Of course it would be awesome if we could actually get heavy hydrogen or other light nuclei to fuse at near room temperatures, outputting tremendous amounts of energy with little energy input, that would be a game-changer for the world. We might finally get our jet-packs, flying cars, and Iron-man suits.

Sci-fi applications aside, it would solve the world’s energy problems in one go. Within 50 years we would be off fossil fuels, would have a zero-carbon energy footprint (CO2 still comes from other sources, like making cement) and the technological applications would likely be stunning.

It is therefore understandable why so many people pursue cold fusion. It is like playing the technology lottery – the odds may be long but we just can’t help playing because the payout is so huge. In fact I don’t mind if serious physicists do serious cold fusion (or low-energy nuclear reactions, LENR) research, as long as they are rigorous and honest about their results.

Unfortunately the cold fusion community has fallen, in my opinion, into a cesspit of pseudoscience. After Pons and Fleishman prematurely announced cold fusion in 1989 (that’s 27 years ago), cold fusion research has been relegated to the fringe. The community became insular, secretive, and suspicious of the mainstream. This made it a playground for cranks and charlatans.

Despite this, is cold fusion a possibility and are we any where close to achieving it? As with any scientific claims, we evaluate them in two basic ways – are the claims scientifically plausible, and what is the actual evidence that the claims are real?

With cold fusion plausibility is very low, but some physicists would argue it is not zero (unlike, for example, perpetual motion or homeopathy).

Fusion, the joining of nuclei lighter than iron into heavier elements, requires a lot of energy to get started. This is because of the electrostatic resistance that these nuclei have to getting close together, called the Coulomb barrier. Regular fusion overcomes the Coulomb barrier with high temperatures and pressure, such as exist in the core of stars.

Attempts at “hot fusion” are underway, but it is technologically very challenging to produce the millions of degrees necessary to start fusion. We’re making progress, but it is still difficult to predict how far away a workable fusion reactor is – at least 30 years, but it could be much longer.

In order for cold fusion to be a reality there would have to be some unknown physics, or our current models would have to be wrong or at least incomplete. Of course, our understanding of physics is incomplete, but that does not mean what we do not currently know allows for cold fusion.

Physicist and blogger Ethan Siegel writes:

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!

OK – so it’s not strictly impossible, but still sounds damn unlikely. Even if favorable quantum fluctuations allowing for tunneling is possible, would it happen often enough for a significant amount of energy to be produced? It sounds like we are in the realm of time travel. This may not be absolutely forbidden by physics, but it may never be practically possible.

While we can argue endlessly about whether or not cold fusion is impossible or just really really improbable, in either case it amounts to an extraordinary claim. That, of course, requires extraordinary evidence. So far I have not seen even ordinary evidence for cold fusion. What we do get is dubious demonstrations.

The pattern is by now very familiar – claims for cold fusion have so far followed a pattern that is typical for cons and pseudoscience. There is a lack of transparency, obvious problems with the setup, lack of reproducibility, and the amounts of energy we are dealing with are too small to be convincing.

In order to be convincing, a demonstration of cold fusion should record all the products that such fusion would create. This includes gamma radiation, the heavier elements that are the product of fusion (for example, if you are fusing hydrogen into helium, we should see helium), and, of course, excess energy. These things need to be recorded in the proper amounts, at least to an order of magnitude.

Further, however (and this is often the fatal flaw), the absolute amount of all of these things have to be enough to measure reliably, with adequate signal to noise ratio. The problem with many experiments (as with free-energy machines) is that the table-top experiments produce minute amounts of “excess” energy – so small that it is difficult to rule out experimental error as a source.

The ultimate test, of course, is a real-world application. Build a working prototype and power a house off the grid.

If cold fusion were real, it should scale up, and given all the claims I would think that by now we would have a working prototype.

Instead we seem to be perpetually in the situation of being on the verge. There is always a claim coming from some obscure lab that they have finally demonstrated cold fusion, and in just a few years we will have working devices. A few years ago the E-cat device was the darling of the cold fusion world (despite the claims coming from a known con artist). Here we are, years later, and nothing.

Now we are getting reports that an obscure commercial Norwegian lab has created cold fusion. They claim to have a working device, and we are just a few years away from practical applications, maybe 5-10. We are on the verge. The mainstream community is now taking it seriously (we are told, but not by mainstream physicists).

The pattern is clear, and is the only thing about cold fusion that is reliably reproducible. This one may turn out to be a reality, but I am not holding my breath. There is no reason to think so until we get credible evidence.

Believers in cold fusion, or perpetual motion machines, or the latest snake-oil cure-all, are like Charlie Brown. They keep trying to kick that football, thinking that this time will be different and it will finally work. But the pattern keeps repeating.