5 ms·

Is there an ELI5 of why cold fusion is so difficult to achieve?

analog31 7y ago
In a nutshell, the reactants (small nuclei such as from deuterium or tritium) have to be brought into intimate contact, against electrical forces that tend to push them apart. The primary effort to achieve fusion has been to overcome those forces and increase the sheer density of nuclei in a way that is not more costly in energy than the fusion energy that can be extracted and used, and without the experiment obliterating itself and its surroundings. Even on a small scale, lack of measurable excess heat is not necessarily a show stopper, because fusion should produce other signatures such as by shedding extra neutrons. The lack of neutron evidence is what generated strong doubts about early reports of CF.
ars 7y ago
The simplest answer is: It's not real. There is no such thing as cold fusion. It's not a matter of "so difficult", it's not actually possible. Are you asking, why is there no such thing as cold fusion? If so then in the simplest way I can explain it: Atoms are like little magnets that repel each other. To get fusion you need to get the atoms to touch - but you can't, they repel. So you have to press them together really really hard, to force them. The only way we know to do that involves lots of temperature and pressure. Cold fusion simply doesn't press them together hard enough. The idea of cold fusion was that certain metals would act like magnet-shields, stopping the atoms from repelling. But all known science says that that is not actually a real thing.
- izend 7y ago
  There does appear to be fair bit of research in LENRs going on right now, note this article claims its the fusion of hydrogen atoms producing the extra heat: https://spectrum.ieee.org/energy/nuclear/scientists-in-the-us-and-japan-get-serious-about-lowenergy-nuclear-reactions https://spectrum.ieee.org/energy/nuclear/scientists-in-the-u...
- tinus_hn 7y ago
  As far as I remember the idea is that you substitute a heavier particle for the electron which causes its orbit to be small enough for fusion to happen at room temperature. The problem is that the particles have a small but non-zero chance of disappearing and it costs a lot of energy to create them, so the process is a net energy loss.
  - ars 7y ago
    That's called https://en.wikipedia.org/wiki/Muon-catalyzed_fusion https://en.wikipedia.org/wiki/Muon-catalyzed_fusion it's not the same thing as cold-fusion.
- criddell 7y ago
  > Atoms are like little magnets that repel each other. Is that a good analogy? I wonder because the first thought that popped in my head is that magnets also attract each other.
  - ars 7y ago
    > is that magnets also attract each other. Electrons attract atomic nuclei (which is the part of the atom that fuses), normally they are too far away to matter, but if you replace them with muons (which are basically heavy electrons) then you can actually help the atoms come close enough because the muon attracts both. Since the muon is heavier it orbits closer to the nucleus of the atom, which helps it cancel out the repelling force. It's too bad muons cost too much energy to be useful this way, or we'd already have commercialized fusion.
    - criddell 7y ago
      > Since the muon is heavier it orbits closer to the nucleus of the atom, which helps it cancel out the repelling force. Even this is hard for me to wrap my head around when I try to also remember that these particles are really just quantum field phenomena.
      - ars 7y ago
        Heavier means a smaller (shorter) wavelength, bend that wavelength into a circle around the nucleus, and it's smaller, since the circle is smaller, it's closer.
  - hguant 7y ago
    Your edge case is correct, but I think it's a useful first order approximation for an 'ELI5" type answer. What's another common situation where two things physically repel each other because of an invisible force?
olooney 7y ago
Because at an atomic level "cold" means "slow" and under the standard model you need to slam protons into each other fast if you want them to fuse. Here is a true "Explain it like I'm five:" Kid: I want candy! Mom: There's candy inside the pinata. Kid: How do I get it out? Mom: Hit it with this stick. If you hit it hard enough, the pinata will break and candy will come out. Kid: gently taps pinata with a stick Mom, it's not working. Mom: well, you have to hit it hard enough to break it. Try swinging the stick faster. Kid: But I don't want to swing it fast. I want to swing it slow! Mom: Then you won't get any candy. Kid: crying Cold fusion is based on the belief that there is some way around this fundamental limitation. This would not be based on any of the known laws of physics (the standard model) and would be by definition new physics. If we discount certain discredited experiments which could not be reproduced, then there is no experimental evidence that this ever occurs, nor is there any unexplained phenomena that would require such new physics. Nevertheless, some people feel the search is still worthwhile. I give a more detailed account (ELI22+) with and physics and numbers above: https://news.ycombinator.com/item?id=20034550 https://news.ycombinator.com/item?id=20034550

In a nutshell, the reactants (small nuclei such as from deuterium or tritium) have to be brought into intimate contact, against electrical forces that tend to push them apart. The primary effort to achieve fusion has been to overcome those forces and increase the sheer density of nuclei in a way that is not more costly in energy than the fusion energy that can be extracted and used, and without the experiment obliterating itself and its surroundings. Even on a small scale, lack of measurable excess heat is not necessarily a show stopper, because fusion should produce other signatures such as by shedding extra neutrons. The lack of neutron evidence is what generated strong doubts about early reports of CF.

ars 7y ago

The simplest answer is: It's not real. There is no such thing as cold fusion. It's not a matter of "so difficult", it's not actually possible. Are you asking, why is there no such thing as cold fusion? If so then in the simplest way I can explain it: Atoms are like little magnets that repel each other. To get fusion you need to get the atoms to touch - but you can't, they repel. So you have to press them together really really hard, to force them. The only way we know to do that involves lots of temperature and pressure. Cold fusion simply doesn't press them together hard enough. The idea of cold fusion was that certain metals would act like magnet-shields, stopping the atoms from repelling. But all known science says that that is not actually a real thing.

izend 7y ago
There does appear to be fair bit of research in LENRs going on right now, note this article claims its the fusion of hydrogen atoms producing the extra heat: https://spectrum.ieee.org/energy/nuclear/scientists-in-the-us-and-japan-get-serious-about-lowenergy-nuclear-reactions https://spectrum.ieee.org/energy/nuclear/scientists-in-the-u...
tinus_hn 7y ago
As far as I remember the idea is that you substitute a heavier particle for the electron which causes its orbit to be small enough for fusion to happen at room temperature. The problem is that the particles have a small but non-zero chance of disappearing and it costs a lot of energy to create them, so the process is a net energy loss.
- ars 7y ago
  That's called https://en.wikipedia.org/wiki/Muon-catalyzed_fusion https://en.wikipedia.org/wiki/Muon-catalyzed_fusion it's not the same thing as cold-fusion.
criddell 7y ago
> Atoms are like little magnets that repel each other. Is that a good analogy? I wonder because the first thought that popped in my head is that magnets also attract each other.
- ars 7y ago
  > is that magnets also attract each other. Electrons attract atomic nuclei (which is the part of the atom that fuses), normally they are too far away to matter, but if you replace them with muons (which are basically heavy electrons) then you can actually help the atoms come close enough because the muon attracts both. Since the muon is heavier it orbits closer to the nucleus of the atom, which helps it cancel out the repelling force. It's too bad muons cost too much energy to be useful this way, or we'd already have commercialized fusion.
  - criddell 7y ago
    > Since the muon is heavier it orbits closer to the nucleus of the atom, which helps it cancel out the repelling force. Even this is hard for me to wrap my head around when I try to also remember that these particles are really just quantum field phenomena.
    - ars 7y ago
      Heavier means a smaller (shorter) wavelength, bend that wavelength into a circle around the nucleus, and it's smaller, since the circle is smaller, it's closer.
- hguant 7y ago
  Your edge case is correct, but I think it's a useful first order approximation for an 'ELI5" type answer. What's another common situation where two things physically repel each other because of an invisible force?

olooney 7y ago

Because at an atomic level "cold" means "slow" and under the standard model you need to slam protons into each other fast if you want them to fuse. Here is a true "Explain it like I'm five:" Kid: I want candy! Mom: There's candy inside the pinata. Kid: How do I get it out? Mom: Hit it with this stick. If you hit it hard enough, the pinata will break and candy will come out. Kid: gently taps pinata with a stick Mom, it's not working. Mom: well, you have to hit it hard enough to break it. Try swinging the stick faster. Kid: But I don't want to swing it fast. I want to swing it slow! Mom: Then you won't get any candy. Kid: crying Cold fusion is based on the belief that there is some way around this fundamental limitation. This would not be based on any of the known laws of physics (the standard model) and would be by definition new physics. If we discount certain discredited experiments which could not be reproduced, then there is no experimental evidence that this ever occurs, nor is there any unexplained phenomena that would require such new physics. Nevertheless, some people feel the search is still worthwhile. I give a more detailed account (ELI22+) with and physics and numbers above: https://news.ycombinator.com/item?id=20034550 https://news.ycombinator.com/item?id=20034550