Science Time Machine | How did the “Big Bang” come about?

On April 1, 1948 , Gamow proposed the Big Bang theory.

On April 1, 1948, the internationally authoritative physics academic journal Physical Review published a paper by Russian-American physicist Gamow entitled "The Origin of Chemical Elements". In this paper, Gamow systematically expounded the Big Bang theory for the first time. The theory holds that the universe originated from an extremely high temperature and high density "primordial fireball" and experienced a process of gradually changing from dense to sparse, and from hot to cold. This process was accompanied by the continuous expansion of the universe, which was particularly violent in the early stages, like an unprecedented explosion, hence the name "Big Bang Universe Model".

The formation of the Big Bang theory is inseparable from the outstanding contributions of three scientists: Lemaître, Hubble and Gamow. In 1924, Hubble confirmed the existence of extragalactic galaxies and further proposed Hubble's law; in 1932, Lemaître proposed the hypothesis of the explosion origin of "primordial atoms"; until 1948, Gamow formally integrated this series of theories into the Big Bang theory.

The phenomenon of galaxy redshift

On April 1, 1948, the American journal Physical Review published Gamow's article "The Origin of the Chemical Elements", which first expounded the Big Bang theory. The theory states that the origin of the current universe can be traced back to a huge explosion.

Back in 1910, when American astronomer Slipher was observing galaxies at the Lowell Observatory, he accidentally observed that the frequency of the spectral line of a certain element in a certain galaxy was lower than the frequency of the spectral line of the same element on Earth. This phenomenon is called "redshift". After further observation, he found that many galaxies had redshifts, which was due to the Doppler effect, indicating that these galaxies were moving away from the Earth at extremely high speeds. Slipher then measured the apparent velocity of more than 40 galaxies, and the results showed that this speed was far faster than that of a jet plane.

In 1929, American astronomer Hubble discovered that the degree of redshift of a galaxy is proportional to its distance from the Earth: the farther the galaxy is, the faster it recedes, which indicates that the universe is in a state of expansion.

The universe began as a "primordial fireball"

Based on the phenomenon of cosmic expansion, if we trace back to an earlier point in time, the volume of the universe must be smaller than it is today. Going back to a certain moment in the origin of the universe, it should be an extremely small and extremely dense collection of matter.

In 1932, Belgian scientist Lemaître conceived a model of cosmic evolution based on the theory of cosmic expansion: all matter in the universe was originally concentrated in an entity called the "primordial atom" or "cosmic egg". The explosion of the cosmic egg caused matter to scatter, eventually forming the current cosmic structure, and the fragments evolved into galaxies. These galaxies continue to spread due to the powerful explosion billions of years ago. This view is called the "atomic model" of the Big Bang theory.

In 1948, physicist Gamow combined nuclear physics knowledge with the theory of cosmic expansion and proposed the "primordial fireball model" of the Big Bang. The model points out that the initial state of the universe is a high-temperature, high-density "primordial fireball" filled with elementary particles. When these particles undergo nuclear fusion reactions, they trigger explosive expansion, and the various elements produced in the process spread out, forming various substances in the universe today.

The Big Bang Theory Gets a New lease of life

When Gamow's Big Bang theory first appeared, it gradually faded out of the public's view due to the lack of direct astronomical observation data to support it. However, in 1965, an unexpected scientific breakthrough gave the theory a new lease of life.

In May 1964, two outstanding scientists from Bell Labs in the United States, Penzias and Wilson, were using an advanced antenna receiving system to precisely measure the noise in the sky. During a routine observation, they accidentally captured an abnormal noise radiation, whose radiation temperature was stable at about 3.5K. In the following nearly a year, no matter how they adjusted and optimized the instrument, this noise always followed them and could not be eliminated. What surprised them even more was that this noise showed isotropic characteristics and had nothing to do with seasonal changes. It was obviously not from any known specific radiation source.

Just when the two scientists were confused, in early 1965, they accidentally came across a theoretical prediction by Princeton University physics professor Pierce Pierce. Professor Pierce proposed that the Big Bang process of the origin of the universe would leave radio noise residues. After in-depth discussion and analysis, they finally came to an astonishing conclusion: what they observed was the mysterious cosmic microwave background radiation - 3K cosmic background radiation.

This conclusion was subsequently widely recognized and confirmed by the physics community. Penzias and Wilson also achieved great success and won the Nobel Prize in Physics in 1978. More importantly, the discovery of cosmic microwave background radiation provided strong empirical support for the Big Bang theory, allowing this theory to regain its luster and become one of the cornerstones of modern cosmology.

Reference sources: Modern Physics Knowledge WeChat public account, China Science Daily