Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

I (Conceptual) Infinity energy via quantum tunneling & Nuclear Fusion?

  1. Jul 21, 2017 #1
    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?
  2. jcsd
  3. Jul 21, 2017 #2


    Staff: Mentor

    No. The problem isn't even the second law of thermodynamics; it's the first law. You can't get out more energy than you put in, and any given amount of nuclear fuel contains a finite amount of energy.

    How do you propose to construct such a barrier? You can't just wave your hands and say one exists at any size you like.

    Why do you think this? What sort of process are you talking about, and where did you learn about it?
  4. Jul 21, 2017 #3
    Yes I clarified that this process doesn't create energy, so I figured this process would involve an never-ending cycling of energy... I just wanted to know what would happen.

    Half lives and the second law of thermodynamics; Heat death of the universe: Won't all particles eventually decay? Just by pure quantum fiat? There's always a nonzero probability that particles decay over time, no? I mean... when I say this process would continue indefinite, I didn't mean it would be quick haha! Each cycle would take many times the age of the universe (I think?).

    So let me clarify: Assuming that particles could be contained in such a small barrier, would they perpetually fuse and decay? I know this doesn't generate energy, which is why I'm asking: What is happening to the energy during this cycle? Would there ever come a point where the particles wouldn't fuse? Would there ver be a point in which the energy just... "goes back" to the nucleus?

    I imagine if this cycle were infinite, it would really just be an infinite cycling of a finite amount of energy. So I suppose my final question is: Would The energy redistribute itself perpetually?
  5. Jul 21, 2017 #4
    I don't know why this part of my post didn't show up: I apologize for double posting:

    I admitted that it was a hypothetical question. In real life, of course this would be impossible! But would it be in principle?
  6. Jul 21, 2017 #5


    Staff: Mentor

    No. Some particles can't decay into anything else without violating a conservation law. For example, electrons can't decay because there's no lighter particle that carries electric charge.

    Also, even if a particle decays, that doesn't mean it will decay into the same thing that you originally made it from. For example, suppose protons decay with some very long lifetime (as some supersymmetric theories suggest), and you produce a bunch of iron nuclei by nuclear fusion. When the protons in the iron nuclei finally decay, they won't decay into lighter nuclei. They'll decay into something else (precisely what depends on the specific supersymmetric model you adopt, but the most likely products would be positrons and neutrinos).

    Why should containing them in a very small barrier make them decay? (And even if they did, as above, it wouldn't in general be into anything that could fuse again.)
  7. Jul 21, 2017 #6


    Staff: Mentor

    Even in principle, you can't make hypotheses that violate the laws of physics. So you would have to figure out some way of making a potential barrier with the desired properties using the known laws of physics. If you say, well, what if there were some other law of physics that made it possible, then there's no way to answer, because we don't know what that unknown law of physics would be so we can't make any predictions at all.
  8. Jul 21, 2017 #7
    Yes I'm aware that elementary particles have nothing to decay into, I should've been more specific: Atomic nuclei.

    Ahh, alrighty then. I didn't realize this was a false assumption, thank you for clearing that up!

    Thank you so much for your answer; I appreciate that you took the time to explain such a silly question. Thank you-!
  9. Jul 21, 2017 #8


    Staff: Mentor

    You're welcome! :smile:
Share this great discussion with others via Reddit, Google+, Twitter, or Facebook

Have something to add?
Draft saved Draft deleted