What is "cold fusion"?

Cold fusion is a hypothetical type of nuclear reaction that occurs at or near room temperature. The work by Martin Fleischmann and Stanley Pons in the late 1980s brought the topic to international notice, but their work and results were called into question by nuclear physicists.

The experiment by Fleischmann and Pons involved using heavy water in an electrolysis cell with a palladium electrode. Their experiment reportedly created excess heat and trace amounts of nuclear products, such as tritium and neutrons. Experiments by other researchers failed to reproduce the supposed results by Fleischmann and Pons. By late 1989, most in the scientific community rejected the possibility of cold fusion. A small number of researchers continued in the search for cold fusion, but with little support of mainstream science.