Hmm. After reading thru the previous two educators responses, I find it difficult to explicate the theory in a more cogent manner.
Or, to say it differently, for most readers, little needs to be added without resorting to Hawking, et. al. We know that:
- The universe apparently had a beginning. Astrophysicists have dated it to between 13 and 14 billion years ago. Sources for this vary, but think of nuclear decay, for one.
- The Big Bang theory implies something similar, but not the same as, an explosion: given this, the universe should be expanding and continue to expand. Measurements of the velocities of galaxies and galactic groups support this.
- Anything similar to an explosion should produce heat. There is a what appears to be a cosmic background radiation that is about 3 degrees above absolute zero.
Recent discoveries point to problems with the theory, but have yet to discredit it completely.
The big bang theory is a widely accepted cosmological model of evolution of our universe. It explains how the universe was 'born' through a 'big bang' and how it has evolved over time.
The theory states that our universe began from a singularity around 13.8 billion years ago and has been expanding ever since. The model provides comprehensive explanation for a number of observed phenomena. The discovery by Hubble (in 1929) that galaxies are drifting apart and the discovery of cosmic microwave background radiation (in 1964) support the big bang theory. Due to these and other discoveries in support of the Big Bang theory, it has become the widely accepted model for the birth and evolution of the universe and is favored over the Steady State Theory (another competing cosmological model for the universe's evolution).
One of the most famous and widely accepted models for the universe's development is the big bang theory. The big bang is an attempt to explain how the universe developed from a very tiny, dense state into what it is today The theory states that about 13.7 billion years ago all the matter, energy and space we could observe in the Universe was compressed to an area of zero volume and infinite density, known as a singularity.
There was so much energy in the universe during those first few moments that matter as we know it couldn't form. But the universe expanded rapidly, which means it became less dense and cooled down. As it expanded, matter began to form and radiation began to lose energy. In only a few seconds, the universe formed out of a singularity that stretched across space. In fact, the big bang explains the expansion of space itself, which in turn means everything contained within space is spreading apart.
The evidence for the Big Bang theory includes the existence of a microwave background radiation, and red-shift.