Stephen Hawking’s superspace and supergravity blackboard: an iconic artefact in the making

Public fascination

Three years ago, the Science Museum first experienced the attractive power of the superspace and supergravity blackboard with its audiences.

The Stephen Hawking at Work exhibition was planned to open in February 2022. This is a small, travelling display of a dozen of the most representative objects from the recent acquisition of Stephen Hawking’s office (see the article by Blyth and Boyle in this issue), featuring a selection of items that best referred, in an interwoven way, to his scientific work, celebrity profile, and approach to living with a worsening disability.^[1]

Just a few months before Stephen Hawking at Work’s opening date (while the blackboard was still on display in at the Library of the Catholic University (KU) of Leuven, Belgium – see Redler-Hawes’s article in this issue), the coronavirus’s omicron variant started to spread rapidly, causing the reintroduction of restrictions to onsite work and travel. At the end of 2021 we were uncertain if we would be able to open on time in February, and we especially doubted that the blackboard would find its way back from Belgium for whatever exhibition we could offer. We only made modest mention of it in press releases, in case it would not be there, and the display was designed to work well in its absence.

With considerable effort, the blackboard was returned home to us at the end of January. And despite its low profile in the lead-up to the opening, it immediately stole the show, starting from the very moment journalists were conducting their review visits near opening day.

Back then we had other worries that now seem (thankfully) unnecessary. We were concerned that our audiences might like some of the objects on display ‘a bit too much’; we worried in particular about Stephen’s wheelchair and communication systems: Would they reinforce the morbid fascination with Hawking’s disability that the theoretical physicist sought to de-emphasise in favour of his science?

This turned out not to be an issue at all. The wheelchair and other MND-related items were paid attention to by our audiences, but in a respectful way representative of shifting sensitivities.^[2]

It was instead the supposedly ‘difficult’ blackboard that fascinated everyone. Within a few days of opening, it had created a full-blown media circus. This contrasted with how, during the exhibition’s planning, we had debated with our interpretation team whether this blackboard and other references to his science would be perceived as too elitist by the Museum’s visitors. How wrong we were!

The blackboard’s visibility further snowballed as a newspaper suggested a Theory of Everything was hidden among all the cartoons, puns and 1980s jokes.^[3] Based on this premise, Hawking’s blackboard made it to the pages of the Guardian, Washington Post^[4] and primetime TV news in Britain and abroad. Not long after, a barrier had to be installed to keep enthusiastic visitors from their object of fascination, while conservators worried about the excess humidity, vibration and ubiquitous smudges on its protective glass, evidence of the prodding hands and noses of audiences enjoying, even appropriating this object – their object, as it is now owned by the nation.

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During the late-pandemic period of autumn 2021 to spring 2022, the curators of the exhibitions at Leuven and London were experiencing the co-construction of a ‘charismatic object’ in real time.^[5] Hawking had long recognised the appeal of this blackboard, displaying it continuously in his offices from the early 1980s onwards; but despite Hawking’s ubiquitous media appearances, the blackboard (unlike other iconic ‘objects’ like his wheelchairs and even his scientific formulas) had not made it to the wider public sphere during his lifetime. The blackboard was beloved by a narrow circle of acquaintances that experienced it first-hand in his office (Hertog, 2023). But unlike other objects in the collection, it was not part of the Hawking iconography during his lifetime, perhaps the difficulty and contested status of its science making it ‘unfit’ for wider public consumption. Alison Boyle, who had been curator of a 2012 birthday display, had long identified its potential; but it took the mobilising power of cosmologist and Hawking disciple Thomas Hertog to jump-start its public life as a showpiece. In Hertog and Redler-Hawes’s exhibition in Leuven in 2021, the blackboard was deliberately displayed among artwork with wild success. Then, upon its unveiling at the Science Museum, as part of the Stephen Hawking at Work exhibition, the blackboard turned out to appeal to audiences of all ages and interests upon first impression, even before having a chance to absorb the importance of its content or historical context. The blackboard has an undoubted “wow” appeal of a showpiece (see Maas, 2013, for more on this topic), which Hawking had already exploited while it was displayed his office. In Cambridge, visitors encountered the blackboard first as a surprise after entering, and we had unknowingly reproduced this ‘surprise’ first impression effect in 2022 through the lack of advertisement for the item and its placement hidden from the outside of the display. We now deliberately reproduce this visceral reaction elsewhere; most recently in the Science Museum’s published book on Stephen Hawking’s office, where the blackboard content is what the reader first encounters, at that point unexplained, as the book’s end-papers (Highfield, 2024).

We must also remark that, unexpectedly, internal Science Museum practices further contributed to the blackboard’s perceived iconic status: our visitors did not just experience a blackboard, but also a heavy, anti-reflective protective frame, which loudly advertises the blackboard’s perceived fragility and value. As this Hawking exhibition tours the different sites of the Science Museum Group, we have an ongoing experiment on how this perceived uniqueness and fragility adds to the blackboard’s attractiveness: the original blackboard is not part of this national tour, but is replaced by an incredibly accurate facsimile, which hangs without any protection, and thus closer to how it would have been seen in Hawking’s office. While both original and facsimile are similarly loved due to their content, the blackboard in a heavy protective frame sparks more fascination, with crowds forming behind the barriers to take selfies as though at the ‘Mona Lisa’ or ‘Guernica’.^[6] The facsimile (assumed original by visitors before they read the text) allows a more casual and personal discovery by the visitor that reproduces how, for three decades, the blackboard hung casually in Hawking’s office with just a thin layer of lacquer for protection, exposed to the sunlight and brushing-by of visitors. The blackboard is a living experiment of conservation science not just in methods of preservation but also on the impact that the visibility of conservation methods have on the status of an object by advertising it as uniquely ‘fragile’ and ‘worthy of protection’.

The appeal of blackboards

Regardless of whether a blackboard contains the answer to the universe (there is no ‘42’ anywhere on ours), blackboards of mathematicians and especially theoretical physics have long exerted public fascination. They are one of the Hollywood tropes that signify ‘mad scientist’, though one based on their true centrality to theoretical scientists for the past two centuries, and for some purposes, still to this day.

They are also an object that older generations can relate to, evoking personal feelings on a wide spectrum from joy to trauma. Most relevant for this article, Hawking’s blackboard evokes those occasions when we turned our classroom blackboard into spontaneous collective artwork. Appropriately, its first public display, in Leuven, was among artists’ creations.

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That physicists’ blackboards already exerted fascination in the early twentieth century can be seen in the response to a famous one in Oxford left with a few formulas by Einstein in 1931. Jim Bennett’s exhibition in Oxford in 2005, Bye Bye Blackboard…from Einstein and others, and its accompanying creative events, provided a foundational moment for museums to reflect on the cultural role of blackboards in the twentieth century, with examples from a variety of strands of human activity.^[7]

While fascination with blackboards featuring prewar theoretical science already existed, it is after 1945, with the onset of the ‘nuclear age’, that physicists’ blackboards, along with theoretical physics in general, attained unique prominence. The obsession with secrecy to prevent Soviet spies from ‘stealing’ the atomic bomb fed the (somewhat misleading) notion that behind the success of the whole Manhattan Project were a few formulas that perhaps could be casually left somewhere in chalk (see, for example, Wellerstein, 2021, and Holloway, 1994). This misperception of theory was soon reinforced in the realms of science fiction^[8], which featured theories and chalkboard formulas that can save or end the world if they are not wiped off by the nonspecialist. Impermanent chalk scribblings could also be one of the postwar theoreticians’ tools to enact authority against their philistine bosses, the wider public and, we should emphasise, also against experimental physicists and other ‘frenemies’ (see, for example, Kaiser, 2005).^[9]

Media-savvy ‘playboy’ physicists of the postwar era made blackboards a key part of their public performance, which were now also recorded and published: multitudes of Richard Feynman’s blackboard photographs from his lectures are kept in the Caltech Archives, for example, with the final marks on his blackboard preserved among them, including the (rather solemn) ‘what I cannot create I do not understand’.^[10]

The fascination with blackboards even feeds on the expectation, reinforced by historians, that private or undecipherable utterings, like Citizen Kane’s “Rosebud”, hold the key to a person’s work or personality: as in the private drawings of the most brilliant and enigmatic mathematical mind of the century, Paul Dirac (Galison, 2000).

Finally, from about 1980 onwards there emerges an element of ‘vinyl nostalgia’ inherent in the choice by scientists and institutions to stick to the traditional chalkboard and make it part of their ‘branding’. Stephen Hawking’s Centre for Mathematical Sciences, the building complex in Cambridge where he spent the last two decades of his working life, a splurge of twenty-first century computer-generated post-modern architecture, is still deliberately chock-full of dusty chalkboard surfaces, as central features of its cafes, corridors, common rooms and offices.

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Traditional blackboards are a conversation starter with theoreticians of a certain age, who will talk at length about their irreplaceability for creative and communicative work, which (they claim) depends on arcane secondary features such as the texture of the chalk, speed limitation, cadence, sound considerations, and even posture and gestures. Barany and MacKenzie (2014) describe chalkboards in such contexts as an ‘ostentatious medium’. Such cultures insist on the stark differences of their medium compared to post-1990s whiteboards and dry markers.

It was the advent of personal computers that most seriously contributed to the chalkboard’s obsolescence, with projections and animations taking over some of the original function of the chalkboard. Their remaining uses, for casual, conversational communication, were gradually replaced by the white marker board. Computer programmers still love their white boards for prototyping, as do the younger, digital-native generations of physicists and mathematicians.^[11]

Stephen Hawking’s blackboard

All the above associations converge in subversive fashion in Hawking’s 1980 blackboard. In addition to being one of the objects in the Science Museum’s acquisition with the deepest scientific content, it immediately invites deep reflection due to Hawking’s peculiar circumstances. What does it even mean to say that it is “Stephen Hawking’s blackboard”? Did he even write on it himself? The answer reflects not just on Hawking’s disability, but on the wider collective nature of scientific research at the end of the twentieth century. And as I show later, the decidedly humorous tone of the scribblings and self-irony evoke a postmodern turn in theoretical physics from the 1980s onwards. How much Hawking appreciated self-irony highlights the aspect of his personality that most contributed to him becoming a public figure, facilitating for example appearances in the most popular comedy shows of his lifetime, from The Simpsons to Big Bang Theory. When questioned on TV why Hawking kept the blackboard in his office, Martin Roček, the then-student who is most visibly caricatured in it, proclaimed: “He had a great sense of humour.”

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The drawings on the blackboard were done during a scientific workshop on the new theories of superspace and supergravity in 1980. It later featured on the cover of the conference proceedings (Hawking and Roček, 1981), so we have chosen to call it Hawking’s superspace and supergravity blackboard, to distinguish it from the other, working chalkboard in his office.

None of this blackboard’s scribblings are by Hawking’s own hand (he had stopped writing on blackboards in the mid-1970s), but were made by a dozen collaborators during the workshop.

This deepens rather than detracts from the interest of the blackboard and indeed one of the reasons we chose it for the exhibition was to evoke the collective nature of scientific work, where Hawking’s co-authorship is evident, even if not drawn by his own hand. The anthropologist and Hawking ethnographer Hélène Mialet best describes how Hawking can be seen not in the uniqueness of his circumstances, but as a typical example of a late twentieth century scientist. Senior researchers rarely work on their own but are rather part of a distributed cognition system. Hawking’s disability just makes this more visible (Mialet, 2012). The blackboard, in all its silliness, is a manifestation of distributed cognition in chalk.

But beyond reflections on authorship and disability, the blackboard incites in its viewers a wide spectrum of questions: from the more ‘scientific’ “Does anybody understand what is in it?” through the cultural, for example, “Is that Kilroy^[12] behind the wall?” to one reflecting the conservators anxiety namely, “Could it just be wiped off?”

Hawking was the driving force behind the 1980 workshop which was set up to explore a fascinating new attempt at a unified theory called supergravity (see below for a more detailed explanation of the science). This was a new approach, unfamiliar to the Sputnik generation that Hawking belonged to. His precursors had done their theoretical discoveries in the 1960s and 70s using almost exclusively Einstein’s general relativity, developing it further with new tools; but until the mid-1970s, they largely kept well within Einstein’s ‘classical’ form, developed before quantum theory, and impervious to the great synthesis of particle physics, the Standard Model. Einstein’s great theory had been quite neglected between the 1930s and 1950s during a period of great advances in particle physics (particularly microphysics) leading to the Standard Model. Microphysics had much wider applications and instrumental overlaps with the Cold War’s military-industrial complex: Hawking’s generation benefitted when these instruments, methods and organisations of research (‘big science’) started to cross-over into cosmic research after Sputnik. Until the 1970s, relativity-based research remained stubbornly separate from microphysics. But through that decade veteran established minds like Richard Feynman, John Wheeler, Yakov Zel’dovich and Andrei Sakharov started to make timid inroads, followed by their disciples and upcoming stars like Stephen Hawking.

In contrast, supersymmetric theories (the content of this blackboard) emerged elsewhere, from new generations of mathematical physicists. Many of the old guard of cold war scientists never quite accepted this development. Yet Hawking, perhaps eager for revolutionary advances that could still take place within his lifetime (which he then feared would not be long), eagerly embraced these new theories, and helped bring them into the mainstream.

As would happen periodically through Hawking’s career, knowledge of a new research methodology (in this case supergravity) arrived through personal connections, via a postdoctoral researcher trained in one the new theory’s Meccas. On this occasion it was Martin Roček, the cartoon ‘Martian’ that features most prominently in the blackboard. Roček was recruited as postdoc at Cambridge out of the State University of New York in Stony Brook, where one of supergravity’s originators, Peter van Nieuwenhuizen, was based.^[13]

Roček and Hawking organised the 1980 workshop, which took place in Cambridge funded by the Nuffield Foundation, inviting the emerging figures working on this new theory. Today, the list of attendees reads like a Who’s Who of a generation of scientists – now starting to retire – working on varied strands of supersymmetry. Just a year before, a much larger foundational workshop on this new theory had been organised in Stony Brook (van Nieuwenhuizen and Freedman, 1979) but without Hawking. The Nuffield Workshop in Cambridge brought the emerging superstars across the pond, jump-starting a Cambridge specialty in this field for the coming decade.

Fittingly for Hawking’s sense of humour, much of what is on the blackboard is not a straightforward display of the ‘serious’ mathematical work within the formal sessions of the workshop, but rather a casual reminder of the silly interactions of a group of young geeky physicists in the early 1980s. The blackboard was placed in the break room,^[14] where participants spontaneously doodled on it over the course of the multi-day event, and a good portion of the cartoons and puns are rather silly references to the participants. Reflective of this period in theoretical physics, the blackboard’s ‘authors’ were mostly young, white men, except for Sylvester James Gates Jr – caricatured as afroed and beret-wearing, and Judy Fella, Hawking’s secretary at the time – modestly self-portrayed with the ironic caption ‘one of the fellas’. It was Judy who decided to preserve the blackboard and lacquered it after the workshop, so that it could feature as the cover image of the book with the event’s proceedings.^[15]

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After the proceedings were published, Hawking asked for the blackboard to be installed in his Silver Street office, where it was placed high on a wall of his old, cramped working space where he first became a celebrity.^[16] Two decades later, at the peak of his influence during the move to his Bond-villain-esque headquarters at the new Centre for Mathematical Sciences (CMS), Hawking insisted on making this blackboard one of the most prominent features of his new office.^[17] Throughout the first decade in his new headquarters, while he still directed graduate students as Lucasian Professor, the blackboard and a group photograph of its ‘authors’ covered the inner wall of the office, surprising visitors who had just entered the space.

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Both in Silver Street and the new CMS, the blackboard is remembered by eyewitnesses as a welcoming surprise when entering the office: a fun conversation starter, but one also inviting reflection on the status of theoretical physics at the turn of the twenty-first century.^[18]

As mentioned earlier, in our Stephen Hawking at Work exhibition, while trying to downplay the presence of the blackboard due to pandemic uncertainty and positioning it partially hidden behind the entrance, we unintentionally ended up reproducing this surprise element: “Woah, and what is THIS?” remarked one of the first journalists invited to tour the space.

In 2010 a new Lucasian Professor was appointed and Hawking stopped advising PhD students, transitioning into his final academic role in semi-retirement as Director of Research.^[19] Hawking’s public appearances took up more of his time during his last decade, aided by lighter academic burdens and also facilitated technological advances in his communication systems. Perhaps reflecting this more public persona, around 2014, the blackboard, which used to be placed at ‘working’ height, was moved higher up the wall to make space for the growing mementos of recent public activities, from a visit to the Vatican to singing together with Monty Python their ‘Galaxy Song’. In those later years, the blackboard did not feature in media appearances, perhaps deemed ‘too difficult’ for the general audiences – something which was proved wrong by the exhibitions in Leuven and at the Science Museum.^[20]

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The science on the blackboard: towards a Theory of Everything

So far, we have described the blackboard’s importance largely in terms of what Ad Maas (2013) calls a showpiece and iconic object. What makes our blackboard so unique, however, is that it also works as what Maas calls a ‘key piece’ of a particular moment in history: the search for a unifying theory, and representative of what I call postmodern physics. Most physicists now see this as a moment when, as sometimes happens in the history of the discipline, theory lost its anchoring in empirical observation.

Hawking’s blackboard is a monument to the early promising years of one of the candidates for a Theory of Everything that could unify quantum physics with general relativity. Hawking’s most significant scientific contribution, from 1974, was the theoretical discovery of what is now called Hawking radiation, the most successful ‘marriage’ of quantum physics and general relativity to date, developed to explain what happens at the event horizon, the edge of a black hole.

Hawking had made his early career as a ‘classical’ student of Einstein’s relativity among a generation that revived it to explain spectacular new discoveries of the universe, from the Big Bang at its origin, to entities such as quasars, pulsars and black holes (see, for example, Blum, Lalli and Renn, 2020). Hawking was part of a generation in constant informal communication with each other through correspondence and preprints (drafts of scientific papers for early circulation). In addition, in the second part of the century, cheaper, widespread air travel allowed much more intense in-person interaction by generations of jet-setting scientists. Hawking was even among the cohort that for the first time easily travelled behind the Iron Curtain and he was in permanent dialogue with Soviet scientists, who were developing their own version of Hawking radiation in parallel.^[21]

The discovery of Hawking radiation propelled Hawking from a temporary postdoctoral fellowship in Cambridge to a visiting professorship at Caltech where soon after he was offered a permanent position. Instead, Hawking chose a permanent position in Cambridge, where he returned in 1976 and where he was to remain for the rest of his life. While at Caltech and Cambridge, his fame grew in scientific circles: he was made the youngest ever Fellow of the Royal Society, and received the highest award of the Vatican’s Pontifical Academy of Sciences. In 1979 he was made Lucasian Professor, the same academic position once held by Isaac Newton and Paul Dirac.^[22]

Throughout all these developments Hawking’s motor neurone disease (MND) progressed, and he focused on the highest-impact scientific contributions that he could make in a life of uncertain length. With a prominent position at Cambridge, Hawking started taking advantage of his growing academic gravitas: the late 1970s signalled a transition towards larger-scale distributed collaborations where he steered theoretical advances by supervising students, obtaining funds, organising workshops and, increasingly, providing a public platform for their work.

Supergravity was also one of the first theories that Hawking learned and contributed to while unable to write by his own hand anymore. By then he communicated by garbled speech and gestures, and his equations were written by his students, who also ‘translated’ for those who did not know him well enough to understand his voice. This unifying theory candidate was one of several of Hawking’s ambitious projects after becoming Lucasian Professor, a platform that facilitated impact not as an individual researcher but as a larger-scale organiser, attracting brilliant minds from around the world and the funds to sustain their work and travels. This would also be the case with other theories, most successfully with cosmic inflation in the early-to-mid 1980s.^[23]

This collaborative style of work intensified after the total loss of Hawking’s speech in 1985. He organised workshops and directed students on variations of unifying theories starting with supergravity, then on to superstrings, M-theory and the ‘holographic’ approaches to the unification of physics of the early twenty-first century. Like a savvy hedge-fund investor, Hawking also inspired and welcomed nascent alternatives such as the causal set theory advanced among others by his first female student Fay Dowker (now at Imperial College).^[24] Hawking’s mobility and communication difficulties made him most valued as an intellectual partner to ‘think theories together’, his succinct comments often leading to new insights and propelling weeks-long calculation efforts. Perhaps more than his advancing disability, what slowed down his scientific productivity in the late 1980s and 90s was his worldwide celebrity after the publication in 1987 of A Brief History of Time.

Witnesses say that during the period between 1979 and 1985 Hawking was at the top of his ambition and optimism in heading the drive towards a final theory. In his 1979 inaugural lecture as Lucasian Professor titled ‘The Future of Theoretical Physics’ he predicted a Theory of Everything ‘by the end of the century’, and what he had in mind would be based on what later ended up on the superspace and supergravity blackboard. At the same time Hawking was assuming that he had years, not decades of life remaining. In an interview, Hawking said the Lucasian professorship had been given to him under the assumption that it would become ‘again available soon’^[25] – but he ended up retiring from it three decades later. The supergravity blackboard accompanied Hawking for the entirety of his long reign on the Lucasian throne.

An analysis of its imagery brings to life the scientific theories that were in creative development at the time. Beyond the jokes and broader cultural references on the blackboard (which readers of a certain age may catch), lies a much deeper scientific content relating to the shifts, developments and co-creation of important theoretical concepts. The principal motifs are creatures such as tadpoles, octopuses, squid and spiders. These are a reference to a mathematical feature called the Vielbein that is used in supergravity (Samtleben, 2007), and it has variations related to the number of supersymmetries and dimensions in the universe one is proposing. In German ‘vielbein’ refers to many-legged animals, hence the cartoons of creatures with different numbers of legs, each representing universes of so many supersymmetries. Their representation as creatures pre-dated the workshop, as one of the participants is wearing an octopus, or ‘achtbein’ T-shirt. Eight-legged creatures appear most frequently in the blackboard, as this happens to be the version of supergravity, N=8 supergravity, which was most favoured.

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Throughout the 1980s, supergravity was the underdog to the more famous superstring theories, based on the analogy of vibrating strings in universes with many extra dimensions. Visualisable string and musical analogies are quite popular with physicists, with a leading role in the revolutionary work by Louis De Broglie, Johannes Kepler and the Pythagoreans.^[26] This helps explain the quick rise of superstring theory compared to alternatives like supergravity. Asked today, theoreticians say that the problems of supergravity lay in its difficult calculations, and that nobody could quite visualise or understand its underlying meaning.^[27] But supergravity was the approach preferred by Hawking for two decades. Hawking himself admitted that he did not grasp it all, but as with other new theories, he still had enough understanding to facilitate progress through his students and collaborators roughly between 1980 and 1995.

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Supergravity would have benefitted from faster computers than were available at the time. But in any case, the theory’s (partial) redemption came in the mid-1990s, long after it had fallen out of favour as unintuitive and difficult to calculate. Supergravity is known or suspected to be (depending on who you ask) another manifestation, a low-energy limit, of the same underlying mathematics present in superstrings. In the mid-90s, Edward Witten demonstrated this identity, while marking the transition from superstrings to what he called M-Theory. This was reminiscent of earlier promising unifications of rival theories in physics such as that which occurred during the births of quantum mechanics and later quantum electrodynamics.^[28] Once Witten’s work consolidated the equivalence between superstrings and supergravity, Hawking became decidedly interested in superstring theory. As with Roček a decade earlier, he now learned it avidly through a disciple, in this case his PhD student Marika Taylor, who first brought superstrings to Hawking’s repertoire and contributed to its progression towards M-Theory while a student of Hawking’s.^[29]

Most striking of all, just as Hawking was dipping into superstrings, came the deepest insight from the generation working on supersymmetric theories. In 1997, Juan Maldacena from Princeton University published a preprint of his discovery of the so-called anti-de Sitter Space-Conformal Field Theory correspondence (AdS-CFT correspondence). This purely mathematical discovery linked a relativistic model on one side (the anti-de Sitter is a long-studied model system in general relativity, also well expressed in superstring theories), with a lower-dimensional system as used in the Standard Model.^[30]

The AdS-CFT correspondence excited theorists around the world, as it seemed to answer questions left by Hawking’s work in the 1970s. The AdS-CFT correspondence shows the uncanny encoding of the bulk or ‘volume’ of a system (which could be a black hole, or even the universe in its entirety) into the lower dimensional boundary or ‘surface’ of another. This is what is called the holographic principle, akin to how one can somehow encode a full three-dimensional object ‘within’ a flat surface. Some theorists think this is relevant for what happens with the event horizon at the edge of black holes, and in fact, the last scientific paper co-authored by Hawking followed up on this correspondence for solving the so-called information paradox: in classical relativity, the information of all that has fallen into the black hole is lost from the universe forever, something that should not happen once quantum physics is taken into account. But thanks to the holographic principle, perhaps information can remain encoded in some way at the event horizon’s surface.^[31] Moreover, one of the life specialties of Hawking consisted in adapting insights developed for understanding black holes, to investigate the universe in its entirety. In fact, the other theory Hawking was working on during his last years, with his former student Thomas Hertog, used the AdS-CFT correspondence at the scale of the entire universe, to understand the cosmos from its beginnings as such a hologram.^[32]

Such conceptualisations of the universe are speculative and difficult to ground empirically, just as the supersymmetrical approaches they are based on. But there is a wider scientific consensus that the AdS-CFT correspondence has uncovered something deeply fundamental that is relevant beyond specific theories. Perhaps most importantly, the supergravity/superstring theory developments that led to the holographic principle point back at an uncanny, fundamental, dimensional feature that led Hawking to the discovery of Hawking radiation in the first place. Years before Hawking’s discovery of black hole radiation came a perhaps deeper scientific contribution, from which this discovery of radiation is derived: Bekenstein-Hawking entropy. Black holes, as physical objects, unavoidably have the thermodynamic properties of temperature and entropy; Bekenstein and Hawking showed in the early 1970s that these thermodynamic properties are somehow encoded on the surface of the black hole’s event horizon (Almeida, 2021).^[33] It remains one of the central physical riddles how thermodynamics, a macroscopic theory considered to be a manifestation of averages, somehow still encodes deeper insight into the most fundamental microscopic aspects of the universe. This is a centuries-old question first contemplated by the likes of James Clerk Maxwell and Ludwig Boltzmann at the end of the nineteenth century, long before quantum physics and supersymmetric theories. This riddle continues to have an uncanny relevance in contemporary physics, as key to the understanding the interrelated notions of time, information, reversibility and entropy.

Black holes may turn out be one of the keys to unlock this ultimate mystery of thermodynamics: back in the 1970s, Bekenstein, Hawking and others made use of thermodynamics to figure out the most intriguing aspects of black holes, which back then were recently formulated, hypothetical entities. Half a century later, now that black holes are well-observed empirical facts, objects that can be studied with rapidly increasing precision, Hawking’s and Bekenstein’s most lasting contribution could be in the opposite direction: they provide the groundwork for using the black holes to gain the deepest understanding possible of the fascinating mysteries still hidden behind the centuries’ old thermodynamics and statistical mechanics. The first, modest step in this direction came with the analysis of data from the observed mergers of black holes provided by LIGO, the Nobel prize-winning gravitational wave observatory. Its scientists, which include Hawking’s close friend Kip Thorne, tested the prediction, based on Bekenstein-Hawking entropy, that the event horizon surface of the resulting black hole of a merger is larger than the sum of surfaces of the originating black holes. This is entirely different to the behaviour of ‘normal’, physical, three-dimensional objects, from raindrops to planets.^[34]

Half a century after the formulation of Hawking’s radiation and the birth of supergravity and superstrings, scientific interviewees admire Hawking’s uncanny ‘nose’ for one of the major riddles of the universe. And it is also an example of his trademark methodology: as in many of his key contributions new insight on the universe is enabled by using black holes as instruments of inquiry. This may turn out to be Stephen Hawking’s most enduring legacy as a scientist

‘The wrong science’ on display

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Supergravity and superstrings, shown to be manifestations of the same underlying mathematics, experienced their heyday in the late 1990s with Maldacena’s discovery, an extremely powerful insight into the mathematical structure of our world, independent of the physical validity of the theories. Bolstered by this finding, supersymmetric theories, while criticised by prominent physicists, remained popular among theoreticians until the 2010s when its predictions failed to materialise experimentally. This means that, unlike most objects on display in science museums today, this highly charismatic blackboard may be interpreted as showcasing or celebrating ‘the wrong science’. Contemporary curators and historians have nuanced understandings of scientific practice that has long superseded judgement of ‘right’ and ‘wrong’; yet, in our everyday practice, we must reflect how to interpret this complexity to potentially millions of visitors with varied understandings of science and with preconceptions of what to expect in museums.

Seen from today, supersymmetric theories are considered by the majority of physicists to be massive cul-de-sacs in the search for a physical theory that corresponds to empirical observation. Some criticise an entire generation led astray by the siren song of theories primarily supported by their mathematical ‘beauty’.

The pursuit of supersymmetry provided brilliant insights, leading to the holographic principle, which many scientists think will play a role in a unified explanation of both black holes and the origin and fate of the cosmos; and at the very least it already hints at something profound in the mathematical underpinnings of our universe.

Yet, as empirically verifiable physical theories, supergravity and other supersymmetric theories were ultimately failures. Especially in the last decade, since the discovery of the Higgs boson (which gave the late Peter Higgs a 2013 Nobel Prize), particle accelerators have not managed to find any evidence pointing in their direction. Supersymmetry was based on the premise that different forces and particles are manifestations of a smaller set of entities at the higher energies that existed at the beginning of the universe. The theory inevitably predicts new, unseen entities, including partner particles to the ones we know well. This would be similar to how, a century ago, Paul Dirac foresaw the positron as antiparticle of the electron based on symmetry considerations while pursuing a relativistic version of quantum mechanics.^[35] For example, supergravity implied the existence of ‘super-partners’ for gravitons, the particles mediating gravity. Theoreticians called them ‘gravitinos’ – which you can see mentioned ironically on the blackboard. Back in the 1970s, physicists were well aware that even the detection of the more widely accepted gravitons would remain empirically impossible due to their predicted weakness. The gravitinos of supergravity would therefore also remain purely hypothetical entities. The confirmation of supergravity and superstrings depended rather on the detection of other, more easily detectable ‘superpartners’ that came with these theories, and their potential detection was one of the drivers for the construction of a new generation of particle accelerators such as the American Superconductor-Supercollider. Alas, at the end of the Cold War this machine was cancelled (Riordan, Hoddeson and Kolb, 2015), leading to an experimental gap until CERN’s Large Hadron Collider started producing results in the 2010s. But in the decade since, no experimental evidence has been found. A majority of physicists are now convinced that supergravity, superstrings and the wider family of supersymmetric theories are among the spectacular failures of the past half century in what amounts to describing how our universe actually operates.

Stephen Hawking himself had moderated his optimism in finding a ‘final theory’ as time passed. In his inaugural lecture as Lucasian Professor in 1979 he had predicted that a unified theory would be found by the end of the century, and he had placed his bets on the N=8 supergravity that is most discussed in the blackboard. Interviewed over two decades later, he jokingly said that he still thought scientists would find a suitable final theory “within this century”, but it was now 2001.

Still, around the time the LHC started operation, Hawking said he hoped the machine would yield surprising results. If the collider instead just reliably found the Higgs boson (something that experts knew ‘must’ be found at those energies), and nothing else, the universe implied would be the most boring possible – and this is what has turned out to be the case.

During their early development in the late 1970s and 1980s, the earlier generations of physicists working on unified theories, including Richard Feynman, John Wheeler, and Bryce DeWitt, had been sceptical of the usefulness of nascent supersymmetric theories to describe the actual physical world. But the 1980s supersymmetric theories coincided with an instrumental winter that engulfed an entire generation, during which theory drifted apart from experiment and observation. This was entirely different to the preceding decades, during which Hawking’s generation came of age. Hawking’s early career as a theoretician had benefitted from frequent, new, spectacular experimental results. The discovery of quasars with radio telescopes had boosted the study of relativity in the early 1960s, and the cosmic microwave background proved the origin of the universe in a big bang. Satellite observations of Cygnus X-1 then made black holes a likely reality as early as the mid-1970s, without which Hawking radiation would have been a much more abstruse exercise. In fact, Hawking was hopeful that evidence of Hawking radiation would be detected very soon, still in the 1970s, by gamma-ray satellites.^[36]

One can see in that earlier era the ‘grounding’ role of the Cold War. The 1960s–70s generation was immersed in an understanding of physics for its potential practical uses, in a world where physical instrumentation for testing physical theories was often based on technologies developed for military use. It is not by chance that Soviet theoreticians were so prominent, and were in such fruitful conversation with those in the West.

Post-1980s supersymmetric theories started under a different, perhaps ‘postmodern’^[37] epistemic, political, and institutional constellation that sometimes even embraced non-empiricism. 1980s post-empirical theories benefitted from how, in previous decades, symmetry considerations in particle physics had indeed led to a series of the most powerful, Nobel Prize-winning theoretical synthesis of what had been an over-empirical ‘particle zoo’, leading up to the Standard Model. This incomplete^[38] yet empirically solid framework of the microscopic world that we currently have has now been further validated with the detection of the Higgs boson.

Supersymmetric theories can be seen as increasingly baroque elaborations of the methodology that successfully led to the Standard Model. They offered a way of unifying all fundamental forces of the universe, finding a role for gravitation among all the other forces; but these theories also predicted countless unobserved entities. Moreover, the families of theories resulting from supersymmetric principles can be tweaked endlessly to explain away unfavourable experimental results, often promising their detection by the next, more powerful generation of particle accelerators. A whole generation of superstring and related theories matured in an experimental vacuum, hoping to find experimental verification when the new generation of accelerators came online.

But since 2010 when CERN’s Large Hadron Collider started producing data, no evidence of supersymmetry has survived detailed inquiry, and rather, the ‘ugly’ and ‘boring’ non-supersymmetric Standard Model, despite its known incompleteness, is today more established than ever before.^[39] Supersymmetric theories continue to be tweaked to predict breakthroughs with the next generation of accelerators, but the unlikelihood that larger, even costlier accelerators would yield such data means they probably won’t be built in the next decades, at least not in democratic countries. Their cost is too disproportionate to their scientific impact on helping to find a ‘final theory’, especially when contrasted with cheaper experiments with other particles such as neutrinos, and with astrophysical observations (Woit, 2006; and Hossenfelder, 2018).

Paraphrasing what a physicist remarked in 2014 as experiments with the Large Hadron Collider (LHC) made supersymmetry less likely: these theories are a most beautiful and consistent theory of the universe; but not ours.^[40]

Conclusion

Throughout this article, we have followed the object biography, historical context and representativeness of Hawking’s superspace and supergravity blackboard with unique multiplicity of facets: on the one hand it is a charismatic object and its treatment and display at the Science Museum is adding to this status. It is a showpiece – an object that is attractive to its audiences even devoid of explanation and historical context. But the blackboard is also one of the most significant key pieces of the Hawking Collection: the blackboard was witness to a turning point in the history of late twentieth century science, indicative of the theoretical developments aiming to unify two great theories of physics. The blackboard best represents its postmodern zeitgeist, a characteristically self-ironic, light-hearted moment in physics which corresponded to a generations-long scarcity of empirical grounding, and which only ended in the 2010s with the coming into operation of the Large Hadron Collider. The Collider’s experiments shattered much of the aspirations of the generation doodling on our blackboard. The blackboard is relatively unique among museum artefacts in celebrating what turned out to be a magnificent scientific failure. Helge Kragh, the brilliant historian of ‘higher scientific speculations’^[41], remarked a decade before the LHC on the uncanny parallels between supersymmetry and a nineteenth century predecessor, ether vortexes. These were hypothetical entities to which a brilliant generation of physicists including Lord Kelvin and James Clerk Maxwell attached their highest hopes, but which then become not just obsolete, but forgotten by mainstream researchers after the relativity and quantum revolutions. But the siren call of ether vortexes diverted many among the most brilliant physicists, and was probably a necessary step to some of their lasting contributions.

At that time physicists worked individually, but strikingly, a century later, when physical inquiry is a much larger, collective enterprise, a whole generation with thousands of contributors still fell down a similar theoretical rabbit hole. These moments seem to be a recurrent, perhaps necessary stage of physical inquiry. A new, necessary role of museums, then, is to interpret failure as an inevitable part of the scientific inquiry, and one that also affects its most brilliant minds.

Institutions born around the turn of the twentieth century, including the Science Museum, kept few remnants of ether vortex theories in their collections, and never put them on display; generations of curators have worried about confounding their audiences and supporters with ‘wrong ideas’ in what is (still) expected by the public to be a national pantheon of ‘correct’ science. But, to continue with the same example, the pursuit of ether vortexes was a driving force behind still-celebrated experimental discoveries such as the electrons of J J Thomson, immortalised in the cathode ray tubes on display in South Kensington. Thomson continued to believe in these vortexes as an underlying mechanism behind his discovered particle.

We now have a unique opportunity to have this difficult conversation, as the undoubted ‘charisma’ of the blackboard will make it one of the beloved pieces of the Museum even before the audience has delved into its history and context in detail. It can then serve as a window into the collective nature of late twentieth century science and its connections to a cultural zeitgeist. But finally, in what is still an unexpected twist in museum environments, visitors can learn (if they don’t know it already) that the depicted theories, while still considered undoubtedly beautiful, ultimately failed in their scientific purpose to represent the world we live in.^[42]

Acknowledgements
The superspace and supergravity blackboard (2021-561/1) is part of Stephen Hawking’s office collection that was accepted in lieu of Inheritance Tax by H M Government from the Estate of Stephen Hawking and allocated to the Science Museum in 2021. Special thanks go to the conservation, design and exhibition teams throughout the Science Museum Group for their ongoing efforts to stabilise and display the blackboard. This article’s analysis of post-empirical physics was deeply enriched by the author’s participation in the research group ‘Historical Epistemology of the Final Theory Programme’, at the Max Planck Institute for the History of Science, Berlin.