Question

Who explain Big Bang theory

Answer 1

The Big bang theory is an effort to explain what happened during and after that moment. According to the standard theory , our universe sprang into existence as " singularity" around 13.7 billion years ago.
The universal expansion was predicted from general relativity be Alexander Friedman in 1922 and Georges Lemaître in 1927.


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Answer 2

Alexander Friedmann  - 1922.
Georges  Lemaitre   -1927.
Edwin Hubble  -  1929.