  The outcome of a single quantum experiment is unpredictable, except in a
pure-state limit. The definite process that takes place in the apparatus may
either be intrinsically random or be explainable from a deeper theory. While
the first scenario is the standard lore, the latter implies that quantum
mechanics is emergent. In that case, it is likely that one has to reconsider
radiation by accelerated charges as a physical effect, which thus must be
compensated by an energy input. Stochastic electrodynamics, for example,
asserts that the vacuum energy arises from classical fluctuations with energy
$\frac{1}{2}\hbar\omega$ per mode. In such theories the stability of the
hydrogen ground state will arise from energy input from fluctuations and output
by radiation, hence due to an energy throughput. That flux of energy
constitutes an arrow of time, which we call the "subquantum arrow of time". It
is related to the stability of matter and it is more fundamental than, e.g.,
the thermodynamic and cosmological arrows.
