Viewpoint presentation process
How can people speculate that there may be a big explosion? It depends on astronomical observation and research. Our sun is just one of the120 billion stars in the Milky Way. Such as our Milky Way, extrasolar galaxies and Qian Qian. From the observation, it is found that those distant galaxies are leaving us. The farther away galaxies are, the faster they fly, thus forming an expanding universe.
In this regard, people began to reflect, if we look at these galaxies that are far away from each other in all directions, they may have been emitted from the same source from the beginning. Was there an unimaginable big bang at the beginning of the universe? Later, we observed the microwave background radiation that filled the universe, that is to say, the aftermath generated by BIGBANG about 654.38+0.5 billion years ago was weak but did exist. This discovery is a strong support for BIGBANG.
The Big Bang theory is a major school of modern cosmology, which can satisfactorily explain some basic problems of cosmology. Although The Big Bang Theory was put forward in the 1940s, it began to sprout in the 1920s. In the 1920s, many astronomers observed that the spectral lines of many extragalactic galaxies had wavelength changes compared with the spectral lines of the same element on the earth, that is, the phenomenon of red shift.
By 1929, American astronomer Hubble summed up the law that the stars whose spectral lines are red-shifted are directly proportional to the distance from the galaxy to the earth. He pointed out in theory that if the red shift of spectral lines is the result of Doppler effect, it means that galaxies outside the river are moving away from us and retreating far away, and the farther away the galaxies are, the faster they are. This is the image of the expansion of the universe.
1932, Lemaistre put forward the modern big bang theory for the first time: the whole universe first gathered in a "primitive atom", and then the big bang happened, and the fragments scattered in all directions, forming our universe. Gamov, an American Russian astrophysicist, first integrated general relativity into the theory of the universe and put forward a cosmological model of the Big Bang: the universe started from high-temperature and high-density primitive matter, and its initial temperature exceeded several billion degrees. As the temperature continues to drop, the universe begins to expand.
The Big Bang theory is the most influential theory about the formation of the universe. It was born in the 1920s, supplemented and developed in the 1940s, but it has been unknown. In the 1940s, American astrophysicist Gamov and others formally put forward the Big Bang theory. According to this theory, the universe was in a state of extreme high temperature and high density in the distant past, which was vividly called "primitive fireball". The so-called primitive fireball is an infinitesimal point, and now the universe will continue to expand, which is infinite. It is possible that when the energy of the universe explosion reaches the limit, the universe will become a primitive flame, that is, an infinitesimal point. After the fireball explodes, the universe will begin to expand, the density of matter will gradually become thinner, and the temperature will gradually decrease until today's state. This theory can naturally explain the red shift of spectral lines of celestial bodies outside the river, and can also satisfactorily explain many astrophysical problems. It was not until 1950s that people began to pay extensive attention to this theory.
In 1960s, penzias and Wilson discovered the new powerful evidence of the Big Bang theory, and they discovered the cosmic background radiation. Later, they confirmed that the cosmic background radiation was a relic left by the Big Bang, which provided an important basis for the Big Bang theory. They also won the 1978 Nobel Prize in Physics.
Hawking embodies the wisdom and perseverance of science in the 20th century. He clearly explained the evolution of the universe since 10-43 seconds after the origin of the universe. The origin of the universe: at first it was a singularity smaller than an atom, and later it was the Big Bang. Some elementary particles were formed by the energy of the Big Bang, and these particles gradually formed various substances in the universe under the action of energy. At this point, the Big Bang model has become the most convincing theory of the universe. However, so far, the Big Bang theory still lacks the support of a large number of experiments, and we still don't know the picture before and after the universe began to explode.
Theoretical viewpoint
The main idea of the Big Bang theory is that our universe once had an evolutionary history from hot to cold. During this period, the cosmic system is not static, but constantly expanding, which makes the density of matter evolve from dense to sparse. This process from hot to cold, from dense to thin, is like a huge explosion. According to BIGBANG's cosmology, the whole process of BIGBANG was in the early universe, and the temperature was extremely high, above 1000 billion degrees. The density of matter is also quite large, and the whole universe system is in equilibrium. There are only some elementary particles in the universe, such as neutrons, protons, electrons, photons and neutrinos. But because the whole system is expanding, the temperature drops rapidly. When the temperature drops to about1000 billion degrees, neutrons begin to lose the condition of free existence, and they either decay or combine with protons to form heavy hydrogen, helium and other elements. It was from this period that chemical elements began to form. When the temperature further drops to 6.5438+0 million degrees, the early process of forming chemical elements ends (see the theory of element synthesis). The substances in the universe are mainly protons, electrons, photons and some lighter nuclei. When the temperature drops to several thousand degrees, the radiation decreases, and the universe is mainly gaseous. Gas gradually condenses into gas clouds, and then further forms various star systems, becoming the universe we see today.
Since Gamov established the concept of the Big Bang in 1948, cosmologists have outlined such a cosmic history for us through decades of efforts:
At the beginning of the Big Bang,150-200 billion years ago, it was very small, with extremely high density and extremely high temperature.
After the Big Bang, the universe emerged from the quantum background in 10-43 seconds.
35 seconds after 10- BIGBANG, the same field is decomposed into strong, weak electric power and gravity.
After the Big Bang, protons and neutrons formed at 10-5 seconds, 10 trillion degrees.
After the Big Bang, it was 0.0 1 sec, 1000 billion degrees, mainly photons, electrons and neutrinos, and proton neutrons only accounted for a part of 1 billion, which was in thermal equilibrium, the system expanded rapidly, and the temperature and density decreased continuously.
0. 1 s after the big bang, and after 30 billion degrees, the neutron-proton ratio decreased from 1.0 to 0.6 1.
After the Big Bang, after 1 second, 1000 billion degrees, neutrinos escaped outward, and the positive and negative electrons annihilated, so the nuclear force was not enough to bind neutrons and protons.
Three billion degrees after BIGBANG 13.8 seconds, deuterium and helium stable nuclei (chemical elements) were formed.
35 minutes after the big bang, at 300 million degrees, the nuclear process stopped and neutral atoms could not be formed.
300,000 years after BIGBANG, at 3,000 degrees, neutral atoms were formed by chemical combination, and the universe was mainly composed of gaseous substances, which gradually condensed into high-density gas clouds under the action of self-gravity until stars and star systems.
Big bang model
A widely accepted theory of cosmic evolution. The main idea is that the universe was created by a "big bang" from a state of extremely high temperature and density. It happened at least 654.38 billion years ago. This model is based on two assumptions: the first is Einstein's general theory of relativity, which can correctly describe the gravitational effect of cosmic matter; The second is the so-called cosmological principle, that is, what the observer sees in the universe has nothing to do with the direction or position of observation. This principle only applies to the large scale of the universe, which also means that the universe is boundless. So the BIGBANG source does not occur at a certain point in space, but at the same time in the whole space. With these two hypotheses, we can calculate the history of the universe from a certain time (called Planck time), but before that, what physical laws are at work is still unclear. Since then, the universe has expanded rapidly, and the density and temperature have decreased from the initial extremely high state. Then, some processes that show proton decay also make the number of matter far exceed that of antimatter, as we see today. Many elementary particles may also appear at this stage. After a few seconds, the temperature of the universe drops, forming some nuclei. This theory also predicts that a certain number of nuclides such as hydrogen, helium and lithium can be formed, and the abundance is consistent with that seen today. After about 6.5438+million years, the universe cooled further and began to form atoms, while the radiation full of the universe spread freely in space. This kind of radiation is called cosmic microwave background radiation, which has been confirmed by observation. In addition to primitive matter and radiation, the Big Bang theory also predicts that the universe should be full of neutrinos, which are massless or uncharged elementary particles. Now scientists are trying to find this substance.
The Big Bang model can uniformly explain the following observations:
(1) Theory holds that all stars were born after the temperature dropped, so the age of any celestial body should be shorter than the period when the temperature dropped to today, that is, less than 20 billion years. The measurement of the ages of various celestial bodies proves this.
(b) It is observed that the spectral lines of celestial bodies outside the river have a systematic red shift, which is roughly proportional to the distance. If it is explained by Doppler effect, then the red shift is a reflection of the expansion of the universe.
(c) Helium is quite abundant in various celestial bodies, most of which is 30%. The mechanism of stellar nuclear reaction is not enough to explain why there is so much helium. According to the big bang theory, the early temperature was very high and the efficiency of producing helium was also very high, which can explain this fact.
(d) According to the expansion speed of the universe and the abundance of helium, temperature of the universe in various historical periods can be calculated concretely.
According to the Big Bang theory, the universe was born at a tiny point 654.38+0.5 billion years ago. From this tiny point, space-time, mass and energy were born, which made small particles of matter gather into mass matter and eventually formed galaxies, stars and planets. Before the Big Bang, there was no matter, no energy and even no life in the universe.
However, the big bang theory can't answer what the universe was like before the big bang, or what was the cause of the big bang? According to the big bang theory, the universe has no beginning. It is just a cyclical process, from the Big Bang to the black hole, which is the process of the creation and destruction of the universe and its rebirth.
This is just an idea, not a perfect theory.
quarrel
Although the big bang theory is not mature, it is still the mainstream theory of the formation of the universe. The point is that there is some evidence to support the big bang theory. More traditional evidence is as follows:
(a) redshift
From any direction of the earth, distant galaxies are moving away from us, so it can be inferred that the universe is expanding, and the farther away galaxies are, the faster they leave.
Hubble's law
Hubble's law is about the relationship between the speed and distance between galaxies. It still explains the motion and expansion of the universe.
V=H×D
Where v (km/s) is the departure speed; H(Km/sec/Mpc) is Hubble constant, which is 50; D(Mpc) is the distance between galaxies. 1MPC = 3.26 million light years.
(c) abundant hydrogen and helium.
The model predicts that hydrogen accounts for 25% and helium accounts for 75%, which has been confirmed by experiments.
(d) rich in trace elements.
For these trace elements, the estimated abundance in the model is the same as the measured abundance.
(e)3K cosmic background radiation
According to the big bang theory, the universe cooled due to expansion, and there should be radiation embers in today's universe. At 1965, the background radiation of 3K was measured.
(f) Tracking background radiation inhomogeneity
It is proved that the initial state of the universe is uneven, which is the reason why the present universe and the present galaxies and clusters of galaxies are produced.
(g) New evidence of the Big Bang theory
In the British journal Nature from June 5 to February 2000, scientists said that they had found new evidence that could be used to confirm the Big Bang theory.
For a long time, there has been a theory that the universe was originally a point with great mass, small volume and extremely high temperature, and then this point exploded, and with the expansion of its volume, the temperature kept decreasing. Today, there are still cosmic rays called "cosmic background radiation" in the universe at the beginning of BIGBANG.
After analyzing the light absorbed from quasars by distant gas clouds in the universe billions of years ago, scientists found that its temperature was indeed higher than that of the universe today. They found that the background temperature was about 263 degrees below zero. 89 degrees Celsius, which is higher than the measured temperature of -273.33 degrees Celsius in temperature of the universe.
Although the above evidence exists, there is still not enough convincing evidence whether the universe originated from the Big Bang theory.
The voice of anti-big bang theorists
On May 22nd, 2004, New Scientist published an open letter to the scientific community signed by 34 scientists and engineers. We translated it in order to let readers know the arguments of people in The Big Bang Theory. After this open letter was posted online, it was signed by 185 scientists (now more than 400):
Nowadays, the Big Bang theory is increasingly based on some assumptions and things that have never been observed empirically: inflation, dark matter and dark energy are some of the most shocking examples. Without these things, we will find that there is a direct contradiction between the actual astronomical observation and the prediction of the Big Bang theory. This practice of constantly resorting to new assumptions to bridge the gap between theory and reality is impossible to accept in any other field of physics. This at least reflects that this theory of unknown origin has serious problems in its effectiveness.
However, without these far-fetched factors, the Big Bang theory could not survive. Without the assumption of inflation, the Big Bang theory cannot explain the uniform and isotropic cosmic background radiation found in actual observation. Because in that case, it can't explain why distant places in the universe have the same humidity and emit the same amount of microwave radiation. If there is no so-called dark matter, which is incompatible with all the substances we have tried to observe on the earth for more than 20 years, then the prediction of the Big Bang theory is completely contradictory to the actual material density in the universe. The density of inflation is 20 times that of nuclear fusion, which may be the theoretical explanation of the source of lighter elements in the big bang theory. Without dark energy, the age of the universe calculated according to the big bang theory is only 8 billion years, even several billion years younger than the age of many stars in our galaxy.
More importantly, the Big Bang theory has never been verified by any quantitative prediction. Defenders of this theory claim that its success is all due to its ability to cater to the actual observation results afterwards, and it is constantly adding adjustable parameters, just as Ptolemy's geocentric theory always needs to prove itself with this round and even rounds. In fact, the big bang theory is not the only way to understand the history of the universe. Both "plasma cosmology" and "steady-state cosmology model theory" are hypotheses about such an evolving universe. They believe that the universe has neither a beginning nor an end. These models, as well as other viewpoints, can also explain the basic phenomena of the universe, such as the proportion of lighter elements in the universe, the background radiation of the universe, and the red shift of spectral lines in distant galaxies with increasing distance. Some of their predictions have even been verified by actual observations, which has never been done by the Big Bang theory. Supporters of the Big Bang believe that these theories cannot explain all the observed astronomical phenomena. But this is not surprising, because their development is seriously lacking in financial support. In fact, until today, such problems and alternative theories cannot be freely debated and tested. Most seminars go with the flow, and researchers are not allowed to exchange views completely and openly. Richard feynman once said that' science is a culture of doubt', but in today's cosmology field, doubts and objections are not tolerated, and young scholars dare not express any negative thoughts on the standard model of the Big Bang. Scholars who doubt the Big Bang theory will lose their funding if they speak out their doubts. Even the actual observation results should be screened according to whether the standards can support the Big Bang theory. In this way, all substandard data, such as the red shift of spectral lines, the ratio of lithium to helium in the universe and the distribution of galaxies, are ignored or even distorted. This reflects an inflated dogmatism, which is totally incompatible with the spirit of free scientific research. Nowadays, in the field of cosmology research, almost all the funds and experimental resources are allocated to projects with the big bang theory as the topic. The sources of scientific research funds are limited, and all the review committees responsible for the allocation of funds are controlled by supporters of the big bang theory. The theory leading to the Big Bang has a comprehensive leading position in this field, which has nothing to do with the scientific validity of the theory. Only subsidizing the subjects subordinate to the big bang theory obliterates a basic principle of scientific method: that is, the theory must be constantly tested by actual observation. This restriction makes it impossible to conduct any discussion and research. In order to cure this stubborn disease, we call on the institutions that fund cosmology research to reserve a considerable part of their funds for research topics of alternative theories and empirical observations that are contrary to the Big Bang theory. In order to avoid unfair allocation of funds, the jury responsible for the allocation of funds can be composed of astronomers and physicists in non-cosmology fields. The fair allocation of funds to the research projects aimed at verifying the Big Bang theory and its replacement theory will enable us to find the most credible model about the historical evolution of the universe in a scientific way.