Alice Gorman, Dr Space Junk vs the Universe (Literary Review)

There's a question Alice Gorman must get asked at every party she attends, and after reading her book I'm still not entirely sure of the answer. What exactly does a "space archaeologist" do?

Let's establish some boundaries. Dr Gorman is not concerned with discovering if Stonehenge was a prehistoric observatory - that's archaeo-astronomy. Nor will you find her scouring antique shops in search of old telescopes - leave that to Bargain Hunt. And while some define space archaeology as the use of satellite imagery to investigate ancient sites, the self-styled Dr Space Junk instead describes herself on Twitter as being interested in "orbital debris, terrestrial launch sites, antennas, planetary landing sites, and popular culture". That's about as good a summary as you'll get.

There's nothing left of Sputnik 1, which burned up three months after lift-off, but America's Vanguard 1, launched in March 1958, is still in orbit - the oldest piece of human hardware in space. Naturally it holds a special place in Dr Gorman's heart: "our first piece of genuine space archaeology". It also serves as a reminder that for her profession, fieldwork poses special problems.

Still, there are places to visit. Dr Gorman's Australian homeland played a significant role in the space race: the Woomera test range launched rockets such as Blue Streak, designed in the late 1950s as Britain's nuclear deterrent. Blue Streak was progressively downgraded and finally scrapped in the early 1970s, but you can stand next to an almost complete one (there's no warhead) at the National Space Centre in Leicester. Or go to the Woomera Heritage Centre and get a selfie next to another relic of British cold-war technology, Black Arrow.

Dr Gorman has made both trips. Others sound less entertaining. Orroral Valley, 50km south of Canberra, was a satellite tracking station until the 1980s. Now there's "only the concrete footings of numerous buildings and antennas". A decade after the last bulldozers moved out and foraging kangaroos hopped in, Dr Gorman chose Orroral for her "first archaeological fieldwork on a space site."

Her findings? "No obvious artefact scatters; no personal objects; no bits of antenna... Occasionally there's a bit of recent rubbish near the picnic/parking area." She was not to be put off. "I wasn't so sure this curated surface would yield nothing to the eagle eye of the archaeologist... On one visit I noticed an old scrubbing brush lying outside the canteen building, the sturdy bristled kind with a wooden back..." As if that wasn't enough, "as the teams moved systematically through recording the artefacts, we became aware that there were quite a few cable ties... and it was the minor individual variations which were the most informative... This ubiquitous, seemingly simple object was raising all kinds of questions." Dr Gorman explores these questions in depth over several pages. Why were there so many cable ties at Orroral? I'll keep you in suspense for now.

Dr Space Junk has all the passion, enthusiasm and ebullience of an interpretive guide at a National Trust centre. The sort who fascinates you with minutiae for five or ten minutes, until you're wondering how you can make a polite escape. What her book lacks is structure and focus; the disjointed sections seem stuck together like a reformed pot that may have been glued the wrong way. It's not until page 120 that we get a clear statement of what space junk is, and how much might be up there: "the equivalent of 1000 African male adult elephants". Page one would have been a better place.

Back to Vanguard 1, though - the Dead Sea Scrolls of space archaeology. It was "tiny - the size of a grapefruit, as Soviet president Nikita Khrushchev joked somewhat nastily." Did he? I would have liked a reference, though none was given, and it was still nagging me 35 pages later when the analogy wheeled round again, prompting Dr Gorman into an analysis of its significance. The grapefruit, we learn, originated as a hybrid of pomelo and shaddock, is bitter due to the chemical naringin, was introduced to Florida in the 1800s... So why did Khrushchev choose it? Noting its role in dieting, Dr Gorman suggests the Soviet leader was "knowingly feminising the satellite."

Time to throw away the book and start googling. A dozen websites gave me Khrushchev's grapefruit jibe. Any one of those could have provided Dr Gorman with her cherished factoid, but none gave me the source I was seeking. So I dug deeper, and found that Khrushchev actually said, "it would take a lot of apelsinsputnik to compare with ours". He called Vanguard an orange - it was American journalists who turned it into a grapefruit. Now I suppose I should go and update Wikipedia.

Oh, and the cable ties? Turns out they were used for tying cables.

Oliver Morton, The Moon; Fraser MacDonald, Escape From Earth (Literary Review)

Doctor Dolittle in the Moon may be one of the animal communicator's less well known adventures, but it served as childhood inspiration for science writer Oliver Morton. In The Moon Morton considers our nearest cosmic neighbour in all its many forms: scientific, historic, cultural, artistic, political. With such an encyclopaedic agenda, a great deal inevitably has to be left out, though an incredible amount is still crammed in.

Dolittle's lunar excursion, published in 1928, was the seventh in Hugh Lofting's series about the doctor, and made use of the then-prevalent theory that the Moon originally flew off from the young molten Earth, leaving a gap that became the Pacific Ocean. Since the 1980s we have had a different picture. In the early solar system, between the orbits of Venus and Mars, there were two planets that some astronomers now call Tellus and Theia. A glancing collision at a speed of about ten kilometres per second destroyed both, their fragments subsequently coalescing into our world and its companion.

Lunar fiction goes back a long way: Lucian of Samosata imagined flying there in the second century AD. Fifteen hundred years later, Johannes Kepler's Somnium gave a detailed account of the Moon's inhabitants, while Kepler's English contemporary John Wilkins wondered if the Selenites were somehow descended from Adam.

As well as such historical nuggets, Morton's book is interspersed with sections of technical detail about the Moon's composition, orbit and gravitational influence. Of chief interest is lunar exploration - past, present and future. Morton is sceptical of Japanese billionaire Yusaku Maezawa's hopes of becoming the first lunar tourist. Last year Maezawa paid Elon Musk's SpaceX an undisclosed sum for a trip due to depart in 2023 - as long as the spaceship can be designed, built and tested on time.

Arranged in thematic chapters that will appeal to fact-hungry space enthusiasts, The Moon describes how early rocket pioneers such as the American engineer Robert Goddard paved the way for Wernher von Braun's V2 and the Apollo program. Fraser MacDonald's Escape From Earth offers a detailed account of a part of the story that is far less well known. While the V2 was being developed in Germany, American scientists were working on their own rocket programme, originally with the aim of helping aircraft take off from short runways. When captured German rockets were brought to the United States at the end of the Second World War it was realised that they could serve as the launch stage of a nuclear missile system. The man behind this was not von Braun but a Czech-born American communist activist, Frank Malina.

In contrast to von Braun, Malina is nowadays virtually unknown. Part of the reason, MacDonald suggests, is that the charismatic von Braun was so good at rewriting history: not only airbrushing his Nazi past but also erasing the achievements of his competitors. Malina, by contrast, was keen to credit his co-workers, even at risk of being undervalued himself. More importantly, though, Malina's pre-war left-wing affiliations - and his post-war opposition to nuclear weapons - made him politically suspect.

MacDonald, an academic historian, has drawn on copious archive material to uncover a tangled, fascinating story that is a mixture of science, politics and soap-opera. Malina himself comes across as somewhat colourless, devoted to his work and social causes, unable to understand why his wife was so unhappy despite his success. Even after they split, he still sent her his laundry. More vivid is Malina's collaborator Jack Parsons, a man who described himself as living "on Peyote, marihuana, morphine and cocaine." In 1941, seeing workmen in Pasadena tarring a roof with asphalt, Parsons had the brainwave of using it as a rocket fuel. Malina refined the idea into the two-part "hypergolic" system still in use. With the older Theodore von Karman - a prestigious theoretician who rated himself just below Newton and Einstein - they founded the Jet Propulsion Laboratory. It would go on to create numerous space missions.

Parsons began attending mystic ceremonies at a Hollywood mansion operating as an offshoot of Aleister Crowley's Ordo Templi Orientis. Working his way through the order's manual of sexual practices, Parsons began systematically abusing his teenage sister-in-law, Betty. In August 1945 a young naval officer, L. Ron Hubbard, entered the scene, took a fancy to Betty, and suggested that Parsons put his by-now substantial rocket fortune into a business venture. Hubbard went off with Parsons' money, his boat, and Betty. Parsons eventually got back the boat and some of his money, but not Betty who became the first Mrs Hubbard.

Malina's own marital breakdown led him to a therapist, Phil Cohen, whom he knew through communist circles. In fact Cohen was a snitch: his "analysis" was a way of gathering information for the House Un-American Activities Committee. Cohen's therapy consisted of cajoling patients into testifying against friends and colleagues.

Despite having J. Edgar Hoover on his tail, Malina escaped persecution: the drug-addled Parsons wasn't worth calling as a witness. Still obsessed with Crowley's "magick", Parsons continued dabbling in explosives until 1952 when, mixing chemicals in his kitchen for a special effects company, he blew himself up.

Self-styled genius Theodore von Karman felt the political heat when it emerged that his assistant, Bill Perl, had been operating as a key figure in the spy ring of Julius and Ethel Rosenberg. Karman hadn't noticed anything untoward, his head presumably in the clouds. He was honoured in old age by President Kennedy, and the official boundary of space - 100km above the Earth - is now named after him: the Karman Line.

Malina relocated to Paris where he worked first as a UNESCO official, campaigning for international scientific cooperation, then as an artist creating "electric-kinetic paintings" using a system of lights and motors he patented. He died in 1981, aged 69. When his ex-wife got the news she wrote in her diary, "I wonder even now if you really loved me, and now it's too late to ask." He is the enigma at the centre of an extraordinary, important yet neglected slice of space history.

Paul Strathern, Mendeleyev's Dream; Tim James, Elemental (Wall Street Journal)

On a cold, snowy morning in February 1869, Professor Dmitri Mendeleyev was preparing to make a two-hundred-mile journey from his home in St Petersburg to a conference of cheese makers. While the distinguished chemist sat at breakfast reading his itinerary, he turned the sheet to jot an idea. He forgot about cheese, missed his train, and after several days of intense effort arrived at the discovery for which he is famous: the periodic table of elements.

The title of Paul Strathern's book refers to how Mendeleyev - "a wild-haired, gnome-like figure" - made his breakthrough. Fond of the car game Patience, Mendeleyev made a deck of the fifty or so then-known elements and laid them out according to their various properties, seeking a regular and consistent pattern. Every attempt having failed, he fell asleep exhausted. The answer came to him in a dream: columns of similar reactivity and rows of ascending weight. Mendeleyev wrote it down as soon as he woke, published it two weeks later, and earned his place in scientific history.

You might suppose that Mendeleyev's Dream is all about the great man himself; in fact he only occupies the prologue and final two chapters. The other twelve take us through a history of chemistry beginning with the ancient Greek philosopher Thales who believed water to be the elemental substance of the universe; then Empedocles with his quartet of fire, water, earth and air; and on to khemeia, the ritual embalming of corpses. This Egyptian "dark art", Mr Strathern says, was the etymological root of the Arabic al-chemia and inspiration for the "gibberish" of European alchemists.

Taking a traditional view of intellectual history, Mr Strathern considers the seventeenth century as the era when the "new science" of chemistry could at last "shed its oriental esoteric past" in works such as Robert Boyle's The Sceptical Chymist, published in 1661. The trouble with this neat periodisation is it leaves much that in retrospect seems "ahead of its time", such as Hero of Alexandria's pneumatic machines from the first century AD, or the thirteenth-century monk Roger Bacon who "predicted steamships, automobiles, submarines and even flying machines".

Having emerged into the light of science we finally reach Mendeleyev and his deck of chemical cards. Laying them out in the right order he realised there must be gaps: elements remaining to be discovered. What did their pattern really signify? Those are questions Mr Strathern need not address, having reached the "culmination of a two-and-a-half-thousand-year epic". We might instead turn to Elemental, subtitled, "How the periodic table can now explain (nearly) everything". Again the title is slightly misleading, for this too is essentially a history of chemistry, albeit with a more complete timespan. And though the subject matter is basically the same, the presentation could hardly be more different. Mendeleyev's Dream is chronological, rather slow, and apart from an occasional quip, pretty sober. Elemental is a frenetic assortment of bangs and smells, gags and anecdotes. While Paul Strathern's book is the most historically comprehensive, Tim James' is the more scientifically informative, and the better of the two.

A science teacher by profession, Mr James knows how to get his audience's attention. Elemental starts by introducing us to a nasty green fluid called chlorine trifluoride, "the most flammable substance ever made". It can ignite almost anything it touches, even water. A spillage at a chemical plant in Louisiana burned a metre-deep hole through a concrete floor before fizzling out.

That chemical was first synthesized in 1930, too late to appear in Mendeleyev's Dream, but there is plenty of overlapping content from earlier times. In both books we find Thales tripping into a pit while looking at the stars, or the German pharmacist Hennig Brand discovering phosphorus after distilling huge quantities of urine. The eighteenth-century Swedish scientist Carl Scheele is hailed by Mr James as "the unluckiest man in the history of chemistry" while for Mr Strathern he "was perhaps the most unlucky scientific discoverer of all time". Scheele's misfortune was almost to have made several discoveries that instead went to other researchers.

Carl Scheele is part of scientific folk-history, and while his hard-luck reputation may be hackneyed, at least it's based on truth. Far more questionable is the much-told tale of dynamite inventor Alfred Nobel. He supposedly read his own premature obituary, headlined "The merchant of death is dead", and decided to set up a peace prize. As Tim James concedes, no one has ever been able to identify the newspaper article. It most likely never existed.

Elemental informs and entertains, with history serving mainly the latter purpose. Where the book excels is in answering those questions left hanging by Mendeleyev's breakthrough. Each element of the periodic table is a particular kind of atom, ordered by the number of protons in its nucleus. Chemical properties arise from the atom's outermost electrons, and it is the arrangement of those particles that accounts for the periodic table's orderly columns. We might be tempted to think of electrons as resembling planets orbiting a star; instead their wavy quantum nature gives rise to shapes that Mr James likens to dumbbells or balloons. He can then explain in admirably simple terms why, for instance, hydrochloric acid is not good for your skin, or why metals are shiny.

With his fondness for superlatives, Mr James introduces us to the "coldest chemical ever created" (a laser-induced union of sodium and potassium) and the sweetest, lugduname, "so sickly it induces vomiting". The rarest naturally occurring element is number 85, astatine - there's probably only about a gram of it in the entire Earth - while the heaviest is element 92, uranium. You can only pack so many positively-charged protons together in a nucleus before electrical repulsion splits the whole thing apart, releasing radioactive particles. Elements heavier than uranium were nevertheless produced artificially in the Manhattan Project and given names inspired by the planets beyond Uranus: neptunium and plutonium. The latter would seem a shoo-in for "most toxic poison", however Mr James says that "judging toxicity is not as a straightforward as you might imagine". He gives polonium the prize as deadliest element, while among chemical compounds the most lethal is botulinum toxin H. The A version, not quite as horrible, is Botox.

With its hand-drawn diagrams, whacky humour and assorted facts, Elemental is great fun, taking us to realms beyond anything Mendeleyev ever dreamed of. The periodic table currently stretches to element 118, oganesson. Scientists are trying to push higher, not knowing if there will ever be an ultimate limit. "And that's the whole point of science," says Tim James. "To see what might be possible."

Graham Farmelo, The Universe Speaks in Numbers (Literary Review)

Nima Arkani-Hamed, an Iranian-born theoretical physicist based at Princeton's Institute for Advanced Study, was trying to name a new concept when he met the novelist Ian McEwan in London's Science Museum. McEwan suggested "the aleph"; Arkani-Hamed instead went for "amplituhedron". That ungainly mouthful serves as climax to Graham Farmelo's rich survey of the growing connections between pure mathematics and fundamental physics. Farmelo is himself a physicist, with a particular interest in the subject's aesthetic dimension. He considers the claim often made, that good physics has to be beautiful, and if it's beautiful it has to be true. How does that apply to the ampli-whatsit? We'll come to that eventually.

The book begins with a brisk gallop through early attempts to quantify the universe, quickly reaching the nineteenth-century Scottish genius James Clerk Maxwell. Under-rated in his lifetime, Maxwell posthumously showed Einstein the way to relativity through equations uniting electricity and magnetism. Among Maxwell's other insights was a little paper, "On Hills and Dales", about contour lines on maps. Maxwell found a formula involving the number of summits and watercourses in a given region, and showed it also applied to their opposites (watersheds and bottoms, as he termed them). With hindsight it was an early contribution to a branch of mathematics called topology, specifically Morse theory. Nowadays that's important in the study of superstrings, the putative fabric of our universe.

Another hero of Farmelo's book is Paul Dirac, who found how to make quantum theory consistent with special relativity. As a result Dirac predicted there should be a particle like the electron but with opposite charge. Discovered soon after and dubbed the positron, it was the first instance of anti-matter; a family of particles predicted mathematically. Buoyed by this, Dirac proclaimed in 1939 that physicists seeking fundamental laws "should strive mainly for mathematical beauty".

The beauty in Maxwell's map formula was that it applied to two completely opposite cases: the highest or lowest features of a terrain. Maxwell found a similar but less perfect duality between electricity and magnetism. It's easy to isolate positive or negative electric charge - for instance by combing your hair to create "static" - yet magnets always have two poles. Dirac showed that in quantum theory there could be "monopoles", isolated particles of north or south polarity. It was another beautiful finding; does that mean it must be true? To this day, monopoles have never been detected.

Farmelo's account acquires an autobiographical dimension as he reaches the 1970s, when he was a graduate student in particle physics, and a succession of discoveries proved the protons and neutrons of atomic nuclei to be made of quarks bound by gluons. By the following decade, when I was making my own entry to the field, there was expectation that the fundamental particles and forces would soon be unified in a "theory of everything". The story since then - the second half of Farmelo's book - is a mixture of success and frustration. The discovery of the Higgs boson in 2012 confirmed a prediction made decades earlier. A huge host of other particles remain, like Dirac's monopoles, as-yet unseen. Most notably absent is any sign of supersymmetry, a theory considered "too beautiful to be wrong" by supporters. They assume it hasn't been observed because particle accelerators aren't yet reaching high enough energies. Unfortunately they can't predict what that threshold might be, or how much it would cost to achieve it.

During the years Farmelo has spent on this book he has worked in some of the world's most prestigious research centres, speaking with many leading theorists. Veteran Nobel laureate Steven Weinberg complained to him that the relative dearth of new discoveries from the Large Hadron Collider was "terribly disappointing". The far younger Jacob Bourjaily instead insisted that, "new mathematics is the new data."

Bourjaily, together with Nima Arkani-Hamed and others, has been working on a novel way of calculating the probabilities of particle interactions. The standard approach, pioneered by Richard Feynman, utilises diagrams representing various ways the processes might occur. Each diagram stands for a complicated mathematical expression, and all must be added together. Even a simple interaction can have hundreds of terms. The alternative involves a geometric object conceived for wholly unrelated reasons by nineteenth-century schoolteacher and polymath Hermann Grassmann. Roughly speaking, the volume of this abstract shape can be used to find the required probabilities for certain particles. Extending the idea leads to a more general object - the amplituhedron.

Feynman's approach was based on the assumption of particles moving in space and time. In the new scheme - it is argued - space and time emerge from the geometry. Might this turn out to be the greatest vindication of mathematical beauty as indicator of truth? Farmelo is cautious: "time will tell".

His book includes many other theoretical breakthroughs, such as Juan Maldacena's remarkable discovery in 1997 that some particle forces were equivalent to gravity in a higher-dimensional space. It was an example of the "holographic principle", named by analogy with the way that a hologram can capture three-dimensional images on a two-dimensional surface. Farmelo calls it "one of the great insights of twentieth-century science". The Maldecana duality, and others like it, hold the promise that problems intractable in one framework might be solvable in a counterpart model.

The trouble, though, is that these dualities have tended to involve "toy" theories with simplified features; for instance particles lacking mass, or space having the wrong number of dimensions. The hope among physicists is that these toys may shed light on reality, and perhaps eventually they will. Given the ever-increasing complexity of the mathematics, though, it's uncertain whether even the greatest brains will be able to figure it all out. At the conclusion of this dense yet rewarding survey, Farmelo wonders if Einstein's successors "will turn out to be descendants of HAL 9000". If that's true then the future might not be so beautiful for us humans.

Ian Stewart, Do Dice Play God? (Wall Street Journal)

You're tested for a medical condition and the result is positive. According to your physician there's a 10% chance it's a false result, and the condition only affects 1% of people like you. But 80% of affected people test positive - so what is the likelihood that you have the condition? Worrying comes naturally to us, probabilities don't, as Ian Stewart explains in his entertaining guide to the mathematics of uncertainty.

A standard approach to probability is "frequentism". If a fair coin is tossed many times, heads and tails will appear about equally, corresponding to probability 0.5 or 50%. But how do we know if a coin is fair? Even after a million tosses there might not be exact parity; it would require an infinite number to decide the matter completely. In fact Professor Stewart reports an experiment which showed that if a coin is tossed identically every time - using a specially designed machine - then whichever side is initially uppermost has a slightly greater chance of being on top when the coin lands. The fairness of coin tossing really resides in the variability of how it is done.

An alternative to frequentism is an approach pioneered by the eighteenth-century philosopher Thomas Bayes, who viewed probability as "degree of belief". Bayesian inference is a way of calculating probabilities from prior knowledge, and it provides the answer to the medical question posed above. The likelihood of having the condition, given a positive test result, turns out to be only 7.5%. Most people - including physicians given the question in a survey - guess a far higher figure.

Professor Stewart describes how similarly mistaken thinking had disastrous results for Sally Clark, an English woman who suffered the loss of her baby son in 1996. The presumed cause was Sudden Infant Death Syndrome, but when Mrs Clark lost a second infant in similar circumstances she was charged with murder. An expert witness said the likelihood of one such tragedy was 1 in 8500, for two it would be 1 in 73 million. Mrs Clark was found guilty and sentenced to life imprisonment; however the prosecution had made two crucial errors. One was to have neglected the possibility of a genetic factor that could make a second death more likely. The other was to have focused entirely on the probability of the event when the real question was the likelihood of guilt. Imagine winning the lottery and going to collect your reward, only to find yourself being arrested. Since the odds of winning are 175 million to 1, surely you must be a fraud? That kind of argument put Mrs Clark in jail, and although she was eventually freed on appeal, the same "prosecutor's fallacy" continues to be deployed in courtrooms.

As an antidote, Professor Stewart would like to see greater use of mathematics in legal cases, with "Bayesian network" computer algorithms weighing up relative probabilities. The legal profession is unenthusiastic - an English judge complained in 2013 that "to express the probability of some event having happened in percentage terms is illusory." Professor Stewart rejects that, but the judge surely had a point. How would an algorithm quantify the likelihood that a defendant is telling the truth, or that a witness's memory is accurate? "Science is the best route humanity has yet devised for sorting fact from fiction," Professor Stewart calmly assures us. Yet we also need to be sure we can sort good science from bad. The expert witness in Sally Clark's case was found guilty of professional misconduct and barred from further court work.

Professor Stewart can be forgiven for placing so much faith in his own particular discipline, and his explanations of concepts from statistical theory are certainly clear, if at times a little dry. As well as discussing applications in areas such as economics and meteorology, he makes room for the history of the subject, though if this book were a Wikipedia article there would be a great many "citation needed" flags. "It's said," we are told, that the Renaissance mathematician Girolamo Cardano predicted the date of his own death. How probable is that? At least we need only refer to a dictionary to confirm the various forms of mystic divination the author amusingly describes, such as haruspicy (reading animal entrails), tasseography (tea leaves), nephelomancy (clouds) or the once popular cromniomancy (onions).

Sociological tidbits like these are thrown in for light relief; Professor Stewart is most at home when dealing with intellectual abstractions, and his book culminates in some of the most challenging - the paradoxes of quantum physics. This is where probability theory - and its arcane generalisation, measure theory - come into their own. A particle such as an electron or photon is described by a wave function encoding the probability that it occupies a given location. Professor Stewart asks, "Is the wave function real?" Perhaps, he suggests, wave functions are like the average family. "No electron actually has one, but they all behave as if they did." Still, it only makes sense to speak of the average family because each real family contains real people. Wave functions would similarly need some underlying stuff - "hidden variables" - that Einstein favoured but Niels Bohr rejected. Professor Stewart describes recent experiments which indirectly support the hidden-variable idea. Tiny oil droplets moving on a vibrating fluid surface can be made to mimic the wave-particle duality of electrons or photons. It suggests, says Professor Stewart, that quantum particles might be riding on hidden "pilot waves" - though we would then have to ask what those are made of.

Professor Stewart also describes Schrödinger's Moon, a paradox larger than the infamous cat, arising from attempts to incorporate gravity in quantum theory. Oddly, though, given the overall theme of the book, he omits to mention quantum Bayesianism - QBism for short - which interprets quantum probabilities as degrees of belief. Professor Stewart considers Thomas Bayes "one of the great unappreciated heroes of mathematics", and while it is nice to see "the good Reverend" being duly celebrated for his posthumous influence in medicine and law, it would also have been appropriate to acknowledge his latest role at the frontier of physics.