The volume of phase space may grow super-exponentially ("explosively") with the number of degrees of freedom for certain types of complex systems such as those encountered in biology and neuroscience, where components interact and create new emergent states. Standard ensemble theory can break down as we demonstrate in a simple model reminiscent of complex systems where new collective states emerge. We present an axiomatically defined entropy and argue that it is extensive in the micro-canonical, equal probability, and canonical (max-entropy) ensemble for superexponentially growing phase spaces. This entropy may be useful in determining probability measures in analogy with how statistical mechanics establishes statistical ensembles by maximising entropy.

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We revisit the pairing model of state spaces with new emergent states introduced in J. Phys. A: Math. Theor. 51 375002, 2018.We facilitate our analysis by introducing a simplified pairing model consisting of balls able to form pairs but without any internal structure.For both the simplified and the original model we compute exactly the probability distribution for observing a state with n p pairs. We show this distribution satisfies a large deviation principle with speed n ln(n). We present closed form expressions for a variety of statistical quantities including moments and marginal distributions.

We revisit the pairing model of state spaces with new emergent states introduced in (J. Phys. A: Math. Theor. 51 375 002, 2018). We facilitate our analysis by introducing a simplified pairing model consisting of balls able to form pairs but without any internal structure. For both the simplified and the original model we compute exactly the probability distribution for observing a state with n p pairs. We show this distribution satisfies a large deviation principle with speed n ln ( n ) . We present closed form expressions for a variety of statistical quantities including moments and marginal distributions.