Whether it's Sudbury crater in Canada or Fort Friedburg crater in South Africa, there is evidence of volcanic eruptions. Large-scale volcanic activity can directly lead to the extinction of many species. Widespread volcanic eruptions increase the dust in the atmosphere, first cooling the climate for a period of time, then gradually leading to a corresponding global destructive warming, and finally deadly acid rain.

It is known that dinosaurs were a large reptile of ancient times, and if they did not become extinct at the end of the Mesozoic Era, then the ancient apes in the age of obscurantism would at least not have a chance to become modern humans. So how did the dinosaurs come to extinction? Scientists have found that in the Cretaceous-Third Boundary sedimentary layer there was a layer of white powder about a few tens of centimeters thick, which is an extremely rare amino acid on Earth.

Therefore, they deduced that 65 million years ago, a meteorite with a diameter of about 10 kilometers collided with the earth, and the huge explosion after the impact caused most of the dinosaurs to die immediately, and the powder after the explosion shrouded the earth, and for several years, the soil temperature changed suddenly, so that none of the dinosaurs survived, and the extinction of the dinosaurs brought life to other new animals, such as the emergence of mammals, and the ancient apes were also forced out of the forest.

Meteorites contributed to the creation of human beings, and due to the influence of meteorites, the creation of living things. Evolution, development, but meteorites can also bring the danger of destroying humanity. For example, the ancient civilization continent of Daxizhou, which has submerged into the bottom of the Atlantic Ocean, because it is on the edge of the giant crater in the Atlantic Ocean mentioned above, the ancient Indians who created the splendid Mayan culture suddenly disappeared because meteorites often appeared there there?

In today's ever-evolving world, there is a world full of wonders and dangers.

In the classroom of the dungeon of Shuguang Academy, Hua Feng, Yun Meng, Bai Feng and other students were sitting quietly under the stage, welcoming their first lesson in the fall semester.

"Welcome back to the classroom, and I'm going to talk about a very important substance—particles. The teacher's voice was elongated so that it attracted enough attention.

"Particle (pa

ticle), which refers to the smallest component of matter that can exist in a free state. The first particles to be discovered were atoms, electrons, and protons, and in 1932, neutrons were discovered, confirming that atoms are composed of electrons, protons, and neutrons, which are more basic components of matter than atoms, so they are called elementary particles.

In addition, some of these particles have not been found to have an internal structure in experiments so far, and some particles have been shown to have obvious internal structure. It seems that these particles do not belong to the same level, so the term elementary particles has become history and are now collectively referred to as particles. Particles are not concrete substances that actually exist such as neutrons and protons, but they are collectively referred to as a model.

In 1897, Thomson discovered the electron, and in 1911, Rutherford proposed the nuclear structure of the atom. Then we discovered photons, and thought that "photons, electrons, protons, and neutrons" were indivisible particles that made up matter, so we called them "elementary particles". ”

Next, Hua Feng learned more in an almost divine state, including the late 19th century, which believed that atoms were the smallest particles that made up matter. After the discovery of electrons, protons, and neutrons, many people believed that photons and them were the "elementary particles" that make up matter.

Gradually, hundreds of new particles that are not composed of protons, neutrons, and electrons were discovered, and protons, neutrons, and so on themselves had their own complex structures. Since the second half of the 20th century, the word "basic" has been removed and collectively referred to as particles.

Since the 30s of the 20th century, some new particles have been discovered in the study of cosmic rays.

There are interactions between particles, there are strong interactions, electromagnetic interactions, weak interactions, and gravitational interactions, among which the gravitational interactions are very weak and can be ignored. Through these interactions, particle transformation phenomena such as new particles are created or particle decay occur.

Particles are classified into the following categories according to the nature of their participation in interactions: canonical particles. That is, the medium particles that transmit interactions, the photons that transmit electromagnetic effects and the W and Z particles that transmit weak effects have been discovered. Lepton. There are 12 kinds of particles that do not directly participate in strong action but can directly participate in electromagnetic action and weak action, including electron, μ, τon and accompanying electron neutrino ve, μ neutrino, τ neutrino and their antiparticles.

Hadrons, which are directly involved in strong action and also involved in electromagnetic action and weak action particles. where the hadron with spin is an integer is called a meson, and the hadron with spin is a semi-integer is called baryon. Hadrons are numerous, most of which are particles that decay through strong action, have a very short lifespan, and are unstable particles, also known as resonance states.

Each particle has its own intrinsic properties, including the mass m (static mass, expressed in energy), the lifetime τ (average lifetime, referring to the average lifetime of the stationary system), the charge Q (in the unit of proton charge), the spin J (in units), the universe P, the isospin I, the third component of the isospin I3, the baryon number B, the lepton number Le, L

, singular number S, number C, base number d, and so on.

With the precision of existing experiments, leptons behave like point particles and do not show to have an internal structure, while hadrons appear to be composite particles with a certain structure. According to the view of modern particle physics, the meson is composed of a pair of positive and negative quarks, and the baryon is composed of three quarks, and the lepton and the quark belong to the same level.

Elementary particles are the basic components that make up all material entities, and also refer to particles that have fundamental forces in quantum theory.

Strictly speaking, elementary particles are particles that can no longer be broken down into any of their constituent parts. Under this definition, there are only two elementary particles, quarks and leptons. However, although protons and neutrons are made up of quarks, it is impossible for both classes of baryons to be decomposed into their quark components, because independent quarks cannot exist. So, although protons and neutrons, as well as other baryons, are made up of quarks, they are often thought of as elementary particles.

Until the end of the 19th century, atoms were considered the basic building blocks of matter. Later, Joseph Joh, a British pioneer in particle physics and a professor at Cavendish Laboratory in Cambridge

Thomso

(1856-1944), and found that a kind of radiation produced by atoms can be explained by the flow of charged particles that split into atoms themselves, and that such charged particles are electrons.

Since the electrons are negatively charged and the atoms are electrically neutral, it is clear that there must be another positively charged particle inside the atom to cancel out the negative charge of the electrons. In the early 20th century, E. Ernest Rutherford, a physicist of New Zealand descent working in Manchester

est Ruthe

fo

d, 1871-1937) (who later succeeded Tomson as director of the Cavendish Laboratory) proved that this positive charge, along with most of the mass of the atom, is concentrated in a very small central nucleus.

At first, it was thought that the nucleus was a mixture of electrons and positively charged protons. It wasn't until 1932 that James Chadwick (1891-1937), who also worked at the Cavendish Laboratory, discovered the neutron, which had an uncharged mass almost identical to that of a proton. The nucleus is thus interpreted as a collection of protons and neutrons held together by strong nuclei interacting with each other, or strong forces.

At that time, these three particles – electrons, protons, and neutrons

- It seems that there are only elementary particles that make up all matter, but cosmic ray studies and experiments with high-energy particle beams bombarding each other in particle accelerators have shown that there are other types of 'subatomic' particles, but these 'new' particles are unstable and will rapidly 'decay' into clusters of other particles, ending with the electrons, protons and neutrons that we are familiar with.

It is important to understand that these new particles are not at all 'inside' of the particles (e.g., protons) that bombard each other in the particle accelerator, but are created from the energy injected into the accelerator according to Albert Einstein's formula (or, in the case in question, more appropriately).

However, during their short lifespan, they are true particles that possess characteristics such as mass and charge. Such particles should have appeared in large quantities in the high-energy conditions of the Big Bang.

Physicists who don't know how to fit these particles into a full-fledged physical theory, they try to explain how the fundamental forces between these particles act. In doing so, they imitate photons that carry the electromagnetic force between charged particles, and want to use another type of particle that carries the force, the meson. But what is the meson made of?

In 1964, physicist Gell-Mann proposed the quark model, which believed that hadrons are composed of more basic components, which are called quark quarks

k。 After decades of development, the quark model has been accepted by most physicists.

There was a time when the situation was extremely chaotic. But the quark theory, developed in the 1960s and 1970s, brought clarity to the picture. The quark theory states that all known particles can be divided into two groups. A family of quarks that can 'sense' the strong forces that only work between quarks are called hadrons. The other group is called leptons, which do not perceive strong forces, but are involved in so-called weak force as a medium of interaction (or weak interaction), for example, the process of radiative decay (including β decay) is caused by weak interaction. Hadrons can both participate in strong interactions and sense weak forces.

Leptons are veritable elementary particles, and they are not made of anything else. The exemplary lepton is the electron, which is associated with another type of lepton called a neutrino (technically an electron neutrino). When electrons are involved in processes such as radiative decay, neutrinos are always involved.

For some unknown reason, this basic image has been replicated twice, resulting in three 'generations' of leptons. In addition to the electrons themselves, there are heavier ones called μ mesons, which are exactly like electrons except that they are 207 times heavier than electrons, and even heavier particles called τ particles, which have nearly twice the mass of protons.

These two heavy electrons each have their own neutrinos, so there are six (three pairs) of particles in the lepton family. While both μ mesons and τ particles can be made with energy in particle accelerators or produced from cosmic rays, they quickly decay and are converted into electrons or neutrinos.