Hi folks, I have what might be a naive question about the decay of unstable nuclei. I've recently been reading about various decay processes (e.g. beta decay, electron capture etc.). Specifically, I'm wondering if it is ever possible for a stable nucleus (say, carbon-12 or any other stable nucleus) to spontaneously become unstable, and then to undergo further decay processes (e.g. a different sequence, resulting in, say, a lighter element)? I understand that the trigger for decay in an unstable nucleus involves quantum vacuum fluctuations, which provide the activation energy required, and that moves towards the ground state result in an increase in entropy. I guess I'm asking if there are vacuum fluctuations large enough to temporarily 'excite' a nucleus into an unstable state, such that an alternative sequence of decay processes can occur (resulting in a larger final entropy). Would the required initial decrease in entropy (to put the nucleus in an excited state) prevent this from occurring? I.e. I would think that this type of process cannot run backwards, but I'm not sure? Put differently: if we consider (hypothetically) an isolated, stable atom (with stable nucleus - again, e.g. carbon-12) floating alone in space, will it remain stable forever? (ignoring the possibility of proton decay etc...) Thanks all. Apologies if my question isn't very clear. J.