“The most incomprehensible thing in the universe is that it is understandable,” Albert Einstein once said. These days, however, the universe can hardly be called comprehensible or even unique. Fundamental physics is in crisis with two popular concepts often referred to as "multiverse" and "uglyverse", which literally stand for "multiple universe" and "ugly universe".
How does the universe work?
Proponents of a multiple universe defend the idea of the existence of innumerable other universes, some of which have completely different physics and the number of spatial dimensions; in these universes, you, I, and everyone else can exist as countless copies. "The multiverse may be the most dangerous idea in physics," said South African cosmologist George Ellis.
From the earliest days of science, the discovery of an unlikely coincidence led to the need to explain it, to look for a hidden cause and motive. Modern examples include this: the laws of physics seem to be fine-tuned to allow intelligent beings to detect these laws - a coincidence that needs explanation.
With the advent of the multiverse, everything has changed: no matter how incredible the coincidence, in the billions of billions of universes that make up the multiverse, at least somewhere - it will be. And if coincidence seems to be conducive to the emergence of complex structures, life or consciousness, we should not even be surprised that we are in a universe that allows us to exist in the first place. But this "anthropic reasoning", in turn, implies that we cannot predict anything. There are no obvious principles for CERN physicists to search for new particles. And there is no fundamental law to be found behind the random properties of the universe.
Another problem has become completely different, but no less dangerous - the "ugly universe". According to theoretical physicist Sabina Hossenfelder, modern physics was baffled by its attraction to the "beautiful", which led to the emergence of mathematically elegant, speculative fantasies with no connection to experiments. Physicists are "lost in mathematics," she says. And what physicists call "beauty" are structures and symmetries. If we cannot rely on such concepts any longer, the difference between understanding and simply conforming to experimental data will be blurred.
Both problems have their roots. “Why doesn't the laws of nature give a damn about what I think is beautiful?” Hossenfelder justly asks. And the answer is: they don't care. Of course, nature could be complex, confusing and incomprehensible - if it were classical. But nature is not like that. The nature is quantum mechanical. And although classical physics is the science of our daily life, in which objects are separable from each other, quantum mechanics is different. The condition of your car is not related to the color of your wife's dress. But in quantum mechanics, all things are causally related to each other, which Einstein called "spooky action at a distance." Such correlations make up structure, and structure is beautiful.
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By contrast, the multiverse seems hard to deny. Quantum mechanics, in particular, treats it well. The firing of individual electrons into a screen with two slits results in the appearance of an interference pattern on the detector behind the screen. In each case, it turns out that the electron passes both slits each time.
Quantum physics is the science behind nuclear explosions, smartphones, and particle collisions - and it's known for its weirdos, like Schrödinger's cat suspended between life and death. In quantum mechanics, different realities can overlap one another (like "particle here" and "particle there" or "cat is alive" and "cat is dead"), like waves on the surface of a lake. The particle can be half here and half there. This is called superposition, and it is this that leads to the appearance of the interference pattern.
Originally developed to describe the microscopic world, quantum mechanics has shown in recent years that it controls ever larger objects as long as they are sufficiently isolated from the environment. However, for some reason, our daily life is somehow protected from too many quantum weirdness. No one has ever seen a half-dead cat, and whenever you measure the position of a particle, you get a certain result.
Direct interpretation assumes that all possible options are realized, albeit in different, but parallel realities of "Everett branches" - named after Hugh Everett, who first defended this point of view, known as the many-worlds interpretation of quantum mechanics. Everett's "many worlds" actually represent just one example of a multiverse - one of four. The other two are less interesting, and the third is the "string theory landscape" to which we will return later.
By resorting to quantum mechanics to justify the beauty of physics, we seem to be sacrificing the uniqueness of the universe. However, this conclusion lies only on the surface. What is usually overlooked in such a picture is that Everett's multiverse is not fundamental. It is only apparent or "emergent," as the philosopher David Wallace of the University of Southern California puts it.
To understand this point, you need to understand the principle underlying both quantum measurements, as well as "eerie action at a distance." Key to both phenomena is the concept of "entanglement", which was pointed out in 1935 by Einstein, Boris Podolsky and Nathaniel Rosen: in quantum mechanics, a system of two entangled spins with a zero sum can consist of a superposition of pairs of spins with opposite directions of rotation with absolute uncertainty in the directions of rotation of individual spins. Entanglement is a natural way to combine parts into a whole; individual properties of the constituents cease to exist in favor of a strongly tied general system.
Whenever a quantum system is measured or associated with the environment, entanglement plays an important role: the quantum system, the observer, and the rest of the universe are intertwined. From the point of view of a local observer, the information is scattered in an unknown environment and the process of "decoherence" begins. Decoherence is an agent of classicality: it describes the loss of quantum properties when a quantum system interacts with its environment. Decoherence works like a zipper between the parallel realities of quantum physics. From the point of view of the observer, the universe "splits" into separate branches of Everett. The observer observes a live cat or a dead cat, but nothing in between. For him, the world appears to be classical, although from a global point of view it is still quantum mechanical. Actually,from this point of view, the entire universe is a quantum object.
Quantum Monism
And here we draw on the most interesting concept of "quantum monism" proposed by the philosopher Jonathan Schaffer. Shaffer pondered the question of what the universe is made of. According to quantum monism, the fundamental layer of reality does not consist of particles or strings, but of the universe itself, understood not as the sum of its constituent things, but rather as a single entangled quantum state.
Similar thoughts have been expressed earlier, for example, by the physicist and philosopher Karl Friedrich von Weizsacker: Taking quantum mechanics seriously predicts a unique, unified quantum reality that underlies the multiverse. The homogeneity and tiny fluctuations in the temperature of the cosmic microwave background, which indicate that the observable universe can be traced back to a single quantum state, usually associated with the quantum field of primordial inflation, support this view.
Moreover, this conclusion extends to other multiverse concepts. Because entanglement is universal, it is not limited to our cosmic bubble. Whatever the multiverse is, if you embrace quantum monism, everything will be part of a single whole: there will always be a more fundamental layer of reality underlying the multiverse within the multiverse, and this layer will be unique.
Both quantum monism and Everett's many-worlds interpretation are predictions of quantum mechanics. They are distinguished only by perspective: what, from the point of view of a local observer, will look like “many worlds”, in reality represents a single unique universe from a global point of view (for example, a creature that can see the whole universe from the outside).
In other words, many worlds are quantum monism through the eyes of an observer with limited information about the universe. In fact, Everett's original motivation was to develop a quantum description of the entire universe in terms of a "universal wave function." Look at it as through a cloudy window: nature is divided into many pieces, but this is only a distortion of perspective.
Monism and multiple worlds can be avoided, but only if someone changes the formalism of quantum mechanics - usually this conflicts with Einstein's special theory of relativity - or someone presents quantum mechanics not as a theory about science, but as about knowledge: human ideas, but not science.
In its current form, quantum monism should be seen as a key concept in modern physics: it explains why "beauty", perceived as structure, correlation and symmetry between externally independent spheres of nature, is not a distorted aesthetic ideal, but a consequence of the splitting of nature from a single quantum state. Furthermore, quantum monism also obviates the need for a multiple universe, as it predicts correlations realized not only in a single born universe, but in any single branch of the multiverse.
Finally, quantum monism could solve the crisis of experimental fundamental physics, which relies on ever larger colliders to study ever smaller constituents of nature. Because the smallest components will not be the fundamental layer of reality. Studying the basics of quantum mechanics, new areas of quantum field theory, or the largest structures in cosmology can be just as rewarding.
All this means that we must not stop searching. In the end, this desire cannot be taken away from us. Somewhere deep below, there is a unique, understandable and fundamental reality.
Ilya Khel
