Many-worlds interpretation

Published 2002/2/18

The many-worlds interpretation is one of the interpretations of quantum mechanics.
Based on the interpretation, there are many worlds different from this world.

Copenhagen interpretation and many-worlds interpretation

Everett's many-worlds interpretation

Hugh Everett, who was a student of Princeton University has proposed a new interpretation of quantum mechanics in 1957. The interpretation is called Everett's many-worlds interpretation.

For example, I put an electron in the box. According to quantum mechanics, the electron spreads like a wave in the box. This wave is called a wave function. If a human look in the box he found the electron at one point in the box. It is called the wave function collapse.

The electrons are always the particle, and the existence probability just follows the wave. The thought is natural. However, the interpretation is not correct. Aspect experiment disproved the interpretation in 1982. An electron is spreading like a wave before we observe it.

This wave function collapse is a very strange phenomenon. For example, I will partition the box into two rooms. Then, a wave of an electron exists in each room. If you look in one room, there may be an electronic, or not.

The wave function in the box

If we found the electron at a place, the wave function of the electron shrinks to the place. On the other hand, we do not find the electron, the wave function of the electron shrinks to the next room. It is very mysterious that the electron collapses when we observe it. However, it is more mysterious that the electron collapses when we don't observe it.

Everett didn't think that the wave function does not collapse. If we express an electron as a wave function, we should express a human as a wave function. The human will be divided as follows when the human observes an electron.

  1. Human A who finds an electron at place x
  2. Human B who finds an electron at place y
  3. Human C who finds an electron at place z

An electron is spreading like a wave. On the other hand, a human is also spreading like a wave.

Encounter with many-worlds interpretation

I touched many-worlds interpretation for the first time in the book "The fate of the universe" of Richard Morris. I have read it when I was about 10 years old. I would like to quote from the book. (I do not have an English version, so it is translated from the Japanese version.)

However, consider the universe is divided into two when a probabilistic event occurs as if science fiction writers say. Many universes exist if it is true. Many kinds of universe we can imagine exist like a little different universe or a big different universe.


Such story is very interesting. The reader may think there is no scientific theory that allows this kind of idea. However, it exists in fact. It is called "many-worlds interpretation" in quantum mechanics. Physicist Hugh Everett III wrote it in his doctoral thesis of Princeton University in 1957 in the United States.


It would seem that such a fantastic idea would be easy to disprove. However, this is not the case; Everett's theory is mathematically identical to the standard version of quantum mechanics. This means that it is not possible to devise an experiment that could distinguish between the two.

At first, I thought that the idea was not probable when I read this book. However, I have got to think that it might be right when I was in university.

It was an opportunity to change my mind to have known "Kaon mixing" in the lecture of "CP violation." The wave function of superposition Kaon and Antikaon appears in the "Kaon mixing."

According to Copenhagen interpretation, physical systems generally do not have definite properties prior to being measured. Then, the superposition of two kinds of particle does not have the superposition of two kinds of particle prior to being measured.

In order to understand the superposition of two kinds of particle those are obviously different, the idea like many-worlds interpretation is much effective.

Copenhagen interpretation and many-worlds interpretation

I have got to think that many-worlds interpretation might be right by the trigger.

Information of many-worlds interpretation

We can find the description about many-worlds interpretation in the book "Taking the Quantum Leap" of Fred A. Wolf. The author introduces the parallel universe interpretation of Everett in this book. In addition, he introduces a quantum computer David Deutsch proposed. However, there was no textbook that describes the many-worlds interpretation.

"I wonder the reason is that the interpretation that allows the parallel world is suspicious idea."

Though I thought like that, one day I found a textbook "Quantum Mechanics. An Introduction" refers to the many-worlds interpretation in the bookstore in the university. The textbook expressed opposition to the many-worlds interpretation. However, it was a landmark that textbooks mentioned the many-worlds interpretation for me.

Then, a book that fully supports the many-worlds interpretation was published in 1994 in Japan. The name of the book was "World view quantum mechanics talks about." I think it's the first book that comments about many-worlds interpretation very favorably, as far as I know.

There is the measurement problem that is the unresolved problem in quantum mechanics. The problem is about "wave function collapse" and "Born rule." Many-worlds interpretation can solve the "wave function collapse" because there is no collapse in the many-worlds interpretation. Therefore, I think the many-worlds interpretation is right.

However, I think the formulation of the many-worlds interpretation of current because it cannot derive "Born rule." The formulation of the many-worlds interpretation depends on the mathematical structure of quantum mechanics, if we are going to adopt the many-worlds interpretation, then it is necessary to extend the mathematical structure, I believe.

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