Reversing a Quantum Force

Usually there is a tiny attraction between two objects that are nearly touching, because of the way they tweak the quantum-mechanical energy of empty space. But in the 14 January Physical Review Letters theorists propose that if the objects are made of the newly-discovered materials known as topological insulators, they can be arranged to either attract or repel one another. Although not the first example of such a repulsion, the result could give insight into both the new materials and the exotic force.