The Ultimate Clock

Keeping precise time on the universe’s scale

Time is an ancient and contrary mystery. Augustine of Hippo, writing his Confessions in a North African monastery, asked “Who can even in thought comprehend it, so as to utter a word about it? But what in discourse do we mention more familiarly and knowingly, than time?”

In what’s called an “optical lattice clock,” thousands of atoms are held in wells made of laser light.