Cold fusion

Back in 1989, a pair of scientists—Fleischmann and Pons—claimed that they'd achieved a remarkable feat: they'd successfully observed nuclear fusion at room temperatures. Momentarily, the finding was heralded as a revolutionary discovery that could transform energy production around the globe. Sadly, their experiments weren't reproducible—but they did inspire scientists to study cold fusion in more depth.

Turns out, the process is in fact theoretically possible. For two atoms two fuse together, they need to come close enough to each other to overcome their mutual electric repulsion, which is caused by the cloud of electrons that orbit them. Usually that's made possible by super-high temperatures—like at the center of the sun—but quantum physics suggests that, because the position of the electric field causing the repulsion is probabilistic, there is at least the possibility that atoms can fuse without the need for energy injection via high temperatures.

And it's that hope that means a small band of scientists still work in the shadows, trying to get cold fusion to work. Of course, while occasional results come and go, they tend to be rather dubious. Fundamentally that's because, even though quantum theory tells us it should be possible, nobody knows how to use that understanding to actually get a fusion reaction going.