What was cold fusion?

Cold fusion is generally the same as “hot” fusion except the temperature at which the fusion occurs is supposed to be lower than what is actually the normal threshold.

Example: Normal temperature for a fusion of hydrogen atoms is around 1,000,000 (or whatever it actually is, I can’t think of it off the top of my head) degrees Celsius or higher. Cold fusion would occur at cooler temperatures resulting in a higher energy yield.

The cold in cold fusion meant room temperature or maybe a little higher (like a few hundred degrees)—rather than typically millions of degrees—as conditions under which energy could be released by fusing hydrogen into helium. The trick is to bring protons (which normally repel due to positive electrical charge) close enough to each other, and this takes extreme heat and pressure.

Nuclear fusion at room temperature.

I would add that cold fusion isn’t necessarily impossible, but physicists can’t even get hot fusion to work on Earth, and there’s no known mechanism for cold fusion. That’s why Pons & Fleischer’s extraordinary claim in the late 1980s got the whole world’s attention—if only momentarily because it turned out to be false.

It never really was, actually. There was one group in Utah that claimed that they achieved it, but it was never able to be reproduced.

Pons & Fleischer claimed to cram hydrogen into platinum and palladium so tightly, in an electrolytic cell, that the hydrogen fused to become helium. They measured a temperature rise in their water slightly higher than expected and slightly more neutrons than expected. Either they had measurement error or God was playing a trick on them.

Note that I, myself, created energy out of nothingness in 12th grade science class, but we attributed that to measurement error (not trying to be petty or anything)