I'm going to go out on a limb and ask a question that will probably be a bit humiliating: Can Thermal Energy be converted into usable energy? I've been reading about conservation of energy, and I know that in no conversion is all the energy usable. There is always some thermal energy (which leads to the conclusion of the inevitable heat death of the universe). But couldn't this problem be avoided by turning the thermal energy into forms of usable energy?
Nothing I've read ever said that thermal energy couldn't be changed back, so why don't we do it? Is it impossible? (Which I find hard to believe). Is it too inefficient? (That would mean that the thermal energy is converted into, well, more thermal energy. Which we can make more usable energy out of. Still more inefficiency? Do it again.) Is there some other reason? Or is there an actual theoretical way to turn thermal energy into usable forms of energy?