The mass-energy formula (e = mc2) points out that the total energy of a substance is equal to its mass multiplied by the square of the speed of light. It shows that energy and mass can be transformed into each other, and the speed of light is constant. This formula was put forward by Einstein when he published his special theory of relativity in 1905. It is considered to be the basis of special relativity, and it also lays a new concept of time and space.
Previously, other physicists have proved the correctness of the mass-energy formula with several indirect experiments. However, scientists believe that these experiments have certain preconditions, which may cause doubts about the wide applicability of the mass-energy formula. American scientists published a paper in the February 22nd issue of Nature on 10, saying that their method can directly support the mass-energy formula.
The principle of this experiment is: according to the mass-energy formula, when a nucleus captures a new neutron, its mass will become the sum of the prokaryotic and neutron masses, and then the neutron binding energy consumed in this process will be subtracted. Neutron binding energy includes gamma ray energy released after nuclear collision and recoil energy. Therefore, the accuracy of the mass-energy formula can be verified by measuring the mass change of the nucleus before and after neutron bombardment and the energy released during bombardment, and then comparing them.
Scientists choose silicon and sulfur atoms for experiments. Scientists at the National Institute of Standards and Technology measure the wavelength of gamma rays according to the scattering angle in the crystal lattice, and the wavelength determines the energy of gamma rays. Scientists at the Massachusetts Institute of Technology use electromagnetic traps to "fix" atoms before and after capturing neutrons and accurately measure their mass.
Their measurement results show that the difference between mass and the product of the square of light speed (MC2) and energy (e) is about four ten thousandths, which is enough to show the correctness of the mass-energy formula. Scientists said in the paper that this is "the most accurate direct verification of the mass-energy formula so far", which is 55 times higher than the previous proof.
As we all know, Italian scientist Galileo and British scientist Newton are the founders of classical mechanics.
1642 65438+Newton was born in a farmer's family in Woolsop village, Lincolnshire on February 25th. 12 years old, when studying in a public school in Grantham, his academic performance was not outstanding, but he loved reading and had a strong curiosity about natural phenomena. 16 1 year, Newton studied at Trinity College of Cambridge University and became an excellent student. 1669, at the age of 27, he became a professor of mathematics at Cambridge University. 1672 was elected as a member of the royal society. 1687, Newton published the famous mathematical principles of natural philosophy. Newton successfully solved the two-body problem and three-body problem in gravity theory with calculus invented by himself. It can be said that classical mechanics made great contributions to the progress and development of mankind under the historical conditions at that time!
There is a term in classical mechanics called inertial system. It refers to all reference frames that allow the establishment of the law of uniform linear motion. If the laws of mechanics are to be established, the motion state of the coordinate system cannot be arbitrary, and there must be no acceleration (just uniform motion) and no rotation (just linear motion). For example, in the solar system, the earth does not move to the sun in a straight line at a uniform speed, so strictly speaking, the earth is not an inertial system. But when we consider some motion phenomena on the ground, the ground reference system can still be regarded as an inertial system.
Classical mechanics holds that the laws of mechanics, time, length, acceleration, mass and simultaneity are absolute, and only the coordinates and speed of object motion are relative. This is Newton's "absolute view of time and space". However, this "absolute concept of time and space" and the defect that it is not suitable for high-speed movement were gradually exposed until the end of 19. 189 1 year, because of the discovery of electrons, scientists face microscopic particles moving at high speed for the first time. At this time, Newton's classical mechanics seems powerless. Therefore, classical mechanics is only a kind of mechanical theory that is only applicable to macroscopic objects moving at low speed.
Albert. Einstein was born in the German town of Ulm on March 1879, and his parents were Jewish. Like Newton, Einstein did not show extraordinary intelligence when he was young. On the contrary, he can't speak when he is over 4 years old, and his family even worries that he is an imbecile. 1888 He is 9 years old and entered middle school. His study is not outstanding. Apart from being good at math, his other classes are not so good. /kloc-at the age of 0/2, Einstein gave up his belief in religion. He found that there is a huge natural world around him, which exists independently of human beings, just like an eternal mystery. Therefore, Einstein especially loved science when he was a teenager, hoping to master the mystery of this nature.
From 65438 to 0896, Einstein was admitted to the Federal Institute of Technology in Zurich. During his college years, Einstein was fascinated by physics. He read the works of famous German physicists Kirchhoff and Hertz, studied Maxwell's electromagnetic theory and Mach's mechanics, and often went to the home of a theoretical physics professor for advice. 1900, graduated from Einstein University. 1902, with the help of his friend Grossman, Einstein became an ordinary technician in the Swiss Federal Patent Office in Bern.
1905 On June 30th, the German Yearbook of Physics accepted Einstein's paper "On Electrodynamics of Moving Objects" and published it in September of the same year. This paper is the first article on special relativity, and later (also in 1905), another paper was published. Is the inertia of an object related to the energy it contains? In addition, in 1907, Einstein published a long article about the principle of relativity and the conclusions drawn from it. These three articles contain the basic ideas and main contents of special relativity, and are also the basis of our discussion.
So, what's the difference between Einstein's special theory of relativity and Newton's classical mechanics? Einstein believed that only the laws of physics and the speed of light in the universe are absolute, while others (including time, length, mass, simultaneity, etc. ) are relative. So both length and time change with the movement of the frame of reference, so space and time are relative and interrelated. This is also the origin of the word "relativity". Why is it also called "special relativity"? This is because this part of the theory is only applicable to inertial systems that do relatively uniform linear motion.
2. Review of the main contents of special relativity.
Einstein's special theory of relativity can be summarized as 10, namely 1 transformation, 2 postulates, 3 formulas and 4 inferences. Let's briefly introduce the main contents of this 10 aspect:
(1) and (1) transformations are Lorentz transformations, which are different from galilean transformation. Galilean transformation believes that in different reference systems, time is absolute and speed (including the speed of light) is relative. Lorentz transformation holds that time is relative and the speed of light is constant. If the speed of an object is much less than the speed of light, the Lorentz transformation is simplified to galilean transformation.
(2) Two postulates: The first postulate is that the laws of physics are the same in all inertial systems, which is what we usually call "the principle of special relativity". This means that in all inertial systems, not only the laws of mechanics, but also the laws of electromagnetism, optics and atoms are established. The second postulate is the "constant speed of light" postulate: that is, the speed of light in vacuum is a constant, which has nothing to do with the movement of the observer or the light source and the color of the light. More specifically, the speed of light c in vacuum has nothing to do with the frequency of light, the movement of light source and the movement of observer, but always keeps a constant value (c=299792458m/s).
(3) These three formulas are velocity synthesis formula, mass velocity formula and mass-energy relationship:
A. Velocity composition formula: When a system moves at velocity v, if an object in the system moves in the same direction at velocity u, the composition velocity w of special relativity is expressed as follows. Obviously, only when you
B, mass velocity formula: m is the dynamic mass of any particle or object, mo is its static mass, if its motion velocity is v >；; C, then m becomes an imaginary number. So Einstein thinks that virtual mass is meaningless, which is one of the reasons why special relativity says that "superluminal motion is impossible".
C. mass-energy relationship: E = mc? In 1922, Einstein explained the formula as follows: It can be seen that mass and energy are similar in essence, and they are just different expressions of the same thing. The mass of an object is not constant, it changes with its energy.
(4) The four inferences are that the length of the moving direction is shortened, the moving clock is slowed down, the photon rest mass is zero, and matter and information cannot move faster than light.
From the above review, we can see that the main contents of special relativity are embodied in "1 transformation and two postulates", and they are closely related. As for the "three formulas and four inferences", it is derived from the above three.
3. The main problems and questions of Einstein's special theory of relativity.
Special relativity has a history of 10 1 year since it was put forward. At present, because the special theory of relativity can't fully explain many modern physics problems, some scientists in China, the United States and Germany are designing various experiments to re-examine the correctness of the special theory of relativity. In recent ten years, the international scientific community's doubts mainly focus on the following four aspects: the hypothesis that the speed of light is constant, the inference that the length of the direction of motion is shortened, the inference that the rest mass of photons is zero, and the inference that matter and information cannot move faster than light. In the final analysis, the reason for questioning is the lack of experimental evidence, while the number of counter-evidence experiments is increasing.
(1). Query on the postulate that the speed of light is constant;
Light is an electromagnetic wave, a wave that propagates in an electromagnetic field. The wave in the electromagnetic field should have its characteristic speed, which is equal to the speed of light, just as the speed of sound wave in still air is a certain value. Moreover, because the speed of light has nothing to do with the source speed, the speed of light is a constant for the absolute coordinate system (this has actually been proved in Maxwell and Lorenz's electromagnetic theory). It can reflect some characteristics of absolute coordinate system, so the speed of light has its invariance.
In addition, the special theory of relativity holds that the speed of light is the same for all observers, and it has nothing to do with the speed of the receiver. However, we think that the speed of light is closely related to the receiver, that is, the speed of the observer will directly affect the speed of light measured by the receiver: the speed of light measured by the receiver running in the same direction of light will decrease, and the speed of light measured by the receiver running in the opposite direction of light will increase. For example, the observation of 3K microwave radiation and radio waves of radio galaxies found obvious anisotropy in the direction of the earth's movement. These astronomical experiments prove that the speed of light is related to the speed of the receiver. So the speed of light is variable.
In a word, the speed of light still plays an important and special role. Its importance means that some basic concepts need to be defined by it (such as absolute coordinate system, etc.). ), and its particularity means that it is a variable and unchangeable quantity.
(2) Questioning the inference that the photon rest mass is zero;
"Photon's rest mass is zero" is actually the second postulate of special relativity, because Einstein believes that there will be no rest system of photons when light propagates at a constant speed c in vacuum, so the rest mass of photons must be zero. At the same time, according to the inference of special relativity, photons will be zero, and photons are particles without volume. Similarly, the photonic clock will stagnate and lose the concept of time. This matter has always worried scientists, and many experiments have been carried out for it. In 1970s, when Ding Zhaozhong, a famous experimental physicist, did experiments on photons and electrons in an accelerator in Hamburg, he found that photons were not without static mass. When the photon energy is high, it will quickly become particles with a certain life and quality. He named this phenomenon heavy photons. The experimental results published by Japanese Masatoshi Koshiba in 1998 show that neutrinos contain static mass, and the value is about 10g, which won the 2002 Nobel Prize in Physics. We know that photons and neutrinos are very similar, which is very noteworthy. On February 28th, 2003, the American Physical Review Express published the new achievements made by Luo Jun, a professor of physics at Huazhong University of Science and Technology in China, and his research group in the research of "Checking the upper limit of photon static mass with precision torsion balance". In any case, the rest mass of a photon will not exceed 10 to the minus 54th power kilogram, which is 1/20 of the upper limit of the previously known photon mass. Or the negative 24th power of electron mass 10. In this regard, American physicist R Luck commented: "You can never say for sure that anything is absolutely zero".
(3) Questioning the inference that there can be no superluminal;
As we know, a group of European physicists founded quantum mechanics in 1925. Although the quantum world it describes is often quite different from human life experience, the scientific historical facts of 8 1 year prove that it is by no means an empty and unrealistic theory, and it has solved many practical problems that need to be solved urgently in the development of science and technology. Therefore, it is an extremely successful branch of science with the characteristics of modern scientific theory.
Special relativity is classical, macroscopic and localized in nature, while quantum mechanics is non-classical, microscopic and non-localized, so they are fundamentally inconsistent. This is also the reason why Einstein insisted on opposing quantum mechanics. Special relativity does not allow superluminal state, but the nonlocality of quantum mechanics shows that superluminal state is possible. In fact, the problem of superluminal just illustrates the sharp contradiction between special relativity and quantum mechanics.
In recent ten years, many scientists have reported superluminal experiments of non-matter (electromagnetic fields, waves, light pulses, etc.). ) and their results. For example, in 1992, the "photon race" experiment conducted by the team headed by R.Chiao at the University of California, Berkeley, USA, obtained the photon speed of 1.7c(c is the speed of light); 1992- 1997 the results measured by professor G.Nimtz of cologne university in Germany are 4.7c and 4.34c；; In the first quarter of 2003, the research group of Beijing Broadcasting Institute, composed of Professor Huang Zhixun, Professor Kuai and graduate student Guan Jian, conducted a radio wave frequency experiment, and obtained the stopband superluminal group velocity with a coaxial system simulating photonic crystals. The data were distributed in (1.5 ~ 2.4) C. At present, in different countries, there are experts and scholars with different backgrounds and professional disciplines who study the problem of superluminal by theoretical or experimental methods and get the affirmative conclusion that superluminal exists. This is by no means accidental.
In a word, Einstein was a great and outstanding scientist and contributor in his life. We know that in natural science research, "practice is the standard for testing truth". At present, many experiments show that Einstein's special theory of relativity is not an absolute truth, but a basically correct theoretical system, which is only applicable to sub-light speed and has its own limitations. Special relativity is still a classical theory to some extent, which needs to be improved and developed according to new situations and new experiments.
refer to
1, Some Problems in the Study of Special Relativity, Professor Huang Zhixun of Beijing Broadcasting Institute.
2. Theoretical development and experimental test of special relativity by Professor Huang Zhixun of Beijing Broadcasting Institute.
3. The theoretical basis of superluminal research is Professor Huang Zhixun of Beijing Broadcasting Institute.