The Big Bang is just a theory, an assumption based on astronomical observations. About 15 billion years ago, all the matter in the universe was highly concentrated at one point, with extremely high temperatures, and a huge explosion occurred. After the Big Bang, matter began to expand outward, forming the universe we see today. The entire process of the Big Bang is complicated, and now the development history of the ancient universe can only be described based on theoretical research. During these 15 billion years, galaxy clusters, galaxies, our Milky Way, stars, solar systems, planets, satellites, etc. were born. All the celestial bodies and matter in the universe that we can see and cannot see now have formed the current form of the universe. Human beings were born in this evolution of the universe.

Process of presenting ideas

How can people speculate that there may have been a Big Bang? This relies on astronomical observations and research. Our sun is just one of one to two hundred billion stars in the Milky Way. There are tens of thousands of extragalactic galaxies like our own Milky Way. From observations, we have found that those distant galaxies are moving away from us. The farther away the galaxies are from us, the faster they fly, thus forming an expanding universe.

In this regard, people have begun to reflect. If we look at the movement of these galaxies that are moving away in all directions in reverse, they may have been emitted from the same source. Did an unimaginable event occur at the beginning of the universe? What about the Big Bang? Later, the microwave background radiation that filled the universe was observed. This means that the aftermath of the Big Bang about 15 billion years ago is weak but does exist. This discovery is a strong support for the Big Bang.

The Big Bang theory is a major school of modern cosmology, which can satisfactorily explain some fundamental issues of cosmology. Although the Big Bang theory was only proposed in the 1940s, it has been sprouting since the 1920s. In the 1920s, several astronomers observed that the spectral lines of many extragalactic galaxies had wavelength changes, that is, red shifts, compared with the spectral lines of the same elements on Earth.

By 1929, American astronomer Hubble concluded that the red shift of the spectral lines of a galaxy is directly proportional to the distance between the galaxy and the earth. He pointed out in the theory: If the red shift of the spectral lines is considered to be the result of the Doppler effect, it means that the extragalactic galaxies are receding away from us, and the farther away the galaxies are, the faster they are receding from us. This is a picture of the expansion of the universe.

In 1932, Lema?tre first proposed the modern Big Bang theory of the universe: the entire universe was initially gathered in a "primitive atom", and then a big explosion occurred, and the fragments scattered in all directions, forming our universe. . The Russian-American astrophysicist Gamov integrated general relativity into the theory of the universe for the first time and proposed the hot big bang cosmology model: the universe began with high-temperature, high-density primitive matter, with an initial temperature exceeding several billion degrees. , as the temperature continued to drop, the universe began to expand.

The Big Bang theory is the most influential theory about the formation of the universe. The Big Bang theory was born in the 1920s and was supplemented and developed in the 1940s, but it has remained unknown. In the 1940s, American astrophysicist Gamow and others formally proposed the Big Bang theory. This theory holds that the universe was in a state of extremely high temperature and density in the distant past. This state is vividly called a "primordial fireball." The so-called primitive fireball is an infinitesimal point. The current universe will continue to expand, that is, it is infinite. It is possible that when the energy of the universe explosion reaches its limit, the universe will become a primitive flame, an infinitesimal point. , the fireball exploded, the universe began to expand, the density of matter gradually became thinner, and the temperature gradually decreased, until it is in today's state. This theory can naturally explain the red shift phenomenon of the spectral lines of extragalactic objects, and can also satisfactorily explain many astrophysics problems. It was not until the 1950s that people began to pay widespread attention to this theory.

In the 1960s, Penzias and Wilson discovered new and powerful evidence for the Big Bang theory. They discovered the cosmic background radiation. Later they confirmed that the cosmic background radiation was the relic left behind by the Big Bang. It provides important basis for the Big Bang theory of the universe. They also won the 1978 Nobel Prize in Physics.

The wisdom and perseverance of science in the 20th century are embodied in Hawking. He gave a clear explanation of the evolution of the universe from 10 to 43 seconds after the origin of the universe. The origin of the universe: initially a singularity smaller than an atom, and then the Big Bang. Some elementary particles were formed through the energy of the Big Bang. , these particles gradually formed various substances in the universe under the action of energy. So far, the big bang universe model has become the most convincing theory of the universe picture. However, the Big Bang theory still lacks the support of a large number of experiments, and we still do not know the picture of the universe starting to explode and before it exploded.

Theoretical viewpoint

The main viewpoint of the Big Bang theory is that our universe once had a history of evolution from hot to cold.

During this period, the cosmic system was not static, but was constantly expanding, causing the density of matter to evolve from dense to thin. This process from hot to cold, from dense to thin is like a huge explosion. According to the perspective of Big Bang cosmology, the entire process of the Big Bang is: In the early days of the universe, the temperature was extremely high, above 10 billion degrees. The density of matter is also quite large, and the entire cosmic system reaches equilibrium. There are only substances in the form of some basic particles such as neutrons, protons, electrons, photons and neutrinos in the universe. But because the entire system is constantly expanding, the temperature drops quickly as a result. When the temperature drops to about 1 billion degrees, neutrons begin to lose the conditions for free existence. They either decay or combine with protons to form heavy hydrogen, helium and other elements; chemical elements began to be formed during this period. After the temperature further drops to 1 million degrees, the early process of forming chemical elements ends (see the theory of element synthesis). The matter in the universe is mainly protons, electrons, photons and some lighter atomic nuclei. When the temperature drops to a few thousand degrees, the radiation subsides, and the universe is mainly gaseous matter. The gas gradually condenses into gas clouds, and then further forms various star systems, becoming the universe we see today.

Since Gamow established the concept of the hot big bang in 1948, through decades of efforts, cosmologists have outlined such a history of the universe for us:

The Big Bang When the explosion began 15 to 20 billion years ago, it had an extremely small volume, extremely high density, and extremely high temperature.

10-43 seconds after the big bang, the universe emerged from the quantum background.

10-35 seconds after the big bang, the same field decomposes into the strong force, the electroweak force and the gravitational force.

10-5 seconds after the Big Bang at 10 trillion degrees, protons and neutrons were formed.

0.01 second after the Big Bang, 100 billion degrees, photons, electrons, and neutrinos dominated, protons and neutrons accounted for only one billionth, thermal equilibrium state, the system expanded rapidly, and the temperature and density continued to decrease.

0.1 second after the big bang and 30 billion degrees, the neutron-proton ratio dropped from 1.0 to 0.61.

One second after the big bang and 10 billion degrees, neutrinos escape outward, annihilation reaction of electrons and positrons occurs, and the nuclear force is not enough to bind neutrons and protons.

13.8 seconds after the big bang and 3 billion degrees, stable atomic nuclei (chemical elements) such as deuterium and helium were formed.

35 minutes after the big bang and 300 million degrees, the nuclear process stops and neutral atoms cannot yet be formed.

At 3000 degrees 300,000 years after the Big Bang, chemical combinations formed neutral atoms. The main component of the universe was gaseous matter, which gradually condensed into denser gas clouds under the action of self-gravity. Down to stars and star systems.

Big-bang model

A widely recognized theory of the evolution of the universe. The gist is that the universe was created by a "Big Bang" from a state of extremely high temperature and density. It happened at least 10 billion years ago. This model is based on two assumptions: the first is the general theory of relativity proposed by Einstein, which can correctly describe the gravitational effect of matter in the universe; the second is the so-called cosmological principle, that is, the things seen by observers in the universe are the same. The direction of observation has nothing to do with the location. This principle only applies to the large scale of the universe, and it also means that the universe is infinite. Therefore, the Big Bang source of the universe did not occur at a certain point in space, but occurred throughout space at the same time. With these two assumptions, it is possible to calculate the history of the universe starting from a certain time (called Planck time). Before that, it is still unclear what physical laws were at work. The universe expanded rapidly from that point on, causing density and temperature to drop from their original extremely high states, and processes that foreshadowed the decay of protons also resulted in far more matter than antimatter, as we see today. Many elementary particles may also appear at this stage. After a few seconds, the temperature of the universe cooled down enough for some atomic nuclei to form. The theory also predicts the formation of certain amounts of hydrogen, helium and lithium nuclides in abundances consistent with those seen today. About another million years later, the universe cooled further, atoms began to form, and the radiation that filled the universe spread freely through space. This radiation is called the cosmic microwave background radiation, and it has been confirmed by observations. In addition to primordial matter and radiation, the Big Bang theory predicts that the universe should now be filled with neutrinos, which are elementary particles without mass or charge. Now scientists are working hard to find this substance.

The Big Bang model can uniformly explain the following observational facts:

(a) The theory maintains that all stars are produced after the temperature decreases, so the age of any celestial body should It is shorter than the period since the temperature dropped to today, that is, it should be less than 20 billion years. Measurements of the ages of various celestial bodies prove this.

(b) It has been observed that extragalactic objects have a systematic red shift of the spectral lines, and the red shift is roughly proportional to the distance. If explained by the Doppler effect, then red shift is a reflection of the expansion of the universe.

(c) On various celestial bodies, the helium abundance is quite large, and most of them are 30%. The mechanism of stellar nuclear reactions 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) Based on the expansion rate of the universe and helium abundance, the temperature of the universe in each historical period can be calculated specifically.

According to the Big Bang theory, the universe was born from a very small point 15 billion years ago. From there, time and space, mass and energy were born, and small particles of matter were aggregated into large groups of matter. , eventually forming galaxies, stars, planets, etc. Before the Big Bang, there was no matter, no energy, or even life in the universe.

However, the Big Bang theory cannot answer what the current universe was like before the Big Bang, or what was the reason for the Big Bang? According to the Big Bang theory, the universe had no beginning. It is just a cyclic process, from the big bang to the black hole, which is the process of creation, destruction and re-creation of the universe.

This is just a hypothesis, not a perfect theory.

Arguments

Although the Big Bang theory is not mature, it is still the mainstream theory of the formation of the universe. The key is that there is currently some evidence to support the Big Bang theory. The more traditional evidence is as follows: shows:

(a) Red shift

Looking from any direction on the earth, distant galaxies are moving away from us. Therefore, it can be deduced that the universe is expanding and getting farther and farther away from us. The farther away the galaxy, the faster it moves away.

(b) Hubble's Law

Hubble's Law is a definite relationship about the speed and distance between galaxies moving away from each other. It still explains the movement and expansion of the universe.

V=H×D

Among them, V (Km/sec) is the away speed; H (Km/sec/Mpc) is the Hubble constant, which is 50; D (Mpc ) is the galaxy distance. 1Mpc=3.26 million light years.

(c) Abundance of hydrogen and helium

The model predicts that hydrogen accounts for 25% and helium accounts for 75%, which has been confirmed by experiments.

(d) Abundance of trace elements

For these trace elements, the abundance predicted in the model is the same as the measured one.

(e) 3K cosmic background radiation

According to the Big Bang theory, the universe cooled due to expansion, and the radiation embers produced at that time should still exist in the present universe. In 1965, 3K of background radiation was measured.

(f) The trace inhomogeneity of the background radiation

proves that the initial state of the universe was not uniform, which is why the current universe and the current galaxies and star clusters are produced.

(g) New evidence for the Big Bang theory

In the British magazine "Nature" in December 2000, scientists said they had discovered 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 extremely large mass, small volume, and extremely high temperature. Then this point exploded, and as the volume expanded, the temperature continued to decrease. To this day, there are still cosmic rays in the universe called "cosmic background radiation" that remain from the early days of the Big Bang.

Scientists analyzed light absorbed by a distant gas cloud from a quasar billions of years ago and found that it was indeed hotter than the universe is today. They found that the background temperature was about -263.89 degrees Celsius, which is higher than the currently measured cosmic temperature of -273.33 degrees Celsius.

Although the above evidence exists, there is still a lack of sufficient convincing evidence as to whether the universe originated from the Big Bang theory.

Voices of anti-Big Bang theorists

An "Open Letter to the Scientific Community" was signed by 34 scientists and engineers and was published in the United Kingdom on May 22, 2004. 's New Scientist magazine. We have translated it in order to give readers an understanding of the arguments of those who believe in the Big Bang theory. After this open letter was posted online, it received online signatures from 185 scientists (now more than 400 people):

Today, the Big Bang theory is increasingly based on some assumptions and some Things that have never been empirically observed are used as arguments in their own right: inflation, dark matter, and dark energy are some of the most shocking examples. Without these things, we would find direct contradictions between actual astronomical observations and the predictions of the Big Bang theory.

This constant recourse to new hypotheses to bridge the gap between theory and implementation is unlikely to be acceptable in any other area of ??physics. This at least reflects that there are serious problems with the validity of this theory of unknown origin.

However, without these far-fetched factors, the Big Bang Theory cannot survive. Without assumptions such as inflation, the Big Bang theory cannot explain the homogeneous and isotropic cosmic background radiation found in actual observations. Because then it would not explain how distant parts of the universe could have the same humidity and emit the same amount of microwave radiation. Without the so-called dark matter that is incompatible with all the matter we have worked hard to observe on earth for more than 20 years, the predictions of the Big Bang theory are completely contradictory to the actual density of matter in the universe. The density required for inflation is 20 times that required for nuclear fusion, which may be a theoretical explanation for the source of lighter elements in the Big Bang theory. Without dark energy, the age of the universe calculated based on the Big Bang theory is only 8 billion years, which is even several billion years younger than the age of many stars in our galaxy.

More importantly, no quantitative predictions of the Big Bang theory have ever been verified by actual observations. The success claimed by the defenders of this theory is all due to its ability to adapt to the results of actual observations after the fact. It is constantly adding adjustable parameters, just like Ptolma's geocentric theory always needs the help of epicycles. Just like the theory that the deferent wheel comes from a circle, in fact, the big bang theory is not the only way to understand the history of the universe. 'Plasma cosmology' and 'steady state universe model theory' are both assumptions about such a continuously evolving universe. They believe that the universe has neither beginning nor end. These models, as well as other views, can also explain the basic phenomena of the universe, such as the proportion of lighter elements in the universe, cosmic background radiation, and the increase in redshift of spectral lines of distant galaxies with distance. Some of them The predictions have even been verified by actual observations, something the Big Bang theory has never done. Supporters of the Big Bang theory argue that these theories cannot explain all observed astronomical phenomena. But this is not surprising, as their development is severely underfunded. In fact, until today, such questions and alternative theories cannot be freely debated and tested. Most seminars follow the crowd and do not allow researchers to have a fully open exchange of ideas. Richard Feynman said, 'Science is a culture of doubt', and in today's field of cosmology, doubts and dissent are not tolerated. Young scholars even have no idea about the standard model of the Big Bang. I dare not express negative thoughts. Scholars who doubt the Big Bang theory will lose funding if they speak out about their doubts. Even actual observations have to be screened based on whether they support the Big Bang theory. As a result, all substandard data, such as the red shift of spectral lines, the proportions of lithium and helium in the universe, the distribution of galaxies, etc., have been ignored or even distorted. This reflects an increasingly expanding dogmatism and is completely inconsistent with the spirit of free scientific research. Today, in the field of cosmological research, almost all financial and experimental resources are allocated to projects based on the Big Bang theory. Research funding sources are limited, and all review committees responsible for allocation of funds are dominated by supporters of the Big Bang theory. The result has been the overall dominance of the Big Bang theory in the field, a situation that has nothing to do with the theory's scientific validity. Funding only projects that belong to the Big Bang theory obliterates a fundamental tenet of the scientific method: the need to continually test theories against actual observations. Such a constraint makes it impossible to conduct any discussion or research. In order to treat this stubborn problem, we call on the institutions that fund cosmological research to reserve a considerable part of their funds for research topics on alternative theories. Empirical observations that contradict the Big Bang theory. To avoid the problem of unfair allocation of funds, the review committee responsible for the allocation of funds can be composed of astronomers and physicists in non-cosmological fields. An equitable allocation of funding to research projects into the validity of the Big Bang theory and its alternatives will allow us to scientifically find the most credible models of the historical evolution of the universe.