If you often watch science fiction movies, you may find that most recent science fiction movies are keen on the multiverse theme. Concepts such as parallel universes, multiple reality, timelines, etc. are often mentioned in movies.
In many movies of this type of theme, they discuss the topic of "If things happen in all places at the same time, then what is the meaning of a single event?"
It is obvious that the concept of multiverse has penetrated into popular culture, but do scientists agree? Is the multiverse based on scientific imagination or baseless nonsense?
Many physicists believe that the existence of the multiverse: either the white hole universe hidden behind the black hole event horizon, or the simultaneous existence of soap bubble-like universe. In quantum theory , the multi-world hypothesis is even more magical: every possibility can create a world.
In fact, if we think about the history of the concept of the universe from a scientific perspective, the multiverse is not that strange. The concept of the universe has been expanding. Human beings once thought that the earth was the only planet and the whole of our world, but now we already know that there are countless other planets outside the earth, which is a vast universe. Along this line of thought, there are other universes outside our universe, and this idea is not surprising at all.
So, which multiverse theory is closest to the truth? Will there really be another version of you and me in a certain universe in the Multiverse? Are the laws of physics in different universes the same?
The universe experienced a rapid surge after the "Big Bang"
Based on the multiverse in the theory of surge
This theory originated from cosmology, especially after astronomers discovered that our universe is expanding, the theory of surge is becoming more popular. Some people have suggested that since our universe experienced a surge 13.8 billion years ago, will the same surge happen many times in space and time away from our universe? The basic view of the
surge theory is that our universe is an independently evolved space-time region, which expands in all directions at the same pace and at the same scale. If you go back to the moment our universe begins to skyrocket, you will find that our universe comes from a point 13.8 billion years ago.
Adams is the author of The Multiverse We Live in, and he also published a paper on this issue in the academic journal Physical Reports. He believes that other regions of the multiverse will also have their own "big bang" and then go through their respective surges. This means that their surge has no effect on our universe. Therefore, they are their own independent universes, and the collection of all these universes constitutes the multiverse.
, a multi-universe theory, is quite popular among science fiction works, but the main reason why cosmology has gradually accepted this theory is that it can not only solve some persistent problems, but also will not destroy the existing physical laws of our universe.
In the words of Deng Heling, postdoctoral fellow of cosmology, particle physics and astrophysics , "The concept of multiple universes based on the surge theory can be accepted by many people because it can naturally emerge from the surge theory."
Theoretical physicists The respective research of Andre Lind and Alex Wilenkin show that if there is really a surge, countless isolated space-time areas can be created in space-time.
Although our universe ended its surge 13.8 billion years ago, Deng Heling believes that quantum effect will trigger a new surge in other time and space regions, and eventually form one "eternal surge" after another, resulting in countless "different universes".
Linde further envisioned the configuration of these multiverses and regarded them as expanding "bubbles", which were produced and stayed away from each other under the effects of never stopping and irregular surges. What is the difference between these "bubble universes" and these "bubble universes" is also one of the focus of the current debate. Adams believes that these isolated space-time regions are unlikely to follow the same laws of physics.
Adams said that in different "bubble universes", a series of physical parameters may be different from the gravitational constant to the expansion rate of the universe, etc.
The differences in the laws of physics mean that many "bubble universes" cannot produce large-scale celestial structures such as stars and galaxies, and even elementary particles are completely different from our universe.
So these universes are likely not replicas of our universe, there may be no life there, and of course there is no need to worry about whether another you and me will appear.
string theory attempts to interpret the world as subtle strings
Based on the multiverse in string theory
string theory is a solution proposed by physicists to unify quantum mechanics and general relativity , because quantum mechanics and general relativity are largely contradictory. The basic view of string theory is that basic particles such as quark and electrons are actually one-dimensional string (like rubber bands). The only difference between them is that their respective vibration frequency is different.
String theory describes a "string picture" and also provides a mainstream setting for the multiverse, thanks to a key element of string theory: in order to be mathematically consistent, string theory requires the existence of "extra dimensions".
The extra dimension here is different from the parallel space-time we see in science fiction. In fact, string theorists believe that these extra dimensions are curled up in the three-dimensional space we are familiar with and are completely unaware of for humans who have evolved in three-dimensional space, but it is these extra dimensions that can open a door to the multiverse of string theory.
In string theory, space has 10 or 11 dimensions in total, and we may need to go into these additional dimensions to discover other universes.
Even if the above theory is correct, we can indeed enter other universes through additional dimensions that can never be perceived and observed, because the surge will set us a detectable boundary of the universe, and the space outside the boundary will be completely isolated from our universe. If the individual universes in the multiverse are isolated from each other, then whether they exist cannot be verified experimentally.
In this regard, Adams believes that all the "evidence" at present comes from theory, not experiments, and unfortunately, we cannot prove or falsify what is happening in other universes through direct measurements.
is completely unverifiable for the string theory multiverse, actually a double-edged sword. On the one hand, being unable to verify means being unable to prove their existence, but on the other hand, we cannot prove that they do not exist.
A black hole may form a brand new "baby universe"
Multiverse is connected through black holes
When a massive star consumes all nuclear fusion fuel, it will collapse into a black hole. A black hole is a special space-time region surrounded by a boundary called the event horizon. Once any object crosses this boundary, it will be doomed, and even light cannot escape the powerful gravity of the black hole.
Einstein's general theory of relativity tells us that mass can distort space and time. General Relativity also predicts that there will be a singularity in the center of a black hole, which is so dense that it will cause space and time to bend infinitely, where the laws of physics will not work. This strange singularity is a headache for physicists, but there is a hypothesis that singularity can be eliminated at the cost of replacing it with another universe - and therefore, the multiverse emerges.
Nicodom Popewawski, a theoretical physicist at Connecticut State University New Haven, said: "The singularity does not obey physical rules, because it cannot be measured, so its existence actually indicates that general relativity is still flawed. In my hypothesis, each black hole will form a completely new 'baby universe' in the center, and this universe is located on the other side of the event horizon, and the black hole actually becomes a ' Einstein-Rosen Bridge ', which is called a wormhole, which connects the 'baby universe' and the mother universe where the black hole is located.”
According to this theory, in the view of the new ' Baby Universe ', the mother universe is the universe on the other side of the white hole. The so-called white hole can be regarded as a "reverse black hole", and no object cannot enter the white hole area from the outside.
"Matter falling into the black hole will appear in another universe. The process is like blowing soap bubbles in a ring ," Popewavsky explained. "The ring is equivalent to the event horizon of a black hole, but it is only one-dimensional, and soap water is the matter that falls into the black hole, and the surface of the soap bubble blown out on the other side is equivalent to that new universe. ”
According to Popewavsky's assumption, there may be billions of black holes in a universe, and each black hole can form a "baby universe". According to researchers' estimates, our universe alone can contain about 40 trillion "baby universes". If so, there will be too many "baby universes".
These "baby universes" are hidden by the mother universe in the light-impermeable swaddle garment of the event horizon. Once you step into this boundary, you will never have any more The law turns back, and the white holes cannot enter (this is just a hypothesis at the moment, but it does not violate general relativity). This means that the "baby universe" and the mother universe must be isolated from each other and cannot communicate with each other.
However, if there are two black holes, each of which forms a new universe, then the two new universes may merge with each other, "just like two black holes can fuse into a black hole," Popewavsky said.
He continued, Such fusion will make the "baby universe" appear asymmetry in large-scale space, that is, if we can observe that our universe is biased towards a certain direction, such as higher density of matter and energy in a certain direction, it may mean that our universe is also fused with other universes.
As for whether there is another version of you in the event horizon, Popewavsky believes that the possibility is very small. "There will never be a 'parallel you', an object will only exist in In a universe, he emphasized.
In the quantum version of the multi-world theory, it must contain each version of you and me
quantum version of the multi-world theory
Quantum mechanics describes the physical laws of the subatomic world. In quantum mechanics, there is no concept of multiple universes. Instead, it is called the so-called "multi-world theory". The strange concept of parallel worlds is what we mentioned before The multiple universes we go to are completely different because they do not correspond to a real space-time region. The hypothesis of
was first proposed by American physicist Hugh Everett III, aiming to explain how a quantum system can be in two contradictory states at the same time, namely the so-called " superposition state ", and how these contradictory states disappear. The explanation of superposition states by the multi-world hypothesis of
can be used to use Schrödinger's famous thought experiment - Schrödinger's cat explains it.
In this thought experiment, a helpless kitten is placed in a sealed box. There is also a bottle of deadly poison gas and a small amount of radioactive atoms in the box. If the atom decays, it will trigger the mechanism and release the toxic gas. If the entire experimental device and the cat are regarded as a single quantum system, then "the cat dies" or "the cat is alive" is this. The two possible states of the system correspond to two wave functions . These two wave functions can be further superimposed into a wave function. Under this superimposed state , the cat is in both "dead" and "live" state, which means that the poor kitten is both dead and alive in quantum mechanics. The incredible state of
will exist until the box is opened, which is equivalent to observing the system. At this time, the wave The function will collapse immediately, and the superposition state will no longer exist. You will know whether the cat dies or lives. However, why observations lead to the collapse of the superposition wave function, or " decoherence ", is still an unsolved mystery.
more world hypotheses completely abandon the concept of decoherence. This hypothesis believes that the behavior of opening a box will not only not cause the wave function to collapse, but will also cause the wave function to grow exponentially, and ultimately "enjoin" the entire universe, including the observer.
"In multi-world versions of quantum mechanics, each state of the system is a physically different world." explains Jeffrey Barrett, professor of philosophy of science at the University of California, Irving.
This means that a chandelier switch can create countless worlds - the moment when the light is turned on, every photon passes through every possible path, there is a world corresponding to it, far more than the world where the dark bedroom is located when the light is not turned on.
Re-examine Schrödinger's cat from this perspective. Then, when the observer opens the box, he is no longer the dead or alive cat. But the moment the observer opened the box, the world was split into two. In one world, the observer sees the cat dead, and in another world, the observer sees the cat alive.
At the beginning, the split world was very similar, with only slight differences, but as the world further splits, the differences between different worlds will become bigger and bigger, and in the end it will completely "divided ways" from the initial world.
"Objects, events and physical records in different worlds are completely different. Maybe in a certain world, the Eiffel Tower is located in Los Angeles," Barrett said. "All these worlds, or the universe, are just part of the overall universe. From our branch world, this overall universe is the same as the universe we feel."
As for whether other versions of you will be included in these "multi-worlds", Barrett's answer is that it must be included, and it must be included in the quantum multi-world theory.
He explained, "This is the basis for the multi-world hypothesis to explain the problem of quantum measurement."
These characteristics make the quantum version of the multi-world theory the multi-world theory the most in line with popular culture, at least in theory, because in the multi-world of quantum mechanics, it is not only possible, but inevitable.
