“Sure.....2H2 + Quantum effects -—> He4 + ~24 MEV”
I would have expected such from a 9th grader, not a PhD ...
It's called "sarcasm". In the same exact vein as which you posted the reply that it responded to.
But I'll expand it a bit using an exact chemical analogy. Suppose I want to convert benzene to cyclohexane. I can put benzene and hydrogen in a sealed pot, and jack up the temperature and pressure. Some of the benzene will be converted to cyclohexane, but there will be side reactions and low conversion efficiency. As "hot fusion".
OR, I can toss in a heterogeneous catalyst, and the reaction will happen and a much lower temperature and pressure, and with much greater yield.
In both cases, the overall reaction is hydrogen plus benzene to cyclohexane. But in the case of the heterogeneous catalyst, the exact steps that take place are not known. As "cold fusion".