Does time actually exist?Bruce Rolff/Stocktrek Images/Getty Images
The passage of time may be nothing more than an illusion that emerges from the quantum interactions between different parts of the universe – at least, this is true in a toy model of the cosmos. The experiment may offer hints as to the nature of time in our own universe.
Giovanni Barontini at the University of Birmingham, UK, started thinking about time while watching his 6-year-old son play. “He was building his own small universe, and I was thinking that that’s pretty much what we do also in our labs, when we build an ultracold-atoms system,” he says. “But then I was starting to think that this is also quite boring as a universe, because there’s not much going on there, and if nothing happens, it’s like if time is not passing by.”
To investigate whether time is truly an illusion in such systems, Barontini used lasers and electromagnetic forces to cool around 20,000 rubidium atoms to temperatures close to absolute zero. He divided the atoms of this toy universe into two sectors, one labelled “bright” and the other “dark”, in analogy to dark matter.
This initial universe was essentially timeless and unchanging, but then Barontini used lasers to coax the two sectors into exchanging atoms and thus interacting on a quantum level. This changed the entropy, or disorder, of the universe, and we know that in our universe, time flows in the direction of increasing entropy. Consequently, Barontini could define an internal time for the toy universe. What’s more, he could use this new time in the Schrödinger equation, which describes how quantum systems evolve, to calculate the atoms’ quantum states, finding that it matched with the results of the experiment.
