What was the cause of the big bang?

In the very , very beginning , before the universe came into existence , there was an immensely vast empty space , devoid of all matter ; not even one atom or particle is present in the entire space . But the energy field was inherently existing , which caused a quantum fluctuation to create the simplest element , hydrogen atoms , that appeared from nothing . It took the whole of past eternity to produce such hydrogen atoms or particles to an extent that they accumulated in just enough quantity of infinite density and mass . The resulting extreme pressure and temperature caused a thermonuclear reaction which eventually exploded into the Big Bang , 13. 7 billion years ago . That was the beginning of time and space and the start of the Universe .