Bose-Einstein Condensate Evolves Across 44 Cycles Of Recollapse

Researchers at the University of Birmingham have demonstrated a novel approach to understanding the fundamental nature of time by observing cycles of expansion and recollapse in a Bose-Einstein condensate . The experiment partitioned the ultracold gas using a thin optical barrier, creating “observed” and “unobserved” sectors designed to mirror concepts within the Wheeler-DeWitt framework and relational-time theories. By constructing an entropic time from an experimentally defined coarse-grained entropy, Giovanni Barontini at the University of Birmingham constructed the entropic time and demonstrated that it can robustly order the events in the observed sector across repeated cycles of expansion and recollapse. These results, published in Physics Letters A, establish a controlled experimental setting for quantitatively testing constructions related to the problem of time in quantum gravity.