How often do you think about how our world would be arranged today if the result of some key historical events were different? What would our planet be like if dinosaurs, for example, were not extinct? Our every action and decision automatically becomes a part of the past. In fact, there is no real: everything that we do at a given moment cannot be changed, it is recorded in the memory of the Universe. However, there is a theory according to which there are many universes where we live a completely different life: each of our actions is associated with a certain choice and, making this choice in our Universe, in a parallel one, the “other self” makes the opposite decision. How scientifically justified is such a theory? Why did scientists resort to it? Let's try to figure it out in our article.
The multi-world concept of the universe
For the first time, the theory of a probable set of worlds was mentioned by the American physicist Hugh Everett. He offered his answer to one of the main quantum mysteries of physics. Before proceeding directly to the theory of Hugh Everett, it is necessary to understand what this secret of quantum particles is, which has haunted physicists all over the world for more than a dozen years.
Let's imagine an ordinary electron. It turns out that as a quantum object, it can be in two places at the same time. This property is called the superposition of two states. But the magic doesn't end there. As soon as we want to somehow concretize the location of the electron, for example, try to knock it down with another electron, then from quantum it will become ordinary. How is this possible: the electron was at both point A and point B and suddenly jumped to B at a certain moment?
Hugh Everett offered his own interpretation of this quantum conundrum. According to his many-worlds theory, the electron continues to exist in two states simultaneously. It's all about the observer himself: now he turns into a quantum object and is divided into two states. In one of them he sees an electron at point A, in the other - at B. There are two parallel realities, and in which of them the observer will be is unknown. The division into reality is not limited to the number two: their branching depends only on the variation of events. However, all these realities exist independently of each other. We, as observers, find ourselves in one, from which it is impossible to leave, as well as to move to a parallel one.
From the point of view of this concept, the experiment with the most scientific cat in the history of physics, Schrödinger's cat, is easily explained. According to the many-worlds interpretation of quantum mechanics, the unfortunate cat in the steel chamber is both alive and dead. When we open this chamber, we seem to merge with the cat and form two states - living and dead, which do not intersect. Two different universes are formed: in one an observer with a dead cat, in the other - with a living one.
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It should be noted right away that the many-worlds concept does not imply the presence of many universes: it is one, simply multi-layered, and each object in it can be in different states. This concept cannot be considered an experimentally validated theory. So far, this is just a mathematical description of a quantum puzzle.
Hugh Everett's theory is supported by physicist Howard Wiseman, professor at Griffith University in Australia, Dr. Michael Hall from the Center for Quantum Dynamics at Griffith University, and Dr. Dirk-André Deckert from the University of California. In their opinion, parallel worlds really exist and are endowed with different characteristics. Any quantum riddles and regularities are a consequence of the "repulsion" of neighboring worlds from each other. These quantum phenomena arise so that each world is not like another.
The concept of parallel universes and string theory
From school lessons, we remember well that there are two main theories in physics: general relativity and quantum field theory. The first explains the physical processes in the macrocosm, the second - in the micro. If both of these theories are used on the same scale, they will contradict each other. It seems logical that there should be some general theory applicable to all distances and scales. As such, physicists have put forward string theory.
The fact is that on a very small scale, certain vibrations occur, which are similar to vibrations from an ordinary string. These strings are charged with energy. "Strings" are not strings in the literal sense. This is an abstraction that explains the interaction of particles, physical constants, their characteristics. In the 1970s, when the theory was born, scientists believed that it would become universal to describe our entire world. However, it turned out that this theory only works in 10-dimensional space (and we live in 4-dimensional space). The other six dimensions of space simply collapse. But, as it turned out, they do not fold in an easy way.
As with the many-worlds concept, string theory is difficult to prove experimentally. In addition, the mathematical apparatus of the theory is so difficult that for each new idea a mathematical explanation must be sought literally from scratch.
The hypothesis of the mathematical universe
Cosmologist, professor at the Massachusetts Institute of Technology Max Tegmark in 1998 put forward his "theory of everything" and called it the hypothesis of the mathematical universe. He in his own way solved the problem of the existence of a large number of physical laws. In his opinion, each set of these laws, which are consistent from the point of view of mathematics, corresponds to an independent universe. The universality of the theory is that it can be used to explain all the variety of physical laws and the values of physical constants.
Tegmark proposed to divide all worlds into four groups according to his concept. The first includes the worlds that are beyond our cosmic horizon, the so-called extrametagalactic objects. The second group includes worlds with other physical constants, different from the constants of our Universe. In the third, the worlds that appear as a result of the interpretation of the laws of quantum mechanics. The fourth group is a certain set of all universes in which certain mathematical structures are manifested.
As the researcher notes, our Universe is not the only one, since space is unlimited. Our world, where we live, is limited by space, the light from which reached us 13.8 billion years after the Big Bang. We will be able to learn about other universes reliably in at least another billion years, until the light from them reaches us.
Stephen Hawking: black holes - the way to another universe
Stephen Hawking is also a proponent of the multiple universes theory. One of the most famous scientists of our time in 1988 first presented his essay "Black Holes and Young Universes". The researcher suggests that black holes are the road to alternative worlds.
Thanks to Stephen Hawking, we know that black holes tend to lose energy and evaporate, releasing Hawking radiation, which received the name of the researcher himself. Before the great scientist made this discovery, the scientific community believed that anything that somehow gets into a black hole disappears. Hawking's theory refutes this assumption. According to the physicist, hypothetically, any thing, object, object that falls into a black hole flies out of it and falls into another universe. However, such a journey is a one-way journey: there is no way to go back.
It follows from all this that passing through a black hole is unlikely to prove to be a popular and reliable way of space travel. First, you'll have to get there by navigating imaginary time and not caring that your real-time story ends sadly. Second, you really couldn't choose a destination. It's like flying on some kind of airline that got into your head, - writes the researcher.
Parallel universes and Occam's razor
As we can see, it is still impossible to prove the theory of multiple universes with full confidence. Opponents of the theory believe that we have no right to talk about an infinite set of universes, if only because we cannot explain the postulates of quantum mechanics. This approach runs counter to the philosophical principle of William Ockham: "You should not multiply things unnecessarily." Proponents of the theory declare: it is much easier to assume the existence of many universes than the existence of one ideal.
Whose reasoning (supporters or opponents of the theory of the multiverse) is more convincing - you decide. Who knows, maybe you will be the one who will be able to solve the quantum riddle of physics and propose a new universal "theory of everything".