Chapter 231

Condensed matter physics - the study of the macroscopic properties of matter. These phases contain a large number of components, and the interaction between components is very strong. The most familiar condensed phases are solids and liquids, which are formed by atomic bonds and electromagnetic forces. More condensed phases include superfluid and Bose Einstein condensates (found in some atomic systems at very low temperatures); The superconducting phase of conductive electrons in some materials; Ferromagnetic and antiferromagnetic phases in atomic lattice. Condensed matter physics has always been the largest research field. Historically, it grew out of solid physics. It was first proposed by Philip Anderson in 1967.

Atomic, molecular, and optical physics - the study of matter matter and light matter interactions within the atomic size or several atomic structures. These three areas are closely related. Because they use similar methods and related energy scales. They all include classical and quantum processing methods; Deal with problems from a micro perspective. Atomic physics deals with the atomic shell, focusing on the quantum control of atoms and ions; Cooling and trapping; Low temperature collision dynamics; Accurate measurement of basic constants; Collective effects of electrons in structural dynamics. Atomic physics is influenced by the nucleus. However, nuclear internal phenomena such as nuclear fission and nuclear synthesis belong to high-energy physics. Molecular physics focuses on Polyatomic structures and their internal and external interactions with matter and light. Optical physics here only studies the basic characteristics of light and the interaction between light and matter in the microscopic field.

High energy / particle physics - particle physics studies the basic components of matter and energy and their interactions; It can also be called high energy physics. Because many elementary particles do not exist in nature, they only appear when they collide with other particles at high energy in a particle accelerator. According to the standard model of elementary particle interaction, there are 12 elementary particle models of known substances (quarks and light particles). They interact through strong, weak and electromagnetic fundamental forces. The standard model also predicts the existence of a Higgs Bose particle. Is now looking for.

Astrophysics - Astrophysics and modern astronomy apply physical theories and methods to the study of the structure and evolution of stars, the origin of the solar system, and related problems of the universe. Because of its wide range, astrophysics makes use of many principles of physics, including mechanics, electromagnetism, statistical mechanics, thermodynamics and quantum mechanics. In 1931, Carl discovered the radio signals sent by celestial bodies and began radio astronomy. The frontier of astronomy has been expanded by space exploration. The interference of the earth's atmosphere requires infrared, ultra ultraviolet, gamma ray and X-ray to observe space. Physical cosmology studies the formation and evolution of the universe on a large scale. Einstein's theory of relativity plays a central role in modern universe theory. In the early 20th century, Hubble found that the universe was expanding from the picture, which promoted the discussion between the stable state theory of the universe and the big bang. The discovery of the cosmic microwave background in 1964 proved that the big bang theory may be correct. The big bang model is based on two theoretical frameworks: Einstein's general theory of relativity and cosmological principles. Cosmology has established the ACDM universe evolution model, which includes the expansion of the universe, dark energy and dark matter. Many possibilities and discoveries can be expected from the new data of Fermi gamma ray telescope and the improvement of existing universe models. Especially in the next few years, there may be many discoveries around dark matter.

Feynman, a famous physicist, said: "science is a method. It teaches people: how some things are understood, what things are known, to what extent, how to treat questions and uncertainties, what laws evidence obeys, how to think about things, make judgments, and how to distinguish between authenticity and superficial phenomena." Einstein, a famous physicist, said: "Developing the general ability of independent thinking and independent judgment should always be put in the first place, rather than professional knowledge. If a person has mastered the basic theory of his discipline and learned to think and work independently, he will find his own way, and he will be better than the person whose training content is mainly to obtain detailed knowledge Adapt to progress and change.

Physics is a regular summary of people's knowledge of the movement and transformation of matter in nature. There should be two kinds of movement and Transformation: one is the extension of sensory vision in the early days; the other is the indirect understanding of the internal composition of matter based on the results of experiments by inventing scientific instruments for observation and measurement in modern times. From the perspective of research, physics Different degrees and viewpoints can be roughly divided into micro and macro parts: macro physics did not analyze the single action effect in particle swarm but directly considered the overall effect, which had appeared in the earliest stage; the birth of micro physics originated from macro physics, which could not well explain the new experimental phenomena such as blackbody radiation, photoelectric effect and atomic spectrum. It is a part of macro physics With the development of experimental technology and theoretical physics.

Secondly, physics is a kind of intelligence.

As the Nobel Laureate in physics and German scientist born said: "it is not so much because my published work contains the discovery of a natural phenomenon as because it contains a scientific ideological and methodological basis on natural phenomena." Physics is recognized as an important science, not only because it deeply reveals the laws of the objective world, but also because it has formed a set of unique and effective ideological and methodological system in the process of development and growth. Because of this, physics has become the crystallization of human intelligence and the treasure of civilization.

A large number of facts show that physical ideas and methods are not only valuable to physics itself, but also make an important contribution to the development of the whole natural science and even social science. According to statistics, since the middle of the 20th century, more than half of the winners of the Nobel Prize in chemistry, biology and medicine, and even economics have a background in Physics - which means that they have learned intelligence from physics and succeeded in non physical fields. On the contrary, there has never been a case of scientists from non physics majors winning the Nobel Prize in physics. This is the power of physical intelligence. No wonder some foreign experts pointed out sharply that a nation without physical cultivation is a stupid nation!

In short, physics is a summary of the laws of nature and a theoretical understanding of the scientific nature of experience.

Atoms are the smallest particles that cannot be separated by chemical reactions. A positive atom contains a dense nucleus and a number of negatively charged electrons surrounding the nucleus. The nucleus of a negative atom is negatively charged and the surrounding negative electrons are positively charged. The nucleus of a positive atom consists of positively charged protons and electrically neutral neutrons. The antiproton in the nucleus of a negative atom is negatively charged, so that the nucleus of a negative atom is negatively charged. When the number of protons is the same as the number of electrons, the atom is electrically neutral; Otherwise, it is an ion with positive or negative charge. Depending on the number of protons and neutrons, the type of atom is also different: the number of protons determines which element the atom belongs to, and the number of neutrons determines which isotope the atom is. [3] Atoms form molecules, while the same charges in molecular substances repel each other and different charges attract each other.

The order of magnitude of atomic diameter is about 10? 1? m。 The atomic mass is very small, and its order of magnitude is generally 10-27kg. The mass is mainly concentrated in protons and neutrons. Electrons are distributed outside the nucleus, and the electron transition produces a spectrum. Electrons determine the chemical properties of an element and have a great influence on the magnetism of the atom. All atomic elements with the same number of protons, most of which have an unstable isotope and can undergo radioactive decay.

The concept that matter is composed of discrete units and can be arbitrarily divided has spread for thousands of years, but these ideas are only based on abstract and philosophical reasoning, not experiments and experimental observations. With the passage of time and the change of culture and school, the nature of atom in philosophy has also changed greatly, and this change often has some spiritual factors.

Nevertheless, the basic concept of atom was still adopted by chemists thousands of years later because it can concisely explain some phenomena in chemistry.

Atomism is the most concise and scientific theoretical form of the elemental school. Dampier, a British historian of natural science, believes that atomism is "closer to the modern view than any theory before or after it". The founder of atomism was the ancient Greek liujiber (500-440 BC). He was a teacher of Democritus. When ancient scholars talked about atomic theory, they usually mixed their theories together. Liujiber's theory was developed and perfected by his student Democritus, so Democritus is recognized as the main representative of atomism.

Democritus believes that the original or fundamental elements of all things are "atom" and "void". "Atom" means "indivisible" in Greek. Democritus uses this concept to refer to the most basic material particles that constitute concrete things. The fundamental characteristic of the atom is "full and solid", that is, there is no gap in the atom, it is solid and inaccessible, so it is inseparable. Democritus believed that atoms are eternal and immortal; Atoms are infinite in number; The atom is in constant motion, and its only form of motion is "vibration". The volume of the atom is small and invisible to the eyes, that is, it can not be perceived by the senses, and can only be recognized through rationality.

After more than 20 centuries of exploration, scientists confirmed the true existence of atoms through experiments from the 17th century to the 18th century. In the early 19th century, the British chemist J. Dalton put forward the atomic theory with modern significance on the basis of further summarizing the previous experience. This atomic theory created a new era of chemistry. He explained many physical and chemical phenomena.

An atom is the smallest unit of an element that can maintain its chemical properties. An atom contains a dense nucleus and a number of negatively charged electrons surrounding the nucleus. The nucleus consists of positively charged protons and electrically neutral neutrons. Atoms are the smallest particles of chemical changes, molecules are composed of atoms, and many substances are directly composed of atoms.

The English name of atom is transformed from Greek, which originally means inseparable. Long ago, Greek and Indian philosophers put forward the concept of indivisibility of atom. In the 17th and 18th centuries, chemists discovered the basis of Physics: for some substances, they could not be decomposed by chemical means. In the late 19th century and early 20th century, physicists discovered subatomic particles and the internal structure of atoms, which proved that atoms could not be further segmented. The principles of quantum mechanics can provide good modes for atoms

In 932, Julio Curie and his wife discovered that this kind of ray could shoot protons from paraffin; In the same year, James Chadwick, a student of Rutherford, identified this as neutrons [8], and isotopes were redefined as elements with the same proton number and different neutron numbers.

In 1950, with the development of particle accelerator and particle detector, scientists could study the collision between high-energy particles. They found that neutrons and protons are a kind of hadrons, composed of smaller quark particles. The standard model of nuclear physics has also been developed, which can successfully explain the interaction between the whole nucleus and subatomic particles at the subatomic level.

In 1985, Chu and his colleagues developed a new technology at Bell labs that could use lasers to cool atoms. The William Daniel Phillips team managed to place the nano atoms in a magnetic trap. These two technologies, together with a method developed by Claude Cohen donudge team based on Doppler effect, can cool a small number of atoms to the temperature range of micro Kelvin, so that atoms can be studied with high precision, which lays a foundation for the discovery of Bose Einstein condensation [11].

Historically, a single atom was considered too small for scientific research. In 2012, scientists have successfully connected a single metal atom with an organic ligand to form a single electron transistor. In some experiments, atoms are decelerated and captured by laser cooling. These experiments can bring a better understanding of matter.

Using the wave particle duality hypothesis proposed by Louis de Broglie in 1924, erwinsger established an atomic mathematical model to describe the electron as a three-dimensional waveform. However, it is not mathematically possible to obtain the exact values of position and momentum at the same time. Werner Heisenberg proposed the famous uncertainty principle. This concept describes that for a measured position, only an uncertain momentum range can be obtained, and vice versa. Although this model is difficult to imagine, it can explain some properties of atoms that have been observed but cannot be explained, such as the spectral lines of atoms larger than hydrogen. Therefore, people no longer use Bohr's atomic model, but regard the atomic orbit as the region with high probability of electron occurrence (electron cloud).

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