Source: Science and Technology Daily
Physicist Gell-Mann was convinced that the symmetry of the laws of physics was one of the most universal laws of nature. In 1961, based on the idea of symmetry, he divided the strongly acting elementary particles with similar properties into a family, and believed that each family should have 8 members.
But according to the experimental results at the time, there were only 7 members of a family of elementary particles, and Gell-Mann boldly predicted that there would be a new particle that had not been discovered, and the next year he found this new elementary particle in the experiment.
According to the news of the Daily Science website on June 1, a team of European scientists used the Large Hadron Collider (LHC) to reveal new details that occurred within the first 0.000001 seconds of the Big Bang, that is, what happened to a special plasma within the first microsecond, a discovery that attracted the attention of scientists.
The Large Hadron Collider plays a huge role in exploring the composition of the microscopic world and is also an important physical device for exploring new particles. With the development of the Standard Model of particle physics, many of the predicted elementary particles have been verified. But how do scientists predict new particles before they are experimentally verified?
It stems from the exploration of mathematics
In the 1920s, the British physicist Dirac was working on relativistic quantum mechanics to build a wave equation that is linear relativistic to both temporal and spatial coordinates.
Inspired by the "Pauli matrix" proposed by the Austrian physicist Pauli in quantum theory, Dirac evolved the matrix of 2 rows and 2 columns into a matrix of 4 rows and 4 columns, thus obtaining the electron wave equation later known as the "Dirac equation". Many of the properties of the high-speed motion of particles derived from this equation have been demonstrated experimentally, unifying important experimental facts in quantum mechanics that were originally independent of each other.
But dirac's equations have negative solutions to the corresponding eigenstates, do you want to exclude the inconceivable negative energy states, or do you accept it to maintain the perfection of the equations? Dirac bravely chose the latter, and he made a bold vision of the physical picture of negative energy states.
First of all, he innovated the concept of "vacuum" and proposed the hypothesis that the vacuum is a "sea of negative energy electrons" that is filled. Then, he further pondered, since a fully filled sea of negative electrons is equivalent to a vacuum, what is the equivalent of jumping an electron out of a sea of electrons? Then there will be a positive energy state electron and a negative energy state hole. He believes that the positive energy state electron excited is an ordinary electron, with a unit of negative charge, and the hole left in the sea of electrons after the electron is excited, missing a negative value energy and carrying a positive energy. He initially thought it was a "proton," but it was unimaginable that this strange "proton" would have a much smaller mass than the average proton.
Proceeding from the idea of symmetrical beauty, Dirac pointed out that mathematically, this strange "proton" with positive energy must have the same mass as the mass of the electron, thus boldly proposing the hypothesis of "antimatter": this strange "proton" is the antielectron in the vacuum, that is, the positron, and he also proposed a new concept of charge conjugate symmetry.
In 1932, the American physicist Anderson discovered the positron predicted by Dirac while studying cosmic rays. The physics community caused a stir, which inspired people to look for antiparticles of other particles.
People gradually realize that all kinds of elementary particles have corresponding antiparticles, which is a universal law of nature.
Reviewing his discoveries about antiparticles, Dirac points out: "This work is entirely due to the exploration of mathematics. ”
In 1933, Dirac won the Nobel Prize in Physics for his discovery of the "Dirac Equation".
From a belief in the laws of physics
In the 1950s, hundreds of elementary particles had been discovered, classifying these particles, finding out the intrinsic relationship between their properties, studying the properties and structure of these elementary particles, and looking for components that were more "basic" than elementary particles, which became a hot topic in high-energy physics research.
In this type of research, the physicist Gell-Mann was convinced that the symmetry of the laws of physics is one of the most universal laws of nature, and that symmetry actually embodies the harmony of the internal connections and laws that exist in nature. Therefore, Gell-Mann believed that all elementary particles could be classified according to the different symmetries they had.
In 1961, according to the idea of symmetry, Gell-Mann divided the strongly acting elementary particles with similar properties into a family, and believed that each family should have 8 members.
But according to the experimental results at the time, there were only 7 members of a family of elementary particles, and Gell-Mann boldly predicted that there was a new particle that had not been discovered, and the next year (1962) this new elementary particle was found in the experiment - the η° meson.
Gell-Mann was out of control: he predicted the existence of another new particle called Ω. In January 1964, Smio of the Blue Haven Laboratory in the United States found traces of Ω-particle decay in thousands of photos of the bubble chamber. Gell-Mann's prediction has finally come true!
The successive discoveries of η° mesons and Ω-particles confirm the correctness of Gell-Mann's theory, thus establishing the important position of symmetry methods in the study of elementary particles.
According to symmetry theory , there is a three-dimensional underlying representation — there should be 3 particles in this family , with only fractional charges , i.e. 2/3 , -1 /3 , -1 /3 , - 1 / 3 unit charges , but fractional charges are never observed.
But not being observed does not mean not existing. After much thought, Gell-Mann named the 3 particles up, down, and exotic quarks, collectively known as quarks. In its theory, these quarks and their antiparticles can be used to explain the hadrons that were discovered at that time, which is the famous quark model. Physicists have designed many experiments to find these free quarks with fractional charge numbers. Since the results of the quark model matched a series of experimental facts well, it also developed in the subsequent years, and its membership has expanded from 3 to 6 now.
In 1969, Gell-Mann was awarded the Nobel Prize in Physics for his "contributions to the classification and interaction of elementary particles."
The predicted particles are still on the hunt
The particle world is inhabited by two major families: the Fermion family represented by electrons and protons, and the Boson family represented by photons and mesons, which are named after the physicists Fermi and Bose respectively. It is generally believed that each particle has its antiparticle, and fermions and its antiparticles are like a pair of identical-looking but completely opposite-tempered twin brothers, who "fight" as soon as they meet, and the energy generated will even make them annihilate instantaneously.
In 1937, the Italian physicist Etoile Majorana predicted that there might be a special class of fermions in nature, antiparticles that not only look the same as itself, but also have exactly the same temper. The two brothers stand together like looking in the mirror, their antiparticles are themselves, this fermion is called "Majorana fermion", also known as "angel particle". In the eyes of modern physicists, the Majorana fermion is not only an important elementary particle - closely related to supersymmetric theory and dark matter, but more importantly, it can also play a huge role in the field of quantum computing, and is one of the optimal carriers of topological qubits.
Majorana's predictions were directed at uncharged fermions, such as neutrons and neutrinos. Since scientists have discovered neutron antiparticles, according to Majorana's predictions, they believe that the antiparticles of neutrinos may be neutrinos themselves. At present, however, experiments on this assertion are still ongoing and difficult.
About 10 years ago, scientists realized that Majorana fermions might be fabricated in experiments on the physics of materials. Thus began a race to find Majorana Fermions.
On July 21, 2017, a paper published in the journal Science caught the attention of the physics community. The University of California, in collaboration with researchers at Stanford University, claimed the discovery of Majorana fermions in a series of special experiments.
However, this particle is not the other. The discovery announced this time is a "chiral" Majorana fermion, a fermion that can only run in one direction on a one-dimensional path and is itself an antiparticle. This is very different from the 80-year-old Majorana fermion that high-energy physicists have been looking for, which is three-dimensional.
In 2018, Microsoft's quantum team published a blockbuster study in Nature, saying that "there is considerable strong evidence for observing the existence of Majorana fermions." However, 3 years later. Microsoft retracted the paper due to a "technical error."
To this day, the search for "angel particles" is still ongoing. Scientists observe the harmonious relations and solemn order behind natural phenomena, appreciate the power of objective laws, and regard the revelation of this universal law, that is, scientific truth, as their sacred task and the highest spiritual pursuit.