Physicists have created a simple model of the universe using ultracold atoms to explore whether time arises from quantum effects rather than existing independently. The work, led by researchers at the University of Birmingham, offers new experimental support for ideas that have circulated for decades.
Giovanni Barontini and his team cooled around 20,000 rubidium atoms close to absolute zero and split them into two non-interacting groups labeled bright and dark. In this initial state the system showed no change and therefore no passage of time.
By applying lasers the groups were made to exchange atoms. The resulting increase in entropy allowed the team to define an internal time for the model universe. Calculations using this time in the Schrödinger equation matched the observed quantum states of the atoms.
Earlier theoretical suggestions date back to Nevill Mott in the 1930s, with the first experimental hint provided in 2013 using entangled photons. The new cold-atom system is more complex and permits direct use of the internal time in quantum calculations.
Commentators note that while the experiment confirms long-standing ideas it does not prove the same mechanism operates at all scales in the real universe.