Scientists have measured the shortest unit of time ever: the time it takes a light particle to cross a hydrogen molecule.

That time, for the record, is 247 zeptoseconds. A zeptosecond is a trillionth of a billionth of a second, or a decimal point followed by 20 zeroes and a 1.

Previously, researchers had dipped into the realm of zeptoseconds; in 2016, researchers reporting in the journal Nature Physics used lasers to measure time in increments down to 850 zeptoseconds.