To measure small differences in time, you need a really tiny clock, and researchers in Germany have discovered the smallest known clock: a single hydrogen molecule. Using the travel of light across the length of that molecule, those scientists have measured the smallest interval of time ever: 247 zeptoseconds. Don’t know what a “zepto” is? Read on… When a bit of light, called a photon, hits an atom with enough energy, it can kick the electron out of that atom and send it flying. When we carefully set up this situation in a laboratory, we can measure the electron shooting...