As I understand it, 'the beginning' is when 'the universe' had a 'once-in-a-gazillion' moment where the probabilistically unlikely event of entropy shrinking to

As I understand it, 'the beginning' is when 'the universe' had a 'once-in-a-gazillion' moment where the probabilistically unlikely event of entropy shrinking to a very small value happened ( aka 'the beginning' ) and from whence entropy started to increase again as it is wont to do. It all goes back to thermodynamics and the probabilistic understanding that entropy 'always' increases. But if entropy always increases then by reason, it must have started off at small minuscule point sometime in the past. But if energy/mass are constant, how could it have gotten to the low entropy in the first place? Given enough time, a 'once-in-a-gazillion' event actually happened. At a fundamental level, it's all mathematical guesswork.