The Big Bang is the most accepted cosmological theory about the origin of the universe in scientific circles today.
The Big Bang theory is an attempt by physics to explain the origins of the Universe. Quite simply, it states that the entire Universe started from a singularity, which has been expanding for at least 13.8 billion years . The theory was first proposed in 1920 by astronomer and Jesuit priest Georges-Henri Lemaître (1894-1966), which he referred to as the “ primordial atom hypothesis ”. This theory was later developed by the Russian physicist George Gamov (1904-1968). One of his main suggestions was that the formation of atomic nuclei (nucleosynthesis) in the early Universe should leave a detectable radiation in the microwave range.
Main aspects of the Big Bang theory
After the emergence of Lemaître ‘s theory , astronomical observations by Edwin Hubble (1889-1953) showed that galaxies move away from each other in all directions of space and at high speeds. This evidence , together with the accidental discovery of the cosmic microwave background in 1965 by physicists Arno Penzias (1933) and Robert Wilson (1936), reinforced the acceptance of the primordial atom theory . the removalof the galaxies was considered a direct suggestion of an expanding universe, while the detection of the background radiation confirmed the theoretical predictions of the Gamov model , suggesting that the Universe had a beginning , in which atomic nuclei were created at a given time by the process of nucleosynthesis .
Many researchers invested in this theory, which was later called the Big Bang theory. Here’s a timeline with the main stages of the formation of the universe according to this theory:
The beginning of everything
Despite the name suggestion, the Big Bang was not in fact an explosion , but rather a large expansion (for reasons unknown) of a tiny point in space, called a singularity, with infinitely high density and temperature .
When the Universe was approximately 10-35 seconds old , during the inflationary period , its size increased exponentially , doubling about 90 times . At the end of this accelerated expansion , the Universe became colder and less dense . In this period, the fundamental forces of nature, as well as time and space , emerged .
The lightest elements of the periodic table (Hydrogen and Helium) appeared in the first minutes of the universe’s life through the combination of protons , giving rise to the lightest atomic nuclei . This process left a trace of detectable energy , coming from all directions of the universe: the cosmic microwave background . During its first 300 – 400 thousand years of age, the universe was so dense that light could not propagate, everything was like a dense fog , which absorbed all the light.
With the increasing expansion of the universe and decreasing temperature, the free electrons joined the atomic nuclei, forming the first neutral atoms , in the phase known as “ recombination ”. In this phase, light began to propagate more easily through space, and the Universe became increasingly “transparent”.
About 200 million years after its initial expansion, gravitational forces began to coalesce large chunks of gas. At that time, the composition of the universe was approximately 75 % Hydrogen to 25% Helium gas . With the accumulation of atoms in small volumes and under high temperatures and pressures , the process of nuclear fusion of hydrogen atoms began, giving rise to the first stars .
formation of galaxies
After 500 million years since the beginning of the universe, the gravitational force has slowly brought together clusters of stars – the galaxies . These, in mutual attraction, formed the first clusters (galaxies in gravitational attraction) , which, in turn, formed their local groups .
The Big Bang theory was able to explain some important astronomical observations , as well as satisfactorily answer some of our questions about the origin of the universe, however, it left a lot of questions. There is much to discover about the origin of the universe, and astronomers continue to search for answers, digging deeper and deeper into the history of the cosmos.