A new quantum test can tell if big things—like chairs or planets—actually exist when we aren't looking.
March 24, 2026
Original Paper
Using spatiotemporal Born rule for testing macroscopic realism: some applications to the pseudo-density matrices and nonclassical temporal correlations
arXiv · 2603.21793
The Takeaway
Quantum mechanics suggests that tiny particles don't have a definite state until they are measured, but we usually assume the "real world" stays put. This paper provides a mathematical way to check if that assumption is actually true, or if large objects are just as ghostly and undecided as atoms until they are observed.
From the abstract
We show that, given an evolving quantum system and the quasiprobability distribution generated by the spatiotemporal generalization of the Born rule in pseudo density-matrices (PDMs), this distribution deviates from the sequential measurements probability distribution, given by the Lüders von-Neumann distribution, if and only if the non-signaling in time (NSIT) is violated; equivalently, if and only if the macroscopic realism (MR) is violated. Furthermore, we propose a definition of temporal ent