Albert Hofmann was one of the most important scientists of our time, who through his famous discovery of LSD, crossed the bridge from the world of science into the spiritual realm, transforming social and political culture in his wake. He was both rationalist and mystic, chemist and visionary, and in this duality we find his true spirit.

In boyhood, he had experienced inexplicable, spontaneous transfigurations of nature while walking in the woods, which spurred him to investigate the nature of matter through chemistry. While researching ergot and its potential impact on blood circulation, he accidentally discovered a chemical key that unlocked a pathway to a profoundly altered state of consciousness, offering the potential for great insights into the workings of the mind and the cosmos.

After experiencing its power and its dangers first-hand on his infamous bicycle ride (70 years ago today, on 19 April 1943), Hofmann understood that LSD, if used correctly and with care, could be a vital tool for investigating human consciousness. In later research, he realised that the molecule had virtually the same chemical structure as those in plants used as sacraments for thousands of years by indigenous cultures around the world. He was also the first chemist to isolate the psychoactive compounds of psilocybin and psilocine, found in ‘magic’ mushrooms and the closely connected morning-glory seeds.

Following its discovery, LSD was acclaimed as a wonder-drug in psychiatry, speeding-up and deepening the healing process by accelerating access to psychological trauma. Between 1943 and 1970, it generated almost 10,000 scientific publications, leading to its description as ‘the most intensively researched pharmacological substance ever’.

It also had a broader and more profound effect on how science viewed the mind, changing the dominant view of mental illness from the psychoanalytical model to one understood by brain-chemistry and the role of neurotransmitters. The LSD-experience resembled looking through a microscope and becoming aware of a different reality — a manifest, mystical totality, normally filtered out and hidden from view.

Hofmann realised that a substance with such profound effects on perception was likely to arouse interest beyond the medical field — though he never expected it to find worldwide popularity as a recreational drug. But ‘the more its use as an inebriant was disseminated… the more LSD became a problem child’. These negative developments were not to Albert Hofmann’s liking. He was amazed that LSD had been adopted as the drug of choice by the mass counterculture, but once the genie was out of the bottle, the world could never be the same again.

Albert Hofmann during a discussion “about beauty” at the Zürich Helmhaus. Photo by Stefan Pangritz, Lörrach. Creative Commons License.

Harvard-Professor-turned-Pied-Piper Timothy Leary emerged as a messianic guru. The mass consumption of psychedelics that Leary advocated led to LSD’s prohibition in 1967, to the War on Drugs, and to the complete shutdown of all therapeutic use and scientific research involving the substance.

The legacy of LSD is as controversial as it is profound, and its effects on science, technology, politics, art, and music cannot be overestimated. Many creative pioneers of the era claim to have made their breakthroughs either under the influence of LSD, or as a result of insights gained from it. The IT revolution that grew into Silicon Valley is a prime example of this.

In recent years, despite huge obstacles, the experimental use of LSD is, very cautiously, beginning again. Earlier this year, the Beckley Foundation received the first ever permissions for a brain-imaging study of the effects of LSD on human participants, an undertaking that I promised Albert Hofmann I would carry out.

With other psychedelics, the renaissance in experimentation is well and truly underway. Projects have investigated the neural basis of the effects of psilocybin and MDMA, while other research in the USA and elsewhere has made vital first steps into uncovering the clinical efficacy of these drugs — for example, MDMA’s success as an aid to psychotherapy in treating Post Traumatic Stress Disorder.

The Medical Research Council in the UK recently gave a £550,000 grant to investigate the efficacy of psilocybin in treating depression, marking the first time (as far as we are aware) that a government body has funded psychedelic research. There is thus reason for renewed optimism that, as Albert Hofmann hoped, if people could learn to use LSD more wisely, once again ‘this problem child would become a wonder child’.

Amanda Feilding is the Director of the Beckley Foundation, which studies the effects of psychoactive substances and promotes drug policy reform. She is the co-editor of LSD: My problem child by Albert Hoffman with ethnobotanist Jonathan Ott. The Psychedelic Science Conference 2013 will be held in California 18-23 April.

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This year marks the 100^th anniversary of a remarkable discovery by an equally remarkable scientist. He is Henry Moseley, whose working career lasted a mere four years before he was killed in World War I shortly before his 26^th birthday. Born in 1887 in England, Moseley came from a distinguished scientific family. Both of his grandfathers — a mathematical physicist on his father’s side and an oceanographer on his mother’s side — and his father were fellows of the Royal Society. His own father, who died when Henry was just four years old, had also been a zoologist whose book had been praised by Charles Darwin.

Young Henry Moseley attended Eton College on a scholarship and began to show early academic promise. He then studied natural science at Trinity College, Oxford having again obtained a scholarship. He didn’t think much of his teachers at Oxford, whom he once described as being more interested in fox hunting than science. Moseley wasted no time in contacting Britain’s leading physicist, Ernest Rutherford, who was then at the University of Manchester. Rutherford obviously recognized a kindred spirit, accepting the young graduate even though he had only obtained a second-class degree in physics.

Henry Moseley. Photo from Eric Scerri’s collection used by permission from Emilio Segrè Collection.

After preliminary experiments involving radioactivity, which were proposed by Rutherford, Moseley began to develop an interest in X-rays, which had by then become a hot topic. After many years of debate as to their nature it was still unclear whether they consisted of waves or particles. Then in 1912, a breakthrough seemed to occur after von Laue in Germany suggested that X-rays might have very small wavelengths and might consequently be diffracted by objects as small as planes of atoms within crystals.  Even though this prediction was quickly confirmed others continue to wonder whether X-rays might still also have particulate properties.

At this point Moseley teamed up with Charles Darwin, the grandson of the Darwin, and produced a paper based on a detailed study of how X-rays behaved when reflected by metal targets. Soon Moseley, who had always had a keen interest in chemistry, began to examine how a sequence of elements following each other in the periodic table might behave when acting as targets for beams of X-rays. He began with experiments on a sequence of ten elements from calcium to zinc inclusive. He omitted scandium which falls immediately after calcium because he was not able to obtain a sample of it.

Nevertheless, the outcome was remarkably clear and simple. If the square roots of the frequencies of the diffracted X-rays were plotted against a series of whole numbers, a smooth graph was obtained. This meant that he had discovered a method for counting the elements and a means of finding which elements, if any, remained to be discovered. In 1914 he extended his study to encompass most of the known elements between aluminum and gold, and still the same simple relationship held out. In the remainder of his short life he immediately set about applying his method to many long-standing problems and some new ones.

First of all, the lightest elements in the periodic table had long been surrounded in mystery. The former use of atomic weights to order the elements suggested that one or perhaps two elements might be missing between hydrogen and helium, the two lightest known elements. Also, some authors had reported new spectral lines, which were attributed to possible missing elements called coronium and nebulium.

Secondly, there had been much confusion about known many rare-earth elements existed in the sixth row of the periodic table and whether some newly reported elements were genuine or not. Moseley personally examined samples of a supposed new element named celtium. By measuring the X-ray frequencies that this sample produced he confidently ruled against the existence of any new element.

Thirdly, and perhaps most importantly, he was able to resolve the long-standing controversy over the order in which the elements cobalt and nickel should be placed in the periodic table. The former approach of using increasing atomic weights to order the elements implied that nickel should come before cobalt. Moseley’s method showed otherwise because cobalt had the lower atomic number associated with its X-ray spectrum.

But alas all this brilliant work was cut short because World War I broke out and Moseley insisted on volunteering to fight in the trenches in spite of efforts to prevent him from doing so by Rutherford among others. He was killed on 10 August 1915 by a bullet to the head at the battle of Gallipoli in Turkey. It was left to others to apply his X-ray method further and it soon became clear that precisely seven elements remained to be discovered between the limits of the periodic table that stood between hydrogen and uranium.

Oddly enough, the fact that the search had been clearly narrowed down to just seven elements with known atomic numbers did not seem to diminish the level of controversy and argumentation over the next thirty or so years before they had all been correctly identified. The seven elements, all rather exotic, are protactinium (1917), hafnium (1923), rhenium (1925), technetium (1937), francium (1939), astatine (1940), and promethium (1945). Three of them, technetium, astatine, and promethium had to be artificially synthesized before their discovery could be confirmed. Almost all of these seven ‘discoveries’ were surrounded by controversy as well as acrimonious disputes of a personal and, in some cases, of a nationalistic nature. Above all the tale of these seven elements continues to affirm the essentially human and frail nature of scientific discovery.

Eric Scerri is a leading philosopher of science specializing in the history and philosophy of the periodic table. He is the author of A Tale of Seven Elements, The Periodic Table: A Very Short Introduction, and The Periodic Table: Its Story and Its Significance. He is also the founder and editor in chief of the international journal Foundations of Chemistry and has been a full-time lecturer at UCLA for the past twelve years where he regularly teaches classes of 350 chemistry students as well as classes in history and philosophy of science. He is also giving the Moseley Centennial Lecture at the American Physical Society April meeting on Monday, 15 April 2013, 10:45 AM–12:33 PM.

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Sir Arthur Conan Doyle claimed that he wrote the Sherlock Holmes stories while waiting in his medical office for the patients who never came. When this natural teller of tales decided to write a detective story, he borrowed the concept of a cerebral detective from Edgar Allan Poe, who had “invented” the detective story in 1841 when he wrote The Murders in the Rue Morgue. So, in 1887, the brilliant Holmes debuts in A Study in Scarlet. The second Holmes story, The Sign of the Four, is a rewrite of The Murders in the Rue Morgue (1841). Instead of an Orangutan scaling the unscaleable wall and killing the occupant, Doyle uses Tonga, a pygmy from the Andaman Islands to do the job. The third Holmes story, A Scandal in Bohemia, is a rewrite of Poe’s The Purloined Letter. Instead of seeking the Queen of France’s letter, Holmes must find the King of Bohemia’s incriminating photograph.

Doyle wrote a total of 60 Holmes stories and most of the time Sherlock Holmes and Dr. Watson share lodgings in London. Their very lives reflect the superior English education of that era. At 221b Baker Street the conversation is full of mathematical terms such as surds, conic sections, and the fifth proposition of Euclid. We hear about astronomy too: the obliquity of the ecliptic and the dynamics of asteroids. But Holmes is a chemist at heart. Before Watson even meets Holmes he is told by Young Stamford that Holmes “is a first-class chemist.” Almost every one of the tales contains a reference to some chemical. They range from elements like zinc (Zn) and copper (Cu), to industrial chemicals such as sulphuric acid and the dye Tyrian purple. Of course numerous poisons are mentioned, and several are used.

Watson, the narrator, makes Holmes’s devotion to chemistry very clear. While still a student Holmes spent his Christmas break working on experiments in organic chemistry. Holmes had a “chemical table” in their Baker Street flat. On at least one occasion the odors drove Watson to leave the premises. Another time Holmes suspended working on a case because he had “a chemical analysis of some interest to finish.” Would that Sherlock had solved more cases by chemical means, but still the chemist finds much of interest in nearly every one of the 60 tales.

Arthur Conan Doyle was also at the forefront of forensic innovation. Holmes used fingerprints (before Scotland Yard), footprints, dogs, document analysis (before the FBI started its document section), and cryptology. After Doyle’s death it was noted that,

“Poisons, handwriting, stains, dust, footprints, traces of wheels, the shape and position of wounds, the theory of cryptograms — all these and other excellent methods which germinated in Conan Doyle’s fertile imagination are now part and parcel of every detective’s scientific equipment.”

There is more science in the first half of the “Canon” and its prevalence has clearly affected the popularity of the individual tales. The Holmes stories have been ranked several times and the results consistently support the idea that those stories which contain science are preferred over those that do not. Even Conan Doyle’ own rankings agree with this. In 1927 he listed his favorite stories — 19 of them. Fifteen were from the first 30 stories and only four from the last 30. Other rankings yield the same result. In 1959 The Baker Street Journal listed the results of a poll which named the ten best and the ten worst Sherlock Holmes tales. Eight of the ten best were from the first half; while nine of the ten worst were from the last half. Sherlock Holmes was, and is, a detective that every scientist can love.

James F. O’Brien is the author of The Scientific Sherlock Holmes: Cracking the Case with Science and Forensics. Like our country he was born in Philadelphia on the Fourth of July, many years ago. He has degrees in chemistry from Villanova and Minnesota. He played college and professional basketball. He retired from Missouri State University as Distinguished Professor. A lifelong fan of Holmes, O’Brien presented his paper “What Kind of Chemist Was Sherlock Holmes” at the 1992 national American Chemical Society meeting, which resulted in an invitation to write a chapter on Holmes the chemist in the book Chemistry and Science Fiction. O’Brien has since given over 120 lectures on Holmes and science.

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Image credit: Cover of Beeton’s Christmas Annual for 1887, featuring A. Conan Doyle’s story A Study in Scarlet. Public domain via Wikimedia Commons.

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We all agree that heredity, previous experience, and environment influence our choices. But why do some claim that, fundamentally, free will is an illusion? The easy answer: Free will does not fit within a scientific worldview. Free will mysteriously brings about a choice, and a physical event, without a prior physical cause. A motive for denying free will is to explain away that mystery. It’s a good motive. Explaining mysteries is a motive driving the scientific endeavor.

Our strict sense of cause and effect came with Newton’s physics, “classical physics.” To an “all-seeing eye” that knew the position and velocity of each atom in the universe at a given moment, the entire future of universe would be known. The idea that every event, even every thought, has a prior cause is part of our Newtonian heritage; it’s the determinism of classical physics. Most arguments denying free will are ultimately based on this determinism. Classical physics provides an extremely good approximation for the big things we ordinarily deal with, but it’s just an approximation. It fails completely for the atoms and molecules that big things are made of. Reasoning about free will should not be based on classical physics, a fundamentally flawed physics.

Quantum physics, or quantum mechanics, is the most battle-tested theory in all of science. No prediction of quantum mechanics has ever been wrong. It applies universally, to the big as well as the small. One-third of our economy is based on things designed with quantum mechanics. A quantum measurement problem was recognized at the inception of the theory almost a century ago. Physicists usually present it in mathematical terms, where the human issue of free will is obscure. The quantum measurement problem is sometimes, more appropriately, called the observer problem, a name emphasizing that it can be seen directly in quantum-theory-neutral observations.

The observer problem arises because you can demonstrate that a small object had either of two contradictory properties. The usual property considered (in what is sometimes called wave-particle duality) is the property of extension, how big something is. You could, for example, demonstrate that an object had been compact, concentrated in some small location, like a grain of sand. Alternatively, you could demonstrate that the object had been not compact, that it was spread out over a wide range, like a patch of fog.

Problem: Since we feel that we could have demonstrated either of two contradictory properties, what was the “actual” property of the object before we chose which of the two contradictory properties to demonstrate?

The standard quantum physics solution: Accept free will as something beyond physics. (“The free choice of the experimenter” is our preferred physics usage, not “free will.”) The experimenter’s free choice of demonstration, without any physical force on the object, creates the “actual” property the object had.

An alternate solution: Deny free will. Quantum mechanics then requires a determinism that conspires to match the experimenter’s not-free choice to the “actual” property the object had.

Bottom line: Denying free will implies a mysterious conspiratorial determinism.

Bruce Rosenblum and Fred Kuttner are the authors of Quantum Enigma: Physics Encounters Consciousness. Bruce Rosenblum is currently Professor of Physics, emeritus, at the University of California at Santa Cruz. He has also consulted extensively for government and industry on technical and policy issues. His research has moved from molecular physics to condensed matter physics, and, after a foray into biophysics, has focused on fundamental issues in quantum mechanics. Fred Kuttner is a Lecturer in the Department of Physics at the University of California at Santa Cruz. He devotes most of his time to teaching physics after a career in industry, including two technology startups, and a second career in academic administration. His research interests have included the low temperature propoerties o solids and the thermal properties of magnets. For the last several years he has worked on the foundations of quantum mechanics and the implications of the quantum theory.

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Image Credit: Portrait of Isaac Newton (1642-1727) by Sir Godfrey Kneller (August 8, 1646 -October 19, 1723). Public Domain via Wikimedia Commons.

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By Claudio Tuniz

Advanced analytical methods, based on radioactivity and radiation, have recently revealed that therapeutic dental filling was in use during the Stone Age. As part of the team that performed the study, I worked with experts in radiocarbon dating, synchrotron radiation imaging, dentistry, palaeo-anthropology, and archaeology. Our discovery was based on the identification of an extraneous substance on the surface of a canine from a Neolithic human mandible.

In May 1911, Josef Müller, a naturalist from Trieste, found an ancient human jawbone embedded in a rock inside a cave near the village of Lonche, in present-day Slovenia. It was bearing a canine, two premolars, and the first two molars. The human remains were then taken to the Museum of Natural History in Trieste (where Müller would later become one of the Directors), and remained there out of the spotlights. A study was indeed published in 1936, which included an analysis by x-ray radiography, but nothing special was noticed, at the time, given the poor resolution of the images. The radiocarbon method had not been invented yet; hence the date of the remains was vague. As a general assessment, this individual was thought to be alive during the Stone Ages, in accordance with other archaeological finds, including remains of animals that are now extinct and some clay artifacts.

X-ray images of the Lonche jaw. The dotted yellow rectangles show the position of the longitudinal crack partially filled with beeswax.

First we obtained a high-resolution 3D virtual image of the full mandible using X-ray computed micro-tomography, a method similar to hospital CT scanning, but with a much better resolution. The images revealed that the canine had a long vertical crack. In addition, an area of enamel had worn away to create a large cavity, exposing the dentine (and thus producing a terrible pain!). To improve the 3D image we used a particle accelerator, called synchrotron, which was available in Trieste. This large facility, Elettra, produces an intense flux of X-rays, dramatically increasing the imaging performance. When we focused the synchrotron radiation beam on the canine, we noticed that some extraneous material was forming a thin cap that filled the cavity of its crown.

At this point we extracted a minute amount of the filling material from the canine and used a technique called infrared-spectrometry (that you can sometimes see in TV movies for crime scene investigations). This analysis provides ‘chemical fingerprints’ to identify materials of interest. After our visual inspection, we were convinced that the extraneous substance was some kind of natural resin, but infrared spectrometry analysis showed that it was beeswax.

X-ray imaging with synchrotron radiation reveal details of the dental crown: the thickness of the filling material,afterward identified as beeswax, is visible. Beeswax exactly fills the shallow cavity in the exposed dentine and the upper part of the crack).

To rule out a later post-mortem intervention, we had to fix the chronology of the materials under study. When you have organic substances, radiocarbon is the most precise dating method available. Using atom-counting techniques, the so-called accelerator mass spectrometry, only a minute amount of sample is necessary. To be sure, the radiocarbon analysis was performed in two independent laboratories. A bone sample of about one gram was collected from the mandible using a hand drill; its collagen was then extracted and subsequently measured in an Italian laboratory. The tiny beeswax sample (about one milligram) was dated in Australia. Radiocarbon measurements confirmed that both the mandible and the beeswax filling were about 6,500 years old, with a very small error range.

We had found the smoking gun! This was the earliest known example of therapeutic-palliative dental filling, going back to the Neolithic. The so-called Vlaška people, living then near the northern shore of the Adriatic Sea, used beeswax to fix their dental problems. Probably this was a common necessity, as it is well known that in the Neolithic humans were extensively using their teeth as tools, for weaving and other extra-masticatory activities.

Claudio Tuniz leads a programme on advanced x-ray analyses for palaeoanthropology at the Abdus Salam International Centre for Theoretical Physics. He was Assistant Director of the Abdus Salam International Centre for Theoretical Physics in Trieste . Previously he was Nuclear Counsellor at the Australian Embassy to the IAEA in Vienna and Director of the Physics Division at the Australian Nuclear Science and Technology Organization in Sydney. He is co-author of the book The Bone Readers (2009), and the recently published Radioactivity: A Very Short Introduction (2012). Read his blog post: How radioactivity helps scientists uncover the past.

The Very Short Introductions (VSI) series combines a small format with authoritative analysis and big ideas for hundreds of topic areas. Written by our expert authors, these books can change the way you think about the things that interest you and are the perfect introduction to subjects you previously knew nothing about. Grow your knowledge with OUPblog and the VSI series every Friday!

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Galileo Galilei by Domenico Tintoretto, 1605-1607.

Galileo cultivated an interest in Italian literature. He commented on the poetry of Petrarch and Dante and imitated the burlesques of Berni and Ruzzante. His special favorite was Ariosto’s Orlando Furioso, which he prized for its balance of form, wit, and nonsense. His special dislike was Tasso’s Gerusalemme Liberata (The Liberation of Jerusalem), which violated his notions of heroic behavior and ordinary prosody. Galileo tried his hand at sonnets, sketched plots in the style of the Commedia dell’Arte, and delivered much of his science in dialogues.

The literary side of Galileo is not a discovery; a large specialist literature is devoted to it. But there is a gap in scholarship between the literary Galileo and the rest of him. How were his choices in science and literature complementary and reinforcing? What might be learned from his pronounced literary preferences about the unusual and creative features of his physics? How does Galileo’s praise of Ariosto and criticism of Tasso, on the one hand, parallel his embrace of Archimedes and rejection of Aristotle on the other?

Usually Galileo enters his biography already possessed of most of the convictions and concerns that prompted his discoveries and precipitated his troubles. One reason for endowing him with such precocity is that the documentation for his life before the age of 35 is relatively sparse. In contrast, a quantity of reliable information exists for his later life, after he had transformed a popular toy into an astronomical telescope and himself from a Venetian professor into a Florentine courtier (that happened in 1609/10 when he was 45). By paying attention to his early literary pursuits and associates, however, it is possible to tease out enough about his circumstances as a young man to give him a character different from the cantankerous star-gazer, abstract reasoner, and scientific martyr he became.

A quarrelsome philosopher, half-professor and half-courtier, whose discoveries refashioned the heavens and whose provocative use of them brought him into hopeless conflict with authority, is an attractive subject for portraiture. Add Galileo’s life-long engagement with imaginative writing and the would-be portraitist has his or her hands full. But the resultant picture, even if well-executed, would be a caricature. Galileo initially made his living and gained his reputation as a mathematician. Leave out his mathematics and you may have a compelling character, but not Galileo.

The mathematician and the littérateur have different ways of arguing. To fit together, one sometimes must give way. Galileo’s great polemical work, Dialogue on the two chief world systems, which misleadingly resembles a work of science, frequently privileges rhetoric over mathematics. When the scientific arguments are weakest, the two protagonists in the Dialogue who represent Galileo (his dead buddies Salviati and Sagredo) outdo one another in praising his contrivances and in twitting the third party to the discussions, the bumbling good-natured school philosopher Simplicio, for ignorance of geometry.

The mathematical inventions of the Dialogue that Galileo’s creatures noisily rate as unsurpassed marvels are precisely those that have given commentators the greatest difficulty. These inventions are extremely clever but evidently flawed if taken to be true of the world in which we live. Commentators tend either to interpret the cleverness as shrewd anticipations of later science or to condemn the shortfalls as just plain errors. From my point of view, these marvels should be interpreted as literary devices, conundrums, extravaganzas, inventions too good not to be true in some world if not in ours. They are hints at the form, not the completed ingredients, of a mathematical physics. Galileo’s old Dialogue and today’s Physical Review belong to different genres. Unfortunately, just as the Dialogue was not intended to meet the requirements of accuracy and verisimilitude of modern science journals, so the journals don’t reward the sort of wit and style with which Galileo brought together his literary aspirations, polemical agenda, and scientific insights.

John Heilbron is Professor of History and Vice Chancellor Emeritus of the University of California at Berkeley. One of the most distinguished historians of science, his books include Galileo, The Sun in the Church (a New York Times Notable Book) and The Oxford Companion to the History of Modern Science.

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We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the week to explain some of the mysteries of the Higgs boson. Read the previous posts: “What is the Higgs boson?”, “Why is the Higgs boson called the ‘god particle’?”, “Is the particle recently discovered at CERN’s LHC the Higgs boson?”, and “How does the Higgs mechanism create mass?”

By Jim Baggott

The 4 July discovery announcement makes it clear that the new particle is consistent with the long-sought Higgs boson. The next step is therefore reasonably obvious. Physicists involved in the ATLAS and CMS detector collaborations at the LHC will be keen to push ahead and fully characterize the new particle. They will want to know if this is indeed the Higgs boson.

How can they tell?

I mentioned in the third post in this series that the physicists at Fermilab’s Tevatron and CERN’s LHC have been searching for the Higgs boson by looking for the tell-tale products of its different predicted decay pathways. The current standard model of particle physics is used to predict the rates of production of the Higgs boson in high-energy particle collisions and the rates of its various decay modes. After subtracting the ‘background’ that arises from all the other ways in which the decay products can be produced, the physicists are left with an excess of events that can be ascribed to Higgs boson decays.

Now that we know the new particle has a mass of between 125-126 billion electron-volts (equivalent to the mass of about 134 protons), both the calculations and the experiments can be focused tightly on this specific mass value.

So far, excess events have been observed for three important decay pathways. These involve the decay of the Higgs boson to two photons ( H → γγ), two Z bosons (H → ZZ → ι⁺ι^-ι⁺ι^-) and two W particles (H → W⁺W^- → ι⁺υ ι^-υ). You will notice that these pathways all involve the production of bosons. This should come as no real surprise, as the Higgs field is responsible for breaking the symmetry between the weak and electromagnetic forces, giving mass to the W and Z particles and leaving the photon massless.

The decay rates to these three pathways are broadly as predicted by the standard model. There is an observed enhancement in the rate of decay to two photons compared to predictions, but this may be the result of statistical fluctuations. Further data on this pathway will determine whether or not there’s a problem (or maybe a clue to some new physics) in this channel.

But the Higgs field is also involved in giving mass to fermions (matter particles, such as electrons and quarks). The Higgs boson is therefore also predicted to decay into fermions, specifically very large massive fermions such as bottom and anti-bottom quarks, and tau and anti-tau leptons. Bottom quarks and tau leptons (heavy versions of the electron) are third-generation matter particles with masses respectively of about 4.2 billion electron volts (about 4 and a half proton masses) and 1.8 billion electron volts (about 1.9 proton masses).

These decay pathways are a little more problematic. The backgrounds from other processes are more significant and considerably more data are required to discriminate the background from genuine Higgs decay events. The decay to bottom and anti-bottom quarks was studied at the Tevatron before it was shut down earlier this year. But the collider had insufficient collision energy and luminosity (a measure of the number of collisions that the particle beams can produce) to enable independent discovery of the Higgs boson.

ATLAS physicist Jon Butterworth, who writes a blog for the British newspaper The Guardian, recently gave his assessment:

If and when we see the Higgs decaying in these two [fermion] channels at roughly the predicted rates, I will probably start calling this new boson the Higgs rather than a Higgs. It won’t prove it is exactly the Standard Model Higgs boson of course, and looking for subtle differences will be very interesting. But it will be close enough to justify [calling it] the definite article.

When will this happen? This is hard to judge, but perhaps we will have an answer by the end of this year.

Jim Baggott is author of Higgs: The Invention and Discovery of the ‘God Particle’ and a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to pursue a business career, where he first worked with Shell International Petroleum Company and then as an independent business consultant and trainer. His many books include Atomic: The First War of Physics (Icon, 2009), Beyond Measure: Modern Physics, Philosophy and the Meaning of Quantum Theory (OUP, 2003), A Beginner’s Guide to Reality (Penguin, 2005), and A Quantum Story: A History in 40 Moments (OUP, 2010). Read his previous blog posts.

On 4 July 2012, scientists at CERN’s Large Hadron Collider (LHC) facility in Geneva announced the discovery of a new elementary particle they believe is consistent with the long-sought Higgs boson, or ‘god particle’. Our understanding of the fundamental nature of matter — everything in our visible universe and everything we are — is about to take a giant leap forward. So, what is the Higgs boson and why is it so important? What role does it play in the structure of material substance? We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the week to explain some of the mysteries of the Higgs. Read the previous posts: “What is the Higgs boson?”,“Why is the Higgs boson called the ‘god particle’?”, “Is the particle recently discovered at CERN’s LHC the Higgs boson?”, and “How does the Higgs mechanism create mass?”

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We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the week to explain some of the mysteries of the Higgs boson. Read the previous posts: “What is the Higgs boson?”, “Why is the Higgs boson called the ‘god particle’?”, and “Is the particle recently discovered at CERN’s LHC the Higgs boson?”

By Jim Baggott

Through thousands of years of speculative philosophy and hundreds of years of hard empirical science, we have tended to think of mass as an innate property (a ‘primary quality’) of material substance. We figured that, whatever they might be, the basic building blocks of matter would surely consist of microscopic lumps of some kind of ‘stuff’.

But this is not quite how it has worked out. There was a clue in the title of one of Albert Einstein’s most famous research papers, published in 1905: ‘Does the inertia of a body depend on its energy content?’ This was the paper in which Einstein suggested that there was a deep connection between mass and energy, through what would subsequently become the world’s most famous equation, E = mc².

We experience the mass of an object as inertia (the object’s resistance to acceleration) and Einstein was suggesting that the latter is determined not by mass as a primary quality, but rather by the energy that the object contains.

So, when an otherwise massless particle travelling at the speed of light interacts with the Higgs field, it is slowed down. The field ‘drags’ on it, as though the particle were moving through molasses. In other words, the energy of the interaction is manifested as a resistance to acceleration. The particle acquires inertia, and we think of this inertia in terms of the particle’s ‘mass’.

In the Higgs mechanism, mass loses its status as a primary quality. It becomes secondary — the result of massless particles interacting with the Higgs field.

So, does the Higgs mechanism explain all mass? Including the mass of me, you, and all the objects in the visible universe? No, it doesn’t. To see why, let’s just take a quick look at the origin of the mass of the heavy paperweight that sits on my desk in front of me.

The paperweight is made of glass. It has a complex molecular structure consisting primarily of a network of silicon and oxygen atoms bonded together. Obviously, we can trace its mass to the protons and neutrons which account for 99% of the mass of every silicon and oxygen atom in this structure.

According to the standard model, protons and neutrons are made of quarks. So, we might be tempted to conclude that the mass of the paperweight resides in the masses of the quarks from which the protons and neutrons are composed. But we’d be wrong again. Although it’s quite difficult to determine precisely the masses of the quarks, they are substantially smaller and lighter than the protons and neutrons that they comprise. We would estimate that the masses of the quarks, derived through their interaction with the Higgs field, account for only about 1% of the mass of a proton, for example.

But if 99% of the mass of a proton is not to be found in its constituent quarks, then where is it? The answer is that the rest of the proton’s mass resides in the energy of the massless gluons — the carriers of the strong nuclear force — that pass between the quarks and bind them together inside the proton.

What the standard model of particle physics tells us is quite bizarre. There appear to be ultimate building blocks which do have characteristic physical properties, but mass isn’t really one of them. Instead of mass we have interactions between elementary particles that would otherwise be massless and the Higgs field. These interactions slow the particles down, giving rise to inertia which we interpret as mass. As these elementary particles combine, the energy of the massless force particles passing between them builds, adding greatly to the impression of solidity and substance.

Jim Baggott is author of Higgs: The Invention and Discovery of the ‘God Particle’ and a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to pursue a business career, where he first worked with Shell International Petroleum Company and then as an independent business consultant and trainer. His many books include Atomic: The First War of Physics (Icon, 2009), Beyond Measure: Modern Physics, Philosophy and the Meaning of Quantum Theory (OUP, 2003), A Beginner’s Guide to Reality (Penguin, 2005), and A Quantum Story: A History in 40 Moments (OUP, 2010). Read his previous blog posts.

On 4 July 2012, scientists at CERN’s Large Hadron Collider (LHC) facility in Geneva announced the discovery of a new elementary particle they believe is consistent with the long-sought Higgs boson, or ‘god particle’. Our understanding of the fundamental nature of matter — everything in our visible universe and everything we are — is about to take a giant leap forward. So, what is the Higgs boson and why is it so important? What role does it play in the structure of material substance? We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the week to explain some of the mysteries of the Higgs. Read the previous posts: “What is the Higgs boson?”, “Why is the Higgs boson called the ‘god particle’?”, and “Is the particle recently discovered at CERN’s LHC the Higgs boson?”

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We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the week to explain some of the mysteries of the Higgs boson. Read the previous posts: “What is the Higgs boson?” and “Why is the Higgs boson called the ‘god particle’?”

By Jim Baggott

Experimental physicists are by nature very cautious people, often reluctant to speculate beyond the boundaries defined by the evidence at hand.

Although the Higgs mechanism is responsible for the acquisition of mass, the theory does not give a precise prediction for the mass of the Higgs boson itself. The search for the Higgs boson, both at Fermilab’s Tevatron collider and CERN’s Large Hadron Collider (LHC), has therefore involved elaborate calculations of all the different ways a Higgs boson might be created in high-energy particle collisions, and all the different ways it may decay into other elementary particles.

At CERN, the attentions of physicists working in the two main detector collaborations, ATLAS and CMS, have been drawn to Higgs decay pathways involving the production of two photons (which we write as H → γγ), a pathway leading to two Z bosons and thence four leptons (particles such as electrons and positrons, written H → ZZ → ι⁺ι^-ι⁺ι^-) and a pathway leading to two W particles and thence to two leptons and two neutrinos (H → W⁺W^- → ι⁺υ ι^-υ).

Finding the Higgs boson is then a matter of looking for its decay products — in this case the photons and leptons that result — at all the different masses that the Higgs may in theory possess. Just to make life more difficult, at the particle collision energies available at the LHC, there are lots of other processes that can produce photons and leptons, and this background must be calculated and subtracted from the observed decay events. Any events above background that produce two photons, four leptons or two leptons (and ‘missing’ energy, as neutrinos cannot be detected) then contribute to the evidence for the Higgs boson.

What the CERN scientists announced on 4 July was a statistically significant excess of decay events consistent with a Higgs boson with a mass between 125-126 billion electron volts, about 134 times the mass of a proton. This is definitely a new boson, one that decays very much like a Higgs boson is expected to decay. But, until the scientists can gather more data on its physical properties, they can’t say for sure precisely what kind of boson it is.

It’s also important to note that although the Higgs boson is predicted by the standard model of particle physics, there are theories that also predict the existence of a Higgs boson (actually, they predict many Higgs bosons). Until the scientists gather more data, they can’t be sure the new particle is precisely the particle predicted by the standard model.

We just need to be patient and stay tuned.

Jim Baggott is author of Higgs: The Invention and Discovery of the ‘God Particle’ and a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to pursue a business career, where he first worked with Shell International Petroleum Company and then as an independent business consultant and trainer. His many books include Atomic: The First War of Physics (Icon, 2009), Beyond Measure: Modern Physics, Philosophy and the Meaning of Quantum Theory (OUP, 2003), A Beginner’s Guide to Reality (Penguin, 2005), and A Quantum Story: A History in 40 Moments (OUP, 2010). Read his previous blog posts.

On 4 July 2012, scientists at CERN’s Large Hadron Collider (LHC) facility in Geneva announced the discovery of a new elementary particle they believe is consistent with the long-sought Higgs boson, or ‘god particle’. Our understanding of the fundamental nature of matter — everything in our visible universe and everything we are — is about to take a giant leap forward. So, what is the Higgs boson and why is it so important? What role does it play in the structure of material substance? We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the week to explain some of the mysteries of the Higgs. Read the previous posts: “What is the Higgs boson?” and “Why is the Higgs boson called the ‘god particle’?”

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We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the next week to explain some of the mysteries of the Higgs boson. Read the previous post: “What is the Higgs boson?”

By Jim Baggott

The Higgs field was invented to explain how otherwise massless force particles could acquire mass, and was used by Weinberg and Salam to develop a theory of the combined ‘electro-weak’ force and predict the masses of the W and Z bosons. However, it soon became apparent that something very similar is responsible for the masses of the matter particles, too.

The way the Higgs field interacts with otherwise massless boson fields and the way it interacts with massless fermion fields is not the same (the latter is called a Yukawa interaction, named for Japanese physicist Hideki Yukawa). Nevertheless, the Higgs field clearly has a fundamentally important role to play. Without it, both matter and force particles would have no mass. Mass could not be constructed and nothing in our visible universe could be.

In his popular book The God Particle: If the Universe is the Answer, What is the Question?, first published in 1993, American physicist Leon Lederman (writing with Dick Teresi) explained why he’d chosen this title:

This boson is so central to the state of physics today, so crucial to our final understanding of the structure of matter, yet so elusive, that I have given it a nickname: the God Particle. Why God Particle? Two reasons. One, the publisher wouldn’t let us call it the Goddamn Particle, though that might be a more appropriate title, given its villainous nature and the expense it is causing. And two, there is a connection, of sorts, to another book, a much older one…

Lederman went on to quote a passage from the Book of Genesis.

This is a nickname that has stuck. Most physicists seem to dislike it, as they believe it exaggerates the importance of the Higgs boson. Higgs himself doesn’t seem to mind.

Jim Baggott is author of Higgs: The Invention and Discovery of the ‘God Particle’ and a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to pursue a business career, where he first worked with Shell International Petroleum Company and then as an independent business consultant and trainer. His many books include Atomic: The First War of Physics (Icon, 2009), Beyond Measure: Modern Physics, Philosophy and the Meaning of Quantum Theory (OUP, 2003), A Beginner’s Guide to Reality (Penguin, 2005), and A Quantum Story: A History in 40 Moments (OUP, 2010). Read his previous blog post “Putting the Higgs particle in perspective.”

On 4 July 2012, scientists at CERN’s Large Hadron Collider (LHC) facility in Geneva announced the discovery of a new elementary particle they believe is consistent with the long-sought Higgs boson, or ‘god particle’. Our understanding of the fundamental nature of matter — everything in our visible universe and everything we are — is about to take a giant leap forward. So, what is the Higgs boson and why is it so important? What role does it play in the structure of material substance? We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the next week to explain some of the mysteries of the Higgs. Read the previous post: “What is the Higgs boson?”

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On 4 July 2012, scientists at CERN’s Large Hadron Collider (LHC) facility in Geneva announced the discovery of a new elementary particle they believe is consistent with the long-sought Higgs boson, or ‘god particle’. Our understanding of the fundamental nature of matter — everything in our visible universe and everything we are — is about to take a giant leap forward. So, what is the Higgs boson and why is it so important? What role does it play in the structure of material substance? We’re celebrating the release of Higgs: The Invention and Discovery of the ‘God Particle’ with a series of posts by science writer Jim Baggott over the next week to explain some of the mysteries of the Higgs.

By Jim Baggott

We know that the physical universe is constructed from elementary matter particles (such as electrons and quarks) and the particles that transmit forces between them (such as photons). Matter particles have physical characteristics that we classify as fermions. Force particles are bosons.

In quantum field theory, these particles are represented in terms of invisible energy ‘fields’ that extend through space. Think of your childhood experiences playing with magnets. As you push the north poles of two bar magnets together, you feel the resistance between them grow in strength. This is the result of the interaction of two invisible, but nevertheless very real, magnetic fields. The force of resistance you experience as you push the magnets together is carried by invisible (or ‘virtual’) photons passing between them.

Matter and force particles are then interpreted as fundamental disturbances of these different kinds of fields. We say that these disturbances are the ‘quanta’ of the fields. The electron is the quantum of the electron field. The photon is the quantum of the electromagnetic field, and so on.

In the mid-1960s, quantum field theories were relatively unpopular among theorists. These theories seemed to suggest that force carriers should all be massless particles. This made little sense. Such a conclusion is fine for the photon, which carries the force of electromagnetism and is indeed massless. But it was believed that the carriers of the weak nuclear force, responsible for certain kinds of radioactivity, had to be large, massive particles. Where then did the mass of these particles come from?

In 1964, four research papers appeared proposing a solution. What if, these papers suggested, the universe is pervaded by a different kind of energy field, one that points (it imposes a direction in space) but doesn’t push or pull? Certain kinds of force particle might then interact with this field, thereby gaining mass. Photons would zip through the field, unaffected.

One of these papers, by English theorist Peter Higgs, included a footnote suggesting that such a field could also be expected to have a fundamental disturbance — a quantum of the field. In 1967 Steven Weinberg (and subsequently Abdus Salam) used this mechanism to devise a theory which combined the electromagnetic and weak nuclear forces. Weinberg was able to predict the masses of the carriers of the weak nuclear force: the W and Z bosons. These particles were found at CERN about 16 years later, with masses very close to Weinberg’s original predictions.

By about 1972, the new field was being referred to by most physicists as the Higgs field, and its field quantum was called the Higgs boson. The ‘Higgs mechanism’ became a key ingredient in what was to become known as the standard model of particle physics.

Jim Baggott is author of Higgs: The Invention and Discovery of the ‘God Particle’ and a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to pursue a business career, where he first worked with Shell International Petroleum Company and then as an independent business consultant and trainer. His many books include Atomic: The First War of Physics (Icon, 2009), Beyond Measure: Modern Physics, Philosophy and the Meaning of Quantum Theory (OUP, 2003), A Beginner’s Guide to Reality (Penguin, 2005), and A Quantum Story: A History in 40 Moments (OUP, 2010). Read his previous blog post “Putting the Higgs particle in perspective.”

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The world famous Edinburgh International Festival has kicked off, beginning three weeks of the best the arts world has to offer. The Fringe Festival has countless alternative, weird, and wacky events happening all over the city, and the Edinburgh International Book Festival, is underway. Throughout the Book Festival we’ll be bringing you sneak peeks of our authors’ talks and backstage debriefs so that, even if you can’t make it to Edinburgh this year, you won’t miss out on all the action.

As you may know, our author Frank Close spoke with Peter Higgs on Monday. We put out a call for questions earlier on the blog, but didn’t anticipate the warm enthusiasm of the crowd over Twitter (follow Frank Close on Twitter at @CloseFrank). Thank you for all your updates, pictures, and encouraging comments. Here’s a quick recap:

And author Frank Close also sent us these two pictures:

Thank you to everyone for making this a great event!

Frank Close is a particle physicist, author, and speaker. He is Professor of Physics at the University of Oxford and a Fellow of Exeter College, Oxford. He is the author of several books, including The Infinity Puzzle, Neutrino, Nothing: A Very Short Introduction, Particle Physics: A Very Short Introduction, and Antimatter. Close was formerly vice president of the British Association for Advancement of Science, Head of the Theoretical Physics Division at the Rutherford Appleton Laboratory and Head of Communications and Public Education at CERN. Read more of what Frank Close has to say about neutrinos here and here. Read Frank’s reflections on the Nobel Prize nominations for the 4 July discovery.

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Logo courtesy of Edinburgh International Book Festival

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Stars: A Very Short Introduction

By Andrew King

What are you made of? You may never have thought about it before, but every atom in your body was once part of a star, even several stars in succession. And almost all the elements that make up your body — carbon, nitrogen, oxygen, and so on — would not exist at all without the stars.

How can I make such statements? Because astronomers know fairly well how stars work, and have overwhelming evidence to support these assertions and many others. Our understanding of how stars work has been growing for more than a century, in parallel with developments in physics, and is now very sophisticated.

We now know how stars live and how they die, and where to find their dead bodies. We understand how they make all the chemical elements beyond hydrogen, and how these elements are distributed through space, ultimately to make planets, and eventually in a few cases, life. We are learning how new stars are born from the ashes of older ones.

We know all this because stars are surprisingly simple physical systems, whose behaviour is governed by well-understood physical laws. Roughly speaking, we can model a star simply as a (very massive) ball of gas – almost entirely made of hydrogen, the simplest chemical element of all.

We can use physics to work out how a ball of gas like this would behave and evolve, and then compare these predictions with observations astronomers make of the stars around us.

Source: The Hubble Heritage Team (AURA / STScI / NASA).

We live very close to a star — the Sun — and our everyday experience immediately gives us some simple insights. First, we all know that the surface of the Sun is very hot, and gives us light and heat. This is after all what sustains almost all life on Earth, including our own. We survive by eating plant food which grew by absorbing sunlight, or by consuming meat from animals which ate plants.

The Sun is losing energy in sunlight all the time, and this fact already tells us that it must have a finite life; it must run out of energy at some point. Fortunately for us, it turns out that the Sun is only about halfway through an extremely long lifetime of about ten billion years, so we still have about five billion years to go.

You might wonder why, instead of gradually losing all this energy, the Sun does not simply cool down. Of course life itself would not exist on Earth after this happened, so we could never be there to see this melancholy event. But the Sun (fortunately for us) is actually forced to go on giving out sunlight in its prodigal way simply because its interior must be even hotter than its surface; if not, the pressure in the centre of the Sun would not be strong enough to support its enormous weight. The centre of the Sun must have a temperature of about 10 million degrees Celsius to stop the Sun collapsing to a much smaller (and dimmer) object.

A temperature like this is unimaginable, but has an enormous significance.

The gas in the centre of the Sun is so hot that hydrogen atoms can fuse together to make helium atoms. This fusion process is the same that gives the hydrogen bomb its frightening power. Every time it occurs, it releases huge amounts of nuclear energy. Normally this remains dormant, locked in the nucleus of every chemical element. The release is so enormous that just converting one kilogram of hydrogen into helium would supply the entire energy consumption of the entire world for 8 minutes, or the USA alone for about half an hour.

So fusing the nuclei of chemical elements together can release energy, and support the star against its own gravity. You can perhaps now guess how the other elements are made in stars. The temperature rises to the point where for example, helium atoms fuse, to make a combination of carbon and oxygen atoms, and so on. The centres of stars are the only places in the universe where gas is hot enough and dense enough to make these atoms. So take a look at the carbon atoms making up your skin; they were made in a star.

The Sun, and the myriad stars like it, shine because they can resist gravity by doing so. But in the end this resistance is futile: eventually every star exhausts its nuclear fuel and must collapse on itself under gravity, eventually making a cold dead star which can evolve no more.

Astronomers can find these stellar corpses as white dwarfs, neutron stars and black holes.

But these deaths can leave a legacy. As a star collapses towards death, it may throw off its outer layers of gas into space. These are enriched with the new elements created by fusion, and this process gradually adds these elements to all the matter in the universe. Eventually new stars, and often planets around them, form out of this material.

Which is where we came from.

Andrew King is Professor of Astrophysics at the University of Leicester.

The Very Short Introductions (VSI) series combines a small format with authoritative analysis and big ideas for hundreds of topic areas. Written by our expert authors, these books can change the way you think about the things that interest you and are the perfect introduction to subjects you previously knew nothing about. Grow your knowledge with OUPblog and the VSI series every Friday!

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Today the world famous Edinburgh International Festival kicks off, beginning three weeks of the best the arts world has to offer. The Fringe Festival has already begun in earnest with countless alternative, weird, and wacky events happening all over the city. The icing on the cake (for us at least) is the Edinburgh International Book Festival, which gets underway on Saturday. Throughout the Book Festival we’ll be bringing you sneak peeks of our authors’ talks and backstage debriefs so that, even if you can’t make it to Edinburgh this year, you won’t miss out on all the action.

First up: Frank Close prepares to interview Professor Peter Higgs in an event on Monday 13 August 2012. This will be the first time the pair will appear together at a public event since the announcement of the breakthrough boson discovery at the Large Hadron Collider.

By Frank Close

When I interviewed Peter Higgs at the Borders Book Festival in Melrose in June, he had been waiting 48 years to see if his eponymous boson exists. On July 4 CERN announced the discovery of what looks very much like the real thing. On August 13 I am sharing the stage with Peter again, this time in Edinburgh. We shall be discussing his boson and my book The Infinity Puzzle, which relates the marathon quest to find it. How has his life changed?

A century ago, Ernest Rutherford discovered the atomic nucleus. He did so with a piece of apparatus that sat on the top of a small bench, and shared in the experiments with two collaborators, Hans Geiger and Ernest Marsden. Half a century later, science was beginning to identify how matter was created in the aftermath of the big bang, 13.6 billion years ago. But why was the debris of that singular event not rushing hither and thither at the speed of light? How did structure emerge, such as atoms, which lead to molecules and even life?

In the space of a few months during the summer of 1964 Peter Higgs, and five others independently, discovered a mathematical answer to that question. That was itself a triumph, as any novel theory had to be consistent with the great pillars of physical wisdom: Einstein’s relativity theory and the laws of quantum mechanics. The theory of the “Gang of Six,” as they have become known, passed all the tests, but one strand remained. How could one make an experiment to verify if the theory was what nature actually uses, and not simply a piece of clever mathematics?

Peter Higgs uniquely answered that, with his insight that there should exist a massive particle, known in the trade as a “boson,” which has in consequence become known as the Higgs boson. The particle is unstable, so if you can produce many examples of it, and record what happens when they decay, you can hopefully prove the theory to be correct.

Higgs bosons were common in the first moments after the big bang, but have merged into an ubiquitous form of ether subsequently. The only effect of this all-pervading field, in theory, is that it gives fundamental particles mass, which leads to structure and form in bulk matter. However, if one could in a small region of space simulate the intense heat of the new-born universe, one might hope to make Higgs bosons bubble into view. To achieve such conditions, the Large Hadron Collider was built at CERN. Quite a contrast to Rutherford’s homely experiment, the LHC is 27 kilometres in circumference, the Higgs boson is detected by banks of electronic equipment the size of a battleship, and teams of thousands – engineers, physicists and computer scientists from around the world — collaborate to make it all possible.

The LHC is designed to recreate the early universe and reveal many profound truths, not just the Higgs boson. Nonetheless, many incorrectly associate it, including its total cost of billions of euros, with the Higgs alone.

In June I asked Peter: “If after all this effort you discovered a mistake in your calculations…” The question was left incomplete, as the audience laughed — nervously? In any event, Peter had no need to answer as on July 4, after 48 years, the wait was over. Next week I shall be asking him, like some interviewer at the Olympics with a gold medalist: “How does it feel?”

Perhaps more seriously, questions might include: Is it all signed sealed and delivered? Have you celebrated yet (and how)? What’s the future for the LHC? What’s the future for Peter Higgs? Or some other questions that you would like to pose… Post your suggested questions in the comments box below but be quick, I am on stage with Peter Higgs at noon, British Summer Time, on Monday 13 August 2012.

Frank Close is a particle physicist, author, and speaker. He is Professor of Physics at the University of Oxford and a Fellow of Exeter College, Oxford. He is the author of several books, including The Infinity Puzzle, Neutrino, Nothing: A Very Short Introduction, Particle Physics: A Very Short Introduction, and Antimatter. Close was formerly vice president of the British Association for Advancement of Science, Head of the Theoretical Physics Division at the Rutherford Appleton Laboratory and Head of Communications and Public Education at CERN. Read more of what Frank Close has to say about neutrinos here and here. Read Frank’s reflections on the Nobel Prize nominations for the 4 July discovery.

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The Periodic Table

By Eric Scerri

I just returned home from being interviewed for a new public television program on the mystery of matter and the search for the elements. It was very gratifying to see how keen the film-makers were on understanding precisely how Mendeleev arrived at his famous first periodic table of 1869. This in turn meant that I had to thoroughly review the literature on this particular historical episode, which will form the basis of this blog.

The usual version of how Mendeleev arrived at his discovery goes something like this. While in the process of writing his textbook, The Principles of Chemistry, Mendeleev completed the book by dealing with only eight of the then known 63 elements. He ended the book with the halogens, including chlorine, bromine and iodine. On moving on to the second volume he realized that he needed an organizing principle for all the remaining elements. Before arriving at any new ordering principle he started volume 2 by discussing another well-known group of elements, the alkali metals that include lithium, sodium and potassium.

Mendeleev then wondered what elements should be mentioned next and toyed with the idea of turning either to the alkaline earth metals like calcium, barium and strontium or perhaps some intermediate elements including zinc and cadmium which share some but not all the properties of the alkaline earths. Another possibility which he contemplated was a group containing copper and silver which show variable valences of +1 or +2 and so could represent a stepping stone between the alkali metals and the alkaline earths which display oxidation states of +1 and +2 respectively.

Then on 17 February 1869, Mendeleev’s world virtually stood still and it continued to do so for a further 2 or three days during which he essentially arrived at his version of the periodic table and the one that had the greatest impact on the scientific community. It is generally agreed that this was the discovery of the periodic table, although at least five other versions had been previously published, albeit rater tentatively.

Figure 1. Mendeleev’s sketched notes on the back on the invitation to visit a local cheese co-operative. The lower figures show his calculations of the differences between the atomic weights of sodium and lithium (23 – 14* = 9), potassium and magnesium (39 – 24 = 15), rubidium and zinc (85 – 56 = 20), cesium and cadmium (133 – 112 = 21). The lowest line of numbers is Mendeleev’s comparison of his own calculations with the previously published equivalent weights of Dumas, namely lithium (7), magnesium (12), zinc (32) and cadmium (56).

*In fact Mendeleev is using twice the value of the atomic weight of lithium which is seven, hence the value of 14. This seems to be an afterthought since the numbers written underneath 14 and 9 seem to be 7 and 16 in which Mendeleev considered the actual value of lithium, namely 7.

On the 17th of February Mendeleev decided against going on a consultancy visit to a local cheese co-operative in order to stay at home to work on his book. It appears that at some point in the morning he took the invitation to the cheese co-operative and turned it over in order to sketch some ideas about what elements to treat next in his book (figure 1). This document still exists in the Mendeleev Museum in St. Petersburg and it is frequently brought out of the coffers for visiting documentary film-makers wanting to capture Mendeleev’s crucial moment of discovery.

The sketched symbols suggest that Mendeleev’s first attempted to compare the alkali metals with the intermediate group containing zinc and cadmium. He calculated differences between pairs of elements belonging to each of these groups in the hope of finding some significant pattern. But he appears to have been disappointed because the differences between the corresponding elements he considered show no regular pattern.

Nevertheless, Mendeleevdid not quite dismiss the idea of following the alkali metals by the group containing zinc and cadmium because this is precisely what he did in a second classic document in which he now included many more known groups of elements in the first of two tables of elements which appear on the same sheet of paper (figures 2 and 3).

Figure 2. Mendeleev’s two preliminary periodic tables. In the lower table the alkali metals have been raised from the bottom of the table and placed between the halogens and the alkali earths.

Figure 3. Clarification of figure 2. The alkali metals have moved from close to the bottom of the upper table to a place between the halogens and the alkali earths in the lower table. This suggests Mendeleev’s decision to no longer place the intermediate elements (Cu, Ag or Zn, Cd) after the alkali metals as shown in the upper table.

Whereas the upper table shows the zinc and cadmium group directly above the alkali metals, the lower of the two tables shows a rearrangement in which Mendeleev has decided to place the typical alkaline earth metals next to the alkali metals by moving the alkali metals up the table as an entire block. The net result is that the halogens are followed by the alkali metals, which in turn are followed by the alkali earths. The consequence of this move is that the sequence of atomic weights now appears more orderly than it did in the earlier upper table on the same page. As a result of this simple change Mendeleev appears to have realized that a successful periodic table requires not only a correct grouping of elements in adjacent rows but also a set of smoothly increasing sequences of atomic weights.

Here then is Mendeleev’s ‘aha’ or ‘eureka moment’. Here is where he first sees that the periodic table is a display of chemical periodicity that is itself a function of the variation of atomic weight. For example, note the atomic weight sequence of Cl (35.5), K (39) and Ca (40) in the lower table as compared with the less pleasing, although still increasing sequence of S (32), Cl (35.5), Ca (40), in the upper table that he had arrived at earlier in the day. Alternatively, consider the placement of K (39) which seems out of place next to Cu (63) in the upper table as compared to its proximity with elements of similar atomic weights in the lower table.

The essential point seems to be that Mendeleev began by considered groups of chemically similar elements and that the notion of ordering according to atomic weight came to him later. And this document appears to be precisely where he arrived at this conclusion.

Interestingly, the current director of the Mendeleev Museum, Professor Igor Dimitriev, disagrees with this account of the development. He believes that the document sketched on the back of the invitation from the cheese co-operative (figure 1), did not precede the two-tables on a single sheet document (Figures 2 and 3). He does not believe that the document shown in figure 1 had such an influence of the development in Mendeleev’s thought process as has generally been supposed.

Dimitriev’s objections are based on his proposal that groups of elements were not widely recognized at this time and that it was rather the sequence of atomic number values that led the way for Mendeleev in the course of his discovery of the periodic table. But this may be a little short-sighted in my view, because if one looks further afield at the earlier evolution of the periodic table among other chemists, working in other countries, one finds that groups of elements had been well recognized for a long time prior to Mendeleev’s work. This includes the work of Döbereiner, Gmelin, Lenssen, Pettenkoffer, De Chancourtois, Newlands, Odling, Hinrichs, and Lothar Meyer just to mention a few relevant names.

There is little doubt in my own mind that the notion of groups of chemically similar elements was well rather established and that it would have been natural for Mendeleev, who followed the above named authors, to begin with this notion. On the other hand the idea of using the sequence of increasing atomic weights to order the elements was nowhere near as well-established and it had only been a few years since the Karlsruhe conference of 1860 at which atomic weights had been unified and rationalized to produce a more or less definitive list of values that every chemist agreed with.

But you the reader may now be thinking, “but surely Dimitriev knows all of this?”. I think the answer to this question is both yes and no. I suspect that his custodianship of the St. Petersburg museum and archives may have led Dimitriev to concentrate upon the work of Mendeleev above that of all others. Finally, could it be that Dimitriev, who like Mendeleev is a Russian, may have allowed national pride to influenced his judgment of the issue and to perhaps downplay the contributions of foreign scientists.

But let’s return to Mendeleev’s discovery. What did he do after he had produced the lower table in figure 2? The popular story is that he then set about playing a game of chemical solitaire or ‘patience’ using a set of cards that he had carefully made-up to include the symbols for all the known 63 elements and their atomic weights. The aim of this well-known game is to arrange the cards in two senses. First of all the cards must be in separate suits and secondly they must be in order of decreasing values starting with king, queen, knave, ten and so on reading from left to right. Unfortunately no such set of cards has ever been found among Mendeleev’s belongings which raises the question as to whether the story may be merely apocryphal. (The plot thickens further when one learns that Mendeleev kept almost everything as soon as he realized that he would become famous. No such cards have ever been found, although it could just be that Mendeleev had not quite realized his impending fame at this stage.)

But I don’t think it really matters whether the story of the cards is actually true or not. The game of chemical solitaire provides such a good analogy that it is more important to focus on that than trying to determine whether Mendeleev actually used this approach or not. In the case of the periodic table, there is a beautiful analogy given that the elements are arranged in groups as opposed to suits, and along another direction they are arranged in order of increasing values of atomic weights, as opposed to decreasing values on cards.

Although Mendeleev was a true genius for discovering the periodic table, there is a real sense in which the periodic system is inevitable and provided by Nature itself. It was just a matter of uncovering this profound truth. What I am trying to get at is that Mendeleev did not have any choice in how to arrange the elements. At the end of the day they had to be arranged in the same way as a deck of playing cards must be arranged in the game of patience. There is no two ways about it. When the game is completed everyone can see it.

It is the same with the arrangement of the elements. Although the pattern could only be dimly seen at the beginning this was partly because of inaccurate values of atomic weights and because the correct ordering principle had not yet been recognized. Once it was recognized the game was virtually over and it became a matter of filling-in the remaining details. Of course these details were not quite as trivial as I may be implying. They included an entire group of missing elements that neither Mendeleev nor anyone else had predicted — the noble gases. They included the discovery of several missing elements, many of whose properties Mendeleev succeeded in predicting rather well. They also included the vexing fact that atomic weight doesn’t provide the optimal ordering principle.

If atomic weight ordering is followed strictly as many as four pairs of elements occur in reversed positions. In order to clear up this further issue it had to wait until the discovery of atomic number in 1913 and 1914 but that will be the topic of a future blog. The broad outline of chemical solitaire was worked out by Mendeleev above all other contributors and it was first glimpsed on that famous day of 17 February 1869. (This is the date according to the older Julian calendar that was used in Russia at this time. It differs from the more recently developed Gregorian calendar that was introduced to many other western countries in 1582. In 1869 the difference between the two calendars amounted to 12 days.)

Eric Scerri is a chemist and philosopher of science, author and speaker. He is a lecturer in chemistry, as well as history and philosophy of science, at UCLA in Los Angeles. He is the author of several books including The Periodic Table, Its Story and Its Significance, Collected Papers on the Philosophy of Chemistry, Selected Papers on the Periodic Table, The Periodic Table: A Very Short Introduction, and the upcoming A Tale of Seven Elements. You can follow him on Twitter at @ericscerri and read his previous blog post “The periodic table: matter matters.”

The Very Short Introductions (VSI) series combines a small format with authoritative analysis and big ideas for hundreds of topic areas. Written by our expert authors, these books can change the way you think about the things that interest you and are the perfect introduction to subjects you previously knew nothing about. Grow your knowledge with OUPblog and the VSI series every Friday!

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Figures 1 & 2 from Mendeleev’s two incomplete tables of February 17, 1869.
Figure 1 source: Igor S. Dmitriev, “Scientific discovery in statu nascendi: The case of Dmitrii Mendeleev’s Periodic Law,” Historical Studies in the Physical and Biological Sciences, Vol. 34, No. 2, 2004.
Figure 2 source: B. M. Kedrov and D. N. Trifonov, Zakon periodichnosti…, Moscow: Izdatel’stvo “Nauka,” 1969 (via Heinz Cassebaum and George B. Kauffman, “The Periodic System of the Chemical Elements: The Search for Its Discoverer,” Isis, Vol. 62, No. 3, 1971).
Figure 3 Smith, J. R. (1975) ‘Persistence and Periodicity’, unpublished PhD thesis, University of London. Source: Eric Scerri.

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On 4 July scientists at CERN in Geneva declared that they had discovered a new particle ‘consistent’ with the long-sought Higgs boson, also known as the ‘God particle’. Although further research is required to characterize the new particle fully, there can be no doubt that an important milestone in our understanding of the material world and of the evolution of the early universe has just been reached.

Exciting times! But why all the fuss? What is the Higgs boson and why does it matter so much? Was finding it really worth all the effort?

The Higgs boson is important because it implies the existence of a Higgs field, an otherwise invisible force field which pervades the entire universe. Unlike other kinds of force field (such as a gravitational field) it points, but it doesn’t push or pull. It was invented in 1964 in attempts to explain how otherwise massless particles could acquire mass.

The mechanism works like this: Without the Higgs field, elementary particles such as quarks and electrons would flit past each other at the speed of light, like ghostly will-o’-the-wisps. The elementary particles that make up you, me, and the visible universe would consequently have no mass. Without the Higgs field mass couldn’t be constructed and nothing could be.

What actually happens is that these elementary particles interact with the Higgs field and are slowed down by it, as though swimming in molasses. We interpret this ‘slowing down’ as inertia and, ever since Galileo, we have identified inertia as a property of things with mass.

Many of the predicted consequences of the Higgs field were borne out in particle collider experiments in the early 1980s. But inferring the field is not the same as detecting its tell-tale field particle. On 3 July we had hypotheses and compelling theoretical structures. The following day we began to gather hard scientific facts. Our understanding took a giant leap forward.

The publication of Higgs: The Invention and Discovery of the ‘God Particle’ is timely, coming only six weeks after the announcement. But I had the idea for a book about the discovery of the Higgs boson in March 2010, just as CERN’s Large Hadron Collider was setting a new world record for particle collision energy. This is perhaps the first example of a book that has been largely written in anticipation of a discovery.

Precisely what kind of boson has been discovered remains to be seen, and there’s hope of more surprises yet to come.

Jim Baggott is author of Higgs: The Invention and Discovery of the ‘God Particle’ and a freelance science writer. He was a lecturer in chemistry at the University of Reading but left to pursue a business career, where he first worked with Shell International Petroleum Company and then as an independent business consultant and trainer. His many books include Atomic: The First War of Physics (Icon, 2009), Beyond Measure: Modern Physics, Philosophy and the Meaning of Quantum Theory (OUP, 2003), A Beginner’s Guide to Reality (Penguin, 2005), and A Quantum Story: A History in 40 Moments (OUP, 2010).

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Radioactivity: A Very Short Introduction

By Claudio Tuniz

Neanderthal was once the only human in Europe. By 40,000 years ago, after surviving through several ice ages, his days (or, at least, his millennia) were numbered.

The environment of the Pleistocene epoch was slightly radioactive, the same way it is today, but this was not Neanderthal’s problem. The straw that broke the camel’s back was the arrival of a new human, during an already stressful period of extreme and rapid environmental change. The new humans were slender, talkative, and had a round head with a straight face and no protruding brow. They rapidly conquered the steppes, tundra and forests, stretching from Gibraltar to Siberia, where the Neanderthal had been happily striving for hundreds of thousands years, moving around to cope with the vagaries of the weather.

The Neanderthals had broadened their carnivorous diet to include fish, particularly seashells and mollusks. A variety of naturally occurring radioactive atoms contaminated the food that Neanderthals ingested — about the same radioisotopes we eat today, except for some bias introduced by recent accidents like that of Chernobyl and Fukushima. They included uranium, thorium, their decay products and potassium-40, naturally present in rocks and soils. Their ingestion would contribute an absorbed dose of about 300 microsievert per year to Neanderthal’s body, similar to the dose you receive from your meals today.

As uranium accumulated in Neanderthal’s bones, scientists are now able to determine their age, back to 500,000 years ago, measuring the residual radioactivity. This can be done in a non-destructive way analyzing the weak flux of gamma rays emitted by the skull or other bone remains, using sophisticated germanium detectors and other nuclear physics tools. Ideally, these measurements should be performed in special laboratories like those under the Gran Sasso Mountain, in Italy, run by the Italian Institute of Nuclear Physics.  The noise from cosmic rays and environmental radioactivity is so low in these underground laboratories that scientists can reveal the neutrinos emitted by the uranium burnt in nuclear reactors thousands of kilometers away, with useful applications. For example, one could detect whether plutonium, a key ingredient for nuclear bombs, is illegally produced somewhere on the globe.

We will resume below the discussion on nuclear bombs and artificial radioactivity. First, let’s complete the inventory of natural radioactivity sources during Neanderthal times. Like in the present, a radiation of cosmic origin was bombarding the atmosphere, creating new natural radioisotopes that would enter the food cycle. One of these products was radiocarbon. After being produced 40,000 years ago, a fraction of the radiocarbon atoms that were originally present in the bone, about 8 per thousand, survived to the present. The fact that carbon-14′s half-life is 5,730 years makes it the perfect clock to measure with high precision the ages of bones during the last 50,000 years. Indeed, it can be used to study not only the history of the Neanderthals, including the length of their overlap with modern humans, but also that of other human species that existed 40,000 years ago, like Homo floresiensis, nicknamed the ‘hobbit’, whose bones were found in 2003 on a small Indonesian island.

Only the round-headed humans, who arrived in Europe from Africa 40-45,000 years ago, eventually survived. These humans become a global species. Their powerful minds allowed them to conceive art, music, new ways of hunting animals, and fighting different humans. Radioactivity-based clocks confirm that their appearance coincided with the demise of other human species and the extinction of the large animals of the Pleistocene, like Diprotodon and Genyornis in Australia and Smilodon in America.

By discovering natural radioactivity at the end of the nineteenth century, the so-called ‘modern humans’ became capable of reconstructing the detailed history of their ancestors, providing exact dates for the rock art of Chauvet in France and the ‘Venus’ of Hohe Fels in Germany 35,000 to 40,000 years ago.

These humans also learned, in the twentieth century, how to create their own form of radioactivity. While my generation was listening to the first songs of the Beatles and the Rolling Stones, the US and USSR were exploding nuclear bombs in the atmosphere, the ultimate expression of human insanity. Many of the techniques, including mass spectrometers and radiation detectors, useful for dating hominids, were developed by the same scientists who built these nuclear bombs.

The radiation produced by the explosions increased the amount of radiocarbon in the terrestrial environment until 1962, when it reached a concentration that was twice that of the pre-nuclear era. This was the time when Kennedy and the other representatives of the nuclear powers of the time signed the Nuclear Test Ban Treaty.

As a teenager, I received this spike of man-made radiocarbon in my bones. Since then, the concentration of the artificial radiocarbon in the environment has been decreasing, with a half-life of 15 years, due to the exchange of carbon with the biosphere and the oceans.

The radiocarbon bomb pulse offers new applications as a chronometer in forensic science, as shown in popular TV series like CSI and Cold Case. The radiocarbon analysis of a bone sample provides the time of death of an individual during the last 50 years with a precision of a few months. In recent years, this method was applied to investigate the mass killings carried out by the Nazis in Ukraine at the end of World War II and the war crimes perpetrated in the former Yugoslavia in the 1990s.

Some believe the destructive attitude of H. sapiens has deep roots.

Claudio Tuniz leads a programme on advanced x-ray analyses for palaeoanthropology at the Abdus Salam International Centre for Theoretical Physics. He was Assistant Director of the Abdus Salam International Centre for Theoretical Physics in Trieste . Previously he was Nuclear Counsellor at the Australian Embassy to the IAEA in Vienna and Director of the Physics Division at the Australian Nuclear Science and Technology Organization in Sydney. He is co-author of the book The Bone Readers (2009), and the recently published Radioactivity: A Very Short Introduction (2012).

The Very Short Introductions (VSI) series combines a small format with authoritative analysis and big ideas for hundreds of topic areas. Written by our expert authors, these books can change the way you think about the things that interest you and are the perfect introduction to subjects you previously knew nothing about. Grow your knowledge with OUPblog and the VSI series every Friday!

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