Implosion is a process in which objects are destroyed by collapsing (or being squeezed in) on themselves. The opposite of explosion, implosion concentrates matter and energy. True implosion usually involves a difference between internal (lower) and external (higher) pressure, or inward and outward forces, that is so large that the structure collapses inward into itself. An example of implosion is a submarine being crushed from the outside by the hydrostatic pressure of the surrounding water.
Cavitation involves an implosion process. When a cavitation bubble forms in a liquid (for example, by a high-speed water propeller), this bubble is typically rapidly collapsed—imploded—by the surrounding liquid.
Implosion was also a term used by Viktor Schauberger to describe the suctional process that causes matter to move inwards, not outwards as is the case with explosion. This inward (centripetal) motion, however, does not follow a straight (radial) path to the centre; it follows a spiralling, whirling path. This is called a vortex. This usage is unique to Schauberger, whose theories are not widely accepted by scientists.