When Elizabeth Self starts teaching her 11 a.m. class via Zoom, she has to remember that it isn’t 11 a.m. for all of her students. She’s in Tennessee—where she is an assistant professor at Vanderbilt University—but some of the students she’s teaching are now taking the class from California, where it’s only 8 a.m. And a couple of students are back home in China, where it’s midnight.