue of the Spanish monthly "Fun", the two most authoritative experts in the field, physicists Andre Linde and Alan Guth, believe that even if there are other universes, they are In space so far away from us that we will never come into contact with it; their colleagues Paul J. Steinhardt and Neil Turok chose to insist that parallel universes exist at different points in time; and Max Tege Mark and the late scientist Dennis Summer believe that other universes are completely far away from our own space and time.

Cosmic bubbles that expand thousands of times in nanoseconds

On the other hand, some cosmologists believe that the actual situation is that some areas of the universe have lost contact with us due to some accidental factors . Since the universe was born in the Big Bang more than 14 billion years ago, and light travels at a finite and knowable speed, the radius of the visible universe is about 43 billion light-years. And those that are farther away are universes in the same space as us.

In order to delve deeper into the world of theoretical speculation about the existence of parallel universes, we can start from the concept of "inflation" proposed by cosmologist Alan Guth in December 1979. He believed that the universe went through a short-term phase of accelerated expansion in about 10 minus 32 seconds. He also used this theory to explain the problem of uniformity of the universe that troubled cosmologists: this stage of inflation basically smoothed out all irregularities. Starting from this point of view, other theoretical physicists, including the Russian Andrei Linde, developed other possibilities. For example, why can there be only one phase of inflation affecting all universes? This gave rise to the so-called "eternal inflation" theory.

Using football to explain the theory of eternal inflation

In order to better explain this theory, Lind proposed the following analogy: imagine the real universe as a football, with patches of paint on the surface Colored regular pentagons and regular hexagons. The inflationary phase affects the entire sphere, but in different areas, that is, in different polygons. Each of these regions exhibits power growth and is not causally related to any other region. Therefore, people who live in a brown regular pentagon will think that the universe is brown, and people who live in a yellow regular hexagon will also think that the universe is yellow. By analogy to cosmology, each polygon (universe) exists in a football (multiverse), the color of which is determined by the laws of physics that govern it: in some universes these laws are very simple and no stars are formed and the Milky Way, and in others there are not even conditions for the emergence of life, while many other universes, including ours, have strong proliferation capabilities. All this depends on the laws.

In any case, the multiverse theory brought about by eternal inflation has attracted the attention of a large number of physicists, who believe that everything, from particles to natural forces, can be explained by string theory. The basic point of this theory is that the basic unit of everything in the universe is the same, which is a very small linear "string". Just like the strings on a violin can play an astonishing number of melodies, each subatomic particle has a corresponding pattern of vibrating the string. This can demonstrate the two major physics theories of the 20th century: quantum theory and Einstein's general theory of relativity.

If you combine inflation theory with string theory, you can get very interesting results. On the one hand, inflation makes space extend infinitely in the empty space. Quantum effects lead to the creation of new universes, just as a child blowing into a circle creates bubbles.

At the same time, string theory determined that the appearance of these bubbles was not related to each other, but that each bubble contained different types of particles, natural forces, and physical laws. In other words, the alien landscape phenomenon of string theory means that there are as many possible answers (i.e. universes) as 10 to the 500th power in its equations; inflation makes all these possible universes a reality, existing in an unimaginable world. In the infinite multiverse space.

So, why are all the physical constants we know now the way we see them, and not the other way around?

Is the universe we live in the only universe that exists and is reasonable?

If the basic charge and the speed of light were not quantitative as we know now, then life in the universe might not exist. This is a question that experts often think about. The existence of multiple universes can explain this problem: each universe has its own physical properties, and the universe we live in also has various necessary quantifications that match life. However, aren’t we really killing a chicken with a knife? Is it really necessary to introduce the perspective of multiverses to explain some of the small natural phenomena around us?

In 1766, the German astronomer Johann Titius proposed a rule about the distance of the planets in the solar system. The asteroids and Uranus discovered since then also comply with this rule, and in some satellite systems , a similar relationship also exists for regular satellites. Scientists cannot give a theoretical explanation for this, unless they bring out the multiverse perspective: among so many universes as 10 to the 500th power, the one we live in happens to follow this law. But for multiverse skeptics, the theory that explains everything actually explains nothing.

Is there a way to prove that these parallel worlds exist beyond the blackboard of physicists? Some people think that we should search for clues in the cosmic microwave background radiation, which may even contain information left by other universes that existed before ours; others are trying to determine the topology of the universe. In any case, it seems that the multiverse is still just a concept rather than a definite theory.

Countless versions of myself at different points in time

Almost all opinions in the field are little more than a splicing of ideas. So while the inflationary mechanism does exist, it cannot be determined by itself that different physical constants exist in other universes, unless combined with string theory, which is more doubtful.

If parallel universes were linked to deeper and proven theories like quantum mechanics, we might be able to become more convinced that other universes exist in this dimension. It’s even possible to believe that many of these universes are just like our own, with countless different versions of us living in them. These are exactly what the famous physicist Hugh Everett explained in the "many worlds theory" founded in 1957. He also created the "parallel world" quantum theory.

Obviously, no one can be sure of the existence of universe proliferation, and there can be no connection between universes. The idea that there are countless versions of yourself and your sense of self may be somewhat contradictory. The late physicist Bryce DeWitt put it this way: "Quantum jumps on every planet, in every far corner of the universe, fragment our world into countless versions of itself. This is a willing Schizophrenia! ”