CAN ELECTRONS BEHAVE LIKE PLANETS? According to quantum mechanics, an electron in an atom forms a hazy cloud of possible positions around the nucleus. Recently, physicists have pondered the possibility of creating a "Trojan state" in which an electron would conform to quantum mechanical principles yet occupy a small region in space and orbit the nucleus like a little planet. The name comes from Trojan asteroids which revolve around the sun in the same orbit as Jupiter, some in advance of the planet and some behind. To bring about a Trojan state, lasers would first put the electron into a "circular Rydberg state" in which the electron exists in a thin donut of possible positions. A microwave beam would subsequently cause the donut to coalesce into a small sausage-shaped region which then revolves around the nucleus. Two potential obstacles to the creation of Trojan states are the possibility that the electrons would be ionized by the microwave fields (a fear since discounted) or that they would fall to a lower-energy state by spontaneously emitting a photon. Now, researchers in Poland have calculated that such spontaneous emission is millions of times less likely than ionization, paving the way for experimental realization of Trojan electrons. (Zofia Bialynicka-Birula, Institute of Physics, Warsaw, and Iwo Bialynicki-Birula (birula@theta1.ifpan.edu.pl), Center for Theoretical Physics, Warsaw, in Physical Review A, November 1997; illustration at Physics News Graphics.)