Researchers use ultrashort flashes of light to probe fast movements in the atomic world. Femtosecond (1fs=10 ^-15 s ) laser pulses, now routine, are fast enough to follow the motion of atoms and have been used to watch the unfolding of chemical reactions. Attosecond (1as=10^ -18 s ) pulses, demonstrated in the last decade, can capture the movements of electrons. But physicists want to push these limits ever further. Zeptosecond (1zs=10^ -21 s ) flashes, not yet available, could capture the even faster dynamics of subatomic particles, such as neutrons and protons coming together to form a nucleus, or coming apart during nuclear fission.
