A Structural Realizability Criterion for Physical Universes A Non-Anthropic Approach to the Space of Physical Consta

The apparent fine-tuning of physical constants is commonly discussed either through anthropic reasoning or within multiverse and landscape frameworks. While these approaches may be logically consistent, they often rely on observer-dependent selection effects or on ensembles that remain empirically inaccessible. In this work, we propose an alternative, non-anthropic criterion for the realizability of physical universes, based solely on internal structural requirements. We introduce a Structural Realizability Criterion, according to which a universe is considered realizable if its fundamental laws and parameters permit the existence of stable, long-lived structures across at least two hierarchically separated physical scales. We identify a minimal set of dimensionless parameters sufficient to characterize such universes and define realizability as a constrained region in parameter space, expressed through a system of inequalities. By introducing an explicit discretized measure, we estimate the number of distinct realizable universes under a chosen resolution. This work does not propose new physical laws, does not derive the values of physical constants, and does not attempt to solve the fine-tuning problem dynamically. Instead, it reframes fine-tuning as a question of structural viability rather than observational selection.