Tired of feeling like a zombie the first few days in a new time zone? Entrain
, a recently launched app developed by mathematicians at the University of Michigan, can help speed up the recovery process. The free app focuses on light, the most important factor when it comes to resetting your circadian clock. "When people travel, they often want to immediately shift their sleep schedule to the new time zone, but for some trips, that can actually make things worse," says Olivia Walch, one of the app's creators. "You can adjust fastest by exposing yourself to light at times of day that aren't always intuitive. We may, for example, recommend staying in the dark until 10 a.m., even if you wake up at 6. When curing jet lag, sleep matters, but light matters more."