system
Given the following post, respond as if you're commenting on Reddit:
human
What exactly is cold fusion and why is it considered impossible?
gpt
Well, regular fusion involves heating hydrogen to such a high temperature that the protons start fusing into helium. This is what happens in the sun. There are some experiments on Earth trying to achieve this, but they can't do it in an energy efficient manner. In the next decade one should open in France that does this however.

Cold fusion is an attempt to do this without the immense temperatures. To oversimplify, the high temperatures are required because the protons need to be moving fast enough to overcome their electric repulsion. Cold fusion claims to do this by chemical rather than thermal means, or to have extremely localized heating.

It's not considered *impossible*, but people are highly sceptical of it because A. immense energies are required to overcome the electric repulsion and B. pretty much everyone involved in low-energy fusion has been shown to be a fraud (Ponz & Fleischman, Taleyarkhan, Rossi, etc).