In the quantum theory of gravityYanchilina can find an extremely simple answer to the question "What caused the Big Bang?"
The basic formula of this theory shows the relationship between the speed of light and the gravitational potential
In turn a change in the speed of light means a change in the Planck constant
If the gravitational potential is close to zero, then Planck's constant rushes to infinity.
Now let's look at the Heisenberg inequality
It turns out that if the gravitational potential is close to zero, then it rushes to infinity and the left part in the Heisenberg inequality.
In other words in the absence of a gravitational potential quantum fluctuations become infinitely large,
which means the big Bang is inevitable with the formation of a virtual universe-anti-Universe pair.
And after some fairly long time, the universe and the anti-Universe will have to annihilate, and then everything will repeat.