big bang theory Scientific explanation for the beginning of the universe.
The Big Bang theory is the prevailing cosmological model that explains the early development of the Universe. According to the Big Bang theory, the Universe was once in an extremely hot and dense state which expanded rapidly. This rapid expansion caused the Universe to cool and resulted in its present continuously expanding state. According to the most recent measurements and observations, the Big Bang occurred approximately 13.75 billion years ago,which is thus considered the age of the Universe. After its initial expansion from asingularity, the Universe cooled sufficiently to allow energy to be converted into varioussubatomic particles, including protons, neutrons, and electrons. While protons and neutronscombined to form the first atomic nuclei only a few minutes after the Big Bang, it would take thousands of years for electrons to combine with them and create the first atoms, the building blocks of matter. The first element produced was hydrogen, along with traces of helium andlithium. Giant clouds of these primordial elements would coalesce through gravity to form starsand galaxies, and the heavier elements would be synthesized either within stars or during supernovae.
The Big Bang is a well-tested scientific theory which is widely accepted within the scientific community because it is the most accurate and comprehensive explanation for the full range of phenomena astronomers observe. Since its conception, abundant evidence has arisen to further validate the model. Georges Lemaître first proposed what would become the Big Bang theory in what he called his "hypothesis of the primeval atom." Over time, scientists would build on his initial ideas to form the modern synthesis. The framework for the Big Bang model relies on Albert Einstein's general relativity and on simplifying assumptions (such ashomogeneity and isotropy of space). The governing equations had been formulated by Alexander Friedmann. In 1929 Edwin Hubble discovered that the distances to far away galaxies were generally proportional to their redshifts—an idea originally suggested by Lemaître in 1927. Hubble's observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point: the farther away, the higher the apparent velocity.
