Cold-Atom Experiment Shows Time Emerging From Quantum Interactions

Physicists cooled about 20,000 rubidium atoms to temperatures near absolute zero and split them into two sectors labeled bright and dark. Lasers then induced quantum-level exchanges of atoms between the sectors, raising the entropy of the system. Giovanni Barontini at the University of Birmingham defined an internal time for the toy universe based on the direction of increasing entropy.

Using that internal time in the Schrödinger equation produced calculated quantum states that matched the measured states of the atoms. The experiment builds on a proposal first made by Nevill Mott in the 1930s that time can arise from quantum correlations rather than existing independently.

In 2013 Marco Genovese and colleagues at the National Metrology Institute of Italy demonstrated the concept with entangled photons; the new work extends the approach to a larger, more complex system and shows that the Schrödinger equation can be applied with the system’s own time.

@NewScientist reported that Barontini plans to add lasers that create regions atoms cannot leave, analogous to black-hole effects. Claus Kiefer at the University of Cologne stated that the setup connects to efforts to unify gravity and quantum theory, noting that some candidate frameworks predict the absence of time at the most fundamental level. 1103/1h9j-df4k.