Parallel world

Parallel universe

Multiverse is a theoretical set of infinite or finite possible universes, including all existing and possible things: all space, time, matter, energy and the physical laws and constants describing them. The universes contained in the multiverse are called

Parallel universe

（paralleluniverses）。 Also known as

Parallel world

（parallelworlds）、

Parallel space time

（parallelspacetimes）、

Parallel dimension

(parallel dimensions) and

Replace the universe

（alternativeuniverses）。

Generally speaking, parallel universes refer to other universes similar to what we know (i.e. the first level of parallel universes in classification) that may exist outside our universe.

Basic summary

Parallel universe refers to other universes which are separated from a certain universe and parallel to the original universe. Among these universes, there are also universes born under the same conditions as our universe. There may also be planets with the same history as the planets inhabited by human beings. There may also be people who are exactly the same as human beings. At the same time, in these different universes, the development of things will have different results: the extinct species in our universe may be constantly evolving in another universe.

The parallel universe of parallel forces is opposite to the gravitational planet universe of human beings. The parallel forces do not coincide or intersect. It can be said that "well water does not offend river water", which leads to the pure elementary particle universe just opposite to the gravitational planet universe of human beings.

Some scholars use this analogy when describing parallel universes. They may be in the same space system, and parallel forces move in parallel, just like two trains galloping along the same railway line. They may be in the same time system, but the space systems are different, just like cars driving in the upper and lower passages of an overpass at the same time.

Background

The concept of parallel universe is not put forward because of the time travel paradox. It comes from quantum mechanics, because there is an uncertainty in quantum mechanics, that is, quantum uncertainty. The concept of parallel universe benefits from the scientific discovery of modern quantum mechanics.

In the 1950s, when some physicists observed quantum, they found that the quantum state of each observation was different. Since all matter in the universe is made up of quanta, these scientists speculate that since each quantum has a different state, the universe may also be made up of many similar universes rather than just one.

copenhagen interpretation

Since the 1920s, many physicists have used wave function to describe the state of microscopic particles in quantum mechanics. When a micro particle is in a certain state, its mechanical quantities (such as coordinates, momentum, angular momentum, energy, etc.) generally do not have definite values, but have a series of possible values, each of which appears with a certain probability (when a macro object is in a certain state, its mechanical quantities have definite values). In other words, the motion of micro particles is uncertain and probabilistic. Wave function can describe the probability of the distribution of micro particles in space.

The well-known "single electron double slit interference" experiment in physics is the embodiment of the uncertainty and randomness of micro particle motion. In this experiment, a single electron interferes after passing through a double slit. In the view of classical mechanics, an electron can only pass through one slit at the same time, and it cannot pass through two slits at the same time and interfere with each other. According to quantum mechanics, the motion state of an electron exists in the form of wave function, and the electron may pass through both this slit and that slit at the same time and interfere with each other. However, when scientists try to determine which slit the electron passes through, they will always find the electron in only one of them. The two instruments will not detect electrons at the same time. Electrons can only pass through one slit at a time. It seems that the observation behavior of the measurer has changed the motion state of the electron. What's the explanation for this abnormal phenomenon? Physicist Bohr put forward the famous "Copenhagen explanation": when people do not observe, the electron has the probability to exist in both slit positions; however, once it is measured, for example, the electron is measured in the left slit position, the electron has an accurate position It has a probability of 1 at this point and 0 at other points. In other words, the wave function of the electron "collapses" to this point at the moment of measurement.

Bohr introduced the observer and his consciousness into quantum mechanics, making it related to the motion state of micro particles. But the explanation of the observer and "collapse" is not very clear and convincing, which has also been questioned by many scientists. For example, how does collapse occur, in an instant, or until photons enter people's eyes and trigger electrical pulses on the retina.

Multi world interpretation

So, is there any way to bypass the so-called "collapse" and "Observer" and eliminate the subjective component of the observer from the physics which should study the objective laws.

Everett put forward a bold idea: if the wave function does not "collapse", then it must keep increasing linearly. That is to say, in the above experiment, the electron is still in the superposition state of left / right slit even after re observation. Everett further points out that people's world is also superimposed. When electrons pass through the double slit, it is not only electrons but also the whole world that are in the superimposed state. That is to say, when the electron passes through the double slit, two superposed worlds appear. In one world, the electron passes through the slit on the left, while in the other world, the electron passes through the slit on the right. In this way, the wave function does not need to "collapse" to randomly choose left or right, because it is the superposition of two worlds: people living in one world find that the electrons pass through the slit on the left, while in the other world, the electrons observed are on the right. In the case of Schrodinger's cat, Everett points out that both cats are real. There is a live cat and a dead cat, but they are in different worlds. The problem is not whether the emission atom in the box decays, but whether it decays and does not decay.

When the observer looks into the box,

wave function

It will collapse and the whole world will split into two versions of itself

. The two versions are identical in all other respects. The only difference is that in one version, the atom decays and the cat dies; in the other version, the atom does not decay and the cat is still alive. The above-mentioned "the cat died when the atom decays; the cat is still alive when the atom does not decay" two worlds will evolve completely independently and parallelly, just like two parallel worlds. Quantum process creates "two worlds", which is Everett's avant-garde "multi world explanation".

The advantage of this explanation is that the Schrodinger equation always holds and the wave function never collapses, so it simplifies the basic theory. The problem with it is that the assumption is too bizarre, and the price is that these parallel worlds are all equally real. It is no wonder that someone said: "in the history of science, multi world interpretation is undoubtedly the most bold and ambitious theory put forward at present."

development history

Thought rudiment

In the 5th century BC, Democritus put forward the concept of "innumerable worlds", which was formed by the movement of atoms themselves. He said: "atoms move freely in the void, and because of their rapid and disorderly movement, they collide with each other, and when they collide with each other, because of their various shapes, they collude with each other, thus forming the world and the things in it, or rather forming countless worlds."

In the 4th century BC, Epicurus expressed the idea of world pluralism: "there are infinitely many worlds, some of which are like our world, some of which are not like ours." "In all worlds, there are animals, plants and other things that we see in this world."

In the first century BC, luclesius pointed out that in addition to our "visible world", there were "other worlds" inhabited by "other races of human beings and beasts."

Leibniz put forward his concept of "possible world", which assumes that there are infinitely many "possible worlds" beyond the scope of the inevitable world (the observable universe). He believes that the world is composed of infinite lists. There is no causal relationship between lists, but a certain pre-determined harmonious relationship. Although the lists are independent, there are differences between them. Leibniz interprets the emergence of a real event, such as a specific person, as the result of many combinations of monads. The results of various combinations are related to the dominant role of the better monad in the list. This means that the world can look different, any event is accidental, even the whole universe.

Officially put forward

Physicist Hugh Everett III put forward his own idea of quantum measurement. He pointed out that in quantum mechanics, there are many parallel worlds. In each world, the results of each quantum mechanical measurement are different, so different histories occur in different parallel universes. Multi world interpretation holds that the observation of the measuring device will cause the measuring device to be decomposed into two parts. And in this measurement chain, this decomposition will continue to change

Chinese PinYin : Ping Hang Shi Jie