Here’s a kind of initial edit of my piece and invisibility for Nautilus.
In unseen worlds, science crosses paths with myth.
It seems almost tautological to say that for centuries scientists studied light in order to comprehend the visible world. Why are things coloured? What is a rainbow? How do our eyes work? And what is light itself? These are questions that preoccupied scientists and philosophers since the time of Aristotle, including Isaac Newton, Michael Faraday, Thomas Young and James Clerk Maxwell.
But in the late nineteenth century all that changed, and it was largely Maxwell’s doing. This was the period in which the whole focus of physics – still emerging as a distinct scientific discipline – shifted from the visible to the invisible. Light itself was instrumental to that change.
Physics has never looked back from that shift. Today its theories and concepts are concerned largely with invisible entities: fields of force, rays outside our visual perception, particles too small to see even in the most advanced microscopes, ideas of unseen parallel worlds, and mysterious entities named for their very invisibility: dark matter and dark energy.
Things that we can’t see or touch once belonged to the realm of the occult. This simply meant that they were hidden, not necessarily that they were supernatural. But the occult became the hiding place for al kinds of imaginary and paranormal phenomena: ghosts, spirits and demons, telepathy and other ‘psychic forces’. These things seem now to be the antithesis of science, but when science first began to fixate on invisible entities, many leading scientists saw no clear distinction between such occult concepts and hard science.
To make sense of the unseen, we have to look for narratives. This means we fall back on old stories, enshrined in myth and folklore. It’s rarely acknowledged or appreciated that scientists still do this when they are confronted by mysteries and gaps in their knowledge. Those myths aren’t banished as science advances, but simply reinvented.
What was it about light that impelled this swerve towards the invisible? In the early nineteenth century Faraday introduced the idea of a field – an invisible, pervasive influence – to explain the nature of electricity and magnetism. In the 1860s Maxwell wrote down a set of equations showing how electricity and magnetism are related. Maxwell’s equations implied that disturbances in these coupled fields – electromagnetic waves – would move through space at the speed of light. It was quickly apparent that these waves in fact are light.
But whereas visible light has wavelengths of between about 400 and 700 millionths of a millimetre, Maxwell’s equations showed that there was no obvious limit to the wavelength that electromagnetic waves can have. They may exist beyond both limits of the visible range – where we can’t see them.
These predictions were soon confirmed. In 1887, the German scientist Heinrich Hertz showed that oscillations of electrical current could give rise to long-wavelength radiation, which became known as radio waves. It took less than a decade for the Italian Guglielmo Marconi to show that radio waves could be used to transmit messages across vast distances.
It’s hard to appreciate now how revolutionary this was, not just practically but conceptually. Previously, messages beyond shouting range had to be sent either by a physical letter or as pulses of electricity down telegraph wires. The telegraph was already extraordinary enough, but still it required a physical link between sender and receiver. With radio, one could communicate wirelessly through ‘empty space’.
It is no coincidence that these discoveries happened at the height of the Victorian enthusiasm for spiritualism, in which mediums claimed to be able to contact the souls of the dead. If radio waves could transmit invisibly between a broadcasting device and a receiver, was it so hard to imagine that human brains – which are after all quickened by electrical nerve signals – could act as receivers?
But what of the senders? Already scientists, familiarized to the concept of invisible fields, had begun to speculate about non-material beings that inhabit an unseen plane of existence. Maxwell’s friends Peter Guthrie Tate and Balfour Stewart, both professors of physics, published The Unseen Universe (1875), in which they presented the ether of Maxwell’s waves as a bridge between the physical and spiritual words. Some of the pioneers of the telegraph had already drawn parallels with spiritualism, calling it ‘celestial telegraphy’. Now the wireless spawned a vision of empty space – still thought to be filled with a tenuous fluid called the ether that carried electromagnetic waves – as being alive with voices, the imprint of invisible intelligences. All you had to do was tune in, just as radio enthusiasts would scan the airwaves for crackly, half-heard snatches of messages from Helsinki or Munich. Rudyard Kipling’s short story “Wireless” (1902) described a man who, feverish from tuberculosis, becomes a receiver for fragments of a poem by Keats, while elsewhere in the house a group of amateur radio operators picks up broadcasts from a nearby ship. While the ‘telegraph line’ of the spiritualist medium offered the comfort of words from departed loved ones, now the wireless seemed instead to make the spirit world a source of impersonal, often meaningless fragments adrift in an unheeding universe.
The discovery of X-rays by Wilhelm Röntgen in 1895 stimulated these imaginings yet more. X-rays, it soon became clear, were invisible rays at the other end of the spectrum from radio, with wavelengths much shorter than those of light. But what made X-rays so astonishing and evocative was that they not only were invisible but revealed the invisible – not least, the bones beneath our flesh, in an unnerving presentiment of death. In the late 1890s people flocked to public demonstrations at shows such as the Urania in Berlin or Thomas Edison’s stage spectacles in New York to watch their skeletons appear on fluorescent, X-ray-sensitive screens. X-ray photography seemed a straightforward extension of the ‘spirit photography’ that had become popular in the 1870s and 80s (faked or genuinely inadvertent double exposures), confirming the photographic emulsion as a ‘sensitive medium’ that could render the invisible visible. Others claimed to see evidence of new types of invisible rays recorded in photographs, and even to be able to photograph ‘thought forms’ and souls.
At the fin-de-siecle, invisible rays were everywhere, and no claim seemed too extravagant. There were cathode rays and anode rays, wholly spurious radiations such as N-rays and ‘black light’ (although ultraviolet light also acquired that name), and most famously, the ‘uranic rays’ that Henri Becquerel discovered coming from uranium in 1896. These streamed in an unchecked and unquenchable flow, suggesting a tremendous hidden source of energy that, through the work of Pierre and Marie Curie, Ernest Rutherford and others, was eventually traced to the nuclear heart of the atom. The Curies renamed these rays ‘radioactivity’.
There was an old cultural preconception that invisible ‘emanations’ could have life-enhancing agency, whether these were the ‘virtues’ ascribed to medicinal herbs in the Middle Ages or the ‘animal magnetism’ or ‘mesmeric force’ of the 18th century German physician Franz Anton Mesmer. We shouldn’t be surprised, therefore, that at first radioactivity too was widely believed to have miraculous healing powers. “Whatever your Ill, write us”, said the Nowata Radium Sanitarium Company in 1905, “Testimonials of Cases cured will be sent you.” ‘‘Therapeutic’ radium was added to toothpastes and cosmetics, and spa towns proudly advertised the radioactivity (from naturally occurring radon) in their waters. It wasn’t until the 1920s that quite the opposite was found to be the case: too late to save Marie Curie herself, or the Radium Girls – factory workers who had for a decade been licking paintbrushes dipped in radioactive paint for the dials of watches.
What all these discoveries told us was that the universe we perceive is only a small part of what is ‘out there’. There was a long tradition of ‘spirit worlds’ going back at least to the Middle Ages, when it was common belief that invisible and probably malevolent demons lurked all around us. These beliefs provided the unconscious template for making sense of the ‘invisible universe’, so that leading scientists such as the physicist William Barrett, who co-founded the Society for Psychical Research in 1882, could write a book like On the Threshold of the Unseen (1917) in which he proposed the existence of human-like invisible ‘elementals’. Another physicist, Edmund Fournier d’Albe, put forward the theory that the human soul is composed of invisible particles called ‘psychomeres’ possessing a rudimentary kind of intelligence. He suggested that this hypothesis could account for paranormal phenomena such as ghosts and fairies.
One of the most prominent of these ‘psychical’ scientists was William Crookes. A chemist and entrepreneur who served as the President of the Royal Society between 1913 and 1915, Crookes became famous when he discovered the new chemical element thallium in 1861. Yet he seems to have been particularly credulous of spiritualists’ claims, if not in fact even collusive with them. He was taken in by several mediums, including the famous Florence Cook – like many mediums a striking young woman who found it easy to manipulate the judgement of Victorian gentlemen of more advanced years. Crookes was convinced that “there exist invisible intelligent beings, who profess to be spirits of deceased people” (he evidently took this to be the sceptical view). To investigate the ‘psychic force’ that he thought mediums commanded, Crookes invented a device called the radiometer or ‘light mill’, in which delicate vanes attached to a pivot would rotate when illuminated by light. Although the reason for the rotation was not, as at first thought, due to the ‘pressure’ exerted by light itself, that pressure is a real enough phenomenon, and the radiometer helped to establish it as such. It was thus an instrument motivated by a belief in the paranormal that prompted some genuinely useful scientific work.
The same may be said of Crookes’ ‘radiant matter’, allegedly a “fourth form of matter” somewhere between ordinary material and pure light. In 1879 he claimed that this stuff existed in “the shadowy realm between known and unknown”, and suspected that it, like the ether, might be a bridge to the spirit world.
Radiant matter was another figment of Crookes’ over-active imagination. But this too bore fruit. He invoked radiant matter to explain a mysterious region inside the discharge tubes called the ‘dark space’. But it turned out that this dark region was instead caused by cathode rays, and Crookes’ research on this phenomenon led ultimately to the discovery of electrons and X-rays and, coupled with Marconi’s radio broadcasting, to the development of television. Indeed, several of the early pioneers of television were motivated by their paranormal sympathies, whether it is Crookes refining the cathode ray tube, Fournier d’Albe devising his own idiosyncratic televisual technology, or John Logie Baird, usually regarded as the device’s real inventor, who believed he was in spiritualistic contact with the departed spirit of Thomas Edison.
It is tempting to regard all this as a kind of late-Victorian delirium that engulfed dupes like Crookes – not to mention Arthur Conan Doyle, who famously believed in the photographs of the “Cottingley Fairies”, faked by two teenaged girls in Yorkshire. But there was more to it than that.
For one can argue that radio communication was simply representative of all modern media in that they are ghosts factories, forever manufacturing what in 1886 the psychic researcher Frederic W. H. Myers called “phantasms of the living”: disembodied replicas of ourselves, ready to speak on our behalf. Radio could conjure the illusion that the prime minister, or a film star, had become manifest, though disembodied like a phantom, in your sitting room.
How much more potent the illusion was, then, when you could see electronic ghosts as well as hear them. It might have seemed natural and harmless enough to refer to the double images of early television sets, caused by poor reception or bad synchronization of the electron beam, as ‘ghosts’ – but this terminology spoke to, and fed, a common suspicion that the figures you saw on the screen might not always correspond to real people. After all, they might already be dead. News reporters flocked to the home of Jerome E. Travers of Long Island in December 1953 to witness the face of an unknown woman who had appeared on the screen and wouldn’t vanish even when the set was unplugged. (The family had turned the screen towards the wall, as if in disgrace.)
By appearing to transmit our presence over impossible reaches of time and space, and preserving our image and voice beyond death, these media subvert the laws that for centuries constrained human interaction by requiring the physical transport of a letter or the person themself. We submit to the illusion that the voice of our beloved issues from the phone, that the Skyped image conjured on the screen by light-emitting diodes is the far-away relative in the flesh.
Who could possibly be surprised, then, that the internet throngs with ghosts – that, as folklore historian Owen Davies says, “cyberspace has become part of the geography of haunting”. Here too the voices and images of the dead may linger indefinitely; here too pseudonymous identities are said to speak from beyond the grave. More even than the telephone and television, the internet, that invisible babble of voices, seems almost designed to house spirits, which after all are no more ethereal than our own cyber-presence.
Contemplating the forms attributed to new invisible phenomena a hundred and more years ago should give us pause when we come to the phantasmal worlds of modern science. For we are still generating them, and their manifestations are familiar. It’s undoubtedly true that our everyday perceptions grant us access to only a tiny fraction of reality. Telescopes responding to radio waves, infrared radiation and X-rays have vastly expanded our view of the universe, while electron microscopes and even finer probes of nature’s granularity have populated the unseeably minuscule microworld. However, our theories and imaginations don’t stop there, and each feeds the other in ways we do not always fully appreciate.
Take, for example, the Many Worlds interpretation of quantum mechanics. There’s no agreement about quite how to interpret what quantum theory tells us about the nature of reality, but the Many Worlds interpretation has plenty of influential adherents. It supposes the existence of parallel universes that embody every possible outcome of the many possible solutions to the equations describing a quantum system. According to physicist Max Tegmark of MIT, “it predicts that one classical reality gradually splits into superpositions of many such realities.” The idea is derived from the work of physicist Hugh Everett in the 1950s – but Everett himself never spoke of “many worlds”. At that time, the prevailing view in quantum theory was that, when you make a measurement on a quantum system, this selects just one of the possible outcomes enumerated in the mathematical entity called the wavefunction – a process called “collapsing the wavefunction”. The problem was there was nothing in the theory to cause this collapse – you had to put it in “by hand”. Everett made the apparently innocuous suggestion that perhaps there is in fact no collapse: that all the other possible outcomes also have a real physical existence. He never really addressed the question of where those other states reside, but his successors had no qualms about building up around them an entire universe, identical to our own in every respect except for that one aspect. Every quantum event causes these parallel universes to proliferate, so that “the act of making a decision causes a person to split into multiple copies”, according to Tegmark. (More properly, they have always existed, but it’s just that things evolve differently in each of them.)
The problem is that this idea itself collapses into incoherence when you try to populate it with sentient beings. It’s not (as sometimes implied) that there are alternative versions of us in these many worlds – they are all in some sense us, but there’s no prescription for where to put our apparently unique consciousness. This conundrum arises not (as some adherents insist) as an inevitable result of “taking the math seriously”, but simply because of the impulse, motivated by neither experiment nor theory, to make each formal mathematical expression a ‘world’ of its own, invisible from ‘this one’. That is done not for any scientific reason, but simply because it is what, in the face of the unknown, we have always done.
Much the same consideration applies to the concept of brane worlds. This arises from the most state-of-the-art variants of string theory, which attempt to explain all the known particles and forces in terms of ultra-tiny entities called strings, which can be envisioned as particles extended into little strands that can vibrate. Most versions of the theory call for variables in the equations that seem to have the role of extra dimensions in space, so that string theory posits not four dimensions (of time and space) but eleven. As physicist and writer Jim Baggott points out, “there is no experimental or observational basis for these assumptions” – the “extra dimensions” are just formal aspects of the equations. However, the latest versions of the theory suggest that these extra dimensions can be extremely large, making these so-called extra-dimensional ‘branes’ (short for membranes) potential repositories for alternative universes, separated from our own like the stacked leaves of a book. Inevitably, there is an urge to imagine that these places too might be populated with sentient beings, although that’s optional. But the point is that these brane worlds are nothing more than mathematical entities in speculative equations, incarnated, as it were, as invisible parallel universes.
Dark matter and dark energy are more directly motivated by observations of the real world. Dark matter is apparently needed to account for the gravitational effects that seem to come from parts of space where no ordinary matter is visible, or not enough to produce that much of a tug. For example, rotating galaxies seem to have some additional source of gravitational attraction, beyond the visible stars and gas, that stops them from flying apart. The ‘lensing’ effect by which distant astrophysical objects get distorted by the gravitational warping of spacetime seems also to demand an invisible form of matter. But dark matter does not ‘exist’ in the usual sense, in that it has not been seen, nor are there theories that can convincingly explain or demand its existence. Dark energy too is a kind of ‘stuff’ required to explain the acceleration of the universe’s expansion, something discovered by astronomers observing far-away objects in the mid-1990s. But it is just a name for a puzzle, without even a hint of any direct detection.
It is fitting and instructive that both of these terms seem to come from the age of William Crookes, whose investigations with gas discharge tubes led him to report a mysterious region inside the tubes called the ‘dark space’, which he explained by invoking his radiant matter. It turned out that there was no such thing as radiant matter; the effects that led Crookes to propose it were instead caused by invisible ‘cathode rays’, shown in 1898 to be streams of subatomic particles called electrons. It seems quite possible that dark energy, and perhaps dark matter too, will turn out to be not exactly ‘stuff’ but symptoms of some hitherto unknown physical principle. These connections were exquisitely intuited by Philip Pullman in the His Dark Materials trilogy, where (the title alone gives a clue) a mysterious substance called Dust is an amalgam of dark matter and Barrett’s quasi-sentient psychomeres, given a spiritual interpretation by the scientist-priests of Pullman’s alternative steampunk Oxford University who sense its presence using instruments evidently based on Crookes’ radiometer.
It would be wrong to conclude that scientists are just making stuff up here, while leaning on the convenience of its supposed invisibility. Rather, they are using dark matter and dark energy, and (if one is charitable) quantum many worlds and branes and other imperceptible and hypothetical realms, to perform an essential task, which is to plug gaps in our knowledge with concepts that we can grasp. These makeshift repairs and inventions are needed if science is not to be simply derailed or demoralized by its lacunae. But when this happens, it seems inevitable that the inventions will take familiar forms – they will be drawn from old concepts and even myths, they will be “mysterious” particles or rays or even entire imagined worlds. These might turn out to be entirely the wrong concepts, but they make our ignorance concrete and enable us to think about how to explore it. The only danger is if the scientists themselves forget what they are up to and begin to believe in their own constructs. Then they will be like William Crookes and William Barrett, looking for spirits in the void, seduced by their own tales into thinking that they already have the answer.