‘The epidemic is a demon,’ declared President Xi Jinping to the WHO on January 28, 2020, ‘and we cannot let this demon hide.’ Within months, on the opposite side of the planet, a nurse despaired about ‘an invisible demon’ that killed half of the residents in her nursing home in Connecticut. Within a year, Sars-CoV-2 infected an estimated 240 million people and would take more than 5 million souls worldwide. Descriptions and depictions of the pandemic as ‘demonic’ and of the horned and miniscule mutant virus as a ‘demon’ or ‘devil’ soon became widespread.

How can advanced technological societies fight against what still seems to us demonic? Science is the obvious candidate. It is credited for developing lifesaving technologies—ranging from antiseptics, antibiotics and anaesthesia to vaccines—as well as many other innovations that have improved the quality of life for many around the world.

Popularisers of science tend to focus on how the discipline increases our ability to control and predict nature, but those aspects of science that introduce new variables into our universe affect us in more alarming ways. The astronomer and science communicator Carl Sagan is a typical example of a thinker who mostly ignored those uncomfortable aspects of science. Yet even he admitted that in the process of discovery ‘surprises—even some of mythic proportions—are possible, maybe even likely.’ Accidental discoveries often beget regret, handwringing, and soul-searching. How can we conduct research so that discoveries pleasantly surprise us? According to Sagan, the only way forward is forward: ‘If we knew beforehand what we’d find, it would be unnecessary to go.’

Five years before the pandemic started, scientists studying bat viruses at the Wuhan Institute of Virology in human cells and in mice were surprised when they created a chimeric mutant that made them sicker. Such an outcome was ‘not expected,’ they said in a paper titled ‘A SARS-like cluster of circulating bat coronaviruses shows potential for human emergence.’ Like many others, the discovery was a game-changer: it showed just how easily new viruses with pandemic potential could be created in a lab. ‘The potential to prepare for and mitigate future outbreaks must be weighed against the risk of creating more dangerous pathogens,’ they concluded.

This type of laboratory research is now under the microscope, as is the claim that the 2015 discovery was unexpected. A letter sent on October 20, 2021 by the US’s National Institute of Health director Lawrence A. Tabak to the House of Representatives reiterated a claim that such research did not qualify as ‘gain of function’ (the potentially dangerous practice of genetically altering organisms to enhance biological functions) because it was not the project’s stated goal. ‘As sometimes occurs in science, this was an unexpected result of the research, as opposed to something that the researchers set out to do,’ he wrote.

The history of science is full of examples of surprising and accidental discoveries. From the field of physics alone we know that the discovery of magnetic effects using electric currents (Hans Christian Oersted), radioactivity (Henri Becquerel), X-rays (Wilhelm Roentgen), and radio waves (Heinrich Hertz) caught those involved in the research by surprise. Albert Einstein, who made some important contributions to the study of nuclear energy, was caught off-guard when he learned that two atomic bombs had destroyed the Japanese cities of Hiroshima and Nagasaki. ‘I did not foresee that [nuclear energy] would be released in my time,’ he declared. His colleague and expert in quantum mechanics Max Born noted his and others’ blind spots when assessing the impact of their research. Reflecting on his own work, he admitted that ‘anyone who would have described the technical applications of this knowledge as we have them today would have been laughed at.’

In science, we can expect the unexpected. Such outcomes do not end after the initial discovery has been made—they continue to occur even at enhanced speeds. Soon after the first ‘unexpected’ discovery of the more lethal mutant coronavirus in the Wuhan lab, other scientists working with chimeric viruses noted that more surprises might be in store: ‘Whereas not generally expected to increase pathogenicity, studies that build reagents based on viruses from animal sources cannot exclude the possibility of increased virulence or altered immunogenicity that promote escape from current countermeasures.’

Scientist’s open-ended journeys into the unknown are not always entirely undetermined. Oersted would not have discovered the magnetic effects had he not been working with electric currents, Becquerel would not have found radioactivity had he not been toying with samples of uranium, Roentgen would not have seen X-rays if it were not for the photographic plates he had stashed in a drawer, and so on. As Louis Pasteur soberly reminded us, in science luck favours the prepared.

Even before scientists start experimenting, their very first speculations about potential areas of future research are not blind. When trails run cold, these experienced practitioners know where it is most profitable to look, what new discoveries might look like, what properties they might possess, and what they might be capable of. Strange beings haunt scientists’ imaginations. Often, these are referred to as demons.

The Oxford English Dictionary defines demons in science as ‘any of various notional entities having special abilities, used in scientific thought experiments … with reference to the particular person associated with the experiment.’ Although these demons are no longer found in the old grimoires of magical spells and incantations, such terms regularly appear in journals, such as Nature and the American Journal of Physics, science magazines, such as Scientific American, and even mainstream news outlets, such as The New York Times. Publications dealing with these demons are widely celebrated, authored by highly respected thinkers and scientists, and point to key discoveries in areas ranging from thermodynamics to quantum mechanics. Certain demons, as it turns out, cannot be easily exorcised.

The first demon in this tradition is Descartes’s demon, named after the renowned thinker known as the founder of modern logic. In one of the classic works of philosophy, Meditationes de Prima Philosophia (1641), René Descartes described fearing a creature who could take over his senses and install an alternative reality in front of him. How could he know what was real and what was illusory? To fend himself from the deceptions of this ‘evil genius,’ he laid out the most certain truths he could find. By doing so, he taught us how to advance knowledge by questioning our dearest assumptions about everything and everyone, including social, religious and political authorities. Thanks to him, scepticism and doubt continue to be the most powerful tools of scientific discovery.

Science’s demons are, by most accounts, mere figments of our imagination; they are characters in thought experiments that have pedagogical or heuristic value. There is, however, much more to them. These imaginings have led scientists to mimic their astounding supernatural abilities by developing experiments and technologies to understand them. To this day Descartes’s demon inspires us to better understand the imperfection of our senses and to push ratiocination to new levels. Yet he also motivates scientists and engineers to improve virtual reality technologies and create deepfakes—actualising the feats of a creature whose possible existence was first imagined in the seventeenth century.

After Descartes conjured the creature that now goes by his name, other demons entered the argot of the laboratory. ‘Laplace’s demon’ is usually listed next. She was named after the statistician Pierre-Simon Laplace, who originally referred to her as ‘an intelligence’ using a feminine pronoun in the original French (she was only labelled a demon in the 1920s). Her special abilities included knowing everything about everything by being able to calculate the future by extrapolating from initial conditions. Laplace’s hypothetical being could calculate the movement of each and every particle in our universe throughout all space and time. All she needed was a sufficiently large brain and knowledge of basic physics:

An intellect which at any given moment knew all of the forces that animate nature and the mutual positions of the beings that compose it, if this intellect were vast enough to submit the data to analysis, could condense into a single formula the movement of the greatest bodies of the universe and that of the lightest atom; for such an intellect nothing could be uncertain and the future just like the past would be present before its eyes.

Although she started off as a product of the French Revolution, she left a mark in history by becoming, in the hands of the nineteenth-century British inventor Charles Babbage, a blueprint for one of the first computers. When Babbage described the ‘calculating engine’ he was planning on building, he cited Laplace directly. ‘Let us imagine a being, invested with such knowledge,’ he wrote, explaining to his readers how the superior ‘being’ described by Laplace had to be powerful, but not infinitely so. ‘If man enjoyed a larger command over mathematical analysis, his knowledge of these motions would be more extensive,’ he wrote, ‘but a being possessed of unbounded knowledge of that science, could trace every minutest consequence of that primary impulse.’

‘Maxwell’s demon’ is the most famous of the lot. He was named after James Clerk Maxwell, a Scottish scientist who most historians would rank third in importance after Albert Einstein and Isaac Newton. It first appeared in print in a section of his book Theory of Heat (originally 1871) appropriately titled: ‘Limitation of the Second Law of Thermodynamics.’ ‘Before I conclude,’ wrote Maxwell towards the end of the section, ‘I wish to direct attention to an aspect of the molecular theory which deserves consideration.’ It pertained to ‘one of the best-established facts’ in thermodynamics, the impossibility of producing ‘any inequality of temperature or of pressure without the expenditure of work’—a fancy way of saying that perpetual motion machines could never be built. Maxwell then described a possible exception to the law. ‘If we conceive a being whose faculties are so sharpened that he can follow every molecule in its course,’ the law could be circumvented, and scientists might find themselves able to produce work without requisite expenditure. Maxwell went on to describe his being in the way it would be frequently pictured by generations to come, as working within an insulated container divided by a small door that could allow only certain molecules to pass through:

Now let us suppose that such a vessel is divided into two portions, A and B, by a division in which there is a small hole, and that a being, who can see the individual molecules, opens and closes this hole, so as to allow only the swifter molecules to pass from A to B, and only the slower ones to pass from B to A.

With his delicate movements, this being could ‘contradict’ the second law nearly effortlessly: ‘He will thus, without expenditure of work, raise the temperature of B and lower that of A, in contradiction to the second law of thermodynamics.’

Decades after Maxwell posited such a creature, the renowned French scientist Henri Poincaré saw him under his microscope. By focusing it on tiny particles that jiggled back-and-forth when floating on liquids—an effect known as Brownian motion—he attributed their seemingly inexhaustible movement to the actions of an operator working behind the scenes at the molecular level. Such zig-zagging movements are not uncommon in nature—they have been attributed to the ‘random walks’ of drunkards and the fluctuations of the stock market. Because it was up to this demon to determine if atoms and molecules were permitted to pass from one place to another, Poincaré baptised him the ‘customs officer’ of the universe.

One of this creature’s essential characteristics was already widely agreed upon by those who studied him: his tiny size reflected inversely on his strength. Like the fish who could eat a whale, a David who could beat Goliath, or the straw that breaks the camel’s back, this miniature Katechon can delay the end of the world, stop entropy, put an end to decay, and with a few deft movements, make the world run in reverse. Scientists, including Nobel Prize winners Ilya Prigogine and Manfred Eigen, suspected that he was not only responsible for being at the origin of life, but that he kept life going on in the face of adverse circumstances. His disregard for human life, however, was frequently noted by myriad investigators.

As interest in the life sciences grew in the post-war period, Maxwell’s demon jumped from physics to biology. Microbiologists interested in studying cell reproduction noticed that something very strange inside them allowed them to self-replicate and organise information in a manner that seems to counter all previously known laws of nature. They started to zero-in on the role played by DNA and mRNA in viruses and phages (viruses that attack bacteria) and started comparing them to Maxwell’s demons.

Laboratories all over the world are still searching for Maxwell’s demon. More recently, a relative of his, called Feynman’s demon (after the physicist Richard Feynman, who imagined a still small imp operating at the level of quantum mechanics) was created in a laboratory setting. ‘Feynman’s Demon has recently been built as a nanoscale Brownian motor,’ stated a recent article. ‘Maxwell’s demon goes quantum,’ was the title of another. The international scientific press and newspapers covered advances in research with articles titled, among others: ‘A demon of a device,’ ‘Maxwell’s demon tamed,’ ‘Demonic chemistry,’ ‘Laws of Nature survive attack by Nano Demon,’ ‘Scientists build Maxwell’s demon,’ and ‘Maxwell’s Demon Created by Scottish Scientists.’

Because of his ability to churn a profit without loss, Maxwell’s demon has fascinated businessmen and economists who have tried to imitate his modus operandi. Jaron Lanier, an interdisciplinary research scientist at Microsoft, recently noticed a particular strategy at play in the banking and tech industries that he compared to the actions of Maxwell’s demon. ‘Finance, and indeed consumer Internet companies and all kinds of other people using giant computers,’ he wrote, ‘are trying to become Maxwell’s demons in an information network.’ Who could blame them? ‘With big computing and the ability to compute huge correlations with big data [the temptation] becomes irresistible,’ he said. The insurance business, for example, depends on such strategies. ‘I’m going to let the people who are cheap to insure through the door, and the people who are expensive to insure have to go the other way until I’ve created this perfect system that’s statistically guaranteed to be highly profitable.’ Success at one level, however, led to catastrophe at another: ‘For yourself you’ve created this perfect little business, but you’ve radiated all the risk, basically, to the society at large.’ ‘And so,’ as Larnier explained, ‘you’re like Maxwell’s demon with the little door.’

One aspect of this creature’s masterful tactics is central to Jeff Bezos’s management strategy at Amazon, the world’s largest multinational online retailer and e-services business. In his annual sales letter to shareholders for 2017, he explained that one reason behind its success lay in a particular decision-making strategy where higher-ups manned one-way doors, just as Maxwell’s demon was known to do. ‘Some decisions are consequential and irreversible or nearly irreversible—one-way doors, and these decisions must be made methodically, carefully, slowly, with great deliberation and consultation.’ By thinking about corporate governance in terms of Maxwell’s demon’s essential implement (one-way doors), Bezos steered his business away from irreversible losses. ‘If you walk through and don’t like what you see on the other side,’ he warned, ‘you can’t get back to where you were before.’ With such caution in mind, he led Amazon to become the fastest company ever to reach a $100 billion valuation.

Science’s demons stop being merely hypothetical the moment experiments are created to understand and imitate the actions of a fine and motley crew, a veritable troupe of colourful characters with recognisable proclivities and abilities who challenge the laws of nature. Thus, they leave the laboratory to impact the world, leaving us at the mercy of a host of modern demons that thrive in the age of reason.

Science advances not just by eliminating falsehoods through trial-and-error testing procedures—it forges ahead by leaps and bounds when researchers imagine things they still do not fully understand. Fighting demons is more pertinent now than it was in the cruel and misguided age of the Spanish Inquisition and witch trials, but it involves more than just following the science—it requires thinking about who, how and where it is leading us.

Bedeviled: A Shadow History of Demons in Science by Jimena Canales is published by Princeton University Press.