Sarah is the one to figure it out. After waking up next to her sister’s groom one too many times, she heads to the diner and begins researching quantum physics. She comes to the conclusion that she and Nyles are “trapped in a box of energy,” and the way to escape is to leave the box “in the 3.2 seconds it takes to travel through the loop itself.” During that narrow window of time, she and Nyles will blow up the cave that sent them into the cyclical timeline — along with themselves.