Schrodinger's cat is a paradox of quantum mechanics explained by Schrodinger in 1935. The cat was kept in a secret room with food and poison in it. There is a hammer on the poison bottle. The hammer is controlled by an electronic switch which is controlled by radioactive atoms. If the nucleus decays, it will release alpha particles, trigger the electronic switch, the hammer will fall, the poison bottle will be smashed, the cyanide gas inside will be released, and the cat will die. This device was designed by Schrodinger, so this cat is called Schrodinger cat. The decay of nuclear is a random event, and physicists can only know the half-life-the time required for semi-decay. If the half-life of a radioactive element is one day, one day later, the element will be half less, and the other day, the remaining half will be half less. However, physicists can't know when it decays, morning or afternoon. Of course, physicists know the probability that it will decay in the morning or afternoon-that is, the probability that a cat will die in the morning or afternoon. If we don't open the lid of the secret room, according to our experience in daily life, we can conclude that the cat is either dead or alive, which are its two eigenstates. However, if Schrodinger equation is used to describe Schrodinger cat, it can only be said that she is in a state of life and death superposition. Only by lifting the lid can we know for sure whether the cat is dead or alive. But at the moment of opening the lid, the wave function describing the cat state immediately collapses from the superposition state to a certain eigenstate, that is, the dead state or the alive state. Quantum theory holds that if you don't open the lid and observe, you will never know whether the cat is dead or alive. She will always be in a state of superposition of life and death, which is usually called half-dead. This seriously violates our daily experience. We either die or live. How can we achieve immortality?

Uncertainty principle:

Uncertainty principle, also known as uncertainty principle, was first put forward by Heisenberg in 1927. It reflects the basic law of microscopic particle motion and is another important principle in physics.

Heisenberg held a negative attitude towards visual images when he founded matrix force. But he still needs words like "coordinates" and "speed" in expression. Of course, these words are no longer equivalent to the words in classical theory. However, how should we understand the new physical meanings of these words? Heisenberg grasped the problem of observing electron trajectory in the cloud chamber experiment and thought about it. He tried to use matrix mechanics to express the electron trajectory mathematically, but he failed. This put Heisenberg in trouble. He thought it over and over again and realized that the key lies in the expression of the electronic orbit itself. What people see is not the real orbit of electrons, but the fog formed by water droplets much larger than electrons, so people may only observe the uncertain positions of a series of electrons, rather than the precise orbit of electrons. Therefore, in quantum mechanics, an electron can only be in a certain position with certain uncertainty, and at the same time, it can only have a certain speed with certain uncertainty. These uncertainties can be limited to the minimum range, but they are not equal to zero. This is Heisenberg's initial thinking on uncertainty. According to Heisenberg's memories in his later years, Einstein was inspired by a conversation in 1926. When Einstein and Heisenberg discussed whether electron orbits could be considered, they asked Heisenberg, "Do you really believe that only observable quantities should enter physical theory?" Heisenberg replied, "Isn't that how you deal with relativity?" You emphasized that absolute time is not allowed, just because absolute time is unobservable. Einstein admitted this, but he said, "It is instructive and helpful for a person to keep in mind what he actually observed." ... in principle, it is completely wrong to try to establish a theory only by observable quantities. In fact, on the contrary, it is theory that determines what we can observe ... Only theory, that is, only knowledge about natural laws, can enable us to infer basic phenomena from sensory impressions. "

Heisenberg said at the beginning of the paper 1927: "If someone wants to clarify the meaning of the phrase' the position of an object' (for example, the position of an electron), then he must describe an experiment that can measure the position of an electron, otherwise the phrase is meaningless at all." Heisenberg said: "This uncertainty is the fundamental reason of statistical relations in quantum mechanics. When talking about some uncertain relations of regular yokes, such as position and momentum, or energy and time."

Heisenberg's uncertainty principle has been proved by some experiments. Imagine observing the coordinates of an electron with a gamma-ray microscope. Because the resolution of gamma-ray microscope is limited by the wavelength λ, the shorter the wavelength λ of the light used, the higher the resolution of the microscope, so the less the uncertainty of determining the electronic coordinates, so △q ∝λ. On the other hand, when light hits electrons, it can be considered as a collision between photons and electrons. The shorter the wavelength λ, the greater the photon momentum, so there is △p∝ 1/λ. After some reasoning and calculation, Heisenberg reached the conclusion that △ q△ p = h/4π. Heisenberg wrote: "At the moment when the position is determined, that is, the photon is deflected by the electron, the momentum of the electron changes discontinuously. Therefore, when the position of an electron is known, we can only know the degree to which its momentum corresponds to its discontinuous change. Therefore, the more accurate the position, the less accurate the momentum, and vice versa. "

Heisenberg also determined the atomic magnetic moment by analyzing the Stern-Gelach experiment, which proved that the longer the atom passes through deflection, the smaller the uncertainty △E in energy measurement. Coupled with the de Broglie relation λ = h/p, Heisenberg obtained △ e△ t < h, and concluded that "the accurate determination of energy can only be obtained by the corresponding uncertainty of time."

Heisenberg's uncertainty principle was supported by Bohr, but Bohr disagreed with his reasoning method and thought that the basic concept he used to establish uncertainty relationship was problematic. There was a heated argument between the two sides. Bohr's point of view is that the basis of uncertain relationship lies in wave-particle duality. He said, "This is the core of the problem." Heisenberg said: "We have a consistent way of mathematical reasoning, which tells people everything we observe. There is nothing in nature that this mathematical reasoning method cannot describe. " Bohr said: "A complete physical explanation should be absolutely higher than the mathematical formal system."

Bohr pays more attention to philosophical thinking. 1927, Bohr gave a speech on quantum postulate and the new progress of atomic theory, and put forward the famous complementary principle. He pointed out that in physical theory, it is always thought that you can observe an object without disturbing it, but it is impossible from the point of view of quantum theory, because any observation of an atomic system will involve changes in the observed object, so there can be no single definition, and the so-called causal relationship will no longer exist. Different properties mutually exclusive with classical theory have become complementary aspects in quantum theory. Wave-particle duality is an important manifestation of complementarity. Quantum mechanics conclusions such as uncertainty principle can also be explained from here.

Twin paradox:

Einstein put forward the famous theory of relativity, and time can be changed. Soon after, some geniuses accused it of the paradox of twins. Although this paradox has long been falsified, we can still get a glimpse of the counter-intuitive thinking of genius. It is said that if twins are born on the earth, one child stays on the earth and the other child leaves the earth in a spaceship near the speed of light. When the children on earth reach the age of twenty, the spaceship returns at the same speed. When the children on earth reach the age of forty, the spaceship arrives safely. If we think that time will become slower when it approaches the speed of light, then most people will think that children who leave the earth at the speed of light are younger. However, when the spacecraft leaves the earth at the speed of light, we can also think that the spacecraft is stationary and the earth leaves the spacecraft at the speed of light. So now most people must think that children on earth are younger! Who is younger? Of course, the answer is simple. Just compare the two children together. Don't tell everyone that these two children are the same age! This will upset Einstein's soul. ...

Maxwell demon:

Maxwell demon is an imaginary "shemale-like" or mechanism, which has the same function and can detect and control the movement of a single molecule in physics. It was conceived by Maxwell, a British physicist in the 187 1 century, to explain the possibility of violating the second law of thermodynamics.

At that time, Maxwell realized that there was an energy control mechanism in nature, which was opposite to the increase of entropy. But he can't explain this mechanism clearly. He can only humorously assume that a "demon" can distribute particles doing random thermal motion to certain cells in a certain order and rule. Maxwell demon is the prototype of dissipative structure.

/kloc-In the early 9th century, many people were addicted to the manufacture of a mysterious machine-the first perpetual motion machine, because the envisaged machine only needed an initial force to make it work, and then it could automatically and continuously do work without any power or fuel. Before the first law of thermodynamics was put forward, people had a heated discussion on the possibility of making perpetual motion machines.

It was not until the first law of thermodynamics was discovered that the myth of the first perpetual motion machine was broken.

The first law of thermodynamics is the concrete expression of the law of conservation and transformation of energy in thermodynamics, which shows that heat is a form of material movement. This shows that the energy (heat) transmitted by the outside world to the material system is equal to the sum of the increase of internal energy and the work done by the system. It denies that energy is born out of nothing, so the first perpetual motion machine that can do work without power and fuel becomes a fantasy.

The first law of thermodynamics came into being at the end of 18 and the beginning of 19. With the wide application of steam engines in production, people pay more and more attention to the transformation of heat and work. Thus, thermodynamics came into being. 1798, Thompson denied the existence of thermal mass through experiments. German doctor and physicist Meyer in 184 1? In 843, the idea of mutual transformation between heat and mechanical motion was put forward, which was the first time that the first law of thermodynamics was put forward. Joule designed an experiment to measure the electrothermal equivalent and mechanical equivalent of heat, and determined the first law of thermodynamics through the experiment, which supplemented Meyer's argument.

After the first law of thermodynamics, people began to consider the efficiency of converting thermal energy into work. At this time, someone designed such a machine-it can infinitely take heat from a heat source to do work. This is called the second perpetual motion machine.

1824, French army engineer Carnot conceived an ideal heat engine that did no external work and had no friction. By studying the simple cycle of heat and work (Carnot cycle) between two heat sources with different temperatures in this heat engine, it is concluded that the heat engine must do work between the two heat sources, and the efficiency of the heat engine depends only on the temperature difference with the heat sources. Even in an ideal state, the efficiency of a heat engine cannot reach 100%. That is, heat cannot be completely converted into work.

1850, Clausius unified the law of conservation and transformation of energy and Carnot principle on the basis of Carnot, and pointed out that it is impossible for automatic machines to transfer heat from low-temperature objects to high-temperature objects without change, which is the second law of thermodynamics. Soon, Kelvin suggested that it is impossible to obtain heat from a single heat source and make it completely useful without other effects; In other words, it is impossible to use inanimate machines to cool any part of matter below the lowest temperature around, thus obtaining mechanical work. This is the Kelvin expression of the second law of thermodynamics. Ostwald put it this way: The second perpetual motion machine cannot be built successfully.

Clausius put forward the concept of entropy S=Q/T while putting forward the second law, and expressed the second law of thermodynamics as: in an isolated system, the actual process always increases the entropy of the whole system. However, after that, Clausius mistakenly extended the law of entropy increase of isolated systems to the whole universe, thinking that in the whole universe, heat constantly changed from high temperature to low temperature until there was no temperature difference at a certain moment, and the total entropy of the universe reached a maximum. At this time, there will be no power to transfer heat. This is the so-called "theory of heat death".

In order to refute "theory of heat death", Maxwell imagined an invisible soul (Maxwell Demon), which was at a door in a box. It allows fast particles to reach one side of the box through the door and slow particles to reach the other side of the box through the door. In this way, after a period of time, there will be a temperature difference on both sides of the box. Maxwell demon is actually a prototype of dissipative structure.

1877, Boltzmann discovered the relationship between macroscopic entropy and thermodynamic probability of system S=KlnQ, where k is Boltzmann constant. 1906, Nernst put forward △S/O = 0 when the temperature is close to absolute zero T→0, that is, "Nernst thermal principle". On the basis of Nernst's research, Planck pointed out that the perfect crystal of various substances has zero entropy (S 0 = 0) at absolute zero, which is the third law of thermodynamics.

The three laws of thermodynamics are collectively called the basic laws of thermodynamics, and the basis of thermodynamics has been basically completed since then.