Physics
Casimir Force
Quick fact
The Casimir force is so strong at sub-micrometer distances that it can cause tiny components in microelectromechanical systems (MEMS) to stick together, a problem engineers call 'stiction'.
Why this is interesting
Imagine two uncharged metal plates placed nanometers apart in a perfect vacuum – they should feel nothing, yet they mysteriously attract each other. What invisible hand pulls them together?