Even physicists are annoyed by the multiverse theory.

What do you think about the multiverse? The question was not entirely unexpected for our improvised lecture at the dinner table, but he caught me by surprise. Not that I have never been asked about the multiverse before, but explaining a theoretical construct is one thing, but explaining my feelings for it is quite another. I can voice all the standard arguments and main questions on the multiverse, I can navigate in facts and technical details, but I’m getting lost in the results.

Physicists are not used to talking about how they relate to something. We are for solid knowledge, quantitative assessments and experiments. But even the best of impartial analyzes begin only after we decide which way to go. In a nascent area, there is usually a choice of possibilities, each of which has its merits, and often we choose one of them instinctively. This choice is determined by the emotional reasoning above logic. The position you associate yourself with is, as Leonard Susskind, a physicist at Stanford University, says, “more than just scientific facts and philosophical principles. This is a matter of good taste in science. And, like all disputes about tastes, aesthetic feelings are involved. ”


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I myself am engaged in string theory, and one of its features is the possibility of the existence of a multitude of logically consistent versions of universes that are different from ours. The process that created our Universe can create those others, which leads to an infinite number of universes, where everything that can happen is happening. The sequence of reasoning begins with a place I know, and I can follow the curlicues that make the equations in their dance on the page that leads to this conclusion, but although I imagine the multiverse as a mathematical construction, I cannot believe that it will jump out of field of theories and show itself in reality. How can I pretend that I have no problems with an infinite number of copies of me, walking around parallel worlds, and making decisions, both similar and different from mine?

I am not the only one who is dual. The debate on the multiverse was hot, and it remains a source of controversy among the most eminent scientists of our time. The multiverse debate is not just a discussion of the details of a theory. It is a struggle on the subject of identity and results, on what the explanation is based on, what the evidence consists of, how we define science, and whether there is a sense in all this.

Whenever I talk about the multiverse, I have an answer to one of the inevitable questions. Whether we live in the universe or the multiverse, these classifications refer to scales whose size goes beyond the imagination. Regardless of the result, life around us will not change. So what's the difference?

There is a difference, because where we are affects who we are. Different places lead to different reactions, from which different possibilities arise. One object may look different on a different background. We are determined by the space we inhabit in much more ways than we realize. The universe is the limit of expansion. It contains all places of action, all contexts in which we can imagine being. It represents the total amount of possibilities, the complete set of everything we can be.

Measurement makes sense only in the reference system. Numbers are obviously abstract, until they are assigned to units of measure, but even such vague definitions as “too far”, “too small”, “too strange” imply a certain coordinate system. Too far implies a point of reference. Too small refers to the scale. Too strange implies context. In contrast to the always declared units of measurement, the reference system of assumptions is rarely determined, but still, the values ​​assigned to things — objects, phenomena, experience — are calibrated along these invisible axes.

If we find that everything that we know and can find out is only in one of the pockets of the multiverse, the whole foundation on which we positioned our coordinate grid will move. Observations will not change, but conclusions will change. The presence of other bubble universes may not affect the measurements that we take, but may affect the way we interpret them.

The first thing that strikes the multiverse is its immensity. It is more than anything that mankind has dealt with — such exaltation is implied in the name itself. It would be possible to understand if the emotional reaction to the multiverse came from a sense of self-understatement. But the size of the multiverse is probably the least controversial of its properties.

Gian Giudice, the head of the CERN theorists, speaks on behalf of physicists when he claims that one glance at the sky clears our brains. We already imagine our scope. If the multiverse exists, then, as he says, “the problem of opposing me and the immensity of the universe will not change.” Many even reassured by such a cosmic perspective. Compared to the universe, all our problems and life dramas diminish so much that “everything that happens here doesn't matter,” says physicist and author Lawrence Krauss. "This is very comforting for me."

From stunning photographs taken with a telescope. Hubble, before the poems of Octavio Paz about Monty Python's “extensive night” and “galactic song”, there is romanticism associated with our Lilliputian scale. At some point in our history, we resigned ourselves to our infinite smallness.



Is it because of our fear of scale that we are so reluctant to accept the concept of the multiverse, including worlds that are out of our sight, and doomed to be there? This, of course, is a very frequent complaint that I hear from my colleagues. The South African physicist George Ellis, who strongly opposes the multiverse, and the British cosmologist Bernard Carr, who also agitates strongly for her, discussed these issues in several charming conversations. Carr believes that their point of discrepancy relates to "what properties of science must be considered inviolable." Experiments are a common indicator. Comparative observations are a valid substitute. Astronomers are not able to control galaxies, but they are surveyed by millions, in different forms and states. None of the methods fit the multiverse. Does it lie, then, outside the scientific field?

Susskind, one of the fathers of string theory, reassures us. In empirical science there is a third approach: to draw conclusions about invisible objects and phenomena from what we are able to see. For example, it will suffice to take subatomic particles. Quarks are forever bound into protons, neutrons and other composite particles. “They are, so to speak, hidden behind a veil,” says Susskind, “but now, although we have not seen a single isolated quark, no one will seriously question the correctness of the quark theory. This is part of the foundation of modern physics. ”

As the universe expands with acceleration, the galaxies that are now on the horizon of the field of view will soon disappear behind it. We do not believe that they will go into oblivion, just as we do not believe that the ship will be disintegrated, hiding behind the horizon. If galaxies known to us can exist in remote areas beyond the field of view, who can say that there can be no other? Things we have never seen and never will see? As soon as we recognize the possibility of the existence of regions beyond our horizons, the consequences grow exponentially. British royal astronomer Martin Rees compares this line of reasoning with therapy aimed at producing disgust. When you recognize the presence of galaxies outside our current horizon, you “start with a small spider that is very far away”, but you don’t have time to look back and give free rein to the possibility of the existence of a multiverse inhabited by endless worlds, perhaps very different from yours - that is, "Find a tarantula crawling over you."

The inability to directly manage objects has never been my personal criterion for determining the suitability of a physical theory. If something worries me about the multiverse, I'm sure it has nothing to do with it.

The multiverse challenges another representation that is dear to us - uniqueness. Could this be causing problems? As cosmologist Alexander Vilenkin explains, no matter how large the observed region is, as long as it is finite, it can be in a finite number of quantum states. And the description of these states uniquely determines the contents of the region. If there are infinitely many of these regions, the same state will necessarily be reproduced somewhere else. Even our words will be accurately reproduced. As the process continues to infinity, our copies will also be an infinite number.



“Having these copies makes me depressed,” says Vilenkin. - Our civilization has many negative features, but at least we could claim its uniqueness - as a work of art. And now we cannot say that either. ” I understand what he means. It worries me, but I'm not sure that this thought is the basis of my dissatisfaction. As Vilenkin speaks with longing, "I am not arrogant enough to tell reality what it should be."

The main mystery of the debate lies in strange irony. Although the multiverse expands our concept of physical reality to an almost unimaginable size, it evokes a feeling of claustrophobia, as it draws the line between our knowledge and our possibilities of obtaining knowledge. Theorists dream of a world without arbitrariness, described by self-sufficient equations. Our goal is to find a logically complete theory, strongly limited by self-sufficiency, and taking only one form. Then for us, not even knowing where this theory came from or why, its structure will not look random. All the fundamental constants of nature will appear “from mathematics, numbers π and twos,” as Berkhley physicist Raphael Bousso says.

This is the attraction of Einstein's General Theory of Relativity - the reason why physicists of the whole world exclaim because of its unusual immortal beauty. Considerations of symmetry dictate equations so clearly that theory seems inevitable. That is what we wanted to repeat in other areas of physics. And while we did not succeed.

For decades, scientists have been looking for physical reasons for why fundamental constants are required to take exactly those values ​​that they have, but so far no single reason has been found. And in general, if we use the available theories to calculate the possible values ​​of some of the known parameters, the results are ridiculously far from the measured values. But how to explain these parameters? If there is only one single universe, then the parameters controlling it should be clothed with a special meaning. Either the process that controls the choice of parameters is random, or there is some logic in it, or even a deliberate goal.

None of the options looks attractive. We, scientists, spend our lives looking for laws, because we believe that everything happens for some reason, even if it is unknown to us. We are looking for patterns, because we believe in a certain order in the universe, even if we do not see it. Pure chance does not fit into this worldview.

But I don’t want to talk about a rational plan either, because it implies the existence of some kind of force that preceded the laws of nature. This force must choose and judge that, in the absence of such a clear, balanced and tightly limited structure, such as GR, implies arbitrariness. The idea of ​​the possibility of the existence of several logically consistent universes, of which only one was chosen, is something frankly unsatisfactory. If this were the case, then, as the cosmologist Dennis Sciama says, you will have to think that “there is someone who studies such a list, and sentencing, 'No, we will not have such a universe, and there will not be such a universe. It will only be like this. ”

Personally, I have this option, with all its implications about what could be upsetting. Various scenes come to mind: abandoned children in a shelter from some forgotten film, when one of them is adopted; the faces of people who frantically pursued a dream but did not achieve it; miscarriages in the first trimester. Such things that are almost born, but could not, torment me. If there is no theoretical limit excluding all possibilities except one, this choice seems cruel and unfair.

In such a carefully crafted creation how to explain unnecessary suffering? Since these philosophical, ethical, and moral issues are not related to the field of physics, most scientists avoid discussing them. But the Nobel Prize winner Steven Weinberg [Steven Weinberg] spoke on their behalf: “Are there any traces of a generous creator in our lives — everyone will answer this question for themselves. My life was amazingly happy. But still, I saw my mother painfully dying of cancer, Alzheimer's disease destroying her father’s personality, and how many cousins ​​and second cousins ​​were killed during the Holocaust. Signs of the presence of a generous creator are very well hidden. ”

In the face of pain, it is much easier to accept chance than stale disregard or deliberate evil deed present in a meticulously crafted universe.

The multiverse promised to distract us from these terrible thoughts, to give us a third option, overcoming the explanation dilemma.

Of course, the multiverse physics was not invented for this. She appeared from other considerations. The theory of cosmic inflation should have explained the large-scale smoothness and the absence of the curvature of the Universe. “We were looking for a simple explanation for why the Universe looks like a big ball,” says Stanford physicist Andrei Linde. - We did not know that something will go to this idea in the load. The burden was the realization that our Big Bang was not unique, and that, in fact, there must be an infinite number of such explosions, each of which creates space-time not related to ours.

Then came the string theory. Today it is the best candidate for a unified theory of everything. She not only achieves the impossible - the reconciliation of gravity and quantum mechanics - but she insists on it. But for a scheme that reduces an incredible diversity of the universe to a minimal set of building blocks, string theory suffers from a humiliating problem: we do not know how to determine the exact values ​​of the fundamental constants. According to current estimates, there is $$$10 ^ {500}$potential - an immeasurably huge number for which we do not even have a name. String theory lists all the forms that the laws of physics are capable of accepting, and inflation makes it possible to implement them. With the birth of each new universe, an imaginary deck of cards is shuffled. The open hand determines the laws governing the universe.

The multiverse explains how constants from equations have acquired their intrinsic values ​​without attracting randomness or a reasonable choice. If there are a lot of universes in which all possible laws of physics are implemented, we get exactly these values ​​when measuring, because our universe is located on this place of the landscape. There is no deeper explanation. Everything. This is the answer.



But, freeing us from the old dichotomy, the multiverse leaves us in a disturbed state. A question that we have been fighting for so long may not have a deeper answer than “this is the way it is.” Perhaps this is the best we can do, but we are not used to such answers. He does not tear the covers and does not explain how everything works. Moreover, he breaks the dream of theorists, arguing that a unique solution cannot be found, since it does not exist.

Some people do not like this answer, others believe that it is impossible to call it an answer, while others simply accept it.

Nobel laureate David Gross [David Gross] seems that the multiverse “smacks of angels.” He says that accepting the multiverse is akin to giving up, assuming that you will never understand anything, because everything observable can be reduced to "historical coincidence." His colleague in the Nobel Prize, Gerard 't Hooft, complains that he cannot accept the scenario in which it is necessary to “go through all the decisions until you find the appropriate one for our world.” He says: “Physicists have not worked this way in the past, and it is still possible to hope that in the future we will have better evidence”.

Princeton cosmologist Paul Steinhardt calls the multiverse "the theory of anything" because she admits everything and does not explain anything. “A scientific theory must be selective,” he says. “Her strength is in the excluded number of possibilities.” If it includes all the possibilities, it does not exclude anything, and its strength is zero. " Steinhardt was one of the early proponents of inflation, until he realized that it leads to the multiverse, and generates a space of opportunity, instead of making specific predictions. Since then, he has become one of the loudest critics of inflation. In a recent Star Talk episode, he introduced himself as a champion of the multiverse alternatives. “Why are you so annoyed by the multiverse? - joked the presenter. “She destroyed one of my favorite ideas,” Steinhardt replied.

Physicists had to deal with truth, absolute concepts, predictions. Or things like that, or not like that. Theories should not be flexible or inclusive, they should be restrictive, rigorous, and exclude options. For any situation I want to be able to predict the likely - and ideally, the only and inevitable - result. The multiverse doesn't give us anything like that.

The debate on the multiverse often results in a lot of controversy, where skeptics blame the advocates of the idea of ​​betraying science. But it is important to realize that no one has chosen this state of affairs. Everyone wants a universe that arises organically from beautiful deep principles. But from what we know, there is no such thing in our universe. She is what she is.

Do I have to argue against the idea of ​​the multiverse? Should she stay on the sidelines? Many of my colleagues are trying to present it in a more favorable light. Logically, it is easier to work with an infinite number of universes than with one - less things have to be explained. In the words of Stsiam, the multiverse "in some sense satisfies Occam's razor, because you want to minimize the number of random constraints imposed on the universe." Weinberg says that the theory, free from arbitrary assumptions, and not subjected to "careful adjustment to fit the observations," is beautiful in itself. It may turn out that this beauty is similar to the beauty of thermodynamics, with statistical beauty explaining the state of the macroscopic system, but not each of its individual components. “In search of beauty, you cannot be sure in advance where you will find it, or what kind of beauty you will find,” says Weisenberg.

Many times when I reflected on these complex intellectual problems, my thoughts returned to the simple and beautiful wisdom of the Little Prince from the work of Antoine de Saint-Exupéry, who, considering his favorite rose to be the only one for all worlds, turned out to be in a rose garden. Bewildered by such betrayal and distressed by the loss of importance - his roses and himself - he is crying. As a result, he realizes that his rose is “more important than hundreds of others”, because it is his.

In our universe there can be nothing special, except that it is ours. Isn't that enough? Even if all our lives and all that we can know will be insignificant on the scale of the cosmos, they are still ours. There is something special about here and now, that something is mine.

Several times in the past months I have been reproducing my conversation with Jian Judis in my mind. I found confidence in how calmly he felt about the huge number of possible universes and seemingly random choices made by ours. Perhaps the multiverse simply informs us that we are not working on those issues, he says. Perhaps, like Kepler with the orbits of the planets, we are trying to find a deeper meaning in numbers than there is.

Since Kepler knew only about the existence of the Solar System, he believed that some important information was hidden in the shape of the orbits of the planets and in the distances between them, but it turned out that this was not so. These values ​​were not fundamental, they were just data about the environment. At the time, this might seem regrettable, but from the point of view of GR, we no longer feel a sense of loss. We have a great explanation for gravity. Just in this explanation, the values ​​associated with the orbits of the planets are not fundamental constants.

Perhaps, says Judis, the multiverse implies something similar. Maybe we need to give up what we grab. Maybe you need to think more broadly, regroup, change the questions we ask nature. According to him, the multiverse can open "extremely satisfactory, pleasant and eye-expanding opportunities."

Of all the arguments in favor of the multiverse, this one I like the most. In any scenario in any physical system you can ask infinitely many questions. We try to unravel the problem to its foundations and ask the most basic questions, but our intuition is built on what it was before, and it is possible that we are based on paradigms that are no longer relevant to the new areas that we are trying to explore.

The multiverse is more like a key than a closed door. From my point of view, the world was painted with hope and filled with possibilities. It is no more wasteful than an arbor full of roses.