Do parallel universes exist? String theory, right?

The parallel universe was first proposed by general relativity, and later it was used to explain the wave function collapse in quantum mechanics. But note that these two things are different and don't confuse them.

There is no evidence that parallel universes exist. All discussions are hypothetical, so different people have different views on this issue.

First, let's talk about general relativity. At present, there are few solutions of general relativity, but each solution will be singular, and the singularity will appear in the black hole region and the dual region (currently called the white hole region), and the interface between the two regions is a wormhole. Then there are other areas besides the black hole area and the white hole area, including our world and other worlds-that is, parallel universes.

If we artificially remove these parallel universes, there will be no problem with general relativity. But for some bold space explorers, they may think that they can reach another world through black holes. If this thing is really proved, then the parallel universe has been discovered, otherwise it means that there is no parallel universe. This is the basic idea of general relativity.

In fact, the concept of parallel universe is not science fiction, but comes from the "multi-world explanation" in quantum mechanics. Everything in the universe is made up of quantum, and its state is uncertain before we observe it. The parallel universe theory holds that when we observe, we will separate unrelated universes, which are all in a specific state, and of course our universe is no exception.

When it comes to parallel universes, we have to mention quantum mechanics. The charm of this theory is that the measurement behavior of the observer will affect the quantum state. Before observation, the quantum system is in an uncertain superposition state. When an observer measures a quantum system, it will collapse to a certain state, and the results obtained from each observation will not be exactly the same. In this regard, some physicists believe that quantum systems are not in an uncertain superposition state, but that all possible states really exist in parallel universes. When we get a certain result, we are evolving into this universe; When we get another result, it is an evolution to another universe.

For example, suppose you are making a decision, whether to read a book or play a mobile phone. According to the parallel universe theory, both options are real. In a universe, you choose to read. In another parallel universe, you choose to play with your mobile phone. So, your life now is just the result of your choice in this universe. In the parallel universe, you made other choices and had a different life. Parallel universes contain countless possibilities, but they don't interfere with each other. In this way, it makes sense to say that fate is in your own hands.

So, if parallel universes exist, where are they? This question is difficult to answer. Parallel universes may be around us, or outside our universe, or exist in other dimensions. Although the concept of parallel universe is very eye-catching, it is too illusory after all, and it is only a mathematical concept in essence. It is difficult for us to verify the existence of parallel universes, or it is impossible to verify them at all.

The explanation of quantum mechanics needs to introduce the principle of superposition of states in quantum mechanics. The wave function of any particle is actually a linear superposition of all eigenstates of all good operators. According to the principle of superposition of states, we can measure a physical quantity of particles, such as momentum. Particles can have many different momentum eigenstates, and the value we measure at a time can only be one momentum value. How to understand this matter?

Some physicists think that this is decoherence, and the particles themselves enter different parallel universes and produce different measurement results. An inappropriate analogy is Schrodinger's cat. If we measure the cat's life and death, we may find out whether the cat is dead or alive. According to the explanation of parallel universe, in fact, every time a cat is measured, it has experienced a big adventure-it may enter a different parallel universe, resulting in different results.

The interpretation of parallel universe overcomes the difficulty of Copenhagen interpretation-that is, what is the physical image of measurement itself. But it also brings many problems. What is the dynamics of parallel universes? Quantum mechanics cannot explain it.

Finally, let's talk about string theory. There is nothing mysterious about string theory itself. It's just that the physics and mathematics involved are very difficult, so they are often mysterious. The embryonic form of string theory is the string model in the early 1970s. This model is used to explain the strong interaction. Only because of the establishment of quantum chromodynamics, the string model was rejected.

But soon, in the 1980s, supersymmetric gravity was established.

The renormalization of supergravity was talked about by many physicists at that time, and some even thought that the proposal of supergravity heralded the end of theoretical physics. However, supergravity is only a low-energy effective theory, not a high-energy theory. His high-energy theory was later proved to be superstring theory.

Superstring theory can predict the high-energy behavior of particles and can also be used to study the very early universe. The black hole I just mentioned can also be studied by superstring theory. But at present, superstring theory has no experimental basis and is just empty talk.

Superstring theory is the most beautiful physical theory in mathematics so far, and it is also one of the most difficult theories to prove (the other is loop quantum gravity theory, and all energy scales need Planck energy).

Therefore, it cannot be said that string theory is correct, and the experiment has not given the answer.

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