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Physicists have long been able to snap atomic-scale pictures by shining a beam of electrons at a target, but filming the electronic structure of an atom as it changes in time is the next goal. A rapid "strobing" of electron pulses less than a millionth of a billionth of a second long should do the trick, according to a theoretical analysis in the 24 December Physical Review Letters. The authors demonstrate with computer simulations that ultrafast electron pulses could track the "breathing" state of an excited atom or the hopping of electrons between atoms in a molecule. Such movies open up the possibility of controlling the electrons that drive chemical reactions.