The Universe and Galaxies: Theory of the Big Bang

Discovery Space: Theory of the Big Bang

Most cosmologists accept the big bang theory as a realistic model of the origin of the universe. The model suggests that the universe evolved from an extremely condensed primeval state.

Nobody knows for sure what really happened during the first moments. The part of the universe that we can observe with our telescopes today was very condensed and most likely measured no more than a few millimeters. Radiation continuously turned into particles of matter and back.

Expansion of the universe

Although the universe expanded rapidly, there was no explosion as there was no surrounding space for explosive power to go to. Space itself simply expanded. The more the universe swelled, the cooler it became, and the less energy was emitted by radiation. The original matter slowly formed the building blocks of atoms: protons, neutrons, and electrons.

About ten seconds after the big bang, protons and neutrons could combine to form the first stable and lightweight atomic nuclei. The radiant energy became too weak to separate the particles. After further cooling, these atomic nuclei were able to capture electrons, forming the first atoms a few hundreds of thousands of years after the big bang.

The universe started becoming transparent. Radiation could now pass through space without barriers, since only very few electrically charged particles were still floating around. Today it is possible to measure cosmic background radiation in any direction. This is thought to be the radiation that was originally released in the early phase of the universe. Once the radiative pressure decreased, gravity was able to take over and the first large accumulations of material could form, approximately one million years after the big bang.

Later on, the first galaxies and stars began to conglomerate. The big bang theory is based on both quantum field theory and Albert Einstein’s general theory of relativity, as well as the cosmological principle. Quantum field theory deals with describing the characteristics and forces of elementary particles. Einstein’s general theory of relativity attempts to explain gravity by the warping of space-time, using a mathematical model which creates a close connection between the three dimensions of space and the passage of time.

Space-time is warped by material and this warp, in turn, determines the movement of material. The cosmological principle states that on the large scale, material is generally distributed evenly throughout the universe, although locally distinct structures may be obvious. Taken together, these assumptions result in the mathematical expansion of the universe.


ACCORDING TO the big bang theory, the universe rapidly expanded from a condensed state about 13.7 billion years ago.