4 ms·

It's not a bit strong. You refute your own refutation. You use the words 'somehow', 'if', and 'currently'. That's kind of the whole point. _Currently_ there is

It's not a bit strong. You refute your own refutation. You use the words 'somehow', 'if', and 'currently'. That's kind of the whole point. _Currently_ there is no theory that explains how to do fusion without massive amounts of heat, ergo cold fusion IS (currently) theoretically impossible.

ZenoArrow 11y ago
> "_Currently_ there is no theory that explains how to do fusion without massive amounts of heat, ergo cold fusion IS (currently) theoretically impossible." http://scienceblogs.com/startswithabang/2011/11/25/cold-fusion-is-it-possible-is/ http://scienceblogs.com/startswithabang/2011/11/25/cold-fusi... "Unfortunately, their results were hugely flawed, and their experiments were not reproducible, and cold fusion is now synonymous with ideas like perpetual motion machines: very appealing promises of virtually limitless energy, but that are unfortunately physically impossible." "Now, that’s not necessarily fair. While perpetual motion machines would violate known physical phenomena — like the conservation of energy — cold fusion is, in principle possible. If we go back to the Sun, where nuclear fusion definitely occurs, it isn’t like the temperatures there are sufficient to cause the individual nuclei to overcome their mutual electric repulsion and fuse together. Instead, something else remarkable happens to the two nuclei that are about to fuse." "Remember that instead of being solid particles, these nuclei are quantum mechanical objects, meaning they act both as particles and waves. The quantum mechanical wavefunctions of these nuclei — in the Sun, at any rate — wind up overlapping, so that there’s a small but finite (and important) probability that two of them will find themselves in a more energetically favorable state! When that happens, they can tunnel into that energetically favorable state, and fusion can occur!" "Now, this has never been observed at cold temperatures, but from a theoretical physics standpoint, it may be possible."
- lmm 11y ago
  This is misleadingly phrased. We have precise, verified models for quantum tunneling and at what rates under what circumstances it does and doesn't occur.
  - ZenoArrow 11y ago
    Based on those models, what circumstances are required for quantum tunnelling to occur?
    - lmm 11y ago
      Loosely the main points are that the rate falls off exponentially with the "width" of the barrier, and that energy is still conserved (you can say the particle "must have" had more energy at some point because it crossed the barrier, but you'll never observe it with more energy than it has). For more precise answers, just plug the potential you're trying to tunnel through into the Schrödinger equation.
      - ZenoArrow 11y ago
        You're referring to the 'Gamow window' right? From what I understand, the Gamow window only refers to the energy levels of the particles, rather than temperature per se. I'm guessing that's why approaches like Muon-catalysed fusion can work at lower temperatures. https://en.m.wikipedia.org/wiki/Muon-catalyzed_fusion https://en.m.wikipedia.org/wiki/Muon-catalyzed_fusion
        lmm 11y ago
        Muon-catalysed fusion reduces the width of the barrier - the muon is ~200 times closer to the nucleus (since it's that much heavier) and so the coulomb barrier is that much narrower - and the reaction rate is exponential in that.
        ZenoArrow 11y ago
        Sure, it makes sense that it affects the Coulomb barrier (or the Gamow factor/window https://en.m.wikipedia.org/wiki/Gamow_window https://en.m.wikipedia.org/wiki/Gamow_window ), but doesn't muon-catalysed fusion kind of prove that cold fusion could exist? The Wikipedia article suggests that the reactions can take place at room temperature, with the main issue being the reliability of the required reactions. In other words, we already have one proven method for reducing the Coulomb barrier, why is that the only one that's possible?
pdonis 11y ago
> ergo cold fusion IS (currently) theoretically impossible You can't qualify "theoretically impossible" with "currently", because that concedes the point. Honest theorists don't say something is "impossible" unless it is known to be impossible, period; not just "our current theories can't explain it", but "our current theories, in regimes where they are well confirmed experimentally, contradict it". For example, the scam about a "water-fueled engine" is theoretically impossible--it's not just that our current theories of chemistry can't explain how such a thing would work; it's that our current theories of chemistry can explain, in detail, why such a thing cannot work, based on a huge body of experimental knowledge about chemical reactions involving water. That is not the case with cold fusion. Our current theories can't explain how it would work, but they also can't rule it out. The regime in question is not well explored experimentally. Honest theorists don't make claims about something being "theoretically impossible" if the regime in question is not well explored experimentally. They may say it is "theoretically extremely unlikely", but that's an opinion based on someone's judgment about how likely it is that something new will turn up in this experimental regime that our current theories don't cover. It's not the same as "impossible".

ZenoArrow 11y ago

> "_Currently_ there is no theory that explains how to do fusion without massive amounts of heat, ergo cold fusion IS (currently) theoretically impossible." http://scienceblogs.com/startswithabang/2011/11/25/cold-fusion-is-it-possible-is/ http://scienceblogs.com/startswithabang/2011/11/25/cold-fusi... "Unfortunately, their results were hugely flawed, and their experiments were not reproducible, and cold fusion is now synonymous with ideas like perpetual motion machines: very appealing promises of virtually limitless energy, but that are unfortunately physically impossible." "Now, that’s not necessarily fair. While perpetual motion machines would violate known physical phenomena — like the conservation of energy — cold fusion is, in principle possible. If we go back to the Sun, where nuclear fusion definitely occurs, it isn’t like the temperatures there are sufficient to cause the individual nuclei to overcome their mutual electric repulsion and fuse together. Instead, something else remarkable happens to the two nuclei that are about to fuse." "Remember that instead of being solid particles, these nuclei are quantum mechanical objects, meaning they act both as particles and waves. The quantum mechanical wavefunctions of these nuclei — in the Sun, at any rate — wind up overlapping, so that there’s a small but finite (and important) probability that two of them will find themselves in a more energetically favorable state! When that happens, they can tunnel into that energetically favorable state, and fusion can occur!" "Now, this has never been observed at cold temperatures, but from a theoretical physics standpoint, it may be possible."

lmm 11y ago
This is misleadingly phrased. We have precise, verified models for quantum tunneling and at what rates under what circumstances it does and doesn't occur.
- ZenoArrow 11y ago
  Based on those models, what circumstances are required for quantum tunnelling to occur?
  - lmm 11y ago
    Loosely the main points are that the rate falls off exponentially with the "width" of the barrier, and that energy is still conserved (you can say the particle "must have" had more energy at some point because it crossed the barrier, but you'll never observe it with more energy than it has). For more precise answers, just plug the potential you're trying to tunnel through into the Schrödinger equation.
    - ZenoArrow 11y ago
      You're referring to the 'Gamow window' right? From what I understand, the Gamow window only refers to the energy levels of the particles, rather than temperature per se. I'm guessing that's why approaches like Muon-catalysed fusion can work at lower temperatures. https://en.m.wikipedia.org/wiki/Muon-catalyzed_fusion https://en.m.wikipedia.org/wiki/Muon-catalyzed_fusion
      - lmm 11y ago
        Muon-catalysed fusion reduces the width of the barrier - the muon is ~200 times closer to the nucleus (since it's that much heavier) and so the coulomb barrier is that much narrower - and the reaction rate is exponential in that.
        ZenoArrow 11y ago
        Sure, it makes sense that it affects the Coulomb barrier (or the Gamow factor/window https://en.m.wikipedia.org/wiki/Gamow_window https://en.m.wikipedia.org/wiki/Gamow_window ), but doesn't muon-catalysed fusion kind of prove that cold fusion could exist? The Wikipedia article suggests that the reactions can take place at room temperature, with the main issue being the reliability of the required reactions. In other words, we already have one proven method for reducing the Coulomb barrier, why is that the only one that's possible?

pdonis 11y ago

> ergo cold fusion IS (currently) theoretically impossible You can't qualify "theoretically impossible" with "currently", because that concedes the point. Honest theorists don't say something is "impossible" unless it is known to be impossible, period; not just "our current theories can't explain it", but "our current theories, in regimes where they are well confirmed experimentally, contradict it". For example, the scam about a "water-fueled engine" is theoretically impossible--it's not just that our current theories of chemistry can't explain how such a thing would work; it's that our current theories of chemistry can explain, in detail, why such a thing cannot work, based on a huge body of experimental knowledge about chemical reactions involving water. That is not the case with cold fusion. Our current theories can't explain how it would work, but they also can't rule it out. The regime in question is not well explored experimentally. Honest theorists don't make claims about something being "theoretically impossible" if the regime in question is not well explored experimentally. They may say it is "theoretically extremely unlikely", but that's an opinion based on someone's judgment about how likely it is that something new will turn up in this experimental regime that our current theories don't cover. It's not the same as "impossible".