   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. also, it is helpful to note that due to the processes that cause an implosion, the object reacts from the inside out. == examples == ===nuclear weapons=== in an implosion-type nuclear weapon design, a sphere of plutonium, uranium, or other fissile material is imploded by a spherical arrangement of explosive charges. this decreases the material's volume and thus increases its density by a factor of two to four, causing it to reach critical mass and create a nuclear explosion. in some forms of thermonuclear weapons, the energy from this explosion is then used to implode a capsule of fusion fuel before igniting it, causing a fusion reaction (see tellerâulam design). in general, the use of radiation to implode something, as in a hydrogen bomb or in laser driven inertial confinement fusion, is known as radiation implosion. ===fluid dynamics=== 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 collapsedâimplodedâby the surrounding liquid. ===astrophysics=== implosion is a key part of the gravitational collapse of large stars, which can lead to the creation of supernovae, neutron stars and black holes. ===controlled structure demolition===  large buildings of various structural types such as masonry, steel frame, or reinforced concrete may be reduced to an easily removed pile of rubble by selective destruction of supporting elements by sequenced and confined explosions. the goal is to confine the materials to specific areas, usually to avoid harm to nearby structures. the technique involves the firing of precisely placed demolition charges in specific timed intervals that use gravity to cause the center of the building to fall vertically while simultaneously pulling the sides inward, a process often erroneously described as an implosion. === cathode ray tube and fluorescent lighting implosion === a high vacuum 
Mechanics