  The absorption of photons by atoms encompasses fundamental quantum mechanical
aspects, particularly the emergence of randomness to account for the inherent
unpredictability in absorption outcomes. We demonstrate that vacuum
fluctuations can be the origin of this randomness. An illustrative example of
this is the absorption of a single photon by two symmetrically arranged atoms.
In the absence of a mechanism to introduce randomness, the Schr\"odinger
equation alone governs the time evolution of the process until an entangled
state of the two atoms emerges. This entangled state consists of two
components: one in which the first atom is excited by the photon while the
second remains in the ground state, and another in which the first atom remains
in the ground state while the second is excited by the photon. These components
form a superposition state characterized by an unbreakable symmetry in the
absence of external influences. Consequently, the absorption process remains
incomplete. When vacuum fluctuations come into play, they can induce
fluctuations in the weights of these components, akin to Brownian motion. Over
time, one component diminishes, thereby breaking the entanglement between the
two atoms and allowing the photon absorption process to conclude. The remaining
component ultimately determines which atom completes the photon absorption.
Similar studies involving different numbers of atoms can be conducted. Vacuum
fluctuations not only introduce randomness but also have the potential to give
rise to the Born rule in this context. Furthermore, the Casimir effect, which
is closely tied to vacuum fluctuations, presents a promising experimental
avenue for validating this mechanism.
