Question:What are the details of the Big Bang Theory?
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 young Universe to cool and resulted in its present continuously expanding state. All the energy in the current Universe must have been there in a the much smaller early Universe.
The sudden expansion of an extremely hot early universe is understandably often compared to an explosion, which is why an Astronomer in the 1949 nicknamed it the "Big Bang".
The idea for the Big Bang Theory comes mainly from the fact that all the Galaxies are currently moving away from each other. This obviously means that in the past all the Galaxies were closer together. This would also mean that the universe would have been hotter in the past. Following this thinking back far enough Scientists have worked out that the early Universe must have been very hot; so hot in fact that even atoms would not have existed.
The Big Bang Theory does not provide any idea for how the Universe came to exist in the first place or what came before it.
Measurements indicate that Universe has expanded for approximately 13.7 billion years, which is therefore the age of the Universe. There is no way to know what there was before this point - if anything; so we usually say that the Universe began at this time.
The early universe was too hot for atoms to exist and it took thousands of years of expansion and cooling before the temperature fell enough for the first atoms to form.
The first element produced was hydrogen, along with traces of helium and lithium.
All the heavier elements were synthesized within stars by nuclear fusion (lighter than iron) or when the star went exploded in a Supernova the end of its life (everything heavier than iron).
Summary of the Big Bang theory:
1.The Universe started with an explosion
2.The Universe is still expanding.