The vast space is full of stars. Where did they come from and where are they going? Where is the earth where we live in the universe?

The vast space is full of stars. Where did they come from and where are they going? Where is the earth where we live in the universe?

According to the big bang theory, the universe was originally a chaotic body, but according to the big bang theory, the universe expanded from a dense and hot singularity to its present state. The Big Bang theory is a theory about the origin of the universe in cosmic physics. According to the Big Bang theory, the universe evolved from a state of extremely high density and temperature about 654.38+0.4 billion years ago. This theory comes from the speed at which galaxies are moving away observed under Hubble's law. According to Friedman's general theory of relativity, space may expand. Extending (mathematically contrary to interpolation) to the past, these observations show that the universe began to expand from its initial state. In this initial state, the temperature and density of matter and energy in the universe are extremely high. As for what happened before this, general relativity thinks that there is a gravitational singularity, but physicists have different views on it.

The narrow sense of "Big Bang" refers to the drastic changes that the universe experienced at the early stage of its formation, about 65.438+03.7 billion years ago (654.38+0.37× 654.38+006.54.38+00). But in a broad sense, it refers to the popular theory that reveals the origin and expansion of the universe. The direct corollary of this theory is that the universe we live in today is different from that of yesterday or tomorrow. According to this theory, George Gamow predicted the existence of cosmic microwave background radiation in 1948. In the 1960 s, this kind of radiation was detected, which strongly supported the big bang theory, thus denying another popular steady-state universe theory.

Development history

The Big Bang theory was developed through experimental observation and theoretical deduction. In the experimental observation, in the 19 10 era, Vesta Slipher and Karl wertheim Vilt confirmed that most spiral nebulae are moving away from the earth, but they don't think it means anything to cosmology, and they don't think that the discovered nebulae are actually other galaxies outside the Milky Way. At the same time, in theory, Einstein's general theory of relativity successfully established and deduced the universe without stable state. The universe described by metric tensor is either expanding or contracting. Einstein thought he had solved the mistake and added a cosmological constant to correct it. The first person who really applied general relativity to cosmology without using cosmological constants was Alexander Friedman. The universe described by his equations is called Friedman-Ma Le? Tre-Robertson-Walker universe, the time is 1922. 1927, the Belgian Catholic priest Lemaistre independently deduced Friedman-Ma Le? Tre-Robertson-Walker equation, and put forward that the universe "exploded" from a "primary atom" on the basis of the shrinking phenomenon of spiral nebula-this is the later big bang.

From 65438 to 0929, Edwin Hubble provided experimental conditions for Lemaistre's theory. Hubble proved that these spiral nebulae are actually galaxies, and measured the distance between them by observing the stars in the Cepheus Delta. He found that the speed of galaxies leaving the earth is just proportional to their distance from the earth, which is the so-called Hubble law. According to the principle of cosmology, there is no special direction and special point when observing a large enough space, so Hubble's law shows that the universe is expanding. There are two opposing possibilities in this view: one is the Big Bang theory put forward by Lemaistre and supported and perfected by Gamov; The other is Huo Yier's stable universe model. In the steady-state universe model, the space left by distant galaxies constantly produces new substances, so the universe is basically unchanged. In fact, this theory was put forward to satirize Lemaistre's "The Big Bang Theory", which was first spread through the BBC radio program in 1949, and the paper "The Essence of Things" was published in 1950.

For many years after that, the two theories coexisted, but the observed facts began to support a universe that evolved into a thermally dense state. 1965 The discovery of cosmic microwave background radiation makes people think that the Big Bang theory is the best theory for the origin and evolution of the universe. Before 1970, many cosmologists thought that the universe might contract before it expanded, so as to avoid deducing an infinitely dense "absurd" singularity from Friedman's model. The representative model is Richard tolman's Oscillating Universe. At the end of1960s, Stephen Hawking and others proved that this hypothesis is not feasible, because singularity is a direct and important inference of Einstein's theory of gravity. After that, most cosmophysicists began to accept that the universe described by general relativity is limited in time. However, due to the lack of understanding of the law of quantum gravity, it is still uncertain whether this singularity is an infinitesimal point in the true sense, or whether the physical contraction process can go on indefinitely, thus indirectly reaching the infinity of the universe in time.

At present, almost all the research of cosmic physics is related to the Big Bang theory, or it is an extension or a further explanation, such as how galaxies were formed under the Big Bang theory, the physical processes that occurred during the Big Bang, and the new observations are explained by the Big Bang theory. At the end of 1990s and the beginning of the 20th century, due to the development of telescope technology and the large amount of data collected by artificial detectors, the Big Bang theory made a major breakthrough. The situation and data of the universe during the Big Bang can be calculated more accurately, which has produced many unexpected results, such as the acceleration of the expansion of the universe. See dark energy.

theory

The Big Bang theory estimated the age of the universe as 137 2 billion years, which was obtained through the observation of type Ia supernovae, the measurement of cosmic background radiation intensity and the measurement of galaxy correlation function. The results of these three independent calculations are consistent, which is considered as strong evidence of the so-called Lambda-CDM model that describes the properties of galaxies in the universe in more detail. The early universe was full of homologous substances, and its temperature, pressure and energy were extremely high. With the expansion and cooling, the matter in the universe changes phase, which is similar to the condensation process of steam cooling and the solidification process of water, but the difference is that the former occurs at the more basic particle level.

affect

About 10 after the Planck period? In 35 seconds, the phase change leads to the exponential growth of the universe, which is called inflation. After that, inflation stopped. At this time, the material form of the universe is quark-gluon plasma (there are also other particles, such as quark-gluon liquid that may be discovered in recent experiments), and the motion of these substances conforms to relativity. The universe continues to expand in space and the temperature continues to drop. At a certain temperature, the so-called baryon phase transition will occur, which is unknown so far. Quarks and gluons form baryons, that is, protons and neutrons, and there is asymmetry between matter and antimatter, which has been confirmed by experiments. With the further decrease of temperature, more asymmetric phase transitions occur, forming the basic particles and basic interactions. Later, some protons and neutrons combine to form nuclei of deuterium and helium. This process is called big bang nuclear synthesis. With the cooling of the universe, matter no longer moves according to relativity, but the energy density of static mass exists in the form of gravity, which exceeds radiation. About 300,000 years later, electrons and nuclei combined to form atoms (mainly hydrogen atoms), while matter emitted radiation through decoupling and spread relatively freely in space, which is today's cosmic microwave background radiation.

With the passage of time, in the almost evenly distributed material space, the slightly denser areas attract nearby materials through gravity, thus increasing the density, forming today's astronomical structures such as gas clouds, stars and galaxies. The specific process depends on the form and quantity of cosmic matter, among which there may be three forms: cold dark matter, hot dark matter and baryon matter.

The earth we live in is just a planet in the solar system. The solar system is revolving around the Milky Way, and the Milky Way is also revolving around a larger galaxy. Therefore, from a philosophical point of view, the movement is absolute, which is why the earth we live in has been moving. According to the big bang theory, the universe is constantly moving and expanding.