The mammalian zygote enters a prolonged transcriptionally silent interval after fertilisation, yet during this period it prepares for the abrupt onset of coordinated developmental activity. Although the molecular components of the maternal‑to‑zygotic transition are well characterised, the physical mechanism that determines when these processes become synchronised across the approximately 120 micrometre cytoplasmic volume remains unresolved. Here we propose a photonic‑threshold model in which fertilisation initiates a capacitor‑like excitation regime at the mitochondrial–endoplasmic reticulum (ER) interface. Electrochemical energy, metal‑centred redox activity and spectrally refined ultra‑weak photon emission (UPE) accumulate at mitochondria‑associated membranes until a critical excitation density is reached. Crossing this threshold triggers a nonlinear transition from stochastic mitochondrial fluctuations to a stable, system‑wide oscillatory regime that can be described using distance‑dependent Kuramoto coupling. The model integrates quantum‑influenced local processes, including electron tunnelling, radical‑pair dynamics and excitonic interactions, with mesoscale photonic refinement and classical synchronisation. These mechanisms do not generate long‑range quantum coherence but enhance local timing precision, enabling a multi‑scale cascade that culminates in global phase alignment. Evolutionary parallels with cyanobacterial reaction‑centre activation suggest that threshold‑based, metal‑mediated excitation control represents a conserved physical strategy for initiating new dynamical states. The model yields specific and falsifiable predictions. Most notably, it predicts a measurable collapse of the second‑order photon correlation function g²(0) from thermal values near 2 towards values approaching 1 at ignition, reflecting the emergence of temporally ordered emission associated with synchronised mitochondrial activity. Additional predictions include the expansion of ΔΨm synchronisation domains and threshold‑dependent modulation by retinoids and metal ions. These features provide a non‑invasive optical signature of developmental onset and a potential metric for embryo viability.
Nadia (Thu,) studied this question.