The Crisis of the Standard Model: Physicists Rethink the Nature of Nature
Back to Park 04-28 08: 49
Although the Standard Model is considered one of the most successful theories of physics ever, there have been growing signs in recent years suggesting a crisis in the Standard Model. In fact, the Standard Model has not been perfect since its inception, or even a self-consistent theory. It is "unnatural", especially with regard to the "hierarchy problem" raised by the mass of the Higgs boson, which has so far no fundamental answer. There is a simple and convenient theory that can explain these problems, that is, supersymmetry theory, but experimentally, the most powerful collider has not found any supersymmetric particles. This has forced many physicists to rethink the nature of the model, perhaps at the most basic level, that reductionist ideas do not solve the problem, even though they have led the way in physics for hundreds of years. Now, many physicists have found a "mixed" model of different energy targets to solve the problem of "naturalness", breaking the original reductivist form.
Written by | Natalie Wolchover
Translate | Liu Hang
For nearly three decades, scientists have been futilely searching for new elementary particles to explain the nature we observe. When physicists face failure in their search for new particles, they have to rethink a long-standing hypothesis: that the big stuff is made up of the small ones.
Emily Buder/Quanta Magazine;
Kristina Armitage and Rui Braz for Quanta Magazine
In the classic book The Structure of the Scientific Revolution by the philosopher of science Thomas Kuhn, Kuhn observes that scientists sometimes take a long time to take a small step. They come up with a conundrum and synthesize all the data within a fixed worldview or theoretical framework to solve the conundrum, which Kuhn calls paradigms. Sooner or later, however, the fact that it conflicts with the dominant paradigm will suddenly emerge. A crisis ensued. Scientists racked their brains, revisited their hypotheses, and eventually made a revolutionary shift to a new paradigm of fundamentally different and more real understandings of nature. Then restart the steady progress of science.
For years, particle physicists who study the most basic components of nature have been in the midst of this textbook Kuhn crisis.
The crisis became undeniable in 2016. Despite major upgrades at the time, the Large Hadron Collider (LHC) in Geneva still hadn't "summoned" any new elementary particles — something theorists had been looking forward to for decades. The additional swarm of particles will primarily solve a puzzle about known particles, the famous Higgs boson. This conundrum is known as the Hierarchy problem, "Why the Higgs boson is so lightweight" — 1017 times smaller than the highest energy scales that exist in nature. Compared to those higher energies, the mass of the Higgs particle seems too small to be unnaturally small, as if the enormous numbers in the fundamental equations that determine their value have been miraculously canceled out.
The extra particles could explain why the mass of the Higgs particle is so tiny (relative to the Planck scale), restoring what physicists call "naturalness" in their equations. After the Large Hadron Collider became the third and largest collider, physicists still haven't found them. This seems to suggest that the logic of what nature is in our current theory of nature may itself be wrong. "It is necessary for us to rethink the guiding principles that have been used for decades to solve the most fundamental problems in the physical world." Gian Giudice, head of the theoretical department at CERN, said in 2017.
At first, the particle physics community despaired. "You can feel a sense of pessimism." Isabel Garcia Garcia, a particle theorist at the Caffrey Institute for Theoretical Physics at the University of California, Santa Barbara, said she was a graduate student at the time. The truth is that not only has the $10 billion Proton Collider failed to answer a 40-year-old question, but even the beliefs and strategies that have long guided particle physics are no longer unbreakable. People wonder more strongly than before whether the universe we live in is really unnatural, just the product of fine-tuned mathematical cancellation. There could be a multiverse, all of which had randomly adjusted Higgs masses and other parameters; we find ourselves living here only because the unique properties of our universe contributed to the formation of atoms, stars, and planets that led to the birth of life. While this "anthropic argumen" may be correct, it is frustratingly unverifiable.
Nathaniel Craig, a theoretical physicist at the University of California, Santa Barbara, says many particle physicists are turning to other fields where "the puzzles in other areas aren't as intractable as the hierarchy problem." ”
Nathaniel Craig and Isabel Garcia Garcia explore how gravity can help reconcile very different energy scales in nature. 丨 Image source: Jeff Liang
Some physicists are ready to take a closer look at the assumptions of decades ago. They began to rethink the unnatural and remarkable features of nature, all of which seemed to be finely tuned by unnatural, such as the small mass of the Higgs boson, and a seemingly unrelated fact that space itself was unnaturally low-energy. "The really fundamental problem is the problem of naturalness." Garcia said.
Their reflective work is bearing fruit. Researchers are increasingly focusing on weaknesses in traditional reasoning about naturalness. It is based on a seemingly mild hypothesis that has been considered scientific since ancient Greece: that the big stuff is made up of smaller, more fundamental things — a idea known as Reductionism. Nima Arkani-Hamed, a theoretical physicist at the Princeton Institute for Advanced Study, said: "The reductionist paradigm is closely related to the question of naturalness. ”
Now, a growing number of particle physicists believe that the problem of naturalness and the zero result of the Large Hadron Collider may be related to the failure of reductionism. "Is this going to be a game changer?" Arkani Hamid asked. In a recent series of papers, researchers have left reductionism behind. They are exploring new ways to potentially coordinate at different scales to derive parameter values that are unnaturally fine-tuned from a reductionist perspective.
"Some people call it a crisis. There's an atmosphere of pessimism, but I don't think so," Garcia said, "and I think it's time to do something profound." ”
What is naturalness?
In 2012, the Large Hadron Collider (LHC) finally made the most important discovery, the Higgs boson, which is the cornerstone of a system of equations for the 50-year-old Standard Model of Particle Physics (SM), which describes 17 known elementary particles.
The discovery of the Higgs particle confirms a fascinating story described in the Standard Model equations. Moments after the Big Bang, an entity called a Higgs field was suddenly filled with energy throughout space. The high-energy Higgs field is filled with the Higgs boson, and elementary particles derive mass from the energy of the Higgs field. As electrons, quarks, and other particles move through space, they interact with the Higgs boson and acquire mass in this way.
In 1975, the Standard Model was completed, and its creators noticed a problem almost immediately[1].
When a Higgs particle gives the mass of other particles, the mass of the other particles in turn affects the mass of the Higgs particle; all particles interact together. Physicists can write an equation for the mass of the Higgs boson, which includes the action of each particle that interacts with it. All discovered mass Model particles contribute to the equation, but the equation should, in principle, include other contributions. Higgs particles should mix (interact) with mathematically heavier particles until they include a Planck-scale phenomenon that reaches energy levels associated with the quantum properties of gravity, black holes, and the Big Bang. The idealism of the Planck scale would in principle contribute a magnitude of magnitude to the Higgs mass—about 1017 times the actual Higgs mass. Naturally we would expect the Higgs boson to be about as heavy as they are, thus increasing the mass of other elementary particles. Because the particles are too heavy to form atoms, the universe will be empty.
To explain why the Higgs particle relies on such a high energy but can be so light, it must be assumed that the Planck scale contributes negatively to one part of its mass while the other part is positive, and both are finely tuned just right to cancel it out completely. This may seem ridiculous, unless there is some reason — like to make the tip of the pencil balanced, to let the airflow and table vibration cancel each other out. Physicists believe that this fine adjustment to cancel each other out is "unnatural".
In the years that followed, physicists found an ingenious solution—supersymmetry, a theory that assumed the doubling of elementary particles in nature. In supersymmetry theory, each boson (spin to integer) has a supersymmetric companion fermion (spin is a half integer), and vice versa. Bosons and fermions contribute positive and negative terms to higgs masses, respectively. Therefore, if the two always appear in pairs, then they will always cancel each other out.
Since the 1990s, the Large Electron-Positron Collider has been looking for a supersymmetric companion. The researchers hypothesized that the particles were only a little heavier than their Standard Model partners and required more collision energy to achieve, so they accelerated the particles to near the speed of light, smashed, and then looked for heavy companions in the debris.
Hierarchy problem: The Higgs boson assigns mass to other elementary particles, which in turn affect the mass of the Higgs particle. Supermassive particles at the Planck scale (the high-energy scale associated with quantum gravity) should expand the mass of the Higgs boson and the mass of everything else. But this is not the case.
Problem: The mass of the Higgs boson is hundreds of billions of times smaller than the Planck scale.
Possible Solution 1: The Planck-scale effect is truncated because the more complete Higgs boson theory works at higher energies.
Possible Solution 2: The Higgs scale and planck scale are linked by a complex set of push-pull effects.
丨Education: Merrill Sherman for Quanta Magazine
A vacuum, even without matter, seems to be filled with energy—all the ups and downs of the quantum field run through it. When particle physicists summed up all possible contributions to space's energy, they found that, like the Higgs mass, an injection of energy from Planck-scale iconography exploded its mass (mass is infinite). Albert Einstein demonstrated that space energy, which he calls the Cosmological constant, has a gravitational repulsive effect. It makes the space expand faster and faster. If space had been injected with a Planck-scale energy density, the universe would have torn apart in an instant after the Big Bang. But that didn't happen.
Instead, cosmologists have observed that the expansion of space is only slowly accelerating, suggesting that the cosmological constant is small. Measurements in 1998 showed that the value was 1/4 to the power of 1030 times lower than planck energy. This time, the inputs and outputs of all the enormous energies in the cosmological constant equation seem to be perfectly canceled out again, leaving an unusually calm vacuum.
"Gravity... Mixed physics of all length scales — short distances, long distances. Because of its characteristics, we have found a way out of the problems we encounter. ”
—Nathaniel Craig
These two major problems of naturalness were already evident in the late 1970s, but for decades physicists thought they were unrelated. Arkani-Hamed said: "People were fanatical about it at that stage. "The cosmological constant problem seems to have a mysterious quantum implication of gravity, since the energy of space can only be detected by gravitational effects. Hamid says the hierarchy problem looks more like a "dirty little detail problem" that, like other puzzles in the past, will eventually reveal some missing parts of the theory. For the Higgs boson to be so light, Judich called it "Higgs bosonism" that could not be cured by a few supersymmetric particles in the Large Hadron Collider.
In hindsight, these two questions about naturalness are more like different manifestations of the same deeper problem.
"It's useful to think about how these problems arise," Garcia said in a phone interview with Zoom from Santa Barbara this winter. "The hierarchy problem and the cosmological constant problem arise in part because of the tools we're trying to answer the question—the way we understand the characteristics of the universe."
The precise prediction of reductionism
Physicists honestly calculated the Higgs mass and cosmological constant in their own way. The calculation method reflects the peculiar nesting doll structure of the natural world.
Zoom in on an object and you'll see that it's actually made up of many smaller things. Galaxies far away from us are actually a collection of stars with a huge number; each star is made up of many atoms; each atom can be further decomposed into subatomic hierarchical structures. In addition, when zoomed in to shorter distance scales, you'll see heavier, higher-energy elementary particles and phenomena — the deep connection between high-energy and short-range — explaining why the high-energy particle collider is like a microscope in the universe. The link between high energy and short distance is reflected in many aspects of physics throughout physics. For example, quantum mechanics says that particles are waves; the larger the mass of a particle, the shorter its associated wavelength. Another view is that energy must be gathered more densely to form smaller objects. Physicists refer to low-energy, long-range physics as "infrared" (IR) and high-energy, short-range physics as "ultraviolet" (UV), which is an analogy between the infrared band (IR) and ultraviolet (UV) bands that use light.
In the 1960s and 1970s, particle physics giants Kenneth Wilson and Steven Weinberg pointed out the beauty of nature's energy level structure: If we were only interested in what was happening on the macroscopic infrared energy scale, then we wouldn't have to know what was "really" happening under the more microscopic, ultraviolet energy scale. For example, you can use a hydrodynamic equation to model water, treating water as an ideal fluid and ignoring the complex dynamics of water molecules. The fluid dynamics equation consists of a term that characterizes the viscosity of water—a quantity that can be measured under the infrared energy scale, which contains the interaction of all water molecules under the ultraviolet energy scale. Physicists say that infrared and ultraviolet energy scales are mutually "decouple", which allows them to effectively describe the world without having to study the deepest case, the ultimate UV energy scale, the Planck energy scale, corresponding to the energy of 10^(-35) meters, or 10^19GeV. In such a delicate structure of space-time there may be another scene.
Kenneth Wilson, an American physicist of condensed matter and particles, was active from the 1960s to the early 2000s, developed a mathematical method (lattice point quantum field theory) to describe how the properties of a system change with the scale of measurement. 丨Education: Cornell University Faculty Archives #47-10-3394, Cornell University Library Treasured Resources and Manuscript Collections Division.
Riccardo Rattazzi, a theoretical physicist at the Swiss Federal Institute of Technology in Lausanne, said: "We can still do physics research because we don't have to know what's going to happen in the short distance." ”
Like the different levels of the matryoshka world, how do particle physicists simulate it? Wilson and Weinberg independently developed their frameworks: Effective field theory (EFT). In the context of effective field theory, the question of naturalness arises.
Efficient field theory can simulate a system within a certain range of energy scales. Take a bundle of proton and neutron streams, for example, to enlarge protons and neutrons, which still appear to be protons and neutrons; within this range, their dynamics can be described by "Chiral EFT". However, if further amplified, the effective field theory will reach its "ultraviolet truncation", that is, in the short-range, high-energy scale range, the manual effective field theory will no longer be an effective description of the system. For example, at the truncation point of 1GeV, the sign-effective field theory fails because protons and neutrons no longer behave like individual particles, but like three quarks. A different theory began to work.
It is important to note that there is a reason why the effective field theory fails at its UV truncation. Truncation means that new, higher-energy particles or iconography must be found here, and these new particles or phenomena are not contained in the original effective field theory. So how to solve this problem?
In the energy regions to which it applies, scientists use efficient field theory to absorb unknown effects above truncated UV physics into the "correction" term. It's like the fluid equation has a sticky term to capture the net effect of short-range molecular collisions. There is no need to know the real physics of the truncation, physicists can write these corrections; They simply use the critical value to estimate the magnitude of the impact.
Typically, at the infrared energy scale, when you calculate the amount of interest, the UV correction is small, proportional to the length scale associated with truncation (relatively small). However, the situation is different when you use efficient field theory to calculate parameters with mass or energy units such as the Higgs boson mass or cosmological constant. The UV correction of these parameters is large because (with the correct dimension) the correction is proportional to energy, not to the length corresponding to truncation. So despite the small length, the energy is high. Such parameters are called "UV-sensitive".
Efficient field theory is a strategy that determines where its theory must be truncated (i.e., the energy scales of new physics). The concept of naturalness appeared in the 1970s along with the effective field theory itself. The logic goes like this: if a mass or energy parameter has a high truncation point, then its value should naturally be large, pushed higher by all the UV corrections. Therefore, if the parameters are small, the truncation energy should be lower.
Some critics argue that naturalness is simply an aesthetic preference. But it has also been pointed out that this strategy reveals the hidden truth of nature. "This logic is feasible." Craig said. He is a leading figure in recently rethinking this logic. The Question of Naturalness "has always been a signpost, prompting us where there are changes in the picture and the emergence of new physics." ”
The splendor of naturalness
In 1974, a few years before the term "naturalness" appeared, Mary Ann Thompson Mary K. Gaillard and Benjamin Whisoh Lee used this strategy to surprisingly predict the mass of a then-hypothesized particle, the charm quark. Craig said: "Her predictions of success and their relevance to the hierarchy problem are grossly underestimated in our field of study. ”
That summer in 1974, Gaillard and Lee were puzzled by the magnitude of the mass difference between two K mesons (composite particles made up of positive and negative quarks). Poor quality measurements are small. But when they tried to calculate this mass difference using the equations of efficient field theory, they found that its value was at risk of overflow. Because the mass difference of the K meson has mass units, it is sensitive to ultraviolet radiation and obtains a high-energy correction from the unknown physics at the truncation. The truncated value of this theory was not well known, but physicists at the time thought it could not be very high, otherwise the resulting K meson mass difference would be surprisingly small compared to the corrected value – as physicists today say, this is unnatural. Gaillard and Lee deduced that their truncated energy scales in effective field theory were relatively low, and at this energy scale, the new physics should be revealed. They reasoned that a new particle called a cannabis quark proposed at the time should have a mass of no more than 1.5 GeV.
Three months later, the cannabis quark was discovered experimentally and weighed 1.2 GeV. The discovery sparked a revival of awareness known as the "November Revolution" and quickly led to the completion of the Standard Model. In a recent video call, Gaillard, now 82, recalled that she was visiting CERN in Europe when the news broke. Lee sent her a telegram: Cantonese quark had been found.
In 1974, Mary K. Gaillard and Ben Lee used the naturalness argument to predict the mass of a hypothetical elementary particle known as a cannabis quark. Cantonese quarks were discovered a few months later. (Above in the 1990s) 丨 Image source: AIP Emilio Segrè Visual Archives
Such triumphs have convinced many physicists that the new particles predicted by the hierarchy problem should not be much heavier than the Standard Model. If the Standard Model's truncation point is as high as close to the Planckian scale (if so, scientists must know that the Standard Model has failed because quantum gravity is not taken into account), then the ultraviolet correction to the Higgs mass would be enormous—such a light Higgs mass would naturally be unnatural. If the truncation point is not far above the mass of the Higgs boson, it will make the Higgs particles have a mass similar to the correction from the truncation point, and everything will look natural. "The choice of truncation point is the starting point for the last 40 years of trying to solve the hierarchy problem." Garcia said, "There are great ideas that come up with supersymmetry, [Higgs's] compounding, some of the possibilities that we haven't observed in nature yet."
After Garcia spent a few years in 2016 studying for a PhD in particle physics at Oxford University, she became acutely aware that liquidation was necessary. "I became more interested in the missing parts, which we usually don't include when we discuss these issues, which is gravity — recognizing that the content of quantum gravity is far richer than what we can learn from efficient field theory."
Gravity mixes everything
In the 1980s, theorists learned that gravity does not conform to the usual reductionist rules. If you slamme two particles together with such force, energy can gather at the point of collision and even form a black hole — a region with such gravitational pull that nothing can escape. If particles are slammed together more violently, they form a larger black hole. More energy doesn't allow you to see shorter distances; the harder you bump into each other, the larger the invisible area is created—contradicting reductionism. The theory of black holes and the quantum gravity that describes their interior completely overturns the usual relationship between high energy and short distance. "Gravity is anti-reductionist." Sergei Dubovsky, a physicist at New York University, said.
Quantum gravity seems to be joking with the architecture of nature, "physicists using effective field theory have become accustomed to simple and ingenious nested standard systems, and quantum gravity has "mocked" this set of things." Craig, like Garcia, began thinking about the effects of gravity shortly after the LHC's search was to no avail. While trying to solve the hierarchy problem in a variety of new ways, Craig reread a 2008 article on naturalness by CERN's theoretical physicist Juditche. Juditche wrote that the solution to the cosmological constant problem might involve "some complex interaction between infrared and ultraviolet effects," and Craig began to think carefully about its implications. If infrared and ultraviolet have complex interactions, that would violate the usual decoupling properties, and infrared and ultraviolet decoupling is the basis for making the effective field theory work. "I Googled keywords like 'hybrid ultraviolet-infrared.'" That led him to some interesting papers from 1999, Craig said, "and then I started thinking about that direction." ”
By breaking the reductionist system of effective field theory, ultraviolet-infrared hybridization may solve the problem of naturalness. In effective field theory, quantities like the Higgs mass and cosmological constant are UV sensitive, but for some reason they do not explode, as if all UV physics had reached a conspiracy between them—all the UV effects were canceled out, and then the question of naturalness arose. "In the logic of effective field theory, we give up this possibility." Craig explained. Reductionism tells us that infrared physics also derives from ultraviolet physics—the viscosity of water comes from its molecular dynamics, the properties of a proton come from its internal quarks, and when you zoom in on the signifier, the interpretation manifests itself—not the other way around. However, ultraviolet is not affected or explained by infrared, "so the effect of [the UV effect] on the Higgs particle cannot be inferred from very different energy levels." ”
The question Craig now asks is: "Will the logic of effective field theory fail?" "Maybe the interpretation can really flow in both directions between ultraviolet and infrared." This isn't entirely nonsense, because we know that gravity can do it. "Gravity doesn't satisfy the normal reasoning of effective field theory because it mixes physics on all length scales—short distances, long distances." Because of such characteristics, we have found a way out of the problems we encounter. ”
How the UV-IR blend protects naturalness
Several new studies on UV-IR hybrids, and how it solves the problem of naturalness, date back to two papers published in 1999. "There is growing interest in these more exotic, non-efficient field theory solutions." Patrick Draper said he was a professor at the University of Illinois at Urbana-Champaign, and his recent work[3] continued with the unfinished portion of the 1999 paper.
Dreb and his colleagues studied CKN constraints (named after the authors of the 1999 paper, Andrew Cohen, David B. Kaplan, and Ann Nelson). The authors consider a model in which numerous particles are put into a box and the box is heated, and the energy of the particles continues to increase until the box collapses into a black hole. They calculated that the number of high-energy particle states that could be put into the box before it collapsed was proportional to the three-quarters of the surface area of the box, rather than being proportional to the volume of the box as generally thought. They believe this characterizes a peculiar ultraviolet-infrared relationship. The size of the box sets the infrared scale, which severely limits the number of high-energy particle states in the box - the ultraviolet scale.
Then they realized that if this constraint applied to our entire universe as well, they could solve the problem of the cosmological constant. In this case, the observable universe is like a very large box. The number of high-energy particle states it can contain is proportional to the power of three-quarters of the surface area of the observable universe, rather than the much larger volume of the entire universe.
This means that the efficient field-theoretic calculations of the usual cosmological constants are naïve. The calculation of efficient field theory tells us that when you zoom in on the structure of space, the phenomenon of high energy should appear, and this should cause the energy of space to explode. But the CKN constraint implies that there may be much less high-energy motion than is assumed in efficient field theory calculations—meaning that particles can occupy very few high-energy particle states. Cohen, Kaplan, and Nelson did a simple calculation that showed that for a box of our universe's size, their constraints could explain tiny values of observed cosmological constants.
Their calculations suggest that large and small scales may be related to each other in some way, and this correlation becomes apparent when you look at the infrared properties of the entire universe, such as the cosmological constant.
In another rough calculation last year, Dreb and Nikita Blinov confirmed that the CKN constraint successfully estimated the observed cosmological constant; they also showed that this approach does not undermine many of the successes of efficient field theory in experiments at lower energy levels.
The CKN constraint doesn't tell us why UV and IR are interrelated—i.e., why the size of the box (infrared) severely limits the number of high-energy particle states in the box (UV). To know why, we may need to understand quantum gravity.
Other researchers look for answers in another specific theory of quantum gravity, string theory. Last summer, string theorists Steven Abel and Keith Dienes showed how ultraviolet-infrared hybrids in string theory solve the hierarchy problem and the cosmological constant problem.
As a candidate for gravity and other fundamental theories, string theory holds that all particles are strings that vibrate on or off. Standard Model particles such as photons and electrons are the low-energy vibration modes of the fundamental strings. But strings can also vibrate more vigorously, producing infinite chordal energy spectra of higher energies. In this case, the hierarchy problem is concerned with why these string-state corrections do not inflate the mass of the Higgs particles without supersymmetry to protect them.
Dines and Abel calculated that due to the different symmetries of string theory, the so-called Modular invariance, the correction of the chord states of all energies in the infinite energy spectrum from infrared to ultraviolet would cancel each other out in a reasonable way, thus keeping the Higgs mass and cosmological constant small. The researchers note that this association between low-energy and high-energy chords does not explain why the Higgs mass and Planck energy are so far apart, but the difference is stable. Still, in Craig's opinion, "it's a really good idea." ”
The new model represents a growing number of hybrid UV-IR concepts. Another of Craig's research angles can be traced back to another 1999 paper by Nathan Seiberg, a prominent theoretical physicist at the Institute for Advanced Study (IAS) in Princeton, and two collaborators. They studied the situation in which the background magnetic field fills space. To understand how the ultraviolet-infrared hybrid is produced here, imagine a pair of particles with opposite charges attached to a spring, perpendicular to the magnetic field flying through space. As you increase the energy of the magnetic field, the charged particles accelerate their separation, stretching the spring. In this toy scene, higher energies correspond to longer distances.
Seiberg and his colleagues found that UV correction in this case has a particular property — it can illustrate how the arrow of reductionism rotates, and infrared affects the case at the UV energy mark. This model is different from the real world, because the real universe does not have such a background magnetic field to apply direction. Still, Craig has been exploring whether a similar approach can be used to solve the hierarchy problem.
Craig, Garcia, and Seth Koren also co-founded an idea of quantum gravity, known as the Weak gravity conjecture (WGC), which, if proven correct, could impose a consistency condition on the hierarchy problem — making a huge separation between the Higgs mass and the Planck scale necessary.
New York University's Dubowski has been thinking about these questions since 2013, when it was understood that supersymmetric particles were slow to appear in the Large Hadron Collider. That year, he and two collaborators discovered a new model of quantum gravity,[4] which solved the hierarchy problem. In their model, the reductionist arrow points from the middle scale to both ultraviolet and infrared scales. While the results are interesting, this model only works in two-dimensional space, and Dubowski doesn't know how to generalize it. Later he turned to other issues. Last year, he again encountered the UV-IR hybrid problem: in the study of colliding black holes, he found that the problem of naturalness in it could be solved by "hidden" symmetry, which is related to the low and high frequencies of black hole deformation .[5]
Like other researchers, Dubowski doesn't seem to think that any particular model currently discovered has a distinctly Kuhn Revolutionary component. Some argue that the entire UV-IR hybrid concept lacks promise. "There is no sign of effective field theory failing." David E. Kaplan, a theoretical physicist at Johns Hopkins University(who has no relationship with the authors of the CKN paper), said, "I don't think there is." "Convincing ideas require experimental evidence, but so far existing hybrid ultraviolet-infrared models lack experimental predictions; they aim to explain why we don't see new particles outside the Standard Model, rather than predicting what we should see." However, for predicting and discovering new physics, even if it cannot be realized in the collider, there is still hope for the future in cosmology.
Taken together, the new hybrid ultraviolet-infrared model illustrates the short-sightedness of the old paradigm based on reductionism and effective field theory, which may be just the beginning.
"In fact, when you get to the Planck scale, reductionism fails, so gravity is anti-reductionist." Dubowski said, "I think, in a sense, it would be unfortunate if this fact didn't have a profound hint at what we observed." ”
exegesis
[1] https://journals.aps.org/prd/abstract/10.1103/PhysRevD.14.1667
[2] https://journals.aps.org/prd/abstract/10.1103/PhysRevD.10.897
[3] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.82.4971
[4] https://arxiv.org/abs/1305.6939
[5] https://journals.aps.org/prl/abstract/10.1103/PhysRevLett.127.101101
本文译自Natalie Wolchover, A Deepening Crisis Forces Physicists to Rethink Structure of Nature’s Laws 原文链接：
https://www.quantamagazine.org/crisis-in-particle-physics-forces-a-rethink-of-what-is-natural-20220301/
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