Speaker
Description
We study the limitations for defining spatial and temporal intervals when the only available reference frame is a single composite quantum system, whose internal degrees of freedom serve as a temporal reference — a clock — and whose centre-of-mass degrees of freedom act as a spatial reference — a rod. By combining quantum speed limits with the mass–energy equivalence of special relativity, we show that spatial localisability and temporal resolution are not independent: sharpening one inevitably blurs the other. Specifically, the internal-energy coherence needed for precise timekeeping affects the centre-of-mass dynamics, enhancing position spreading during free evolution. As a result, a single composite system cannot act as a perfect quantum reference frame for both space and time, leading to a Heisenberg-like uncertainty relation between spatial and temporal intervals.