First of all, I don't know how much you know about quantum mechanics, so my answer will be a little longer. As we all know, the Copenhagen interpretation of quantum mechanics holds that the observer has an influence on the micro-world. Interesting experiments worth mentioning include "which crack does the electron pass through", "quantum suicide" and "Schrodinger's cat". However, it seems that there are many philosophical difficulties in the decision of the micro-world, so that many scientists later put forward other explanations different from this, especially Flat's multiverse theory, which won a lot of support.
In order to make you better understand the explanation of the multiverse, I might as well describe the electronic double-slit experiment in detail.
According to the classical theory, in the experiment of electron double-slit interference, a single electron only passes through one slit, but the particles passing through one slit interfere. If we want to install some instruments on both slits, so as to record the electronic path or give an alarm, wouldn't it? This instrument is not complicated and can't be made. In fact, we can install this instrument. However, once we try to determine which crack the electron has passed through, we can always find the electron only in one of the cracks. These two instruments don't sound at the same time. Electrons are particles that can only pass through one slit at a time. Strangely, once we started measuring, the interference fringes disappeared. Copenhagen explained that the participation of human consciousness led to the collapse of electron wave function.
(The following content is selected from the reference "Does God Roll Dice-A History of Quantum Physics",)
We can't define an "observer" accurately! What's the difference between a person and a camera? Everyone can't explain it, so they use it to "consciousness". And it is this damn collapse that forces us to define what an observer is. An observer makes the wave function collapse? This seems to give the so-called observer a supreme position in the universe. They enjoy some privileges beyond the basic laws of physics and can create something really wonderful.
Really, the culprit is the ambiguous "wave function collapse". This seems to be the curse of Copenhagen School, which still makes us deeply immersed in it, and the future of physics is bleak under its curse. Take Kurt, a physicist at Cornell University, for example. In the words of Kurt Gottfried, this kind of "collapse" is like "ugly scar in the theory of beauty". It is overcast, specious and vague, and everyone has his own opinion, so the argument is endless. How to draw a clear line between observers and non-observers? Schrodinger's cat's wave function collapsed at the moment we opened the box? Or will we wait until photons enter our eyes and trigger electrical pulse signals on the retina? Or do you have to wait a little longer until this signal reaches somewhere in the cerebral cortex and eventually becomes a "mental activity" before it really collapses? If we fall into it, the future doesn't seem bright.
Then, is there any way to bypass the so-called "collapse" and "observer" and kick the intervention of intelligent creatures out of physics and make them return to the track we are familiar with and love? Let's revisit the classic double-slit problem: does the electron pass through the left slit or the right slit? According to Copenhagen's explanation, when we don't observe it, its wave function presents two possible linear superposition. But once observed, there is a peak on one side, and the wave function "collapses" and randomly chooses to pass through a slit on the left or right. The randomness of the quantum world is best reflected in the collapse.
In order to get rid of this dilemma and not admit collapse, it is only necessary to admit that the wave function has never been "selected" to the left or right, and it always maintains a state of linear superposition regardless of observation or not. But this is obviously inconsistent with our actual experience, because in reality, no one has ever observed that electrons pass through the left and right slits at the same time, and no one has ever seen cats that are both dead and alive (quite a few are dying). Now, we are riding a tiger, in a dilemma, and the curse of Copenhagen has entangled us. If we don't get up the courage and make the most shocking assumptions, we are doomed to get stuck.
If the wave function does not collapse, it must keep linear superposition. Electrons must be left/right superimposed, but this phenomenon has never been observed in the real world.
There is a fantasy that can lift this hateful curse. Although it sounds really crazy, we are desperate. We have nothing to lose. All you lose is the shackles, but what if you win the whole world?
Yes! Even after observation, electrons are still in the state of left/right superposition, and our world is only a part of superposition! When the electrons pass through the double slit, not only the electrons but also our whole world are in the superposition state! In other words, when electrons pass through the double slit, two superimposed worlds appear. In one world, electrons pass through the slit on the left, while in another world, electrons pass through the right!
The wave function does not need to "collapse" to randomly select left or right. In fact, both possibilities have happened! It's just the superposition of the whole world: people living in one world find that electrons pass through the slit on the left, while in another world, the electrons observed by people are on the right! The quantum process has created "two worlds"! This is the "multi-world interpretation" of quantum theory (MWI for short).
In order to better understand MWI, we must learn from its founder Hugh, who has a legendary life. Downgrade three (his grandfather and father were also named Hugh Everett, so he was actually "downgrade three"). 1October 9th, 1930, 165438+ Einstein published his famous article on science and religion in The New York Times magazine. His famous saying still echoes in our ears: "Science without religion is lame, and religion without science is blind." Two days later, Little Flatt was born in Washington.
Mr Flat has deep respect for Einstein. When he was only 12 years old, he wrote to Einstein in Princeton and asked some questions about the universe. Einstein really wrote back and answered him. When he got a bachelor's degree in chemical engineering, he also entered Princeton University. At first he entered the department of mathematics, but he soon managed to transfer to the department of physics. In 1950s, quantum theory was in the ascendant, and Copenhagen interpretation was in full swing, dominating the world. Mr. Flat met many physics students in this field, including Bohr's assistant, Aage Peterson. He discussed the observation problem in quantum theory with him, which aroused Mr. Flat's great interest. He got in touch with John soon? Wheeler, Wheeler encouraged him to think in this regard. 1954, Mr. Ping submitted two papers to Wheeler, and the multi-world theory (sometimes called "Mr. Ping Doctrine-Everytism") first appeared.
According to Mr Flat, the wave function never collapses, but the world and the observer themselves enter a superposition state. When electrons pass through the double slit, the whole world, including ourselves, becomes two independent superpositions. In every world, electrons appear as a possibility. Unfortunately, Mr Flat used a misleading and vague word "split". He made an analogy and said that the universe is like an amoeba. When electrons pass through the double slit, the worm will split itself and reproduce into two almost identical amoebas. The only difference is that one bug remembers that electrons pass from the left, and the other bug remembers that electrons pass from the right.
Wheeler may have realized that this word is not appropriate. He wrote in the margin of the paper: "Split? It is best to change the word. " But most physicists don't know his point of view. Perhaps, Wheeler should make it more dramatic, such as writing "I think of a great word, but the blank is too small to write it down." For a long time, Mr. Flat's theory was understood as: when electrons pass through a double slit, the universe magically "splits" into two independent universes, one of which passes through the left slit and the other is the opposite. In this way, the history of the universe is like a fork in the road. Every time you make an observation, it will branch into several paths, and each path corresponds to a possible result. And every fork in the road, under constant observation, is further divided until infinity. But every road is real, just can't communicate with each other.
Suppose we observe the double-slit experiment and find that the electron has passed through the left slit. In fact, when we observe that moment, the universe has unconsciously "split" into two almost identical ones. We are now in a "left universe" and a "right universe", where we will find electrons passing through the right slit, but otherwise everything is exactly the same as our universe. You may ask, "Why am I in the left universe and not in the right universe?" This kind of question is obviously meaningless, because in another universe, you may also ask, "Why am I in the right universe, not the left universe?" The position of the observer is no longer important, because the universe will split anyway, in fact, "all the results" will appear, and everything produced by quantum processes may correspond to a corresponding universe, but in most "wild universes", no intelligent creatures ask questions.
So Schrodinger's cat doesn't have to worry about life and death. It's just that the universe has split into two, one with a live cat and the other with a dead cat. For the universe of living cats, cats are always alive, and there is no superposition of life and death. For the dead cat universe, the cat actually died at the moment of division. Don't wait for someone to open the box to "collapse" before you can draw a conclusion.
Since the birth of the universe, there have been countless such splits, the number of which has increased geometrically and soon tends to infinity. The universe we live in now is just one of them, and there are many other universes besides. Some of them are close to us and have only recently left the family tree, while those universes that have parted ways with us from distant ancient times may be very different. Maybe in some universe, asteroids didn't hit the earth, and dinosaurs still ruled the world. In a certain universe, Cleopatra's nose was a little shorter, which didn't excite Caesar and Anthony. Those "nose historians" who oppose historical determinism will be interested in the later development to see if there is really a historical butterfly effect. In a certain universe, grouchy was not late at Waterloo, and Hitler did not give the order to stop attacking before Dunkirk. In more universes, there are no life and planets at all because of inappropriate physical constants.
Strictly speaking, everything that may happen in history and in the future has actually happened or will happen. It's just that they are in other universes and have no physical contact with the universe we live in. These universes are parallel to our world and have no connection with each other. According to Occam's razor principle, these wonderful universes are meaningless to us. The multi-world theory is sometimes called the "parallel universe" theory, which is for this reason.
The "split" of the universe should actually be regarded as a misunderstanding, but until now, most people, including many physicists, still understand Mr. Ping in this way! From this point of view, this theory seems to be too picky. For the question of whether a small electron passes from the left or the right, we should participate in the division of the whole universe! Many people's evaluation of this is "killing the chicken with a cow knife". Einstein once said, "I can't believe that a mouse has changed the universe dramatically just by looking at it." This statement was originally aimed at the Copenhagen faction, but it does represent the thinking of many people: it is not economical and cheap to cater to the random selection of electrons at the expense of the universe, and it also produces so many unobservable "parallel universe" wastes. One of the most active advocates of MWI, Bryce of the University of Texas? Bryce S. DeWitt described the first time he heard about MWI. He said, "I still clearly remember the shock when I first met the multi-world concept. 100 The slightly defective self-replicating shell keeps splitting into further copies, and finally it is unrecognizable. This idea is hard to follow common sense. This is complete schizophrenia ... "For us, it may be easier to accept" consciousness "than to believe in" division of the universe "!
It is not difficult to imagine that, after Vlat's MWI was published as a doctoral thesis in 1957, despite Wheeler's recommendation and revision, it was still given a cold shoulder in physics. Ping once flew to Copenhagen on 1959 to meet Bohr, but Bohr didn't want to discuss any new explanation of quantum theory or comment on it, which made him disheartened. Of course, as Bohr, he firmly defended Copenhagen theory all his life. For other explanations that arose in 1950' s, such as Bohm's implicit function theory (which we will talk about later), his comment is "as if we hope to prove 2 × 2 = 5 in the future." In his last interview before his death, Bohr was still criticizing some philosophers, claiming: "They don't know that it is an objective description, and it is the only possible objective description."
Being left out in the cold, Mr. Flatt gradually withdrew from physics. He first worked in the Ministry of National Defense, and later became one of the founders and chairman of the famous Lambda company, which made him a millionaire soon. But his view-later called "one of the deepest secrets of the 20th century"-has long been ignored by people. It was not until 1970s that Dewey rediscovered his multi-world explanation and popularized it among physicists that MWI was known and quickly became one of the hot topics. Today, this explanation has a large number of supporters, and it has occupied the second place after the Copenhagen explanation, and it is likely to come from behind. To this end, Mr. Ping himself intended to return to the physical world to do some research work in quantum mechanics, but unfortunately died of a heart attack in 1982.
At the University of Texas where Wheeler and Dewit are located, Mr. Flatt is one of the most respected people. When he was invited to give a lecture on quantum theory, he was specially allowed to smoke because he was a heavy smoker. This is the only exception in the history of that auditorium.
In Did God Roll the Dice-A History of Quantum Physics, the author also explained WMI in two pages, so I won't paste them one by one. If you are interested, you can find this book online. Especially about the cause and effect of this theory, you will have a fairly comprehensive harvest after reading it.