Note on Big bank theorem

It looks like you're asking for a note on the "Big Bang Theory". Assuming "Big bank Theorem" is a misspelling of the Big Bang Theory, here is a brief explanation:

The Big Bang Theory is the leading scientific explanation for how the universe began. It proposes that the universe started from an extremely hot, dense point about 13.8 billion years ago and has been expanding and cooling ever since. This expansion led to the formation of all matter, energy, space, and time that make up our universe today.