where did that mass go?

Fusion. The combination of two atoms to form one heavy atom. Sounds boring, huh? There is a small amount of discrepancy between the mass of two hydrogen atoms and one helium atom. One can actually fuse most two atoms that are light. This process in reverse is known as fission, which is what powers our nuclear power plant. Both these processes are used in hydrogen bombs, in which the fission is used to trigger fusion. Fusion is also the source of energy for our sun. In both, Einstein's most famous equation, E=mc^2, gives us the relationship between the small amount of mass lost and the extravagant amount of energy created from said mass.

So what does this matter? well, nuclear power (fission) produces vast amounts of radioactive waste that is mostly stored on-site and is a significant risk to those around it. If we could make energy using fusion rather than fission, the resulting by product would be the gas that makes our voices go high when we inhale it, helium. The amount of energy is vast.

Two ex-printer engineers from Canada have undertaken an experiment that seems to bypass steps that have been hampering scientists for years. instead of using a tomahak chamber, these ingenious people created a device that uses pneumatic pistons to create a shock wave that compresses the plasma inside the chamber to a level critical to allow fusion to begin, and once it begins, use that energy to power the next resulting shock wave, creating a pseudo-perpetual motion machine. This, with hydrogen (mainly in the form of deuterium and tritium, which, it turns out we can extract from water) can run creating electricity from the small amount of mass lost in the fusion. If this works... well nearly infinite energy from water. Sounds like peak oil would be inconsequential.