Scientists can put two uncharged metal plates close together in a vacuum, and 'voila!' — they will attract each other. In 1948, Dutch theoretical physicist Hendrick Casimir first predicted an attractive force responsible for this effect. Scientists have wondered, can there be an equal yet opposite kind of Casimir force? Physicists have shown for the first time that the Casimir force can be reversed and made repulsive, tunable or enhanced, based on the material inserted in between the plates.