The Casimir force is a force exerted between separate objects due to resonance of electromagnetic energy fields in the intervening space between the objects. This is sometimes described in terms of virtual particles interacting with the objects. Because the strength of the force falls off rapidly with distance, it is only measurable when the distance between the objects is extremely small. On a submicrometre scale, the Casimir force becomes so strong that it can be the dominant force between uncharged conductors. Indeed at separations of 10 nm — about a hundred times the typical size of an atom — the Casimir effect produces the equivalent of 1 atmosphere of pressure (101.3 kPa).