cold fusion

Diagram of an open-type calorimeter used at the New Hydrogen Energy Institute in Japan

Cold fusion is a hypothesized type of nuclear reaction that would occur at, or near, room temperature. It would contrast starkly with the "hot" fusion that is known to take place naturally within stars, artificially in hydrogen bombs, and within prototype fusion reactors; all of which occur at temperatures of millions of degrees. It is also distinguished from muon-catalyzed fusion. There is currently no accepted theoretical model that describes how cold fusion could occur.