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The smallest original particle? Will quarks be the foundation of everything? The answer is wonderful.()

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Original title: The热点新闻 smallest particle? Will quarks be the foundation of everything? The answer is wonderful.

What is quark?

In the depths of the atoms that make up our bodies, and even inside the protons and electrons that make up the nucleus, there is a tiny particle-quark.

An artist's illustration with a white swirl pattern and a blue background.

(Source: The Best Design of Getty Images)

Quarks are the most basic components of all visible matter in the universe. If we zoom in on an atom in our body, we can see that the nucleus is made up of protons and neutrons, and electrons revolve around the nucleus. If you zoom in on a proton or neutron, you can see that the particle itself is composed of three particles. These particles are so small that the size can be almost completely ignored. They are quarks.

Quarks are elementary particles. Like electrons, they are not composed of other particles. It can be said that they are at the bottom of the standard model of particle physics.

Keith Cooper is a British freelance science journalist and editor with a degree in physics and astrophysics from Manchester University.

Discover quarks

In 1964, two physicists of California Institute of Technology (CalTech), Murray gherman and George Zweig, first put forward the theory of quarks' existence, but their conclusion was that quarks existed independently of each other, contrary to the scientific facts often described in the media. Gherman and Zweig's conclusion was not a sudden discovery, but was discovered through careful observation based on years of hard work.

In 1950s, physicists were building a library of known particles, but they lacked the basic theory to prove the existence of particles. It's a bit like botany cataloguing all kinds of plants and their characters. In the end, this theory was named the standard model, but in order to complete this theory, several important discoveries were needed, including the discovery of quarks.

The most puzzling thing is the hyperon, which is unstable and decays quickly, but it does not become the expected particle after decay. Gherman realized that there must be an unknown quantum property at work. Because of its singularity, he named it "singularity".

Just like odd numbers, charges and spins, quantum numbers must be conserved. If a particle with a specific quantum number decays, all the quanta of the decay product must add up to the quantum number of the decaying particle. In addition, the quantum numbers of particles have "degrees of freedom"-basically the range of values these quantum numbers have. These degrees of freedom are called multiplets, which can be arranged between different particles, which makes gherman and Zweig believe that if each particle is formed by two or three smaller particles, then these particles and their multiplets can be explained clearly.

Zweig called these tiny elementary particles "trump cards", but the name didn't catch on. Gherman has always liked some strange and unforgettable names. He called these tiny particles quarks, which originated from a line in James Joyce's experimental novel Finnegan's Wake: "Call Mark quarks three times!" In the novel, quark refers to the three children of the protagonist Mr. Mark.

These quarks are called "upper quarks", "lower quarks" and "strange quarks". The upper and lower quarks do not refer to anything, and the singular quantum number is 0. The singular quantum number of the singular quark is -1, which is why it is "singular".

Quarks in quantum physics

The Large Hadron Collider is located in a circular underground tunnel with a circumference of nearly 17 miles (27 kilometers).

(Source: xenotar of Getty Images)

Although this theory was very thoughtful, it didn't catch on quickly because there was no experiment to prove the existence of quarks. Four years later, in 1968, the Stan National Accelerator Laboratory (SLAC) in California achieved this goal. The experimenter first emits electrons to the proton, and then emits muons. It is found that the electrons and muons are scattered by three smaller particles in the proton, and each smaller particle has its own charge. These small particles are quarks.

Facts have proved that there are six types of quarks: in addition to upper quarks, lower quarks and strange quarks, there are also "charm quarks", "top quarks" and "bottom quarks". Each quark has its own set of quantum numbers, and their masses are also very different. The upper quark and the lower quark have the lightest mass, and the top quark has the heaviest mass, which is more than 61,000 times that of the upper quark. Why it is so massive is not completely clear at present, but it does decay quickly into a lighter quark. Particle accelerators such as the Large Hadron Collider can produce top quarks and bottom quarks briefly, which is the only way for scientists to know their existence.

The difficulty in studying quarks is that quarks do not exist alone under normal circumstances. Powerful nuclear forces always bind them together, thus forming composite particles called hadrons. Particles composed of two quarks are called mesons, and particles composed of three quarks are called baryons, including protons (two upper quarks and one lower quark) and neutrons (one upper quark and two lower quarks). Particles composed of four quarks are called four quarks, and those composed of five quarks are called five quarks. Some of them are stable, but eventually they will decay.

In order to conform to the theory of quantum physics, the behavior of quarks is controlled by the quantum chromodynamics model, or QCD for short. "chromo" in the name refers to "color" which is not red, green or blue, but a noun with a specific quantum number owned by quarks. The role of color in strength is just like the role of charge in electromagnetic force. The same colors repel each other, and different colors attract each other, thus forming a stable quark pair. Like other quantum numbers, it is also conserved.

BIGBANG and quark gluon plasma

The universe was born 13.8 billion years ago.

(Source: ALFRED PASIEKA/ of Getty Images/Science Photo Library)

There is a tiny elementary particle called gluon in hadron, which carries strong force to bind quarks together, and gluons exchange among quarks. It takes a lot of energy to separate a single quark group. This primitive energy only exists between one billionth of a second and one millionth of a second after the Big Bang, when the temperature is about 3.6 trillion degrees Fahrenheit (2 trillion degrees Celsius). In this short early period, the nascent universe was filled with quark-gluon plasma, a liquid substance composed of free-floating quarks and gluons.

With the expansion of the nascent universe, the temperature and pressure drop rapidly, and quarks combine to form hadrons, which eventually form the basis of all visible substances in the cash universe, such as stars, galaxies, planets and people.

Although quark-gluon plasma only existed for a short time after BIGBANG 13.8 billion years ago, scientists successfully recreated it by colliding two heavy nuclei (such as lead nuclei) at near the speed of light. The experiment was first achieved in the super proton synchrotron at CERN in 2000.

Therefore, in order to better understand the state of the universe after the Big Bang, it is an important way to study quark-gluon plasma in particle accelerator experiments.

quark star

In nature, there is an imaginary object called "Quaker", whose internal conditions are extreme and quarks can't combine in it. If this is real, it may be an extreme neutron star. Neutron star is the highest density object in the universe, and it does not collapse to form a black hole under the action of gravity. Supernova is a violent explosion, which marks the destruction of massive stars. Neutron stars are born in supernovae. When the outer layer of the star dissipates, the core of the star collapses under the action of gravity, and the pressure there becomes very large, so that positively charged protons combine with negatively charged electrons, and the charges cancel to form neutral neutrons. Neutron stars are about 6 miles (10 kilometers) in diameter, and a spoonful of neutron star material is equivalent to the mass of a mountain.

However, in theory, the core density of dying stars may become higher. In this case, the neutron will split and release quarks freely. This is Kwame-King.

However, for the time being, Kwakexing is still a pure hypothesis; Although a few candidate neutron stars seem to have slightly different properties from ordinary neutron stars, such as smaller diameter and greater mass, astronomers have not found a quark star in the end.

One candidate neutron star was not actually formed in a supernova, but was formed by merging two neutron stars, resulting in the gravitational wave event of GW 190425. In 2019, both the Laser Interference Space Antenna (LISA) and Virgo Gravitational Wave Detector captured the gravitational wave. The mass of the combined celestial bodies is between 3.11 and 3.54 solar masses. Its mass is too large for a neutron star (theoretically, the mass of a neutron star cannot exceed 2.4 solar masses), but it is not enough to become a black hole (a black hole needs at least about 5 solar masses). Will it be a quark buster?

Another possibility is that neutron stars may be mixed celestial bodies, with ordinary neutron star matter in the outer layer and quark matter deep in the inner core.

BY:Keith Cooper

FY: Zhang guagua

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