Is quantum randomness a real gap in causality, or just a gap in what we know?

[BlackMamba]

Quantum mechanics describes certain events, like exactly when a specific radioactive atom decays, as genuinely, irreducibly random, not merely unpredictable because we lack sufficient information, but random at the deepest possible level the theory can describe. Whether that randomness reflects an actual, ontological gap in the causal fabric of the universe itself, or merely reflects a limitation in our current best theory that some future, deeper theory could eventually close, is a question that sits right at the very foundation of how we understand physical causation.

The standard interpretation of quantum mechanics treats this randomness as genuinely fundamental. There simply is no deeper fact of the matter about exactly when that specific atom will decay, the probability distribution actually is the complete, exhaustive story, full stop, with nothing further underneath it waiting to be discovered by a smarter future theory. If that reading is correct, then the universe does contain genuine, uncaused events, moments where absolutely nothing about the prior state of the universe determines the specific outcome that actually occurs.

Hidden variable advocates resist this framing directly, arguing that apparent randomness nearly always turns out, historically, to reflect incomplete underlying knowledge rather than a genuine metaphysical gap in causation itself. Statistical mechanics famously looked like it involved fundamental randomness before we correctly understood it as our own coarse grained ignorance of an enormous number of deterministic individual particle collisions happening far too fast and numerous for us to track directly. Perhaps quantum randomness is simply the same familiar story playing out again, just one additional level further down in the underlying physical description.

Bell's theorem specifically complicates this hidden variable response considerably, since it rules out entire broad classes of local hidden variable theories that would have preserved a fully deterministic underlying picture. Any hidden variable theory that survives current experimental constraints has to be non-local in some genuine sense, which is its own separate and considerable philosophical cost to accept, even setting aside whether it ultimately succeeds in fully restoring determinism at some deeper level.

What makes this question genuinely different from a typical unresolved empirical puzzle in physics is that, much like the broader interpretation debate it sits within, it may not actually be experimentally resolvable at all, even in principle. If a hidden variable theory is specifically constructed so that its extra hidden variables can never, even in principle, be directly measured or accessed, then the entire dispute risks collapsing into a genuinely metaphysical disagreement dressed up carefully in the language and formalism of physics, one that no possible future experiment could ever definitively settle either way.