Basic introduction Chinese name: BIGBANG mbth: Universe? Big bang; Theoretical time of the Big Bang: 65.438+0.382 billion years ago? Formation: The founders of dense and hot singularity expansion and explosion theory: Lemaistre, Gamow, Hubble, etc. Introduction, generation principle, basic hypothesis, research process, initial stage, verification stage, mature stage, brief explosion history, observation facts, related concepts, expansion space, horizon, microwave radiation (1978 Nobel Prize in Physics), helium abundance, main evidence, theoretical award, explosion. Introduction "The Big Bang Theory" holds that the universe was formed by the expansion of a dense and hot singularity after a big bang 654.38+03.7 billion years ago. 1927, Belgian astronomer and cosmologist Lemaistre (George Ma Le? Tre) put forward the big bang hypothesis for the first time. 1929, American astronomer Hubble put forward Hubble's law that the redshift of galaxies is proportional to the distance between galaxies, and deduced the theory of inflated universe with long distance between galaxies. The most influential theory in modern cosmology. Its main point is that the universe once had an evolutionary history from hot to cold. During this period, the universe system kept expanding, which made the density of matter evolve from dense to sparse, just like a huge explosion. One of the founders of this theory is Gamov. 1946, Gamov, an American physicist, formally put forward the big bang theory, arguing that the universe was formed by a big bang about1400 million years ago. At the end of last century, the observation of Ia supernovae showed that the universe was expanding at an accelerated pace, because the universe might be mostly composed of dark energy. At the initial stage of explosion, matter can only exist in the form of elementary particles such as neutrons, protons, electrons, photons and neutrinos. The continuous expansion after the explosion of the universe caused the temperature and density to drop rapidly. With the decrease and cooling of temperature, atoms, nuclei and molecules are gradually formed and combined into common gases. Gas gradually condensed into nebulae, which further formed various stars and galaxies, and finally formed the universe we see today. The idea that the universe does not exist forever, but is created from nothingness can be said to be deeply rooted in western culture. Although Greek philosophers have considered the possibility of the eternity of the universe, major western religions have always insisted that the universe was created by God at some time in the past. Basic Assumptions The establishment of the Big Bang theory is based on two basic assumptions: the universality of physical laws and cosmological principles. Cosmological principle means that the universe is homogeneous and isotropic on a large scale. At first, these ideas were introduced as transcendental axioms, and now there are related research works trying to verify them. For example, for the first hypothesis, experiments have proved that the relative error of the fine structure constant will not exceed 10 (-5) for most of the time since the birth of the universe. In addition, through the observation of solar system and binary star system, the general theory of relativity has been verified by very accurate experiments; On a broader cosmic scale, the empirical success of the Big Bang theory in many aspects is also a strong support for general relativity. Assuming that the large-scale universe is isotropic from the earth, the cosmological principle can be deduced from the simpler Copernican principle. The Copernican principle means that there is no preferred (or special) observer or observation position. According to the observation of microwave background radiation, the cosmological principle has been proved to be established on the order of 10 (-5), while the observed cosmic uniformity on a large scale is on the order of 10%. What many people don't know at the initial stage of the research process is that compared with today when the Big Bang theory has become common sense, the attitude of the world scientific community has been "sneering" for a long time after it was just put forward. This strange phenomenon is because the scientific community at that time was influenced by the philosophical trend of thought that evolution overthrew God's creationism, blindly opposed the traditional theory and refused to admit that the universe had a starting point, just as the Bible said. During this period, the western scientific community generally insisted that the universe and matter were unchanged, with no beginning or end. Therefore, all theories that involve the universe and everything "have a starting point" are not recognized. Including great scientists like Einstein, are also influenced by it. Einstein summed up the gravitational field equation and found that the formula of Rμv-( 1/2)Rgμv=kTμv would deduce that the universe is actually a dynamic universe with endless material changes, so he imposed a "cosmological constant" in this formula to maintain the calculation results of the static universe. That is to say, the original field equation is actually like this: ∧gμv+Rμv-( 1/2)Rgμv=kTμv, where the constant ∧ is the cosmological constant. In the verification stage, however, since the American astronomer Edwin Hubble began to observe the "redshift phenomenon" in 1922, the view of "cosmic expansion" began to take shape. 1929, Edwin Hubble summed up a landmark discovery, that is, no matter which direction you look, distant galaxies are rapidly leaving us, while nearby galaxies are approaching us. In other words, the universe is expanding. This means that the distance between early stars is closer. In fact, it seems that they happened to be in the same place at some time from about 65.438 billion to 20 billion years ago, so Hubble's discovery suggested that there was a moment called the Big Bang, when the universe was at a singularity with infinite density. Hearing this news, Einstein soon came to Wilson Observatory where Hubble worked, and personally observed the redshift phenomenon under the guidance of Hubble. After the interview, Einstein publicly admitted the mistake that his subjective consciousness influenced the scientific conclusion, and removed the cosmological constant in the field equation, so there was the Einstein field equation that we are familiar with today. At the mature stage of 1948, Gamov first established the concept of thermal explosion. The big bang that created the universe was not the kind of explosion that happened at a certain point on the earth and then spread into the surrounding air, but the kind of explosion that happened everywhere at the same time and filled the whole space from the beginning. Every particle in the explosion flew away from other particles. Actually, it should be understood as the rapid expansion of space. "The whole space" can refer to the whole infinite universe, or it can refer to the limited universe that can bend back to its original position like a sphere. According to the Big Bang cosmology, the early universe was a large homogeneous gas composed of microscopic particles, with extremely high temperature, extremely high density and extremely high expansion speed. These gases have a uniform temperature in thermal equilibrium. This unified temperature is an important symbol of the state of the universe at that time, so it is called temperature of the universe. Adiabatic expansion of gas will lower the temperature and make nuclei, atoms and even star systems appear one after another. A brief history of the initial explosion in BIGBANG: About 654.38+0.5 billion years ago, the point with infinitely small volume, infinitely high density, infinitely high temperature and infinitely large curvature of spacetime was called a singularity. Space and time are born out of some kind of eternity-some cosmologists call it quantum vacuum (pseudo-vacuum), which is full of quantum energy disturbance in accordance with Heisenberg's uncertainty principle. 10 -43 seconds (Planck time) after the big bang: about 10 32 degrees, the universe emerged from the background of quantum fluctuations, and this stage is called Planck time. Before that, the density of the universe may exceed 1094g per cubic centimeter, which is 78 times higher than that of protons. All forces in physics are one kind. (Supersymmetry) At this stage, the universe has cooled to the point where gravity can separate and start to exist independently, and there are gravitons that transmit gravitational interaction. Other forces in the universe (strong interaction, weak interaction and electromagnetic interaction) are still one. After BIGBANG 10-35 seconds: about 10 27 degrees. During the inflation period (the first push), gravity has separated, forming quarks, bosons and leptons. At this stage, the universe has cooled to the point where the strong interaction can be separated, while the weak interaction and electromagnetic interaction are still unified in the so-called electric weak interaction. The universe also skyrocketed, only lasting 10-33 seconds. At this moment, the universe has experienced a multiplication of 100 times (2 100), and the obtained scale is 1030 times that of the previous scale (it is the universe itself, that is, space and time itself, which does not violate the light speed barrier). Before inflation, the universe was still in the interconnected range of photons, which could smooth out all rough spots. When inflation stops, what is detected today has stabilized in their respective small areas, which is the so-called inflation theory. After BIGBANG 10-12 seconds: about 10 15 degrees. In the particle stage, protons and neutrons and their antiparticles are formed, and bosons, neutrinos, electrons, quarks and gluons are stabilized. The universe becomes cold enough, and the weak-current interaction is decomposed into electromagnetic interaction and weak interaction. Lepton families (electrons, neutrinos and corresponding antiparticles) need to wait for the universe to continue to cool 10 -4 seconds before they can leave the equilibrium phase with other particles. Once neutrinos are decoupled from matter, they will travel freely in space. In principle, these native neutrinos can be detected. 0.0 1 s after the big bang: about 1000 billion degrees, mainly photons, electrons and neutrinos. Proton neutrons only account for a part of 1 000 million, which is in thermal equilibrium, the system expands rapidly, and the temperature and density decrease continuously. 0. 1 s after the big bang: about 30 billion degrees, and the neutron-proton ratio decreased from 1.0 to 0.6 1. After BIGBANG 1 sec: about 1000 billion degrees, neutrinos escape outward, and the positive and negative electrons undergo annihilation reaction, and the nuclear force is not enough to bind neutrons and protons. 10 second after the big bang: about 3 billion degrees. During the nuclear age, stable nuclei (chemical elements) such as hydrogen and helium were formed. When the universe cools below 10 9 Kelvin (about 100 seconds later), particle transition is impossible. The calculation of nuclear synthesis shows that baryon density only accounts for 2%~5% of the matter needed by a topologically flat universe, which strongly implies that other forms of matter energy (non-baryon dark matter and dark energy) are flooding the universe. 35 minutes after the big bang: about 300 million degrees, the primary nuclear synthesis process stopped and neutral atoms could not be formed. After the big bang, it was101second (10 4) and the temperature was about 10 5 Kelvin, which was the material period. In the early history of the universe, light dominated all forms of energy. With the expansion of the universe, the wavelength of electromagnetic radiation is lengthened, and the corresponding photon energy is also reduced. The radiation energy density decreases inversely with the product of scale (r) and volume (4πR 3 /3), that is, An 1/R 4 decreases, while the energy density of matter decreases inversely with volume 1/R 3. Ten thousand years later, the density of matter caught up with the radiation density and exceeded it. Since then, the universe and its dynamics have been dominated by matter. 300,000 years after BIGBANG: At about 3,000 degrees, neutral atoms were formed by chemical combination. The main component of the universe was gaseous substances, which gradually condensed into high-density gas clouds under the action of self-gravity until stars and star systems. Quantum vacuum reached its peak in the skyrocketing period, and then penetrated into the whole universe in the form of dark energy, and with the rapid decrease of matter and radiation density, dark energy became more and more obvious. Dark energy may occupy 2/3 of the total energy density of the universe, thus promoting the accelerated expansion of the universe. The scientific nature of The Big Bang Theory is convincing. The most direct evidence comes from the study of the light characteristics of distant galaxies. In the 1920s, astronomer Edwin Hubble studied the observation results of Vesta Slipher. He noticed that the color of distant galaxies was slightly redder than that of nearby galaxies. Hubble carefully measured this reddening and made a picture. He found that this reddening (redshift) is systematic. The farther away a galaxy is from us, the redder it appears. The color of light is related to its wavelength. In the white light spectrum, blue light is at the short wave end and red light is at the long wave end. The reddening of distant galaxies means that their light wavelengths are slightly longer. Hubble confirmed this effect after carefully determining the positions of characteristic spectral lines in many galaxy spectra. He believes that the elongation of light waves is the result of the expansion of the universe. This great discovery of Hubble laid the foundation of modern cosmology. The nature of the expanding universe puzzles many people. From the earth's point of view, it seems that distant galaxies are rapidly leaving us. However, this does not mean that the earth is the center of the universe. On average, the expansion images in different parts of the universe are the same. It can be said that every point is the center, and no point is the center (the best explanation is a painting: the cutting of three-dimensional space). We'd better think of it as the space between galaxies is stretching or expanding, rather than the galaxies moving in space. This is different from the explosion from a point we see in our daily life. The fact that space can stretch seems strange, but since Einstein's general theory of relativity was published in 19 15, this is a concept that scientists have long been familiar with. General relativity holds that gravity is actually a manifestation of the bending or deformation of space (strictly speaking, spacetime). In a sense, space is elastic and can be bent or stretched in a certain way, depending on the arrangement of matter. This idea has been fully confirmed by observation. Related Concepts The basic concept of expansive space can be understood by simple simulation. Imagine sewing a row of buttons on an elastic band. Suppose the elastic band is stretched from both ends, and as a result, all the buttons are far apart. No matter which button we choose to look at, the buttons on the adjacent side seem to be far away, and this expansion is the same everywhere, with no special center. Of course, when we draw this row of buttons, it has a central button, but this has nothing to do with the expansion of the system. As long as the elastic belt with buttons is infinitely elongated or wound into a circle, the center will not exist. Starting from any button, the nearest [URL] button retreats at a certain speed, then the next button retreats twice, and so on. In your opinion, the farther away the button is, the faster it goes back. Therefore, this expansion means that the regression speed is proportional to the distance-this is an extremely important relationship. With the help of this image, we can imagine that light waves are. No wonder Hubble found that the redshift is proportional to the distance, which is completely consistent with this simple image simulation result. An important feature of the event horizon explosion is the existence of the event horizon: because the age of the universe is limited and the speed of light is limited, there may be some past events that cannot transmit information to us through light. From this analysis, we can see that there is such a limit or past horizon, and only events within this limit distance can be observed. On the other hand, because the space is expanding, the farther away the object is, the greater the speed of retrogression, so that the light we emit may never reach there. From this analysis, we can see that there is such a limit or future horizon, and only events within this limit distance can be influenced by us. The existence of the above two horizons depends on the concrete form of FLRW model describing our universe: our existing knowledge about the very early universe means that the universe should have a past horizon, but in the experiment, our observation is still limited by the opacity of the early universe to electromagnetic waves, which leads us to be unable to observe more distant events through electromagnetic waves when the past horizon has deteriorated due to space expansion. On the other hand, if the expansion of the universe keeps accelerating, the universe will also have a future horizon. Microwave Radiation (1978 Nobel Prize in Physics) As early as the end of the forties, Gamov, the originator of the Big Bang cosmology, thought that our universe was bathed in the residual radiation of the early high-temperature universe, and its temperature was about 6 K, just like a stove, although there was no fire, it could still emit a little heat. Cosmic microwave background radiation 1964, penzias and Wilson, young engineers of Bell Telephone Company in the United States, accidentally received a radio interference noise when debugging their huge horn antenna. The signal strength in all directions is the same, and it has not changed for several months. Is there something wrong with the instrument itself? Or is it caused by pigeons perched on the antenna? They took the antenna apart and reassembled it, but they still received that unexplained noise. The wavelength of this noise is in the microwave band, which corresponds to the electromagnetic wave radiated by the blackbody with an effective temperature of 3.5K (its spectrum is completely consistent with the luminescence in the furnace that reaches a certain thermal balance state, and this radiation is called "blackbody radiation" by physicists). After analysis, they think that this kind of noise is definitely not from satellites, nor can it come from the radio source of the sun, the Milky Way or an extragalactic galaxy, because the noise intensity is always the same when rotating the antenna. Later, after further calculation. It is concluded that the radiation temperature is 2.7K, which is generally called 3K cosmic microwave background radiation. This discovery greatly inspired many scientists engaged in the study of Big Bang cosmology. Because the observation results of penzias and Wilson are so close to the temperature predicted by theory, it is a very strong support for BIGBANG theory! This is another important astronomical discovery after Hubble discovered the red shift of galaxy spectral lines in 1929. The discovery of cosmic microwave background radiation opened up a new field of observing the universe and provided new observation constraints for various cosmic models, so it was listed as one of the four major discoveries of astronomy in the 1960s. Penzias and Wilson won the Nobel Prize in Physics in 1978. The Swedish Academy of Science pointed out in the award-winning decision: This discovery enables us to obtain the information of the cosmic process that occurred during the creation of the universe a long time ago. Helium abundance finally has evidence to prove the theory of the origin of hot high-density universe. As long as we know the temperature of thermal radiation today, it is easy to calculate that the temperature around the universe is about 1 s after the birth of the universe, which is too high for the existing nuclear synthesis. At that time, matter must have been torn into the most basic components, forming a pot of quark-gluon soup, such as protons, neutrons and electrons. However, as the soup gets cold, a nuclear reaction may occur. The Big Bang model can be used to calculate the proportion of light elements such as helium -4, helium -3, deuterium and lithium -7 relative to ordinary hydrogen in the universe. The abundance of all these light elements depends on a parameter, that is, the ratio of photons to baryons in the early universe, and the calculation of this parameter has nothing to do with the specific details of the fluctuation of microwave background radiation. According to the Big Bang theory, the proportion of light elements (here refers to the ratio of total mass of elements rather than the ratio of quantity) is about: helium -4/ hydrogen =0.25, deuterium/hydrogen = 10-3, helium -3/ hydrogen = 10-4, and lithium -7/ hydrogen = 650. Comparing the measured abundances of various light elements with the theoretical values calculated by photon baryon ratio, we can find that they are roughly consistent. Among them, deuterium is the best element in accordance with the measured value, helium -4 is close to the measured value, but there are still differences, and lithium -7 is twice as bad, so there is a large systematic random error in the calculation of the latter two elements. Nevertheless, the abundance of light elements predicted by the big bang nuclear synthesis theory is basically consistent with the actual observation, which is a strong support for the big bang theory. So far, no other theory can explain and give the relative abundance of these light elements well. At the same time, the content of helium that can be "regulated" in the universe predicted by the Big Bang theory cannot exceed or fall below the existing abundance of 20% to 30%. In fact, many observations can only be explained by the big bang theory, such as why the abundance of helium in the early universe is higher than that of deuterium, and the content of deuterium is higher than that of helium -3, and the ratio is constant. Main evidence 201April 17, American physicists announced that direct evidence of the existence of primitive gravitational waves in the universe was discovered for the first time. The first gravitational wave was put forward by Einstein in the General Theory of Relativity published in 19 16. It is a kind of space-time fluctuation at the beginning of the birth of the universe, and it weakens with the evolution of the universe. Scientists say that the initial gravitational waves, like the "echo" of the Genesis Big Bang, will help people trace back to the very short period of rapid expansion at the beginning of the universe, the so-called "expansion". However, since the general theory of relativity was put forward nearly a hundred years ago, other important predictions derived from it, such as the bending of light, the precession of mercury perihelion, and the gravitational redshift effect, have been confirmed one by one, but gravitational waves have never been directly detected. The problem is that their signals are extremely weak and technically difficult to measure.
Physicists from Harvard-Smithsonian Center for Astrophysics and other institutions in the United States use BICEP2 telescope set up in Antarctica to observe the "embers" in BIGBANG-microwave background radiation. Microwave background radiation is formed by microwave background photons that diffuse in the universe. The calculation shows that the original gravitational wave will produce a special polarization mode called B mode when it acts on the microwave background photon. Other forms of disturbance can not produce this kind of B-mode polarization, so B-mode polarization has become the "unique imprint" of the original gravitational wave. The observed B-mode polarization means the existence of gravitational waves.
Antarctica is one of the best places to observe microwave background radiation on earth. The researchers found a much stronger B-mode polarized signal here than expected. After more than three years of analysis, other possible sources were ruled out and it was confirmed that it was caused by primitive gravitational waves. At the beginning of 20 16, scientists from LIGO and Virgo jointly announced that they had detected gravitational waves generated by the merger of two black holes with the mass of about 30 times that of the sun1300 million years ago. This discovery is called "discovery of the century". Saul perlmutter and adam riess, Americans who won the theoretical prize, and brian schmidt, who has dual citizenship of the United States and Australia, won the 20 1 1 Nobel Prize in physics. The jury of the Nobel Prize in Physics commented on the 4th that the three winners "studied dozens of exploding stars, namely' supernovae', and found that the universe is expanding and the expansion speed is accelerating". At the Swedish Institute in Stockholm, Sweden, the Nobel Prize in Physics was announced at 1 1: 45 local time (Taipei time 17: 45). The research object of Perlmutter, Rees and Schmidt is the phenomenon that some massive stars are separated from the star shell in the later stage of evolution, that is, the superexplosion. A star whose mass is 8-25 times that of the sun ends its "life" in the form of a supernova explosion, while the air bag outside the star is thrown away at high speed, and its absolute luminosity can exceed that of the sun by 65.438+000 billion times. Perlmutter, Rees and Schmidt's team analyzed certain types of supernova explosions and found that the luminosity of more than 50 supernovae was darker than previously expected. The explanation for this result is that the universe is expanding at an accelerated rate. This discovery was called "shaking the foundation of cosmology" by the Swedish Academy of Royal Sciences. The jury of the Nobel Prize in Physics decided that the research results obtained by the three winners changed the human understanding of the universe. "For nearly a century, people have realized that the universe is expanding, which is the result of the Big Bang about 654.38+04 billion years ago." The jury said. "Surprisingly, however, we found that the expansion of the universe is accelerating," the jury said. "If the expansion continues to accelerate, the universe will end in a frozen state." In addition, the research of three people confirmed a theory originally put forward by scientist Albert Einstein, who called it "cosmological constant". During the period of 1998, Perlmutter presided over a research group, while Schmidt presided over another research group including Reese. The two groups worked hard, competed with each other, and observed that the results were "coincidental". The jury announced that the prize was 6.5438+million Swedish kronor (about 6.5438+0.46 million US dollars), Perlmutter got half, Schmidt and Reese got the other half. The problem is that in the first few minutes after the big bang, there was a serious lack of relevant observations, and the actual form of the earliest cosmic matter-energy was still largely a guess. The unified theory predicts some types of particles (such as the elusive magnetic monopole), while the multi-dimensional theories such as superstring, supersymmetry and supergravity all predict their original particles and forces. The absolute superiority of matter over antimatter is also an empirical fact that needs to be thoroughly explained. Other major problems are related to the generation and properties of dark matter and dark energy (quantum vacuum is generally considered as the main provider of both). On September 28th, 20 14, American scientists mathematically proved that "black holes do not exist". According to the website of the American Physicist Organization, Laura Mersini Horton, a theoretical physicist at the University of North Carolina at Chapel Hill, published an article on the online physics knowledge base ArXiv, saying that she had mathematically proved that "black holes don't exist". Once her view is proved to be correct by the scientific community, the theory of the origin of the universe in modern physics is likely to be completely overthrown. The report points out that Laura's theory harmoniously integrates the theory of universal gravitation with the theory of quantum mechanics by mathematical methods: the conclusion is that human "black holes don't exist". She and Hawking believe that when a star dies and collapses, it will release Hawking radiation. In this process, the planet itself will lose a large part of its mass. In the end, the density left by the dead planet is not enough to form a black hole. If this theory is proved to be correct, the Big Bang theory may be overthrown, even the theory of the origin of the universe in modern physics may be completely overthrown, or the new theory integrating the theory of universal gravitation and quantum mechanics sets that "black holes do not exist".