Implosion is a reverse explosion that concentrates matter and energy. Buildings are colloquially described to implode when demolished through explosives, causing them to collapse on themselves. Plutonium may be imploded by spherical explosive charges to trigger a fission bomb, which itself may be an implosive trigger for a fusion bomb.

In the context of cavitation, implosion is a 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.

A characteristic feature of a vortex is that the outside of the vortex moves slowly and the centre moves fast. As water is imploded in a vortex, suspended particles, which are denser than water, are sucked into the centre of flow, frictional resistance is reduced and the speed of the flow is increased.

One of the great researchers of implosion in nature was Viktor Schauberger (1885-1958).