There is no scientific explanation for what started the Big Bang in the first place,
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Actually, there is an explanation, a quantum fluctuation. What can’t be explained is the vacuum and its properties that allow the fluctuation to happen. Fining tuning is a related problem that’s yet to be solved.
There are hypothesis, but no working theories. For a theory you need evidence, and there is none. According to the standard model, there was no space or time prior to the Big Bang (which also means there was no ‘prior’). Quantum fluctuations take place in space-time, so what created space-time itself? But there are those who say space-time has always existed at least on the Planck scale, or it oscillates between expansion and collapse infinitely, etc; or it was a collision between two higher-dimensional universes. Or with just as much validity you could say God created it. With no observational evidence, science can make no absolute claims.