The great achievements of basic physics research in the 20th century should be attributed to the establishment of relativity, quantum theory and gravity theory. Relativity, quantum theory and gravity theory are all universal, and an important embodiment of their universality is shown in three universal constants C, H and G respectively. However, whether the three theories are really universal depends on their compatibility. The establishment of general relativity confirms the compatibility of gravity theory and relativity.

The development of quantum theory proves that all kinds of motion forms of matter obey the requirements of quantization, and at the same time, all relativistic fields, such as electromagnetic fields, should also be quantized. In the early stage of field quantization research, there were a series of divergence difficulties. In the late 1940s, the divergence of quantized electromagnetic fields was initially solved by renormalization theory. The most fundamental solution to the divergence difficulty was completed in the 1960s. The establishment of the unified theory of weak current not only solves the divergence difficulty in weak interaction, but also hopes to solve the compatibility problem between relativity and quantum theory in the field of strong interaction under the framework of similar weak interaction. The most difficult step is the compatibility of gravity theory and quantum theory. One of the main goals of this step is to establish a quantized theory of gravity. The study of quantum gravity theory also originated from the singularity problem of general relativity. The singularity theorem proposed by Penrose and finally established by Hawking and Jerosh shows that the solution of the gravitational field equation must be singular in a fairly wide state of matter. The existence of singularity shows that general relativity belongs to the category of classical physics that obeys the law of causality, and the theory is no longer applicable at singularity. It is possible that the singularity will disappear naturally after considering the quantum properties of the gravitational field, which was later supported by Hawking's black hole evaporation theory.

The third driving force that forces people to study the theory of quantum gravity comes from the grand unified theory. The unified theory of weak current has been established, and the unified theory of weak current and strong interaction is a hot spot at present. The research process shows that their unity with gravity must be considered at the same time, and the essence of this unity is to establish the theory of quantum gravity. The theoretical framework of classical physics is based on the law of causality, and classical physics depends on the laws of physics and their corresponding boundary conditions. However, when the problem involves a singularity, which is not caused by mathematical or model defects, it is difficult to eliminate this singularity and give a reasonable boundary condition, which forces people to reconsider the original theory.

Along the reverse course of the expansion and inflation of the universe, applying the framework given by classical cosmology, we can trace back to the state of the universe before inflation, and naturally we will get that the scale of the universe will tend to zero. This means that the strength of the gravitational field and the energy density of the material field will tend to infinity, and the universe will evolve from a singularity, which is not artificially caused by the defects of the model. As early as 1960s, Penrose and Hawking used global differential geometry to prove that (1) singularity is not only highly symmetrical, but also the inevitable product of general relativity. This means that it is impossible to find a solution to the singularity in the theoretical framework of general relativity, or that although general relativity reveals the gravitational bending of space-time, it is not applicable to the space with extremely high curvature. Planck, the founder of quantum theory, thought long ago that all natural forces should be linked. 1899, he first proposed the minimum length Lp of the universe, and then successively proposed Planck time tp, Planck temperature Tp and Planck mass Mp, which were LP = (Hg/C3)1/2 = 4.05× 65433 respectively. TP = (Hg/C5)1/2 =1.35×10-43s, MP = (HC/G)1/2 = 5.45×10-5g. It is not difficult to see that the temperature tp is extremely high, even higher than the temperature at BIGBANG, but the length Lp and time Tp are extremely small, and the mass Mp is not very large. Although these values can't be obtained under laboratory conditions, it makes people think whether these are the scales that can be reached in the universe before the inflation. Therefore, the quantized general relativity should replace the classical general relativity.

At the beginning of this century, after the birth of quantum mechanics, it was the first time to explain the difficulties in the microstructure-atomic structure with the principle of quantum mechanics, and established the Schrodinger equation. At the same time, a series of quantum mechanical descriptions of atomic characteristics are obtained. Since the 1960s, when people tried to explain the structure of this huge system-the universe with quantum mechanics, they found striking similarities between them. First of all, in the tiny system of protons and electrons with electromagnetic action, the important degree of freedom r(t) tends to zero, which leads to the classical difficulty of singularity, while in the large matter system with gravitational action, the scale factor R(t) of the important degree of freedom also leads to the classical difficulty of singularity. The quantum length of Bohr radius of micro-electromagnetic system is 10-8cm, and the Planck length of gravitational system is 10-33cm. The microscopic system obeys the dynamics law of Schrodinger equation, while the gravitational system has Wheeler-Devit equation. In recent years, new progress has been made in the research on the similarity and relationship between the two systems. In 1960s and 1970s, Devit (B.S.), Mesner (C.W.) and Wheeler and others did important basic work in quantum cosmology. They established the Wheeler-Devit equation to describe the quantum properties of the universe, but solving this equation faces the establishment of boundary conditions. Because the initial state of the universe is still uncertain.

D, the progress of cosmology

With the in-depth development of physics research, people are also trying to understand the universe from the large scale of time and space, that is, as a whole. The origin, structure and evolution of the universe are all topics that people care about. The combination of physics and high technology has created giant optical telescopes, space X-ray and infrared telescopes with a diameter of 25 meters, and large antenna array radio telescopes, which not only expand the window for people to observe the universe from infrared and visible light to the full band of X-ray and γ-ray, but also expand the space-time scale of observing the universe to 65.438+07 billion light years. Nowadays, a vivid and magnificent picture of the universe has been presented to mankind.

Based on modern high-energy particle physics and theoretical cosmology of general relativity, the whole process from the initial fireball explosion to the formation and evolution of galaxies can be described theoretically. The Big Bang model has been confirmed by modern astronomical observations, such as the red shift of galactic spectral lines, 3K microwave background radiation and helium abundance. At the same time, in the process of solving the problems of this model itself, such as horizon problem, straightness problem and magnetic monopole problem, it is combined with the theory of high-energy physical vacuum phase transition to develop into a more perfect expanding universe model. Although the Big Bang model with inflation mechanism has laid the foundation for the development of cosmology, with the development of quantum gravity theory, a series of deeper issues about quantum cosmology, such as the topological structure of universe space-time, the vacuum parameters of basic coupling constants, and the dynamic explanation of cosmology constants, have caused a new round of heated debates. The source of this important progress in theoretical research is the establishment of Hubble's law, which leads the world's attention from general celestial bodies to the whole universe.

1. Hubble's law and the expanding universe

Studies show that the age, evolution and end of the universe are largely determined by its expansion rate. The observation of the expansion of the universe can be roughly divided into two aspects, namely, measuring the motion rate of galaxies and measuring the distance from the earth to galaxies. The former is related to the formation model of the universe and the development of related theories, while the latter is an important basis for estimating the brightness, mass and size of celestial bodies. However, both of them depend on the measurement of Hubble constant. Hubble constant has become one of the most important basic constants in modern cosmology. At the beginning of the 20th century, several large telescopes with the diameter of 1 m were built one after another, which created conditions for systematic observation of extragalactic galaxies. Hubble (Edwin Powell1889 ~1953), an American astronomer, has made great contributions to modern astronomy and cosmology. Hubble 19 10 graduated from the Astronomy Department of the University of Chicago, and then went to Oxford University, England, with a master's degree in law. 19 14 to 19 17 studying for a doctorate in astronomy at Yerkes Observatory. During the First World War, he served in France, and after the war, he was engaged in the observation and research of galaxies at Mount Wilson Observatory. At that time, Mount Wilson Observatory had built a 100-inch telescope. Using this telescope, Hubble focused his observations on what he called "bright fog patches", which are nebulae. Some astronomers of Hubble's time also made a lot of observations on these nebulae. For example, American astronomer Curtis (Heberdoust1872 ~1942), who works at Rick Observatory, devoted himself to the study of extragalactic galaxies. By observing new stars and estimating the distance by using the angular size of galaxies, he believes that most of the observed nebulae belong to extragalactic galaxies. Shapley (Shap-ley, Harlow 1885 ~ 1972), an American astronomer who used to be the director of the Observatory of Harvard University, used the telescope 19 15 ~ 1920 of Mount Wilson Observatory. He took the Cepheid Variable (Leavitt, Henrietta Swan-0/868 ~1921) discovered by Loewit as the scale, determined the distance of these nebulae, and thought that they were about 50,000 light years away from the sun and should belong to the Milky Way, so he expanded the scale of the Milky Way to three times. Shapley was the first person who suggested that the solar system was not at the center of the Milky Way. Although he drove the sun away from the center of the Milky Way, he put the Milky Way in the center of the universe. Curtis has a different view. He believes that the universe is full of a large number of star systems like the Milky Way. 1920, in the National Academy of Sciences, Curtis and shapley formally confronted each other. Although Curtis gained the upper hand in this debate, he did not reach a generally agreed conclusion. It was not until three years later that the observation facts given by Hubble made the above debate have a decisive result. 1923, Mount Wilson Observatory built a 2.5-meter telescope. Hubble used it to find a Cepheid variable at the outer edge of Andromeda Nebula. According to the relationship between the light variation period and luminosity, he deduced that the distance of the star is 150000 parsec (actually 800000 parsec), which is much larger than the Milky Way in shapley. This shows that Andromeda Nebula is an extragalactic galaxy, thus ending the debate on the existence of extragalactic celestial bodies and making astronomers' research field out of the Milky Way. Slipher (Vestomelvin1875 ~1969), another astronomer of Hubble's contemporaries, is also interested in the study of nebulae. He made a lot of observations on the spectra of galaxies. 192 1 year, he applied the Doppler-Fizeau effect to Andromeda nebula for the first time, and found that most of the observed galaxies have longer spectral wavelengths than those observed in the laboratory, which indicates that these nebulae are moving away from the earth, and their receding speed is much higher than the apparent speed of stars. 1929, on the basis of colleagues' research results, Hubble made a velocity-distance diagram only based on the observation data of 24 galaxies with known distances. The speed shown in the figure is in direct proportion to the distance value, that is, vr=H0r, vr is the apparent speed from the galaxy to the Milky Way, and the above formula is Hubble's law, where the constant H0 is Hubble's constant, and the age of the universe obtained from this constant H0 is-1=1.84×108, which is the ancient rocks in the crust observed by scattering method at that time. Hubble's results not only prove that the whole universe is expanding, but also the expansion speed is proportional to the distance r, so there is no center everywhere, and it is centered everywhere. In order to expand the observation range, it is necessary to be able to observe galaxies in more distant clusters. Due to the sudden increase of workload, Hubble began to cooperate with Huma-Son (Milton Lasalle1891~1972). Hubble measures the brightness of galaxies and Hudson measures the redshift. Hermanson was not born in an ordinary class. At first, he was just a janitor at Mount Wilson Observatory. His work made him fall in love with astronomy. He showed outstanding talent and skillful observation skills in the astronomical observation of celebrating the holidays for others, and soon he officially devoted himself to astronomical research. After Hubble died, he continued Hubble's astronomical observation. 1956, he cooperated with others and improved Hubble's law by using observation data, which was consistent with Lemaistre's and Gaymov's Big Bang theory.

2. Three climaxes of Hubble constant correction.

In principle, the determination of Hubble constant seems simple, that is, as long as the distance between galaxies and the regression rate are measured, Hubble constant can be obtained from Hubble law. However, this is not the case. The speed of galaxies can be directly obtained from the red shift of spectral lines, but the measurement of distance is difficult and complicated. For the distance of nearby galaxies within 65.438+0 billion light years, astronomers' measurement results are relatively consistent, and this measurement is based on Cepheid variables. During the observation in South Africa from 65438 to 0908, Loewit, who worked at Harvard Observatory, found that the brightness of Cepheid variable changed periodically, and the longer the light change period, the greater the average brightness. This discovery is of unusual significance, because observing the whole process of brightness change, we can get the period and apparent brightness of light change, and then we can calculate its absolute brightness. According to the relationship between increasing distance and decreasing apparent brightness, the distance of Cepheid variable can be determined by the ratio of absolute brightness to apparent brightness. Therefore, taking Cepheid variable as the measuring ruler and gradually expanding the measuring range by using the triangular parallax method, we can measure not only the size of the Milky Way, but also the size and distance of galaxies outside the river. In the 1920s, after Hubble confirmed the existence of other galaxies with Cepheid Variables outside the Milky Way, from 1930s to 1950s, Hubble and Sandage (,Allen Rex1926 ~) and others searched for more Cepheid Variables in nearby galaxies to establish updated scales, and did a lot of work. They successfully measured the distance between more than a dozen galaxies and improved the basis for determining Hubble constant.

The initial value of Hubble constant is H0 = 550/s/million parsec (abbreviated below). 1936, the Hubble constant was revised to H0=526 considering the interstellar extinction factor. At first, this value was considered accurate, because the age of the universe based on H0- 1 was consistent with the geological observation results at that time. After World War II, the Hubble constant was gradually revised with Cepheid variable as the measuring scale. 1952, Walter 1893 ~ 1960, a German astronomer living in the United States, worked on the rooftop of Palo Marvin in Mount Wilson, which set off the first climax of Hubble constant correction. The climax was caused by modifying the measuring ruler. At this time, the 5-meter-diameter astronomical telescope of Paloma Observatory was built and started to operate. Using his precise and systematic measurements, Budd not only found more than 300 Cepheid Variables in Andromeda, but also found that stars are divided into two constellations, each of which has its own Cepheid Variables, which are only applicable to nearby galaxies. The original Hubble's Law is aimed at Cepheid Variables based on the first constellation. With the correction of the perihelion curve of Cepheid variable and the increase of observation scale, it is necessary to replace the original scale in the determination of Hubble constant. According to Budd's calculation, the distance of distant galaxies will be doubled compared with the original estimate, and the Hubble constant will also be doubled. 1952, Budd announced his results at the 8th International Astronomical Congress held in Rome, H0=260.

The second climax of Hubble constant correction was initiated by Sandach, Hubble's successor. Sandage is a famous observational astronomer. Starting from 1956, he systematically measured Hubble constant at Paloma Observatory. In a few years, he obtained the data of more than 600 galaxies, and the maximum redshift value reached Z=0.202, and the Hubble constant value obtained was H0= 180. On this basis, Sandage further revised the Hubble constant, and they changed the scale again, further expanding the observation range. At this time, the original method of determining the distance is no longer applicable, because when the distance of the galaxy reaches several million parsec, the telescope can no longer distinguish a single star in the galaxy, so it is necessary to find an "indicator" to replace Cepheid variable stars as a new distance standard. Through the relationship between the absolute magnitude and apparent magnitude of celestial bodies, they first determine the distance of the indicator, and then determine the distance of the galaxy by the indicator. They believe that Cepheid variables, H ⅱ regions, spherical nebulae, supernovae and elliptical galaxies can all be used as distance indicators. 196 1 year, Sandage announced at the international astronomical conference held in Berkeley, USA, that the Hubble constant should be between 75 and 1 13, with the most likely value being H = H=98 15 and the general value being 100. This result shows that the scale of the universe is much larger than people expected in the early days.

Since the 1970s, astronomers have paid more and more attention to the measurement of Hubble constant, and the measurement methods have become more systematic and the measurement accuracy has been continuously improved, thus forming the third climax of Hubble constant correction. However, after the climax of this revision, the situation has become increasingly complicated. The measured value of Hubble constant is getting closer and closer to the high and low value. Sandage and his collaborator Taman got a value of 50, while Devo Kohl of the University of Texas got a value of 100. The measurement methods of both values are based on Cepheid variable stars, and then the indicators with different distances are selected. The difference of the results is two times, which not only leads to the dispute of Hubble constant, but also leads to people's random choice in practical operation. There are 50 candidates, there are candidates 100, and the average number of candidates is 75. Although these values are authoritative, it is still uncertain which one is the most accurate. At present, it is too early to make a ruling on Hubble constant, but from the evidence obtained from other aspects, biased opinions can still be put forward.

According to the Hubble constant, the Hubble age of the universe should be t0= 19.7× 109, and t9=9.8× 109. However, there are other ways to estimate the age of the universe. One method is to measure the content of radioactive elements in ores and estimate them according to their half-lives. The comprehensive measurement results of various radioactive elements show that the age of the universe is 1× 10 10. Another effective method is to determine the age of globular clusters. According to the Herro diagram of globular clusters, their ages are (10 ~ 20) ×10/0. Based on these estimates from different angles, the age of the universe is less than 20 billion years, which shows that it is more practical to take a small Hubble constant.

Since Hubble constant has become one of the most important and basic constants in modern cosmology, the research on it has become a very active topic in recent years. Hundreds of papers on Hubble constant have been published. 1989, the famous astrophysicist Vandenberg wrote an authoritative paper for Astronomy and Astrophysics Review, which summarized all the measurement and research results of Hubble constant up to the end of 1980s, and finally concluded that the value of Hubble constant should be H0 = 67 8.

3. Discovery of redundant antenna temperature

At the beginning of 1963, young physicist penzias (Arno Allan1933 ~) working in Bell Laboratories and radio astronomer Wilson (Robert Woodrow 1936~ ~) cooperated to measure the silver halo radiation of high-latitude galaxies in the Milky Way. The radio telescope they used was originally made of a large horn antenna and a radiometer for receiving satellite echoes. They also adopted the ruby traveling wave maser with the lowest noise at that time, and used the waveguide cooled by liquid helium as the reference noise source, because it can produce noise with a certain power as the noise reference, so that the power of the noise can be expressed by the equivalent temperature. As there happened to be a 7.35cm ruby TWT maser at hand, they started the antenna test at 7cm band.

Penzias and Wilson's measurement results ① show that the equivalent temperature of the antenna is about 6.7±0.3K, and the temperature of the antenna itself is 3.2±0.7K, in which the atmospheric contribution is 2.3±0.3K, and the contribution of the ohmic loss and the back lobe response of the antenna itself is about1k.. After deducting these factors, it is concluded that there is redundant noise in the antenna, and its equivalent temperature is about 3.5 65438+. Although they have taken various measures to eliminate all kinds of estimated noise sources as much as possible, the equivalent temperature value of this redundant noise still exists, which is not only stable, but also uniform and unpolarized and can be received in any direction.

Penzias and Wilson observed the phenomenon of antenna noise and excessive temperature, which was accidental, because the experiment was not predicted or guided by theory. What is valuable, however, is that they attach importance to the observation results and are faithful to the original data. They don't give up the phenomena they observe by accident easily, but catch them and chase them to the end. And try their best to dig out the meaning behind the observed facts, which enables them to make important discoveries without losing time. In this success, what is even more commendable is the support of Bell Laboratories for the experimental work. Today, the largest industrial laboratory has thousands of talented scientific and technological workers. While developing telephone and telegraph technology, they always attach importance to the research of basic science, especially basic physics. It plays a mainstay role in the world communication industry and has made many remarkable achievements in physics research. For example, in astrophysics, in 193 1 year, Jansky, a telecom engineer in Bell Laboratories, first discovered silver. Observations of penzias and Wilson were made by Bell Laboratories in cooperation with the National Radio Observatory. Bell Laboratories gave great support from manpower, equipment and funds with foresight, and provided the world-class sensitive millimeter-wave spectrum radio telescope, thermionic radiometer and liquid helium refrigeration reference noise source at that time, which played a vital role in the success of the experiment.

4. Verification of cosmic microwave background radiation

While observing with penzias and Wilson, others are looking for the same goal. They are a research group of Princeton University headed by Dicke (Robert Henry1916 ~) and are conducting exploratory research on cosmology. Dick received his doctorate from the University of Rochester. 1946 taught in physics department of Princeton University. Dick became famous because of his important achievement-scalar-tensor field theory. This theory keeps pace with Einstein's theory of gravity, and can also successfully explain some observation phenomena in gravity research, so that it is difficult to know who is right or wrong in gravity field research. In 1960s, with the rise of cosmology research, Dick became interested in Gamov's Big Bang theory. He once imagined that there should be remnants of the Big Bang in the universe so far, such as some kind of radiation left by the high-temperature and dense period of the early universe. He and his collaborators believe that this radiation may be an observable radio wave. Dick suggested that Rolle (P.G.) and Wilkinson (D.T.) make observations and peebles (P.J.E) make theoretical analysis. Peebles and others clearly pointed out in the paper published in March 1965 that residual radiation is an observable microwave radiation. The picture of light elements reappearing after the decomposition of heavy elements in the very early universe is described. Peebles later made an academic report at Hopkins University, which also clarified this idea. 1965, penzias told B. Burke, a radio astronomer at MIT, about the unnecessary antenna noise that they could not explain. Burke immediately remembered peebles's speech mentioned by his colleague Turner (K.) who works at Carnegie Institution, and suggested that penzias contact Dick's group. In this way, the convergence of experimental and theoretical discoveries has promoted the rapid development of the situation. First, penzias telephoned Dick, and then Dick sent a preprint of the papers by peebles and others. Then Dick and his colleagues visited the experimental bases in penzias and Wilson. After discussing the observation results in Crawford Mountain, which is only a few miles away from Princeton University, the two sides agreed to publish two briefings in Astrophysics, one of which is Dick's theoretical article "Cosmic Blackbody Radiation" (2). The other is penzias and Wilson's experimental report "Measurement of antenna overheating at 4080MHz" (3). Although the latter paper thinks that no work has been done in cosmology, out of caution, it does not involve the theory of the origin of the background radiation universe, but only mentions that "a possible explanation for the observed excessive noise temperature is given in another short message written by Dicke, Peebles, Roll and Wikinson in this issue". However, after the publication of the two papers, it caused great repercussions. People realize that if it can be proved that the antenna overheating really comes from the cosmic background radiation, the impact of this achievement on the development of cosmology will be immeasurable. According to theoretical analysis, the light radiation in the extremely hot state of the early universe is in a state of thermal balance and should be isotropic, and the energy density distribution of thermal radiation obeys Planck's law. With the thermal expansion and gradual cooling of the universe, the remaining optical radiation spectrum should still maintain Planck distribution. Whether the radiation detected by penzias and Wilson conforms to this distribution should be an important criterion to test whether the antenna overtemperature comes from cosmic background radiation. From 1965 to the mid-1970s, many research groups have successively completed various experiments. Dick's team got 3.0±0.5K at 3.2cm, Shackgaft and Gerber got 2.8±0.6K at 20.7cm, and penzias and Wilson got 3.2 0.1cm. However, the peak value of 3K blackbody radiation should be around 0. 1cm. In order to obtain the measurement value of about 0. 1cm, the rocket team of Cornell University and the balloon team of MIT observed the existence of 3K blackbody radiation in the far infrared region. Woody's team at the University of California, Berkeley, measured with a high-altitude balloon that there is 2.99K blackbody radiation in the band from 0.25 cm to 0.06 cm. At this point, the experimental results are very consistent with the theory. The redundant antenna temperature observed by penzias and Wilson is indeed cosmic microwave background radiation, which is isotropic and unpolarized and has a blackbody spectrum of about 3K in the whole universe. This achievement is of great significance to the study of cosmology. For this reason, penzias and Wilson won the 1978 Nobel Prize in physics.