I was unsure whether or not to post this question here or in the Nuclear physics sub-section, but it's a relatively simple question: Given that quantum tunneling exists, would it be possible to produce infinite energy via repeated nuclear fusion reactions? Now given the second law of thermodynamics, I know this to be impossible, so I wanna know why this process wouldn't work. So here's my thought process Here's my Idea: We entrap particles lighter than Iron together in an insurmountable potential barrier, so they can never escape. Given a long enough duration, these particles will eventually fuse together to form heavier elements, resulting in their potential energy being converted to usable energy. Lets also assume, for sake of argument, that these barriers entrap the particles in very close distances... lets say with a radius of 10 carbon 12 atoms. Over time, these particles will inevitably have to decay back into their constituent particles, because there wouldn't be enough energy to form heavier elements. Given an infinite time, wouldn't this cycle continue indefinitely? But I see two problems with this (That I'm unsure of, which is why I'm asking). The first is as I've mentioned, the second law of thermodynamics: This process, by it's very nature, must by definition have something that will make it fail, so I know it must exist. Another problem I can see is that (this is on a hunch) I don't think this process... "generates" energy. When light nuclei collide, energy isn't created, it comes from the change in the nucleus (of which Im unsure of. I read it in an article, but I can't find it in my book). So over time, wouldn't there be a net decrease in frequency of nuclear fusion? There would come a time when particles decay back into their constituents, when their nuclei won't generate energy from fusion (or wouldn't be able to fuse at all?) One final problem I can see is that with the hypothetical: No barrier is insurmountable. There must always be some non-zero probability that the particles may tunnel outside any arbitrarily long barrier, so even if the above two issues aren't a problem, we still have a small chance that the particles will collapse elsewhere... (my retort is that given an infinite time, wouldn't they return to their initial position? Reminds me of infinite random walks in 3D haha!) So I'm curious: What problems would arise with this? Even if it doesn't generate infinite energy, wouldn't it still be the best (most efficient) hypothetical way to harvest chemical energy?