“If the world has begun with a single quantum, the notions of space and time would altogether fail to have any meaning at the beginning; they would only begin to have a sensible meaning when the original quantum had been divided into a sufficient number of quanta. If this suggestion is correct, the beginning of the world happened a little before the beginning of space and time.” Georges Lemaître
The Belgian priest Georges Lemaître was the first to propose, in 1927, that the Universe began with the explosion of a primeval atom. His proposal came after observing the red shift in distant galaxies. Two years later, Edwin Hubble made systematic measurements of the red shift. He found that distant galaxies in every direction are going away from us with speeds proportional to their distance.
Evolution of the temperature of the Universe
Our Universe started somewhat 14.5 billion years ago. It took less than one millionth of a second to make disappear heavy quarks, one hundredth of a second to make protons and three minutes to make hydrogen and helium but 300,000 years to decouple the light from the matter.
“This is the most beautiful and satisfactory explanation of creation to which I have ever
listened.”
Albert Einstein