Fusion

The release of nuclear energy by the fusing or joining together of light elements to form a heavier element. The Sun obtains its central power from the fusing of four hydrogen atoms into one helium atom. Nuclear fusion is a main source of energy in H-bombs. Nuclear fusion is being studied as a possible controlled power source, but this has not yet proven to be feasible.

Figure: Controlled nuclear fusion reactors do not exist at this time although they remain the subject of considerable research. Uncontrolled nuclear fusion reactors do exist: they are called H-bombs, or thermonuclear weapons. To give you some idea of the power of E=mc² if we consider your basic 10 megaton nuclear explosion (pictured), the energy given off (10 megatons) represents the energy found in 47 grams of matter (about one and a two thirds ounces). This would be produced through the fusion of just under 7 kilograms of hydrogen.