Implosion (mechanical process)

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Implosion is a process in which objects are destroyed by collapsing (or being squeezed in) on themselves. The opposite of explosion (which expands the volume), implosion reduces the volume occupied and 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, or into the space it occupied if it is not a completely solid object.^{[citation needed]} Examples of implosion include a submarine being crushed from the outside by the hydrostatic pressure of the surrounding water^[1] and the collapse of a massive star under its own gravitational pressure.

An implosion can propel material outward (for example due to the force of inward falling material rebounding, or peripheral material being ejected as the inner parts collapse), but this is not an essential component of an implosion and not all kinds of implosion will do so. If the object was previously solid, then implosion usually requires it to take on a more dense form—in effect to be more concentrated, compressed, or converted into a new material that is denser than the original.