In these days of soaring energy prices, it is worth thinking about nuclear fusion as a possible source of energy. I know at least one person who has spent their entire career working on this project, during which time the goal seems not to have come any closer. The question we should now ask is, what is the reason for this? Is a nuclear fusion reactor (a) a technological challenge, (b) practically impossible, or (c) theoretically impossible? Looking at the project from the outside, it seems that in the past 40 years or so it has progressed from (a) to (b). In this post I want to suggest that it may soon progress to (c), at which point the attempt becomes futile.
For this purpose I want to distinguish four different types of energy: (1) gravitational energy, (2) nuclear energy, (3) kinetic energy and heat, and (4) electromagnetic energy. The point of a power station is to convert energy from (1), (2) or (3) into (4). Some, like wind farms, go directly from (3) to (4). Hydroelectric power converts (1) to (3) to (4). Nuclear (fission) reactors convert (2) to (3) to (4). Conventional fossil fuel power stations convert (4) into (3) and back into (4) again, but in a more useful form. A fusion reactor is also supposed to convert (2) to (3) to (4), so the question is, why doesn’t it work?
Now we need to understand that we do not have a complete theory of the transfer of energy between these four different forms. We have two inconsistent theories that describe parts of this energy transfer. The part that links (2) and (4) at a fundamental level is the standard model of particle physics. This model also describes (3), so is the one we need for understanding how a fusion reactor does or does not work. There are several crucial parameters that describe the interface between (2) and (4) in the standard model. One of these is the mass of the W boson.
You may have heard that there is an inconsistency in the measurement of the mass of the W boson, significant at the 99.999999% level. Even if this confidence level is exaggerated (as it usually is in particle physics experiments), it suggests there is something badly wrong in the standard theory of the interface between (2) and (4). If so, then the current theory, that predicts a transfer of energy from (2) to (4) in nuclear fusion, may need to be replaced by a new theory, in which there is no such transfer of energy, or at any rate, a smaller transfer of energy. A smaller transfer of energy could easily transform a promising project into a dead end (q.v.).
In practice, a nuclear fusion reactor uses a very strong magnetic field to hold the fuel in place so that the fusion reaction can occur. It therefore uses a lot of (4) as input to the process that converts (2) into (3), before (3) is converted to (4) in a conventional manner. If we don’t have a proper hold on the transfer of energy from (4) to (2), then we don’t have a proper hold on the cycle of energy from (4) to (2) to (3) to (4). In the normal run of things, entropy ensures that if we cycle energy between different forms, then we lose some of that energy on the way around. This is why it is not possible to build a perpetual motion machine without some way of topping up the energy that is lost. Is it possible that a nuclear fusion reactor is actually a perpetual motion machine, and therefore theoretically impossible?
Experiment certainly seems to support this conclusion, but theory does not. The theory is known to be incomplete, and possibly even wrong in places, but surely not that badly wrong? After all, nuclear fusion does take place in the core of the Sun, and does release a lot of energy that ultimately causes the Sun to shine, so we know it is possible to get a lot of energy out of nuclear fusion. The only question is, where does that energy ultimately come from? In experiments on Earth, it may come from the electromagnetic energy that provides an artificial gravity to keep the fuel in a confined space. This suggests that we need to consider the effects of gravity, that hold the Sun together, and keep the fuel in the Sun in a confined space at high temperature and pressure to enable the nuclear fusion reactions to take place.
At this point we have no plausible theory to unify gravity with the nuclear forces, so we are reduced to speculation. But the hypothesis that the energy for nuclear fusion actually comes ultimately from gravitational energy is not at all unreasonable. We know that nuclear fusion only occurs in nature in regions of very strong gravity. Inside the Sun, the gravitational energy (1) is first converted into electromagnetic energy in the form pressure x volume (4) as well as kinetic energy in the form of heat (3), which then get converted into nuclear energy (2) by the fusion reaction, with a byproduct of more heat (3) and electromagnetic energy in the form of sunshine (4).
In other words, inside the Sun the energy lost in the fusion cycle (4) to (2) to (3) to (4) is topped up by gravitational energy. We do not have that option on Earth. Therefore a nuclear fusion reactor on Earth is a form of perpetual motion machine, which is theoretically impossible.
Hidden assumptions 
October 2, 2022 at 9:52 am |
We know, of course, that the Earth is big enough and heavy enough to convert (1) into (4) in the form of chemical energy. For example, gravity creates the extreme pressure which creates diamonds. But it does not seem to be big enough to convert (1) into (2). Although, to be fair, we don’t really know what is going on in the hot core of the Earth.
Chemistry is all about converting between (3) and (4). Converting between (2) and (3) (or (4)) is known historically as alchemy, and its modern name is nuclear fission. Converting between (1) and (2) is known historically as magic, and its modern name is nuclear fusion. Unfortunately, magic does not exist in the real Earth with live on.
October 3, 2022 at 3:31 am |
Fusion occurs in a H Bomb. No gravity needed.
October 3, 2022 at 8:30 am
Correct. The energy to create the required pressure and temperature to ignite the fusion reaction comes from the initial fission reaction. This is what creates the necessary “artificial gravity” for the very short period of time required.
October 3, 2022 at 8:58 am
The problem, of course, is that this technology does not translate to a fusion reactor, where the artificial gravity needs to be maintained for much longer periods of time. Moreover, the use of fission reactions to create this artificial gravity would negate the entire purpose of a fusion reactor, which is to avoid producing radioactive waste products.
October 3, 2022 at 9:44 am |
The overall (very simplified) picture of the gravitational/nuclear energy cycle that I am suggesting here is that from primordial (or not so primordial) hydrogen, gravity eventually creates stars, which are factories to convert gravitational energy into nuclear energy via the process of nuclear fusion. Stars die in various different ways, according to their size and type, one of which is in an enormous explosion which scatters all the atoms through a vast volume of space. This explosion converts a large part of the nuclear/electromagnetic energy into gravitational energy, so that the cycle repeats.
This is not the whole story, however, because not all of the nuclear energy is converted back to gravitational energy: some of it remains, stored in the nuclei of heavier atoms. These atoms then eventually come together into planets like the Earth, which runs on a combination of solar power (that keeps the weather going) and nuclear power (that powers volcanoes and keeps the tectonic plates moving).
These details apart, the life-cycle of many stars is essentially a long slow conversion of gravitational energy into nuclear energy, followed by an explosive conversion of nuclear energy into gravitational energy. This enables the universe to recycle itself on a timescale of billions of years, or perhaps longer, and suggests that a Big Bang may not have been necessary to start things off. Of course, the devil is in the detail, but we can’t start to talk about the detail until we have a unified theory of gravity and particle physics.
This is why the JWST results are so important: they provide experimental evidence against the Big Bang Theory, and therefore provide the equivalent of the Michelson-Morley experiment that is required for a paradigm shift in *both* theories of gravity and theories of particle physics. Most importantly, they show that you can’t consider one without the other. There are many aspects of unification which need to be considered, but the conversion between gravitational energy and nuclear/electromagnetic energy is the main theme.
This conversion is defined by the concept of mass, which describes the equilibrium point between gravitational and nuclear/electromagnetic energy in any given context. But this equilibrium point depends on the context. Therefore the concept of mass depends on the context. As I keep saying. One day people will realise that this makes sense.
October 3, 2022 at 11:35 pm |
Late to reply but the h bomb has the inward squeeze of the fission radiation (and it is beyond imagination as it is liked to a metal wall) that starts the fusion reaction. So these are inertial forces supplanting gravitational force. Under Einstein there is an equivalent between inertia and gravity but the I read where this is not quite right. Whatever. There are inertial fusion machine, z pinch as an example which are considered inertial method to fusion. These would operate as a succession of implosions to take advantage of the over unity influx to energy advantage. But like you say inertial methods are definitely not approaching anything like the perpetual path machine
October 4, 2022 at 8:57 am
Yes, I think it may well be useful to think in Einstein’s terms, of general relativity being a unification of gravity with inertia. It is generally understood that when the inertia changes, the gravity also changes. What is not understood is that general relativity *also* implies that as the gravity changes, the inertia also changes. I don’t think even Einstein fully appreciated that, although he did write a paper in 1919 in which he considered this idea.
October 5, 2022 at 1:12 pm |
It’s entropy again – the Standard Model of Particle Physics is inconsistent with the Second Law of Thermodynamics. Which one is going to win in the end? My money is on the Second Law of Thermodynamics!