Measuring time with stationary quantum clocks

TL;DR

This paper demonstrates that quantum clocks can measure the passage of time while being switched off, providing experimental support for the substantival theory of time through counterfactual measurement techniques.

Contribution

It introduces a novel quantum measurement method showing stationary clocks can detect time flow, challenging classical assumptions about clock functionality.

Findings

Quantum clocks can measure time while switched off.

Counterfactual measurements enable observing time flow without active operation.

Supports the substantival theory of time with quantum experimental evidence.

Abstract

Time plays a fundamental role in our ability to make sense of the physical laws in the world around us. The nature of time has puzzled people -- from the ancient Greeks to the present day -- resulting in a long running debate between philosophers and physicists alike to whether time needs change to exist (the so-called relatival theory), or whether time flows regardless of change (the so-called substantival theory). One way to decide between the two is to attempt to measure the flow of time with a stationary clock, since if time were substantival, the flow of time would manifest itself in the experiment. Alas, conventional wisdom suggests that in order for a clock to function, it cannot be a static object, thus rendering this experiment seemingly impossible. Here we show, with the aid of counterfactual measurements, the surprising result that a quantum clock can measure the passage of time even while being switched off, thus lending constructive support for the substantival theory of time.