How often do you think about how our world would be structured today if the outcome of some key historical events had been different? What would our planet be like if dinosaurs, for example, had not gone extinct? Our every action and decision automatically becomes part of the past. In fact, there is no present: everything we do at this moment cannot be changed, it is recorded in the memory of the Universe. However, there is a theory according to which there are many universes where we live a completely different life: each of our actions is associated with a certain choice and, making this choice in our Universe, in a parallel one, the “other me” makes the opposite decision. How justified is such a theory from a scientific point of view? Why did scientists resort to it? Let's try to figure it out in our article.
Many Worlds Concept of the Universe
The theory of a probable set of worlds was first mentioned by the American physicist Hugh Everett. He offered his solution to one of the main quantum mysteries of physics. Before moving directly to Hugh Everett’s theory, it is necessary to understand what this mystery of quantum particles is, which has haunted physicists around the world for decades.
Let's imagine an ordinary electron. It turns out that as a quantum object it can be in two places at the same time. This property of it is called the superposition of two states. But the magic doesn't end there. As soon as we want to somehow specify the location of the electron, for example, we try to knock it down with another electron, then from quantum it will become ordinary. How is this possible: the electron was at both point A and point B and suddenly at a certain moment jumped to B?
Hugh Everett offered his interpretation of this quantum mystery. According to his many-worlds theory, the electron continues to exist in two states simultaneously. It's all about the observer himself: now he turns into a quantum object and is divided into two states. In one of them he sees an electron at point A, in the other - at B. There are two parallel realities, and in which of them the observer will find himself is unknown. The division into realities is not limited to the number two: their branching depends only on the variation of events. However, all these realities exist independently of each other. We, as observers, find ourselves in one, from which it is impossible to leave, as well as to move to a parallel one.
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From the point of view of this concept, the experiment with the most scientific cat in the history of physics - Schrödinger's cat - is easily explained. According to the many-worlds interpretation of quantum mechanics, the poor cat in the steel chamber is both alive and dead. When we open this chamber, it is as if we merge with the cat and form two states - alive and dead, which do not intersect. Two different universes are formed: in one, an observer with a dead cat, in the other, with a living one.
It is worth immediately noting that the many-worlds concept does not imply the presence of many universes: it is one, simply multi-layered, and each object in it can be in different states. Such a concept cannot be considered an experimentally confirmed theory. For now, this is just a mathematical description of the quantum mystery.
Hugh Everett's theory is supported by physicist and professor at Australia's Griffith University Howard Wiseman, Dr Michael Hall from the Griffith University Center for Quantum Dynamics and Dr Dirk-Andre Deckert from the University of California. In their opinion, parallel worlds really exist and are endowed with different characteristics. Any quantum mysteries and patterns are a consequence of the “repulsion” of neighboring worlds from each other. These quantum phenomena arise so that each world is different from the other.
The concept of parallel universes and string theory
From school lessons we remember well that in physics there are two main theories: general relativity and quantum field theory. The first explains physical processes in the macrocosm, the second - in the microcosm. If both of these theories are used on the same scale, they will contradict each other. It seems logical that there should be some general theory that applies to all distances and scales. As such, physicists put forward string theory.
The fact is that on a very small scale certain vibrations arise that are similar to vibrations from an ordinary string. These strings are charged with energy. “Strings” are not strings in the literal sense. This is an abstraction that explains the interaction of particles, physical constants, and their characteristics. In the 1970s, when the theory was born, scientists believed that it would become universal to describe our entire world. However, it turned out that this theory only works in 10-dimensional space (and we live in four-dimensional space). The remaining six dimensions of space simply collapse. But, as it turned out, they are not folded in a simple way.
In 2003, scientists found out that they can collapse in a huge number of ways, and each new method produces its own universe with different physical constants.
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As with the many-worlds concept, string theory is quite difficult to prove experimentally. In addition, the mathematical apparatus of the theory is so difficult that for each new idea a mathematical explanation must be sought literally from scratch.
Mathematical Universe Hypothesis
Cosmologist and professor at the Massachusetts Institute of Technology Max Tegmark put forward his “theory of everything” in 1998 and called it the hypothesis of a mathematical universe. He solved the problem of existence in his own way large quantity physical laws. In his opinion, each set of these laws, which are consistent from the point of view of mathematics, corresponds to an independent universe. The universality of the theory is that it can be used to explain all the variety of physical laws and the values of physical constants.
Tegmark proposed that all worlds, according to his concept, be divided into four groups. The first includes worlds located beyond our cosmic horizon, the so-called extra-metagalactic objects. The second group includes worlds with other physical constants, different from those of our Universe. The third is worlds that appear as a result of the interpretation of the laws of quantum mechanics. The fourth group is a certain set of all universes in which certain mathematical structures appear.
As the researcher notes, our Universe is not the only one, since space is limitless. Our world, where we live, is limited by space, the light from which reached us 13.8 billion years after the Big Bang. We will be able to reliably learn about other universes in at least another billion years, until the light from them reaches us.
Stephen Hawking: black holes are a path to another universe
Stephen Hawking is also a proponent of the many universes theory. One of the most famous scientists of our time first presented his essay “Black Holes and Young Universes” in 1988. The researcher suggests that black holes are a path to alternative worlds.
Thanks to Stephen Hawking, we know that black holes tend to lose energy and evaporate, releasing Hawking radiation, which is named after the researcher himself. Before the great scientist made this discovery, the scientific community believed that everything that somehow fell into a black hole disappeared. Hawking's theory refutes this assumption. According to the physicist, hypothetically, any thing, object, object that falls into a black hole flies out of it and ends up in another universe. However, such a journey is a one-way movement: there is no way to return.
Even before Everett and his idea of multiple universes, physicists were stumped. They had to use one set of rules for sub atomic world, which is subject to quantum mechanics, and a different set of rules for the large-scale everyday world that we can see and touch. The complexities of moving from one scale to another twist the brains of scientists into bizarre shapes.
For example, in quantum mechanics, particles do not have certain properties unless someone is looking at them. Their nature is described by the so-called wave function, which includes all possible properties, which a particle can have. But in a single universe, all these properties cannot exist at the same time, so when you look at a particle, it takes on one state. This idea is metaphorically depicted in Schrödinger's cat paradox - where a cat sitting in a box is both alive and dead until you open the box to check. Your action turns the cat into a warm and alive cat or into a stuffed cat. However, scientists cannot agree with this either.
In the multiverse, you don't have to worry about killing the cat with your curiosity. Instead, every time you open a window, reality splits into two versions. Unclear? I agree. But somewhere out there there may be another version of the event that just happened before your eyes. It didn't happen somewhere else.
It remains to be seen what reasons scientists have found to tie this incredible theory to facts.
In a 2011 interview, Columbia University physicist Brian Greene, who wrote the book Hidden Reality: Parallel Universes and the Deep Laws of the Cosmos, explained that we are not entirely sure how big the universe is. It may be very, very big, but it is finite. Or, if you go from Earth in any direction, space can stretch on forever. This is roughly how most of us imagine it.
But if space is infinite, it must be a multiple universe with infinite parallel realities, according to Green. Imagine that the universe and all the matter in it are equivalent to a deck of cards. Just as there are 52 cards in a deck, there will be exactly the same number of different forms of matter. If you shuffle the deck long enough, the cards will eventually return to the original order. Likewise, in an infinite universe, matter will eventually repeat itself and organize itself in a similar way. A multiple universe, the so-called multiverse, with an infinite number of parallel realities, contains similar but slightly different versions of everything that is, and thus provides a simple and convenient way to explain repetition.
This can explain how the Universe begins and ends
Humans have a particular passion - and it is related to the brain's ability to form patterns - we want to know the beginning and end of every story. Including the history of the universe itself. But if the Big Bang was the beginning of the universe, what caused it and what existed before it? Will the universe end and what will happen after it? Each of us has asked these questions at least once.
The multiverse can explain all these things. Some physicists have suggested that the infinite regions of the multiverse could be called brane worlds. These branes exist in multiple dimensions, but we cannot detect them because we can only perceive three dimensions of space and one of time in our own braneworld.
Some physicists believe that these branes are slabs piled together like sliced bread in a bag. Most of the time they are separated. But sometimes they collide. Theoretically, these collisions are catastrophic enough to cause repeated "big bangs" - so that parallel universes start over, over and over again.
Observations suggest multiple universes may exist
The European Space Agency's Planck Orbiting Observatory collects data on the cosmic microwave background, or CMB, background radiation that is still glowing from the first and hottest stage of the universe.
Her research also led to possible evidence for the existence of a multiverse. In 2010, a team of scientists from the UK, Canada and the US discovered four unusual and unlikely circular patterns in the CMB. Scientists have suggested that these marks may be “bruises” that were left on the body of our Universe after a collision with others.
In 2015, ESA researcher Rang-Ram Hari made a similar discovery. Hari took the CMB model from the observatory's celestial image, and then removed everything else we know about it - stars, gas, interstellar dust, and so on. At this point the sky should have become mostly empty except for background noise.
But it didn't. Instead, in a certain range of frequencies, Hari was able to detect scattered spots on the map of space, areas that were about 4,500 times brighter than they should have been. Scientists have come up with another possible explanation: these areas are imprints of collisions between our Universe and a parallel one.
Hari believes that unless we find another way to explain these markings, "we will have to conclude that Nature can play dice after all, and we are just one random universe among many others."
The universe is too big to exclude the possibility of the existence of parallel realities
There is a possibility that multiple universes exist, although we have not seen parallel realities, because we cannot disprove its existence.
This may seem like a clever rhetorical trick at first, but consider this: even in our world, we have found many things we never knew existed, and these things have happened - the 2008 global crisis is a good example. Before him, no one thought that this was even possible. David Hume called these kinds of events "black swans": people will assume that all swans are white until they see black swans.
The scale of the Universe allows us to think about the possibility of the existence of multiple universes. We know that the universe is very, very large, perhaps infinite in size. This means that we will not be able to discover everything that exists in the universe. And since scientists have determined that the Universe is approximately 13.8 billion years old, we can only detect the light that managed to reach us during this time. If a parallel reality is located further than 13.8 light years from us, we may never know about its existence, even if it existed in the dimensions distinguishable by us.
Multiple universes make sense from an atheistic perspective
As Stanford University physicist Andrei Linde explained in a 2008 interview, if the physical world obeyed slightly different rules, life could not exist. If protons were 0.2% more massive than they are now, for example, they would be so unstable that they would decay into simple particles instantly without forming an atom. And if gravity were a little more powerful, the result would be monstrous. Stars like our sun would collapse tightly enough that they would burn out their fuel within a few million years, giving planets like Earth no chance to form. This is the so-called “fine-tuning problem.”
Some see in this precise balance of conditions evidence of the participation of an omnipotent force, a supreme being who created everything, which greatly angers atheists. But the possibility of the existence of a multiverse, in which this force will simply be in a separate reality with all the factors necessary for life, suits them quite well.
As Linde said, “For me, the reality of multiple universes is logically possible. We can say: perhaps this is some kind of mystical coincidence. Perhaps God created the universe for our benefit. I don't know anything about God, but the universe itself could reproduce itself infinite number times in all possible manifestations.”
Time travelers can't disrupt history
The popularity of the Back to the Future trilogy has made many people fascinated by the idea of time travel. Since the film's release, no one has yet developed a DeLorean that can travel back and forth in time, decades or centuries. But scientists believe that time travel may be at least theoretically possible.
And if it is possible, we could end up in the same position as main character Back to the Future by Marty McFly - risks unintentionally changing something in the past, thereby changing the future and the course of history. McFly accidentally prevented his parents from meeting and falling in love, thereby successfully removing himself from family photographs.
However, a 2015 paper suggested that the existence of a multiverse does not make such troubles necessary. “The existence of alternative worlds means that there is no single chronology that can be disrupted,” wrote Georg Dworsky. On the contrary, if a person goes back in time and changes something, he will simply create a new set of parallel universes.
We could be a simulation for an advanced civilization
All these topics about parallel universes that we have discussed so far have been extremely interesting. But there is something else interesting.
In 2003, philosopher Nick Bostrom, director of the Future of Humanity Institute at the University of Oxford, wondered whether everything we perceive as reality - particularly our separate parallel universe - could simply be a digital simulation of another universe. According to Bostrom, it would take 10 36 calculations to create a detailed model of all human history.
A well-developed alien civilization - creatures whose technological level would make us look like Paleolithic cave dwellers - could well have enough computing power to do all this. Moreover, modeling each individual living person will not require any absolutely dizzying electronic resources, so there can be much more computer-simulated creatures than real ones.
All this could mean that we live in a digital world, like something out of The Matrix.
But what will happen if this advanced civilization is itself a simulation?
People have thought about multiple universes since time immemorial.
It will be extremely difficult to prove this. But here one cannot help but recall the old sayings attributed either to Picasso or to Susan Sontag: if you can imagine something, it must exist.
And there is something in this. After all, long before Hugh Everett was sipping his cognac, countless people throughout human history have imagined different versions of the multiverse.
Ancient Indian religious texts, for example, are filled with descriptions of multiple parallel universes. And the ancient Greeks had a philosophy of atomism, which stated that there is infinite set worlds scattered in the same endless emptiness.
The idea of multiple worlds was also raised in the Middle Ages. The Bishop of Paris argued in 1277 that the Greek philosopher Aristotle was wrong when he said there was only one possible world because it called into question the omnipotent power of God to create parallel worlds. The same idea was resurrected in the 1600s by Gottfried Wilhelm Leibniz, one of the pillars of the scientific revolution. He argued that there are many possible worlds, each with distinct physics.
All this fits into our scheme of knowledge about the Universe
No matter how strange the concept of the multiverse may seem, in some way it fits into progress modern history and in the way people see themselves and the universe.
In 2011, physicists Alexander Vilenkin and Max Tegmark noted that people in Western civilization were gradually calming down as they discovered the nature of reality. They started with a mindset that the Earth was the center of everything. It turned out that this is not so, and that our solar system- just a tiny part of the Milky Way.
The multiverse must take this idea to its logical conclusion. If the multiverse exists, it means that we are not the chosen ones and that there are infinite versions of ourselves.
But some believe that we are only at the very beginning of the path to expanding consciousness. As Stanford University theoretical physicist Leonard Susskind wrote, perhaps a couple of centuries from now philosophers and scientists will look back on our time as “a golden age in which the narrow, provincial conception of the universe of the 20th century gave way to a bigger and better multiverse of staggering proportions.”
Monday, 09 May 2011Disputes and hypotheses about the existence of unknown twin planets, parallel universes and even galaxies have spanned many decades. All of them are based on the theory of probability without involving the concepts of modern physics. IN last years to them was added the idea of the existence of a superuniverse, based on proven theories - quantum mechanics and the theory of relativity.
“Polit.ru” publishes an article by Max Tegmark “Parallel Universes”, which puts forward a hypothesis about the structure of the alleged superuniverse, which theoretically includes four levels. However, in the next decade, scientists may have a real opportunity to obtain new data on the properties of outer space and, accordingly, confirm or refute this hypothesis. The article was published in the journal “In the World of Science” (2003. No. 8).
Evolution has given us intuitions about everyday physics that were vital to our early ancestors; therefore, as soon as we go beyond the everyday, we can well expect strange things.
The simplest and most popular cosmological model predicts that we have a twin in a galaxy about 10 to the power of 1028 meters away. The distance is so great that it is beyond the reach of astronomical observations, but this does not make our twin any less real. The assumption is based on probability theory without involving the concepts of modern physics. The only assumption accepted is that space is infinite and filled with matter. There may be many inhabited planets, including those where people live with the same appearance, the same names and memories, who have gone through the same vicissitudes of life as us.
But we will never be given the opportunity to see our other lives. The farthest distance we can see is the distance that light can travel in the 14 billion years since the Big Bang. The distance between the farthest visible objects from us is about 431026 m; it determines the observable region of the Universe, called the Hubble volume, or the volume of the cosmic horizon, or simply the Universe. The universes of our twins are spheres of the same size with centers on their planets. This is the simplest example of parallel universes, each of which is only a small part of the superuniverse.
The very definition of “universe” suggests that it will forever remain in the field of metaphysics. However, the boundary between physics and metaphysics is determined by the possibility of experimental testing of theories, and not by the existence of unobservable objects. The boundaries of physics are constantly expanding, including increasingly abstract (and previously metaphysical) ideas, for example, about a spherical Earth, invisible electromagnetic fields, time dilation at high speeds, superposition of quantum states, space curvature and black holes. In recent years, the idea of a superuniverse has been added to this list. It is based on proven theories—quantum mechanics and relativity—and meets both basic criteria of empirical science: predictive and falsifiable. Scientists consider four types of parallel universes. The main question is not whether a superuniverse exists, but how many levels it might have.
Level I
Beyond our cosmic horizon
The parallel universes of our counterparts constitute the first level of the superuniverse. This is the least controversial type. We all recognize the existence of things that we cannot see, but could be seen by moving to another place or simply by waiting, as we wait for a ship to appear over the horizon. Objects located beyond our cosmic horizon have a similar status. The size of the observable region of the Universe increases by one light year every year, as light emanating from ever more distant regions reaches us, beyond which lies an infinity that has yet to be seen. We'll probably be dead long before our counterparts come within observational range, but if the expansion of the universe helps, our descendants might be able to see them with powerful enough telescopes.
Level I of the superuniverse seems banally obvious. How can space not be infinite? Is there a sign somewhere that says “Beware! The end of space"? If there is an end to space, what is beyond it? However, Einstein's theory of gravity called this intuition into question. A space can be finite if it has positive curvature or an unusual topology. A spherical, toroidal, or "pretzel" universe can have a finite volume without boundaries. Cosmic microwave background radiation makes it possible to test the existence of such structures. However, the facts still speak against them. The data corresponds to the model of an infinite universe, and all other options are subject to strict restrictions.
Another option is this: space is infinite, but matter is concentrated in a limited area around us. In one version of the once popular “island Universe” model, it is accepted that on large scales matter becomes rarefied and has a fractal structure. In both cases, almost all universes in a Level I superuniverse should be empty and lifeless. Recent studies of the three-dimensional distribution of galaxies and background (relict) radiation have shown that the distribution of matter tends to be uniform on large scales and does not form structures larger than 1024 m. If this trend continues, then the space beyond the observable Universe should be replete with galaxies, stars and planets.
For observers in parallel universes of the first level, the same laws of physics apply as for us, but under different starting conditions. According to modern theories, the processes that occurred during the initial stages of the Big Bang randomly scattered matter, so that there was a possibility of the emergence of any structures.
Cosmologists accept that our Universe, with an almost uniform distribution of matter and initial density fluctuations of the order of 1/105, is very typical (at least among those in which there are observers). Estimates based on this assumption indicate that the nearest exact replica of you is at a distance of 10 to the power of 1028 m. At a distance of 10 to the power of 1092 m there should be a sphere with a radius of 100 light years, identical to the one at the center of which we are located; so that everything that we see in the next century will also be seen by our counterparts there. At a distance of about 10 to the power of 10118 m from us, there should be a Hubble volume identical to ours. These estimates are derived by calculating the possible number of quantum states that the Hubble volume can have if its temperature does not exceed 108 K. The number of states can be estimated by asking the question: how many protons can the Hubble volume accommodate at this temperature? The answer is 10118. However, each proton can either be present or absent, giving 2 to the power of 10118 possible configurations. A “box” containing so many Hubble volumes covers all possibilities. Its size is 10 to the power of 10118 m. Beyond it, universes, including ours, must repeat themselves. Approximately the same figures can be obtained based on thermodynamic or quantum-gravitational estimates of the total information content of the Universe.
However, our closest twin is most likely closer to us than these estimates suggest, since the process of planet formation and the evolution of life favors this. Astronomers believe our Hubble volume contains at least 1,020 habitable planets, some of which may be similar to Earth.
In modern cosmology, the concept of a Level I superuniverse is widely used to test theories. Let's look at how cosmologists use cosmic microwave background radiation to reject the model of finite spherical geometry. Hot and cold "spots" on the CMB maps have characteristic size, depending on the curvature of space. So, the size of the observed spots is too small to be consistent with spherical geometry. Their average size varies randomly from one Hubble volume to another, so it is possible that our Universe is spherical, but has anomalously small spots. When cosmologists say they rule out the spherical model at the 99.9% confidence level, they mean that if the model is correct, then less than one Hubble volume in a thousand would have spots as small as those observed. It follows that the superuniverse theory is testable and can be rejected, although we are not able to see other universes. The key is to predict what the ensemble of parallel universes is and find the probability distribution, or what mathematicians call the measure of the ensemble. Our Universe must be one of the most likely. If not, if within the framework of the superuniverse theory our Universe turns out to be improbable, then this theory will encounter difficulties. As we will see later, the problem of measure can become quite acute.
Level II
Other post-inflationary domains
If it was difficult for you to imagine a Level I superuniverse, then try to imagine an infinite number of such superuniverses, some of which have a different dimension of space-time and are characterized by different physical constants. Together they constitute the Level II superuniverse predicted by the theory of chaotic eternal inflation.
Inflation theory is a generalization of the Big Bang theory that eliminates shortcomings of the latter, such as its inability to explain why the Universe is so large, homogeneous and flat. The rapid expansion of space in ancient times makes it possible to explain these and many other properties of the Universe. Such stretching is predicted by a wide class of particle theories, and all available evidence supports it. The expression "chaotic perpetual" in relation to inflation indicates what is happening on the largest scale. In general, space is constantly stretching, but in some areas the expansion stops and separate domains arise, like raisins in rising dough. An infinite number of such domains appear, and each of them serves as the embryo of a Level I superuniverse, filled with matter born from the energy of the field causing inflation.
The neighboring domains are more than infinity away from us, in the sense that they cannot be reached even if we move forever at the speed of light, since the space between our domain and the neighboring ones is stretching faster than we can move in it. Our descendants will never see their Level II counterparts. And if the expansion of the Universe is accelerating, as observations indicate, then they will never see their counterparts even at level I.
The Level II superuniverse is much more diverse than the Level I superuniverse. The domains differ not only in their initial conditions, but also in their fundamental properties. The prevailing opinion among physicists is that the dimension of space-time, the properties of elementary particles and many so-called physical constants are not built into physical laws, but are the result of processes known as symmetry breaking. It is believed that space in our Universe once had nine equal dimensions. At the beginning of cosmic history, three of them took part in the expansion and became the three dimensions that characterize the Universe today. The remaining six are now undetectable, either because they remain microscopic, maintaining a toroidal topology, or because all matter is concentrated in a three-dimensional surface (membrane, or simply brane) in nine-dimensional space. Thus, the original symmetry of the measurements was broken. Quantum fluctuations causing chaotic inflation could cause different symmetry violations in different caverns. Some could become four-dimensional; others contain only two rather than three generations of quarks; and still others - to have a stronger cosmological constant than our Universe.
Another way of the emergence of a level II superuniverse can be represented as a cycle of births and destructions of universes. In the 1930s physicist Richard C. Tolman proposed this idea, and recently Paul J. Steinhardt of Princeton University and Neil Turok of Cambridge University expanded on it. Steinhardt and Turok's model envisions a second three-dimensional brane, perfectly parallel to ours and only displaced relative to it in a higher-order dimension. This parallel universe cannot be considered separate, since it interacts with ours. However, the ensemble of universes - past, present and future - that these branes form represents a superuniverse with diversity apparently approaching that resulting from chaotic inflation. Another hypothesis of a superuniverse was proposed by physicist Lee Smolin from the Perimeter Institute in Waterloo (Ontario, Canada). His superuniverse is close to Level II in diversity, but it mutates and generates new universes through black holes rather than branes.
Although we cannot interact with Level II parallel universes, cosmologists judge their existence by indirect evidence, since they may be the cause of strange coincidences in our Universe. For example, a hotel gives you room number 1967, and you note that you were born in 1967. “What a coincidence,” you say. However, upon reflection, you come to the conclusion that this is not so surprising. There are hundreds of rooms in a hotel, and you wouldn't think twice about it if you were offered a room that meant nothing to you. If you knew nothing about hotels, to explain this coincidence you might assume that there were other rooms in the hotel.
As a closer example, consider the mass of the Sun. As is known, the luminosity of a star is determined by its mass. Using the laws of physics, we can calculate that life on Earth can exist only if the mass of the Sun lies in the range: from 1.6x1030 to 2.4x1030 kg. Otherwise, the Earth's climate would be colder than Mars or hotter than Venus. Measurements of the mass of the Sun gave a value of 2.0x1030 kg. At first glance, the solar mass falling within the range of values that supports life on Earth is accidental.
The masses of stars occupy the range from 1029 to 1032 kg; If the Sun acquired its mass by chance, then the chance of falling exactly into the optimal interval for our biosphere would be extremely small.
The apparent coincidence can be explained by assuming the existence of an ensemble (in this case, many planetary systems) and a selection factor (our planet must be suitable for life). Such observer-related selection criteria are called anthropic; and although the mention of them usually causes controversy, most physicists agree that these criteria cannot be neglected when selecting fundamental theories.
What do all these examples have to do with parallel universes? It turns out that a small change in the physical constants determined by symmetry breaking leads to a qualitatively different universe - one in which we could not exist. If the mass of a proton were just 0.2% greater, protons would decay to form neutrons, making atoms unstable. If the electromagnetic interaction forces were 4% weaker, hydrogen and ordinary stars would not exist. If the weak force were even weaker, there would be no hydrogen; and if it were stronger, supernovae could not fill interstellar space with heavy elements. If the cosmological constant were noticeably larger, the Universe would become incredibly inflated before galaxies could even form.
The given examples allow us to expect the existence of parallel universes with different values of physical constants. Second-level superuniverse theory predicts that physicists will never be able to deduce the values of these constants from fundamental principles, but will only be able to calculate the probability distribution of various sets of constants in the totality of all universes. Moreover, the result must be consistent with our existence in one of them.
Level III
Quantum many universes
Superuniverses of levels I and II contain parallel universes that are extremely distant from us beyond the limits of astronomy. However, the next level of the superuniverse lies right around us. It arises from the famous and highly controversial interpretation of quantum mechanics - the idea that random quantum processes cause the universe to "multiply" into many copies of itself - one for each possible outcome of the process.
At the beginning of the twentieth century. quantum mechanics explained the nature of the atomic world, which did not obey the laws of classical Newtonian mechanics. Despite the obvious successes, there were heated debates among physicists about what the true meaning of the new theory was. It defines the state of the Universe not in terms of classical mechanics, such as the positions and velocities of all particles, but through a mathematical object called the wave function. According to Schrödinger's equation, this state changes over time in a way that mathematicians call "unitary." It means that the wave function rotates in an abstract infinite-dimensional space called Hilbert space. Although quantum mechanics is often defined as fundamentally random and uncertain, the wave function evolves in a quite deterministic manner. There is nothing random or uncertain about it.
The hardest part is relating the wave function to what we observe. Many valid wave functions correspond to unnatural situations such as when a cat is both dead and alive at the same time, in what is called a superposition. In the 20s XX century physicists got around this oddity by postulating that the wave function collapses to some specific classical outcome when one makes an observation. This addition made it possible to explain the observations, but it turned an elegant unitary theory into a sloppy and non-unitary one. The fundamental randomness usually attributed to quantum mechanics is a consequence of precisely this postulate.
Over time, physicists abandoned this view in favor of another, proposed in 1957 by Princeton University graduate Hugh Everett III. He showed that it is possible to do without the postulate of collapse. Pure quantum theory does not impose any restrictions. Although it predicts that one classical reality is gradually splitting into a superposition of several such realities, the observer subjectively perceives this splitting as simply a slight randomness with a probability distribution exactly matching that given by the old collapse postulate. This superposition of classical universes is the Level III superuniverse.
For more than forty years, this interpretation confused scientists. However, physical theory is easier to understand by comparing two points of view: external, from the position of a physicist studying mathematical equations(like a bird surveying the landscape from the height of its flight); and internal, from the position of an observer (let's call him a frog) living on the landscape observed by the bird.
From the bird's point of view, the Level III superuniverse is simple. There is only one wave function that smoothly evolves in time without splitting or parallelism. The abstract quantum world, described by the evolving wave function, contains a huge number of continuously splitting and merging lines of parallel classic stories, as well as a number of quantum phenomena that cannot be described within the framework of classical concepts. But from the frog's point of view, only a small part of this reality can be seen. She can see the Level I universe, but the process of decoherence, similar to the collapse of the wave function, but with the preservation of unitarity, does not allow her to see parallel copies of herself in Level III.
When an observer is asked a question to which he must quickly answer, the quantum effect in his brain leads to a superposition of decisions like this: “keep reading the article” and “stop reading the article.” From the bird's point of view, the act of making a decision causes the person to multiply into copies, some of which continue to read, while others stop reading. However, from an internal point of view, neither of the doubles is aware of the existence of the others and perceives the splitting simply as a slight uncertainty, some possibility of continuing or stopping reading.
No matter how strange it may seem, exactly the same situation arises even in the Level I superuniverse. Obviously, you decided to continue reading, but one of your counterparts in a distant galaxy put the magazine down after the first paragraph. Levels I and III differ only in where your counterparts are located. At level I they live somewhere far away, in good old three-dimensional space, and at level III they live on another quantum branch of infinite-dimensional Hilbert space.
The existence of level III is possible only under the condition that the evolution of the wave function in time is unitary. So far, experiments have not revealed its deviations from unitarity. IN last decades it has been confirmed for all larger systems, including C60 fullerene and kilometer-long optical fibers. Theoretically, the assumption of unitarity was supported by the discovery of violation of coherence. Some theorists working in the field of quantum gravity question it. In particular, it is assumed that evaporating black holes can destroy information, which is not a unitary process. However, recent advances in string theory suggest that even quantum gravity is unitary.
If this is so, then black holes do not destroy information, but simply transfer it somewhere. If physics is unitary, the standard picture of the influence of quantum fluctuations in the early stages of the Big Bang must be modified. These fluctuations do not randomly determine the superposition of all possible initial conditions that coexist simultaneously. In this case, the violation of coherence causes the initial conditions to behave in a classical manner on various quantum branches. The key point is that the distribution of outcomes on different quantum branches of one Hubble volume (level III) is identical to the distribution of outcomes in different Hubble volumes of one quantum branch (level I). This property of quantum fluctuations is known in statistical mechanics as ergodicity.
The same reasoning applies to Level II. The process of breaking symmetry does not lead to a unique outcome, but to a superposition of all outcomes, which quickly diverge along their separate paths. Thus, if physical constants, the dimension of space-time, etc. may differ in parallel quantum branches at level III, then they will also differ in parallel universes at level II.
In other words, a level III superuniverse adds nothing new to what is present in levels I and II, only more copies of the same universes - the same historical lines developing again and again on different quantum branches. The heated debate surrounding Everett's theory appears to be soon subsided by the discovery of the equally grandiose but less controversial superuniverses of Levels I and II.
The applications of these ideas are profound. For example, this question: does the number of universes increase exponentially over time? The answer is unexpected: no. From the bird's point of view, there is only one quantum universe. What is the number of separate universes in this moment for a frog? This is the number of noticeably different Hubble volumes. The differences may be small: imagine planets moving in different directions, imagine yourself married to someone else, etc. At the quantum level, there are 10 to the power of 10118 universes with a temperature no higher than 108 K. The number is gigantic, but finite.
For a frog, the evolution of the wave function corresponds to an infinite movement from one of these 10 to the power of 10118 states to another. You are now in Universe A, where you are reading this sentence. And now you are already in universe B, where you read the next sentence. In other words, there is an observer in B who is identical to the observer in universe A, with the only difference being that he has extra memories. At every moment, all possible states exist, so that the passage of time can occur before the eyes of the observer. This idea was expressed in his science fiction novel “Permutation City” (1994) by writer Greg Egan and developed by physicist David Deutsch from Oxford University, independent physicist Julian Barbour, and others. We see that the idea of a superuniverse can play a key role in understanding the nature of time.
Level IV
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The initial conditions and physical constants in the superuniverses of levels I, II and III may differ, but the fundamental laws of physics are the same. Why did we stop here? Why can't the physical laws themselves differ? What about a universe that obeys classical laws without any relativistic effects? What about time moving in discrete steps, like in a computer?
What about the universe as an empty dodecahedron? In a Level IV superuniverse, all of these alternatives do exist.
The fact that such a superuniverse is not absurd is evidenced by the correspondence of the world of abstract reasoning to our real world. Equations and other mathematical concepts and structures - numbers, vectors, geometric objects - describe reality with amazing verisimilitude. Conversely, we perceive mathematical structures as real. Yes, they meet the fundamental criterion of reality: they are the same for everyone who studies them. The theorem will be true no matter who proved it - a person, a computer or an intelligent dolphin. Other inquisitive civilizations will find the same mathematical structures that we know. Therefore mathematicians say that they do not create, but rather discover mathematical objects.
There are two logical, but diametrically opposed paradigms of the relationship between mathematics and physics, which arose in ancient times. According to Aristotle's paradigm, physical reality is primary, and mathematical language is only a convenient approximation. Within the framework of Plato's paradigm, it is mathematical structures that are truly real, and observers perceive them imperfectly. In other words, these paradigms differ in their understanding of what is primary - the frog point of view of the observer (Aristotle's paradigm) or the bird's view from the heights of the laws of physics (Plato's point of view).
Aristotle's paradigm is how we perceived the world with early childhood, long before we first heard about mathematics. Plato's point of view is that of acquired knowledge. Modern theoretical physicists are inclined towards it, suggesting that mathematics describes the Universe well precisely because the Universe is mathematical in nature. Then all physics comes down to solving a mathematical problem, and an infinitely smart mathematician can only, on the basis of fundamental laws, calculate the picture of the world at the level of a frog, i.e. calculate what observers exist in the Universe, what they perceive and what languages they have invented to convey their perceptions.
Mathematical structure is an abstraction, an unchanging entity beyond time and space. If the story were a movie, then the mathematical structure would correspond not to one frame, but to the film as a whole. Let's take for example a world consisting of zero-size particles distributed in three-dimensional space. From the bird's point of view, in four-dimensional spacetime, particle trajectories are "spaghetti." If a frog sees particles moving at constant speeds, then a bird sees a bunch of straight, uncooked spaghetti. If a frog sees two particles revolving in orbits, then a bird sees two “spaghettis” twisted into a double helix. For a frog, the world is described by Newton’s laws of motion and gravity; for a bird, the world is described by “spaghetti” geometry, i.e. mathematical structure. For her, the frog itself is a thick ball of them, the complex interweaving of which corresponds to a group of particles that store and process information. Our world is more complex than the example considered, and scientists do not know which mathematical structure it corresponds to.
Plato's paradigm contains the question: why is our world the way it is? For Aristotle, this is a meaningless question: the world exists, and that is how it is! But Plato's followers are interested: could our world be different? If the Universe is essentially mathematical, then why is it based on only one of many mathematical structures? It seems that a fundamental asymmetry lies in the very essence of nature. To solve the puzzle, I hypothesized that mathematical symmetry exists: that all mathematical structures are physically realized, and each of them corresponds to a parallel universe. The elements of this superuniverse are not in the same space, but exist outside of time and space. Most of them probably don't have observers. The hypothesis can be seen as extreme platonism, asserting that the mathematical structures of Plato's world of ideas, or the "mental landscape" of mathematician Rudy Rucker of San Jose State University, exist in a physical sense. This is akin to what cosmologist John D. Barrow of Cambridge University called the “p in the heavens,” philosopher Robert Nozick of Harvard University described as the “fertility principle,” and philosopher David K. Lewis ) from Princeton University called “modal reality.” Level IV closes the hierarchy of superuniverses, since any self-consistent physical theory can be expressed in the form of a certain mathematical structure.
The Level IV superuniverse hypothesis makes several testable predictions. As at level II, it includes the ensemble (in this case, the totality of all mathematical structures) and selection effects. In classifying mathematical structures, scientists must note that the structure that describes our world is the most general of those consistent with observations. Therefore, the results of our future observations should be the most general of those that are consistent with the data of previous research, and the data of previous research should be the most general of those that are generally compatible with our existence.
Assessing the degree of generality is not an easy task. One of the striking and reassuring features of mathematical structures is that the properties of symmetry and invariance that keep our universe simple and orderly are generally shared. Mathematical structures usually have these properties by default, and getting rid of them requires introducing complex axioms.
What did Occam say?
Thus, theories of parallel universes have a four-level hierarchy, where at each subsequent level the universes are less and less like ours. They may be characterized by different initial conditions (Level I), physical constants and particles (Level II) or physical laws (Level IV). It's funny that level III has been the most criticized in recent decades as the only one that does not introduce qualitatively new types of universes. In the coming decade, detailed measurements of the cosmic microwave background radiation and the large-scale distribution of matter in the Universe will allow us to more accurately determine the curvature and topology of space and confirm or disprove the existence of Level I. The same data will allow us to obtain information about Level II by testing the theory of chaotic eternal inflation. Advances in astrophysics and high-energy particle physics will help refine the degree of fine-tuning of physical constants, strengthening or weakening Level II positions. If efforts to create a quantum computer are successful, there will be an additional argument for the existence of layer III, since parallel computing will use the parallelism of this layer. Experimenters are also looking for evidence of violation of unitarity, which will allow them to reject the hypothesis of the existence of level III. Finally, the success or failure of the attempt to solve the most important problem of modern physics - to combine general relativity with quantum field theory - will answer the question about level IV. Either a mathematical structure will be found that accurately describes our Universe, or we will hit the limit of the incredible efficiency of mathematics and be forced to abandon the Level IV hypothesis.
So, is it possible to believe in parallel universes? The main arguments against their existence are that they are too wasteful and incomprehensible. The first argument is that superuniverse theories are vulnerable to Occam's razor because they postulate the existence of other universes that we will never see. Why should nature be so wasteful and “have fun” with creating an infinite number of different worlds? However, this argument can be turned in favor of the existence of a superuniverse. In what ways is nature wasteful? Of course, not in space, mass or number of atoms: an infinite number of them are already contained in level I, the existence of which is beyond doubt, so there is no point in worrying that nature will spend any more of them. The real issue is the apparent decrease in simplicity. Skeptics are concerned about the additional information needed to describe invisible worlds.
However, the entire ensemble is often simpler than each of its members. The information volume of a number algorithm is, roughly speaking, the length of the shortest computer program, generating this number. Let's take for example the set of all integers. What is simpler - the whole set or a single number? At first glance - the second. However, the former can be constructed using a very simple program, and a single number can be extremely long. Therefore, the entire set turns out to be simpler.
Similarly, the set of all solutions to the Einstein equations for a field is simpler than each specific solution - the first consists of only a few equations, and the second requires specifying a huge amount of initial data on a certain hypersurface. So the complexity increases when we focus on separate element ensemble, losing the symmetry and simplicity inherent in the totality of all elements.
In this sense, superuniverses are more high levels easier. The transition from our Universe to a Level I superuniverse eliminates the need to specify initial conditions. Further movement to level II eliminates the need to specify physical constants, and at level IV there is no need to specify anything at all. Excessive complexity is just a subjective perception, a frog's point of view. And from the perspective of a bird, this superuniverse could hardly be any simpler. Complaints about incomprehensibility are aesthetic, not scientific, and are justified only in an Aristotelian worldview. When we ask a question about the nature of reality, shouldn't we expect an answer that may seem strange?
A common feature of all four levels of the superuniverse is that the simplest and apparently most elegant theory involves parallel universes by default. To reject their existence, it is necessary to complicate the theory by adding processes that are not confirmed by experiment and postulates invented for this purpose - about the finiteness of space, the collapse of the wave function and ontological asymmetry. Our choice comes down to what is considered more wasteful and inelegant - many words or many universes. Perhaps over time we will become accustomed to the quirks of our cosmos and find its strangeness charming.
One model of potential multiple universes is called the Many Worlds Theory. The theory may seem strange and unrealistic to the point that it belongs in science fiction films, not in real life. However, there is no experiment that can conclusively discredit its validity.
The origins of the parallel universes hypothesis are closely related to the introduction of the idea of quantum mechanics in the early 1900s. Quantum mechanics, a branch of physics that studies the microcosm, predicts the behavior of nanoscopic objects. Physicists have had difficulty fitting mathematical model behavior of quantum matter. For example, a photon, a tiny beam of light, can move vertically up and down while moving horizontally forward or backward.
This behavior is in stark contrast to objects visible to the naked eye - everything we see moves either as a wave or a particle. This theory of the duality of matter was called the Heisenberg Uncertainty Principle (HEP), which states that the act of observation affects quantities such as velocity and position.
In relation to quantum mechanics, this observation effect can affect the particle or wave form of quantum objects during measurements. Future quantum theories, such as the Copenhagen interpretation of Niels Bohr, used PNG to argue that the observed object does not retain its dual nature and can only be in one state.
In 1954, a young student at Princeton University named Hugh Everett proposed a radical proposal that differed from popular models of quantum mechanics. Everett did not believe that the observation raised the quantum question.
Instead, he argued that the observation of quantum matter creates a rift in the universe. In other words, the universe creates copies of itself taking into account all probabilities, and these duplicates will exist independently of each other. Every time a photon is measured by a scientist in one universe, for example, and analyzed as a wave, the same scientist in another universe will analyze it as a particle. Each of these universes offers a unique and independent reality that coexists with other parallel universes.
If Everett's Many Worlds Theory (MWT) is correct, it contains many implications that will completely transform the way we perceive life. Any action that has more than one possible outcome leads to the splitting of the Universe. Thus, there are an infinite number of parallel universes and infinite copies of each person.
These copies have the same faces and bodies, but different personalities(one may be aggressive and the other passive) because each of them receives an individual experience. The infinite number of alternate realities also suggests that no one can achieve unique achievements. Every person - or another version of that person in a parallel universe - has done or will do everything.
In addition, it follows from TMM that everyone is immortal. Old age will never cease to be a sure killer, but some alternate realities may be so scientifically and technologically advanced that they have developed anti-aging medicine. If you die in one world, another version of you in the other world will survive.
The most disturbing consequence of parallel universes is that your perception of the world is not real. Our “reality” at this moment in one parallel universe will be completely different from the other world; it is only a tiny fiction of the infinite and absolute truth. You may believe that you are reading this article right now, but there are many copies of you that are not being read. In fact, you are even the author of this article in a distant reality. So does winning the prize and making decisions matter if we might lose those rewards and choose something else? Or live trying to achieve more when we might actually be dead somewhere else?
Some scientists, such as the Austrian mathematician Hans Moravec, have tried to debunk the possibility of parallel universes. Moravec developed a famous experiment in 1987 called quantum suicide, in which a gun connected to a machine that measures a quark is pointed at a person. Each time the trigger is pulled, the spin of the quark is measured. Depending on the measurement result, the weapon either fires or does not.
Based on this experiment, the gun will or will not shoot a person with a 50 percent probability for each scenario. If the TMM is not true, then the probability of human survival decreases after each quark measurement until it reaches zero.
On the other hand, TMM states that the experimenter always has a 100% chance of surviving in some parallel universe, and the person is faced with quantum immortality.
When a quark is measured, there are two possibilities: the weapon can either fire or it won't. At this point, TMM states that the Universe splits into two different universes to account for two possible endings. The weapon will fire in one reality, but not in another.
For moral reasons, scientists cannot use Moravec's experiment to disprove or confirm the existence of parallel worlds, since the subjects can only be dead in this particular reality and still alive in another parallel world. Either way, the many-worlds theory and its startling consequences challenge everything we know about the universe.
The idea of the Multiverse (that is, many universes existing in parallel) has occupied the minds of scientists since the mid-20th century. This theory has both opponents and ardent defenders (for example, Sheldon Cooper from the sitcom “The Big Bang Theory”). But what makes serious people consider this possibility? Is it really possible that somewhere in a parallel universe another you is sitting and reading the same text, perhaps with minor changes? Surprisingly, there is some evidence that strongly supports this concept. Or not, it depends on how you look.
So, what does the idea of parallel universes prove?
Shroedinger `s cat
Schrödinger's famous thought experiment demonstrates that in quantum mechanics there are situations when elementary particles - quanta - can exist in two positions at once. Because of this, the unfortunate cat inside the box can be both alive and dead until you open the lid - depending on how you view the particle. How this is possible in the physical world is difficult to understand. That's why the experiment is called a paradox.
The multiverse eliminates this problem by explaining exactly how this is possible. There are simply two realities: in one, everything is fine with the cat. And in the second... But let's not talk about sad things.
Infinite Universe
The infinity of the Universe is difficult to comprehend, but in general scientists seem to have come to terms with it. This property of the universe also proves the probability of the existence of parallel universes. Remember the hypothesis that if an infinite number of monkeys pound on keys for an infinite amount of time, sooner or later they will type “War and Peace”? It’s the same with matter: if you create new objects an infinite number of times, sooner or later they will begin to repeat themselves and create worlds almost the same as ours. These will be those same parallel universes.
Big Bang
Besides how the Universe can be infinite, people wonder how it came to be in the first place. What caused the Big Bang?
The multiverse may try to explain this. If we assume that parallel realities exist - yes, yes, parallel! - then they may not touch at all, being next to each other in dimensions that are inaccessible to our senses (we know only three dimensions, plus the fourth - time). The accidental contact of universes can lead to catastrophic results, causing the Big Bang. Thus, parallel universes are constantly updated, constantly restarting each other.
Time travel
Yes, time travel is impossible. But if we consider only our Universe! In this case, the time traveler paradox, described many times in science fiction literature and cinema, is inevitable. If you accidentally crush a butterfly, push a person, or do something equally insignificant in the past, it will lead to huge changes in the future.
Parallel universes solve this problem. Once in the past, you find yourself in parallel reality, in which events take place that for your reality have long passed. And changes in her change her, but not your world. Although there is still no need to crush butterflies.
Parallel universes fit into the logic of knowledge
Studying the surrounding world for a person throughout his history is a struggle with the human ego. At first people thought that the Earth was the center of the Universe. Then they agreed to the Sun, casually sending several scientists to the stake. Further - more: the Sun is already just a tiny star on the periphery of one of billions of galaxies. Following this logic, it is likely that we ourselves are not unique and are only one of an infinite number of variants of us existing in a parallel universe. We can only hope that at least somewhere we are conducting parallel healthy image life and don’t do stupid things.
Based on HowStuffWorks.com