Shulou(Shulou.com)11/24 Report--

String theory is supposed to be the physics of the 21st century, but it accidentally falls into the 20th century-- Witten.

Witten of the Princeton Institute for Advanced Studies identified trends in physics as Picasso identified trends in the art world. Hundreds of physicists followed his work to understand his groundbreaking ideas.

Witten was born into a family of physicists. His father, Louis Witten (Iouis Witten), is a professor of physics at the University of Cincinnati and a leading academic authority on Einstein's general theory of relativity. His father said that his greatest contribution to physics was the birth of his son.

Witten studied at Princeton University, then taught at Harvard, and then became a full professor at Princeton at the age of 28. The derivative results of his work deeply influenced the field of mathematics. In 1990, he was awarded the Fields Medal, which can be called the Nobel Prize in mathematics.

Most of the time, Witten stares out of the window, skillfully fiddling with and adjusting a large number of equations. His wife said

He never calculated except in his mind, but I wrote a full page of calculations before I figured out what I was doing, but Edward just sat down and wrote a minus sign, or just twice as much.

Witten said

Most people who are not nurtured by physics may think that physicists are doing very complex computational problems, but that falls short of the crux of the problem. The key is that physics is some concepts, without understanding these concepts, there is no way to understand the principles of the operation of the world.

Witten is a master of superstring theory, which can unify Einstein's gravity theory with quantum theory. However, Witten is not satisfied with the current expression of superstring theory. He is determined to solve the problem of the origin of superstring theory, which may prove to be a decisive step towards explaining the creation of the universe. The key to this theory is that its unique geometry ∶ strings can vibrate only in 10 and 26 dimensions.

What are particles?

The essence of string theory is that it can explain the nature of matter and space-time, that is, the nature of wood and marble. String theory answers a series of difficult questions about particles, such as why there are so many particles in nature. The deeper we study the nature of subatomic particles, the more particles we find. At present, hundreds of subatomic particles form a huge "zoo", and their properties emerge one after another. Even in the standard model, there are a puzzling number of "elementary particles". String theory answers this question because strings about one trillionth of the size of a proton vibrate, and each vibration mode represents a unique resonance or particle. The string is very small, so the resonance of the string is indistinguishable from the particle from a distance. Only when we try to enlarge the particle can we see that it is not a point at all, but a string that vibrates in some pattern.

In this picture, each subatomic particle corresponds to a unique resonance that vibrates at a unique frequency. The idea of resonance is familiar in daily life. Imagine a violin string that vibrates at different frequencies, producing sounds such as A, B and C. The only vibrational patterns that can be left on the string are those that disappear at the end of the string and have integer fluctuations between the two ends. In principle, a string can vibrate at any one of an infinite number of different frequencies. We know that the sound itself is not the most basic thing. The sound An is no more basic than the sound B. However, what is more basic is the string itself. It is not necessary to study each sound in isolation from other sounds. By understanding how the strings vibrate, we immediately understand the properties of an infinite number of notes.

Similarly, the particles in the universe are not fundamental in themselves. Electrons are no more basic than neutrinos. Particles seem basic simply because our microscopes are not enough to reveal their structure. According to string theory, if we can manage to enlarge a point particle, we will actually see a small vibrating string. In fact, according to this theory, matter is nothing more than a harmony produced by this vibrating string. Because for the violin, it can form an infinite number of harmonies, so the vibrating strings can form an infinite number of material forms. This explains the richness of particles in nature. Similarly, the laws of physics can be compared to the laws of harmony allowed on strings. The universe itself, made up of countless vibrating strings, can be compared to a symphony (whether or not you suddenly fall in love with music).

String theory can explain not only the nature of particles, but also the nature of space-time. When a string moves in space-time, it completes a complex set of movements. This string can also be broken down into smaller strings, or it can collide with other strings to form a longer dazzle. The point is that all of these quantum corrections or cycles (the Feynman graph that divides a plane into unconnected regions) are finite and computable. This is the first theory of quantum gravity with finite quantum correction in the history of physics.

All previous theories-- including Einstein's original theory, Karucha-Klein theory, and supergravity theory-- failed on this critical criterion.

In order to accomplish these complex movements, strings must follow a large set of self-consistent conditions, which are so strict that they set some very restrictive conditions on time and space. In other words, a string cannot propagate along itself in any space-time like a point particle.

When the condition of constraining a string in space-time was calculated for the first time, physicists were surprised to find that Einstein's equation came from the string. This is amazing, without assuming any Einstein equations, physicists find that they are derived from string theory, which is simply magic. Einstein's equation is no longer found to be fundamental, it can be derived from string theory.

If string theory is correct, it will unravel the long-standing mysteries of wood and marble. Einstein guessed that marble alone would one day explain all the properties of wood. For Einstein, wood is the kink or vibration of time and space. Quantum physicists, however, are thinking the opposite. They believe that marble can be turned into wood, that is, Einstein's metric tensor can be transformed into gravitons, and gravity is a discrete energy packet of load gravity. These are two diametrically opposed views, and it has always been thought that it is impossible to reach a compromise between them. However, the string is the "missing link" between wood and marble.

String theory can derive not only the matter particles that can be regarded as resonant on the string, but also the Einstein equation by requiring the string to move uniformly in space-time. In this way, we have an all-inclusive theory of mass energy and space-time.

These self-consistent constraints are very strict. For example, they prohibit strings from moving in three or four dimensions. We will see that these self-consistent conditions force strings to move in a particular dimension. In fact, the "magic number" allowed by string theory is 10 and 26 dimensions. Fortunately, the string theory defined in these dimensions has enough "space" to unify all the fundamental forces.

Therefore, string theory is sufficient to explain all the basic laws of nature. Starting with a simple theory of vibrating strings, one can deduce Einstein's theory, Karucha-Klein theory, supergravity, the standard model, and even the grand unified theory. It seems like a miracle ∶, starting from the pure geometric discussion of some strings, one can rederive all the advances in physics in the past 2000 years.

In the past, it was thought that strings might have some shortcomings that would hinder the establishment of a completely self-consistent theory. In 1984, however, two physicists, Schwartz and their collaborator Green, proved that all self-consistent conditions for strings could be satisfied. This in turn sparked a rush of young physicists to solve the theory. By the late 1980s, a veritable "gold rush" began to appear among physicists. The competition among hundreds of excellent theoretical physicists around the world has become very fierce.

Why the strings? Why the strings? Why not vibrating solids or bumps?

If you have a very deep understanding of existing physics, you may see that nature, like Bach or Beethoven, often begins to have a theme, followed by numerous variations around the theme, which are spread throughout the symphony. Using this as a criterion, strings do not seem to be a basic concept in nature.

For example, the concept of orbit appears repeatedly in nature in a variety of variations. Since Copernicus's work, orbits have provided a basic theme, often repeated throughout nature in a variety of variations, from the largest galaxies to atoms to the smallest subatomic particles. Similarly, the Faraday field proved to be one of the preferred themes of nature. The field can describe the magnetic and gravitational interactions of galaxies, as well as Maxwell's electromagnetic theory, Einstein's and Riemann's metric theory, and the Young-Mills field found in the standard model. In fact, field theory emerged as the universal language of subatomic physics, and perhaps the same is true of the universe. All known forms of matter and energy have been expressed in field theory. In addition, like the themes and variations in symphonies, patterns are constantly repeated.

But what about the string? Strings do not seem to be the model that nature likes when designing the world. We can't see the strings in space. In fact, we can't see strings anywhere.

However, an important idea will reveal that nature retains a special role for strings, that is, as a basic component of other forms. For example, the basic characteristics of life on Earth are string-like DNA molecules, which contain complex information and passwords of life itself. Strings seem to be the perfect answer to the construction of raw materials for life and subatomic matter. In both cases, we want to put a lot of information into a relatively simple and replicable structure. The remarkable feature of strings is that a large amount of information is stored in a highly dense way in which information can be copied.

For organisms, nature uses double-stranded DNA molecules, which untie the double strands to form their own replicas. Our bodies also contain trillions of protein strings, which are made up of amino acid components. In a sense, our bodies can be seen as a collection of a large number of strings.

String Quartet Group

At present, the most successful versions of string theory are established by Princeton physicists Gross, Martinez, Harvey, and Roma, sometimes referred to as the Princeton string Quartet. The elder of the four of them is Gross. At most seminars in Princeton, Witten may ask questions in a low voice. But Gross's voice was clear. Anyone who attends a seminar at Princeton lives in fear of a barrage of sharp questions from Gross. What matters is that his questions often hit the nail on the head. Gross and his collaborators came up with the so-called heterochord. Today, it is this kind of heterochord, which is different from the various Kalucha-Klein theories proposed in the past, that is likely to unify all the laws of nature.

According to Gross, string theory solves the problem of turning wood into marble. " It is necessary to construct matter itself in terms of geometry-in a sense, that is the problem to be solved by string theory. It can be thought that that method, especially in theories like heterostring, is essentially a theory of gravity, in which matter particles and other natural forces appear in the same way that gravity emerges from geometry.

As we emphasized, the most striking feature of string theory is that Einstein's theory of gravity is automatically included in it. In fact, the graviton (gravitational quantum) appears as the minimum vibration of a closed string. The grand unified theory tries to avoid mentioning Einstein's theory of gravity, but superstring theory requires Einstein's theory to be included. For example, if we think of Einstein's theory of gravity only as the vibration of a string, then the theory becomes inconsistent and useless. In fact, this is why Witten was attracted to string theory in the first place. In 1982, he read a review written by Schwartz and was surprised to realize that gravity could emerge from superstring theory based on the requirement of self-consistency alone. He recalled that it was

The biggest intellectual tremor of my life.

Witten says ∶ "string theory is very attractive because gravity is imposed on us. All known consistent string theories include gravity, but when gravity is impossible in quantum field theory as we know it, it has to be in string theory.

Gross was sure that if Einstein were alive, he would love superstring theory. Einstein's love for the elegance and conciseness of superstring theory ultimately stems from its geometric principles whose essence is still unknown. Gross asserted, "Einstein will be satisfied with this, if not satisfied with the realization, at least satisfied with this goal." he will like to have a fundamental principle of geometry, which unfortunately we do not really understand.

Witten even went further to say that ∶

All the really great ideas in physics are "derivatives" of superstring theory.

What he means is that all the great advances in theoretical physics are included in superstring theory. He even thought that Einstein's general relativity, which was discovered before the superstring theory, was "an accident on earth". He believes that somewhere in space, "other civilizations in the universe" may have first discovered superstring theory and then derived general relativity as a by-product of superstring theory.

Compact and beautiful string theory is such a promising candidate in physics because it gives a simple origin of symmetry found in particle physics and general relativity.

Supergravity is neither renormalized nor too small to accommodate the symmetry of the standard model. Therefore, it is not self-consistent, and it cannot realistically describe known particles. However, string theory can do both. As we will soon see, string theory eliminates the infinity found in quantum gravity and produces a finite theory of quantum gravity. This alone ensures that string theory should be regarded as a candidate for cosmic theory. However, there is a side benefit. When we compact some dimensions of strings, we find that there is "enough room" to accommodate the symmetry of the standard model or even the grand unified theory.

A hybrid string consisting of a closed string has two types of vibrations, clockwise and counterclockwise, which are treated differently. Clockwise vibrations live in 10-dimensional space. The counterclockwise vibration lives in 26 dimensions, of which 16 dimensions have been compacted.

In Karucha's original five-dimensional theory, the fifth dimension was compacted by rolling it into a circle.

The name heterochord comes from the fact that clockwise and counterclockwise vibrations live in two different dimensions, but they are combined to produce a single superstring theory.

The 16-dimensional compact space is very interesting. In Karucha-Klein theory, the compact N-dimensional space can be accompanied by a symmetry, like a floating balloon. So all vibrations (or fields) defined in N-dimensional space automatically inherit these symmetries. If the symmetry is SU (N), then all vibrations in the space must obey the SU (N) symmetry. In this way, the Kalucha-Klein theory can accommodate the symmetry of the standard model. However, it can also be determined in this way that supergravity is "too small" to accommodate all the particles of various symmetries found in the standard model. This is enough to stifle the theory of supergravity as a realistic theory of matter and space-time.

However, after analyzing the symmetry of this 16-dimensional space, the Princeton string Quartet team found that it is an unusually large symmetry, called E (8) × E (8), which is much greater than that of any grand unified theory ever tried. It means that all the vibrations of the string inherit the symmetry of the 16-dimensional space, which is more than sufficient to accommodate the symmetry of the standard model.

The laws of physics are simplified in high dimensions.

In this case, the 26-dimensional space of counterclockwise vibration of hybrid strings has enough room to explain all the symmetries in Einstein theory and quantum theory. Therefore, pure geometry gives a simple explanation for the first time, which is why the subatomic world must show some kind of symmetry ∶ subatomic kingdom emerging from the curled high-dimensional space. The symmetry of the subatomic kingdom is only the remnant of the symmetry in the high-dimensional space.

This means that the beauty and symmetry of nature can eventually be traced back to high-dimensional space. For example, snowflakes produce beautiful hexagonal patterns, none of which are exactly the same. These snowflakes and crystals inherit the geometrically arranged structure of their molecules. This arrangement is mainly determined by the electronic shell of the molecule, and the molecule brings us back to the rotational symmetry of quantum theory, marked as O (3) symmetry. All the symmetries of the low-energy universe we observe in chemical elements are attributed to the symmetries divided by the standard model, which can be derived by compacting heterochromatic strings.

In short, the symmetry we see around us, from rainbows to blooming flowers to various crystals, can eventually be seen as a manifestation of the original 10-dimensional theoretical fragments. Riemann and Einstein wanted to find out why forces determine the motion of matter and the geometric understanding of its nature. But they lost the key element of the relationship between wood and marble. This missing link is most likely superstring theory. Using 10-dimensional string theory, we see that string geometry may ultimately determine the force and structure of matter.

This article comes from the official account of Wechat: Lao Hu Shuo Science (ID:LaohuSci). Author: I am Lao Hu.

Welcome to subscribe "Shulou Technology Information " to get latest news, interesting things and hot topics in the IT industry, and controls the hottest and latest Internet news, technology news and IT industry trends.