In string theory, you can do with a much smaller number of universes.

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As some modern physicists say, the problem of string theory (hereinafter TC) is that it requires too many universes to work. According to the TS, there is $$$10 ^ {500}$versions of the world, each with its own laws of physics. But if we are faced with such a range of world order options, how can we adapt the theory to explain the principles of our reality?

Again, as most physicists suggest — and perhaps all — additional Universes are in fact compactified; This assumption, in turn, is adopted in order to include in the theory the constancy of dark energy (hereinafter TE), which is still considered the main driving force of the inflationary expansion of the cosmos. However, some scientists have a desire to destroy the "extra" measurements; at the same time, they declare that this is not a step back, but on the contrary, a serious breakthrough in improving the vehicle. Alas, the rest of the scientific community still believes that the “multiverse” approach should be preserved, and in general, in general, this is not such a problem.

Debates on such a burning topic were held in Japan, at the end of June, where string theory supporters gathered from all over the world at the Strings 2018 conference (“Strings 2018”). “A few fresh thoughts led to fierce controversy on some issues,” says Ulf Danielsson, a physicist at Uppsala University, Sweden. The discussion mainly revolved around a pair of scientific papers ( first , second ) published on the ArXiv web resource during the last month, which focused on what is called the “landscape” — an incomprehensible set of potential universes that appeared as a result of solving various equations that TS is described and our world with all its contents, including dark energy. As both works emphasize, if you drag a theory from a “landscape” convenient for it to a so-called “swamp” , then mathematics begins to limp and contradict itself. Over the past few years, many decisions have fallen straight into the “swamp”, but no one has yet expressed the idea that all or almost all the results based earlier on the “landscape” principle should go there. As Kamran Wafa , a physicist at Harvard University, said at the conference: "It is quite possible that we are in principle not able to find the right solution for string theory involving dark energy."
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Lost in the Multiverse

String theory has long been positioned as an attempt to describe the world around us with some kind of unified “Theory of Everything”, by adding additional dimensions to it and treating all particles as miniature continuously vibrating “strings”. Many adherents of the TC still consider it the most appropriate way to finally fulfill Albert Einstein's dream - to combine the general theory of relativity (GTR) with quantum effects. Moreover, it should be noted that the “landscape”, which predicts the behavior of many universes, often repels physicists. “From my point of view,“ landscape ”is killing theory because it loses value as a method of forecasting,” says Paul Steinhardt, a physicist at Princeton University, the author of one of the above-mentioned papers criticizing the CU, “Almost anything is allowed.” Steinhardt and his colleagues see a way out of the situation in the newly discovered problems with the addition of dark energy. “This story with the“ huge multiversum ”is most likely mathematically incorrect,” adds Danielsson. “Which is rather curious, since the theory paradoxically becomes more prophetic than we thought.”

Some theorists like Savedipa Seti from the University of Chicago, on the contrary, are even happy with what is happening: “I think this is wonderful. I have been skeptical about the concept of “landscape” for a long time, and it is good to hear that the paradigm has shifted from the point of blind faith in the ability to prove all these solutions. ” But not everyone likes the idea that the results on the basis of the "landscape" should actually be in the "swamp" - especially the team of researchers who proposed one of the first versions of the "landscape" in 2003, called KKLT after the first letters of the scientists - creators. Shamit Kahru, a member of the KKLT group at Stanford University, expressed doubts about the argumentation of Wafa and the others: “No, of course it’s great to engage in various speculation and try to predict how this will affect the result, but I see no reason to take this "guessing game" seriously. The initial data and how we put them together in a single whole - everything is perfectly justified. ” Juan Maldacena , a theoretical physicist at the Institute for Advanced Study, New Jersey, also said that he will continue to adhere to the idea of ​​the existence of a multitude of universes with dark energy in the framework of string theory.

Yes, many in science are quite satisfied with the multi-subsection vehicle. "It is clear that if the approach using the landscape is correct, then comparing our Universe with a multiverse is like comparing the Solar System with the rest of the Universe," explains Kahra. - "And this is good. Johann Kepler tried to find the fundamental reason why the Earth is at such a distance from the Sun, and not some other one. But now we know that our star is one of the billions even in this galaxy, and many of them also have planets, and the radius of the earth's orbit is just a random number, and not the result of some mathematical relationship hidden deep in the fabric of the universe. Accordingly, if we assume the presence of trillions of other universes, then the parameters of the space around us are just a set of arbitrary numbers, no more. And the conclusion that they seem to fit perfectly for a person’s life is simply a selection error; over time, humanity will surely find similar to itself in those rare corners of the multiverse, where conditions are suitable for people. ”

Accelerating Universe

Well, let us return to the question of dark energy: it is its immutability that doesn’t fit in with string theory. And according to Wafa, this is an excellent reason to doubt the very concept of FC - especially in the form that is called the “cosmological constant . ” The idea, which was proposed by Einstein in 1917, got a second life in 1998, when astronomers found out that the Universe is not just expanding, but doing it with acceleration. The cosmological constant was supposed to be a form of vacuum energy, stable and opposing the forces of gravity. But, as it turned out, this is not the only possible way to justify the accelerating spread of worlds. For example, there is a hypothesis about the "quintessence" as a kind of a certain field, permeating the entire observable Universe and at the same time changeable. “Regardless of whether the adherents of string theory can finally link it with constant dark energy, it suddenly turned out that the idea of ​​inconsistency in fuel cells looks much more natural in the vehicle,” Wafa said, “but in this case, the one who can measure the change dark energy through astronomical observations. "

And since all the data that astronomers have collected before, confirmed the idea of ​​a cosmological constant, now there is some room for maneuver. On the Euclid probe , the NASA WFIRST infrared telescope and the equipment of the Simons Laboratory under construction, a number of experiments have already been planned to see if dark energy was weaker or stronger in the past than it is now. Paul Steinhardt: “We don’t even have to wait for some new technologies to start. We are already in business. "
Surprisingly, even those who were skeptical of Wafa’s suggestion support the search for an alternative to the cosmological constant. For example, you can quote Eva Silverstein , an American cosmologist and theoretical physicist: “I don’t think there is any reason to start guessing what the results of dark energy observations will be. But I agree that [the alternating field of dark energy] it greatly simplifies the creation of a model of accelerated expansion of the Universe. ”

"Quintessence" is not the only option, by the way. Against the background of the work of Wafa, Danielsson and his colleagues presented an alternative way to “make friends” of the FC and TS. In their version, our Universe is a three-dimensional surface of a bubble expanding into space with a large number of dimensions. "Scientists using such a surface can replicate physics with a cosmological constant," explains Danielsson. "Compared to what we thought before, this is a completely different method of substitute dark energy into the equation."

Fine Theory

Without a doubt, the main question behind all discussions about string theory is: what is the meaning of physics as a science? Can we demand explanations about any smallest event in the Universe surrounding us from even the coolest theory, or is it too much? And when the theory contradicts our ideas about the structure of the world - should we discard the theory or what we consider as “knowledge” about the nature of things?

Yes, the TS attracts many with its “beauty” - the solutions to its equations are quite satisfactory, and the explanations offered to it are not without elegance. But gradually there is a lack of evidence - and even worse, there is no certainty that they will, in principle, be found. However, even the assumption that it is impossible to turn on the TE in the vehicle does not stop the fans. “It is so capacious and gorgeous, and so correct in many areas that we have taught ourselves to think -“ error is not in theory, I am mistaken myself, ”reminds the Network -“ But the pursuit of “beauty” is not the best way to develop the correct Common Theory of the Universe. In the end, as Lost in Physics Astray wrote in her latest book, Lost in Math: “Lost in Math: How Beauty Brings Physicists Off the Way”) Sabina Hossenfielder from the Institute for Advanced Study, Frankfurt: “Mathematics is full of amazing and wonderful things, and most of them have nothing to do with the real world. ”

Despite the often opposite views, theoretical physicists are nevertheless nice guys, united by a common thirst - to know everything, including the Universe. Kahra, who created the "landscape", was Wafa's supervisor, a fierce critic of her ideas - but they are still friends. “Once he asked me if I was ready to swear with my life that the“ landscape ”exists,” Kahru laughs. “I replied that I would swear with his life!”

The author of additional materials - Lee Billings.
Article courtesy of Astrobiology Magazine , a Web site sponsored by the NASA Astrobiology Program .