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There's a principle in statistical mechanics called the Fluctuation Theorem (FT), basically an addendum to the 2nd Law. FT states while the average entropy of a large system must increase over time, on time and length scales that are small relative to the characteristics of the system, you can see localized, spontaneous decreases in entropy. The larger the decrease, the smaller the probability.
With this in mind, imagine a highly uniform superspace with positive and negative energy densities yielding an average density of zero (as an analogy, imagine a set of arrows).
FT says this superspace would experience spontaneous decreases in entropy - the average energy density would remain zero, but regions could become more ordered and you could see splits between positive and negative energy densities (see center).
Small fluctuations would be common and would quickly reach thermal equilibrium with the surrounding superspace. But what about a larger fluctuation?
It would be highly improbable, and would take a long time to return to thermal equilibrium, and during that time on scales within the perturbed region you now have gradients between positive and negative energy densities that can drive physics... maybe this is how universes come into existence.
