A new study of the Unruh effect
Published in Classical and Quantum Gravity, 2025
Abstract
We revisit the Unruh effect using probability-level calculations, deriving the transition rate of a uniformly accelerating Unruh-DeWitt monopole detector coupled to a massive scalar field. We examine this from both inertial (Minkowski) and accelerating (Rindler) observer perspectives, showing that both perspectives yield the same transition rate at finite measurement times. The research confirms that an inertial detector in a thermal bath of Minkowski particles responds differently than an accelerated detector perceiving a thermal bath of Rindler particles — except for massless fields, where agreement occurs at all times. The paper also presents new numerical results highlighting transient effects caused by the field initially being in the Minkowski vacuum state.
Layman’s Abstract
Imagine accelerating through completely empty space: no particles, no radiation, nothing. Quantum theory makes a startling prediction: you would feel warmth. An accelerating observer perceives the vacuum as a bath of thermal particles, even though a stationary observer sees nothing at all. This is the Unruh effect, first predicted by Bill Unruh in 1976, and it sits at the heart of deep connections between quantum mechanics, gravity, and thermodynamics.
In this paper, we revisit the Unruh effect using new calculation techniques that work directly with probabilities rather than quantum amplitudes. We show that regardless of whether you analyse the situation from the perspective of a stationary or accelerating observer, you arrive at the same physical prediction, a reassuring consistency check with important theoretical implications. We also reveal previously unexplored transient behaviour: what happens in the moments just after a particle detector is “switched on” in the quantum vacuum. These transients turn out to be surprisingly rich, and understanding them may prove important for future experimental proposals aiming to observe the Unruh effect in the laboratory.
Links
Recommended citation: Dickinson, R., Forshaw, J., Jenkinson, R., & Millington, P. (2025). "A new study of the Unruh effect." Classical and Quantum Gravity.
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