Transcript: The only way in which humans have so far harnessed fusion is in a hydrogen bomb, the most violent product of human creation. We’re obviously interested in fusion as a power source for a simple reason. What goes in in fusion is light elements like hydrogen, and what comes out is deuterium or helium or tritium. Other light elements, if they are radioactive they have very short half-lives and decay quickly. Fusion compared to fission is therefore a very clean energy source and equally efficient. The problem is that fusion requires protons to be brought into close proximity. They are positively charged, and they repel each other with the electrical force. Temperatures of millions of degrees are required to force hydrogen to fuse into heavier elements and release energy. We have so far managed to have this happen in the lab fleetingly and not in a sustained reaction. Since most material substances melt at temperatures of thousands of degrees Kelvin a temperature of millions of degrees cannot be held in a conventional container. Physicists therefore used magnetic bottles to hold hydrogen to make fusion occur. There is still some hope that fusion will be a feasible energy source, but that day may be decades away.