The approaching new year feels especially momentous because it marks the beginning of a new decade. Yet in a sense, new years and decades arent real; theyre merely concepts humans have made up to organize our days. Even the change at midnight from one day to the next is invented. Clocks strike midnight at different times across the globe, according to our definitions of time zones, but time itself keeps passing smoothly.

These imaginary boundaries between days and decades may be abstract concepts that we have dreamed up,…