On June 29, Earth had its shortest day in modern history, measuring 1.59 milliseconds under a full 24 hours. You probably didn’t notice. Scientists watching atomic clocks, however, did.

“Our day-to-day existence doesn’t even recognize that millisecond,” McCarthy said. “But if these things add up, then it could change the rate at which we insert a leap second.”

That will, of course, also not matter or be noticeable.