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Accelerated Detectors Reveal When Time’s Order Truly Matters

Marcello Rotondo and collaborators demonstrate that uniformly accelerated two‑level detectors exhibit a measurable dependence on the sequence of their interactions with a quantum field, but only when the field satisfies the Kubo‑Martin‑Schwinger (KMS) condition and the detector couples via non‑commuting observables. The ordering effect appears already at second order and is quantified using quantum relative entropy, linking it to the Unruh temperature scale (2πa). This reveals a concrete manifestation of thermal time and microscopic irreversibility in relativistic quantum field theory. The authors note that realistic detector imperfections and noisy environments remain to be explored.