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PAMELA bares all

The European collaboration PAMELA has put an end to months of speculation by claiming that its Earth-orbiting satellite could have found the remnants of dark-matter annihilation.

In a preprint uploaded to the arXiv server last week, the collaboration presents data suggesting that cosmic rays above the Earth’s atmosphere contain an excess of high-energy positrons. This excess, the authors say, “may constitute the first indirect evidence of dark-matter particle annihilations” — although they add that there could yet be other explanations, such as the presence of a nearby pulsar (arXiv:0810.4995).

The PAMELA data briefly saw the light of day on a presentation slide at a high-energy physics conference in Philadelphia, US, at the start of August. At the time scientists in the audience spoke of the implicit significance of a positron excess for searches of dark matter, an unknown entity that is believed to make up 23% of the universe’s energy budget. But because the PAMELA researchers were planning to submit their work to Nature, which has a strict embargo policy, they avoided making any comments of their own.

Given that our preliminary conference data are starting to be used by people, we felt this was a necessary step Mirko Boezio, PAMELA collaboration

In an unusual twist, however, it emerged that at least one conference attendee had taken photos of the fleeting slide when a month later other preprints began appearing on arXiv making analyses of the data.

“We wanted to make our final results available to the scientific community once the data analysis was finalized,” PAMELA member Mirko Boezio told physicsworld.com, pointing out that Nature permits its authors to upload preprints to arXiv. “Given that our preliminary conference data are starting to be used by people, we felt this was a necessary step — not least because it provides a proper reference that correctly acknowledges the whole PAMELA collaboration and is available to the scientific community at large.”

Lots of data

Launched in June 2006, the PAMELA (Payload for Antimatter/Matter Exploration and Light-nuclei Astrophysics) satellite was designed by institutions in Italy, Russia, Germany and Sweden to examine the nature of antiparticles in cosmic rays. Unlike other cosmic-ray missions, which mostly consist of short balloon flights, PAMELA operates in space where there is little noise from antimatter generated in the atmosphere. Moreover, the satellite has been working non-stop since its launch and will continue to do so until the mission ends after December 2009.

The result of this so far is a large body of cosmic-ray data which is both statistically robust and which extends high energies of about 80 GeV. It indicates that the fraction of positrons to electrons does not decrease steadily with energy, as would be suggested by theoretical “baseline” predictions (that is, predictions that only take into account the production of positrons from interactions between cosmic rays and interstellar gas). Rather, the positron fraction appears to rise after 10 GeV, implying that there is another, unknown source of positrons.

The PAMELA results are interesting, and they deserve the attention they are receiving Stéphane Coutu, HEAT collaboration

The PAMELA collaboration says that possibilities for this source could be a nearby pulsar or, more interestingly, dark-matter particle annihilations.

“The PAMELA results are interesting, and they deserve the attention they are receiving,” says Stéphane Coutu, an experimental high-energy physicist at Penn State University who has worked on the NASA-supported HEAT mission to study cosmic rays from balloons. But, Coutu adds, “the exact interpretation of what the PAMELA high-energy excess truly means will remain uncertain for some time, and the subject of much debate, I’m afraid.”

Positrons or protons?

Part of the debate over the PAMELA data will likely revolve around how effectively the satellite overlooks protons, which have the same charge as positrons and which are a thousand times more abundant in the cosmos. While a magnet spectrometer can effectively distinguish between an electron and positron by the sign of the charge, it is the length of the electromagnetic showers in an adjacent calorimeter that has to determine whether each positron is not in fact a proton.

The PAMELA collaboration says it has performed tests at the CERN lab near Geneva that showed that just one proton in 100,000 fools the calorimeter into believing it is a positron. But Coutu says that the satellite could have benefited from a “transition radiation detector” (TRD), which would have helped rule-out protons unambiguously. “If the discrimination capabilities of their instrument are any less than they think, as one could imagine in the absence of a TRD, then the outcome could be exactly what they observe: a rise with increasing energy in the fraction of positively charged particles, which could be due to something other than positrons themselves.”

Fermilab ‘ghosts’ hint at new particles

Physicists at the Tevatron collider at Fermilab in the US, which is enjoying extended status as the world’s most powerful particle collider while CERN’s Large Hadron Collider (LHC) awaits repair, have reported signals in their data that hint at the existence of new fundamental particles. Last week members of the CDF experiment, one of the Tevatron’s two huge particle detectors, posted a preprint detailing a large sample of proton–antiproton collisions that cannot be accounted for either by quirks of the CDF detector or by known processes in the standard model of particle physics (arXiv:0810.5357 , submitted to PRD).

If the result does turn out to be due to some unexpected new process, it would be the most significant discovery in particle physics for decades. However, almost a third of CDF’s 600 or so collaborators (including some entire university groups) decided not to put their names on the paper, many believing that publication was premature because more checks need to be done.

“This is a very interesting and statistically significant effect,” says CDF member Mark Lancaster of University College London, who was one of those who removed his name. “The spirit of this paper is to get the result out there so that it can be checked by others, but the analysis is a work in progress.”

No claims

Claiming a discovery of physics beyond the 35-year-old standard model is not something physicists take lightly, which is why the 70 page long CDF paper does not make such a claim. Rather, it describes a subset of proton–antiproton collisions in which newly produced B mesons and anti-mesons fly a certain distance before decaying into pairs of muons, which are tracked by CDF’s inner detector. From some 300,000 events in which at least one muon originated beyond the Tevatron’s 1.5 cm radius beam pipe, CDF finds some 70,000 which contain more muons than expected.

“We present the bare facts,” analysis leader Paulo Giromini told physicsworld.com. “We poked fun at ourselves by publishing the paper on Halloween and calling the events ghosts, but we have performed all the sanity checks we could possibly think of. While each single feature of the signal can be explained by stretching the systematic uncertainty of our detector response, we cannot think of a way to construct a correlation between the different features.”

Unlike some scents of discovery in particle physics, such as claimed sightings of the Higgs boson at CERN’s previous collider LEP in 2000, the CDF data are not limited by statistical uncertainties due to a small event sample. Instead, researchers have to be sure the readings from the CDF detector can be fully trusted in the region close to the Tevatron’s beam pipe and must convince themselves (and one another) that the standard model “background” processes — many of which rely on a detailed understanding of quantum chromodynamics — do not provide a more mundane explanation.

Peter Renton of Oxford University says that independent studies within CDF are investigating possible standard-model backgrounds. “The Oxford CDF group [which did not appear on the paper] believes that these studies should be completed before drawing any conclusion on the nature of the events,” he said.

Your model or mine?

CDF’s vetting procedure, during which publications are assigned “godparents” and must be “blessed” before being released to the outside world, forced some of the original wording about possible interpretations of the excess events to be removed from the paper since July when it was unveiled to the collaboration. But shortly after it was posted last week, Giromini and six others released a separate preprint late on Friday in which they suggest the anomalous events can be explained by the existence of three new particles with masses of about 15, 7.3 and 3.6 GeV (arXiv:0810.5730v1).

Although the team does not know what mechanism could produce the heavier particle to begin with, the idea is that this particle decays into the lighter ones which subsequently decay into pairs of tau particles (heavy copies of muons) and, finally, into muons. Because the lightest state is presumed to decay into a pair of taus with a lifetime of about 20 ps, this can account for the mysterious muons originating beyond the beam pipe.

Other interpretations are sure to follow. In fact, last month Nina Arkani Hamed of the Institute for Advanced Study at Princeton and Neal Weiner of New York University predicted a CDF-like signal from a “superunified theory of dark matter” that was constructed in part to explain possible sightings of dark matter by the PAMELA experiment, which recently detected an excess of positrons in cosmic ray data (arXiv:0810.0714v2).

“Simple explanations of the PAMELA excess seem to require new particles at the GeV scale decaying into leptons [which include taus and muons],” said Weiner. “That CDF may be seeing a similar signature is certainly exciting, but the signature we discussed appears to be at far too low a rate to explain what they see and a lot of work remains before we can determine if the signatures are consistent.”

Cross check

The CDF analysis has parallels with one led by Giromini in 2003, which concerned signs of new physics via an excess in the number of particle “jets” in earlier CDF data. It is exactly this kind of painstaking comparison between data and simulations that LHC physicists will be undertaking in the next few years in their search for new particles, only with detectors considerably more complicated (and presently less well understood) than those at the Tevatron.

All eyes are now on CDF’s sister experiment D0 to see if it can spot the same muon excess and thus harden the case for new physics. “We just learned of this result on Friday, but the D0 detector has an excellent muon system so we should be able to do a meaningful crosscheck of this excess,” explained D0 spokespersons Darien Wood and Dmitri Denisov. “We are not putting everything else on hold, but we will try to investigate it seriously.”

Meanwhile, Giromini is keen that the CDF muon excess does not get overhyped. “In my personal opinion the CDF analysis was not particularly controversial, but definitely the outcome scared the living daylights out of number of people,” he says.

Although highly unusual for so many members of a particle physics collaboration to remove their names from a paper, CDF co-spokesperson Jacobo Konigsberg of Florida University says that overall it was a nice discourse. “It’s expected that some people will feel uncomfortable signing such a technical preprint presenting results that cannot fully be explained, and which may turn out to have a mundane origin,” he said.

Ice: a most curious substance

Ice fishing on the Ottawa River — no Periodic Hartree-Fock Calculations required. (Courtesy: AlainV).

By Hamish Johnston

One of my favourite memories of childhood is travelling across a frozen lake in the backseat of a circa-1975 Buick LeSabre (a very large car) on our way to do a bit of ice fishing.

The ice was over a foot thick, and we were secure in the knowledge that it would hold the LeSabre — and the hundreds of other cars on the lake.

What I didn’t know back then was just how complicated the stuff we were driving on is — and how much grief it has given to physicists brave enough to try to understand it.

For example, Andreas Hermann and Peter Schwerdtfeger of Massey University in New Zealand have just published a paper entitled Ground-State Properties of Crystalline Ice from Periodic Hartree-Fock Calculations and a Coupled-Cluster-Based Many-Body Decomposition of the Correlation Energy .

They say their result “hints at the possibility to accurately simulate ab initio water”. In other words, at some point in the future we may be able to understand why a seemingly simple combination of hydrogen and oxygen has myriad wonderous and life-giving properties.

Indeed, one of the most curious (alleged) properties of water is the Mpemba effect whereby hot water freezes faster than cold water. I’m guessing that it will be a while before this can be explained using Periodic Hartree-Fock Calculations.

Condensed-matter physicist to head DESY

Helmut Dosch will be the next director of Germany’s DESY Research Centre, effective 1 March 2009. Dosch will be the first condensed-matter physicist to lead the accelerator lab. He takes over from Albrecht Wagner, who has been in charge since 1999.

The Deutsches Elektronen-Synchrotron (DESY) was founded in Hamburg in 1959 and currently employs about 1900 people there and at a second site in Zeuthen in the former East Germany. Originally conceived as a particle-physics lab, DESY was home to several colliders — the last being HERA, which shutdown last year.

Today however, much of the lab’s activities are focussed on using the synchrotron radiation created by particle accelerators to do condensed matter physics, materials science, chemistry and biology. DESY is home to several accelerators and numerous beamlines dedicated to such research including the HASYLAB synchrotron facility and the FLASH free electron laser.

It not surprising, therefore, that the lab has chosen a new director who has spent much of his career using synchrotron radiation to investigate solid interfaces and nanostructures. Dosch, 53, is currently director of the Max Planck Institute for Metals Research in Stuttgart and chair of Experimental Solid State Physics at the University of Stuttgart. He is also vice-chair of the Administrative Council of the European Synchrotron Radiation Facility (ESRF) in Grenoble, France.

Dosch will see DESY take an important role in XFEL, the European X-ray Free Electron Laser, which is being built next to the lab’s Hamburg site. He will also oversee DESY’s ongoing contribution to the development of new technologies for the International Linear Collider — the next big particle physics experiment after the LHC.

Memristors model primitive learning

Physicists in the US have modelled a simple electronic circuit that they say is an analogue of how a single-celled organism learns.

The circuit consists of a capacitor, an inductor and a resistor — together with the recently discovered fourth basic circuit element, the “memristor”. The researchers claim it is this element that provides the memory needed for learning, and that the circuit could help in the understanding of primitive intelligence.

Single-celled memory

Earlier this year, Yoshiki Kuramoto of Kyoto University and colleagues showed how the amoeba Physarum polycephalum learns to respond to its environment. They found that when they subjected it to three regularly-spaced dips in temperature and humidity — both of which the organism finds unpleasant — it slowed down with the arrival of each. But they also found that the amoeba continued to oscillate in speed for a while after the last dip, and that in the future just a single dip would set the speed oscillating again. This implied that the amoeba expected a single dip in temperature or humidity to lead to more regular bursts.

Kuramoto’s group argued that the amoeba’s response could be explained by systems of chemicals in which properties fluctuate, known as “chemical oscillators”. The learning, they said, took place when external stimuli, such as the dips in temperature and humidity, synchronize the phase of the different oscillators.

However, Massimiliano Di Ventra, Yuriy Pershin and Steven La Fontaine of the University of California San Diego point out that the many-oscillator model cannot explain how an amoeba responds to a single temperature dip later on. For this, they say, the amoeba requires memory.

Simple circuit

To demonstrate the principle of how this memory could work, Di Ventra and his group linked a resistor, an inductor and a capacitor in series and then placed a memristor across the capacitor. A memristor is a device, predicted in the seventies and realized by scientists in California earlier this year, in which resistance varies according to the amount of charge that has flowed through it.

The result of this property is that when the external voltage is stable or varying non-periodically the memristor exists in a low-resistance state, which dampens the oscillation in voltage across the memristor set up by the inductor-capacitor combination. However, when the external voltage varies periodically — and with a frequency close to the inductor-capacitor resonant frequency — the memristor switches to a high resistance state, and the oscillations are much less damped. This high-resistance state can persist for so long that a single voltage dip in the future can also trigger low-damped oscillations. In other words, after the circuit receives a series of dips at its input it then it “remembers” that, given just a single dip in the future, it should continue to produce a periodic output (arXiv:0810.4179).

Di Ventra’s group points out that an analogue of the memristor exists inside Physarum polycephalum, which is a viscous gel. This gel normally impedes the motion of the organism, but with changing environmental conditions can increase the pressure inside to the point where the gel breaks up, forming low-viscosity channels that alter the organism’s motion. The organism can revert to its initial motion only after a while, which in effect allows it to “remember” how to respond to the new conditions.

According to Di Ventra, the fact that periodic signals trigger the memory mechanism suggests that their circuit could be used to recognize particular inputs, in other words carry out pattern recognition. The three researchers believe that their circuit is in a sense conceptually similar to neurons in the brain, and are currently trying to model multiple memristive circuits to study the complex behaviour that results.

Blog life: The Adventures of My Pet Hamster

Blogger: Steve Sekula
URL: steve.cooleysekula.net/blog
First post: January 2005

Who is the blog written by?

Steve Sekula is a physics postdoc at Ohio State University in the US. Much of his recent work has been on the BaBar experiment, which studies the decay of B-mesons and is based at the Stanford Linear Accelerator Center (SLAC). Although BaBar’s detecting phase ended in April 2008, data-sifting is expected to continue for several years as physicists search for clues about the origin of charge—parity violation (the subject of this year’s Nobel Prize for Physics). Sekula also plays drums in a rock band, which makes a few cameo appearances in his blog.

What topics does the blog cover?

Archived categories include computing and physics, alongside non-science subjects like politics and education. Many entries filed under “random” and “rant” also have a strong science focus. One “rant”, for example, describes a pseudoscientific pamphlet Sekula received in the post, and his subsequent deconstruction of the leaflet’s so-called theory of a geocentric universe. A recent series of entries describes life on the seminar circuit, as Sekula tours universities in the eastern US and Canada talking about his work on BaBar.

How often is it updated?

Almost daily. In September, for example, there were 29 entries, with the combination of US presidential politics and the switch-on of the Large Hadron Collider providing plenty of post fodder. “Each day, I try to find one topic that I find funny, inspiring, frustrating or unique,” Sekula told Physics World. The act of writing things down helps him make sense of life, he says.

Why should I read it?

Although entries on Sekula’s personal life may have limited appeal for outsiders, the sheer volume and variety of posts means that most readers will find something interesting at least once a week. Those seeking a more in-depth treatment of the physics and foibles of BaBar may also want to look at Sekula’s “professional” blog Going Up Alleys (steve.cooleysekula.net/goingupalleys).

Can you give me a sample quote?

The high-energy physics story is “We ask it, we build it, we learn something, and the technology is useful for other purposes we didn’t foresee”. It’s a great story, I think. But Washington wants a better story. They want a “Theory of Spinoffs” — a story that tells them and the public that investment in HEP inevitably leads to new technology, something which changes the world (and makes big bucks for the economy). This [theory] goes more along the lines of “We ask it, we build it, we learn something, and we will use the technology to do other things that weren’t foreseen but were inevitable”. It’s this inevitability that worries me.

Where does the hamster come into it?

Sekula says that when he was an undergraduate, one of his mentors joked that physics students were like hamsters — always running on little wheels, thinking they’re going somewhere fast but never getting anywhere. “This idea stuck with me,” he says. “It makes me ask myself, ‘Am I actually making progress in understanding the universe, or am I spinning my wheels?’ This perspective can be very helpful at times.”

Has Bush been good for science?

Today, the scientific enterprise in the US is strong, highly productive and significantly greater than it was eight years ago. Contrary to popular mythology, President Bush has devoted more attention to science and technology in his official actions than most of his predecessors. Strains and imbalances exist among the various research fields, but the Bush administration has initiated programmes to address many of these on a prioritized basis. However, despite the magnitude of competing national needs and fiscal constraints affecting all domestic federal programmes, science in the US has moved forward substantially during the Bush years.

About one-third of US research and development (R&D) funding comes from federal sources appropriated by Congress, with most of the rest coming from the private sector. The total spent on R&D — $368bn in 2007 — remains remarkably steady year on year as a fraction of Gross Domestic Product (GDP) at about 2.7%. This is the highest figure of any large economy except Japan, where the proportion is 3.4%, and South Korea, where it is 3.2%. China, in contrast, ploughs back just 1.4% of GDP into research.

The federal portion of R&D for 2008 is $144bn. This is 12.7% of the “discretionary budget” — the part that is subject to the annual budgeting process and that excludes “mandatory” expenditures for social security, medical insurance and interest on the national debt. This figure is now higher than at the start of the Bush administration in 2001, when it was 12.3%.

Table 1

In his second term, President Bush has aimed to reduce the overall budget deficit and keep discretionary budget growth below inflation. Nevertheless, on average, R&D budgets during this period fared better than other domestic programmes and have kept ahead of inflation. Over both terms, overall federal R&D has grown 41% in inflation-adjusted dollars to $147bn, and non-defence research has grown by 31% to $61bn. The total inflation-adjusted expenditures in various science categories during the Bush years compared with the previous administration are shown in table 1.

Compared with other countries, these are huge numbers, and it is remarkable that they have held up under the budgetary pressures of the past decade. Surveys, such as the Science and Engineering Indicators carried out this year by the National Science Foundation (NSF), show that scientific research is viewed positively by the US public — a view that is also shared by the Bush administration and both houses of Congress.

Rising above the storm

Beneath this impressive “top line” for US science are issues of emphasis and priority. These issues have energized critics and advocates of every stripe in the politically intense era following the presidential election of 2000, in which all of the administration’s actions were scrutinized. Issues like embryonic stem-cell research and responses to climate change, among others, are contentious for many reasons, but most of these have little to do with science. They comprise a small fraction of the total US science activity, and they do not reflect the deepest or even the most serious challenges in the overall R&D enterprise such as funding imbalances, lagging interest in technical careers and the impact of increased homeland-security measures on the conduct of science.

During the election year of 2004 these topics ballooned into caricatures of the underlying reality. Since then, the public discourse in the US has evolved to reflect a more balanced spectrum of opinion on these issues, especially about climate change. But myths remain about the administration’s attitudes.

It has fallen to the Bush administration to begin a major reorientation of federal science policy in the post Cold War era. Agencies within the Department of Defense (DOD) and the Department of Energy (DOE), the large basic-research programmes of which were generously supported by Congress during the Cold War, came under immediate scrutiny as the former Soviet Union disintegrated.

By the end of the 1990s, the US had withdrawn from the international fusion project ITER, cancelled the Superconducting Super Collider and sustained NASA’s International Space Station by the narrowest of margins in Congress. The DOD began closing research centres, while funding for the DOE’s highly productive physical-science laboratories flattened as Congress demanded a new rationale for their very existence.

Funding for the NSF failed to grow significantly with the booming economy of the 1990s, and the total R&D budget was essentially flat in “constant dollars” during the entire decade. Meanwhile, opportunities in biomedicine were outstripping the resources available at the National Institutes of Health (NIH), the primary sponsor for this field, and a broad consensus formed to double NIH budgets in five years, beginning in 1998.

During the first three years of the Bush administration, budgets for the NIH grew rapidly to half the total of all federal non-defence research. Meanwhile, the relative stagnation of basic research in the physical sciences was causing alarm in those industrial sectors that depend on it for innovation, especially in electronics and IT.

These fields were featured in a series of reports beginning in 2002 and culminating in the highly publicized 2005 report by the National Academies of Science entitled “Rising above the gathering storm”. The report made a dramatic case for economic competitiveness, not national security, as the new rationale for physical-sciences funding. It was also clear that any significant response to climate change and growing demands for energy independence would require major new investments in energy-related R&D.

John H Marburger

The administration quickly reorganized and focused programmes in climate science and technology, rejoined the ITER project and launched substantial new energy-research programmes in the DOE. Following the completion of the NIH budget doubling, and while the aforementioned advisory reports were being written and released, the administration developed the American Competitiveness Initiative. This, among other important objectives, doubles the budgets of the NSF, the DOE science office and the National Institute for Standards and Technology, and reorients DOD research. Congress supported this initiative in its America COMPETES Act in 2006, and has maintained funding for the key agencies, but it has yet to follow through on its commitment of increased funding.

This story of budgets and balances is only one aspect of the vast US science enterprise, but no other has comparable strategic importance. I expect future administrations will sustain the bipartisan momentum that has been achieved in the Bush administration to build basic research in areas vital to the nation’s long-term interests.

Nature’s statute book

During the 17th century, when the scientific revolution was in full swing, people started to talk about the “laws of nature”. Newton set the example when, in the Principia, he proposed his three “axioms, or laws of motion” (axioms surely being a nod to Euclid). Then, throughout the 18th and 19th centuries many laws were propounded. In the 20th century, however, law-naming became less popular in science.

But why the word “law”? What, if any, is the connection with the laws of a nation? National or even international laws are things that we are supposed to obey but often do not. Yet nature cannot help but “obey” its laws. Perhaps Newton and his contemporaries thought of the laws of nature as being God-given, and so therefore unbreakable.

There are also several other words that scientists apply to ideas that they deem important: in addition to axiom, we have hypothesis, principle, equation, theory, theorem and model. The usual practice is to reserve the word “law” for something that can be formulated in one or two sentences, with at most one simple mathematical equation. This, at any rate, is roughly the criterion for inclusion in noted science writer Clifford Pickover’s latest book, Archimedes to Hawking: Laws of Science and the Great Minds Behind Them. Pickover’s other criteria seem to be that a law should be at least moderately important and should hold true — with the usual caveats about appropriate circumstances and approximations.

Some of the deepest ideas in science, however, are too subtle to be encapsulated as a law — for example Darwin’s theory of evolution and Einstein’s theories of relativity. Even Newton’s laws are preceded by eight definitions and a “scholium”, or explanatory comment, asserting that space, time and motion are absolute. Indeed, the latter could be called Newton’s zeroth law.

Schrödinger’s equation, on the other hand, is short enough when written in symbols but is difficult to translate as a sentence, and even harder to explain, so it does not qualify as a law. The Navier–Stokes equations of fluid flow are presumably too mathematical and complex to be included, and even the apparent simplicity of E=mc² is deceptive.

Pickover’s book presents 40 scientific laws together with explanations of what they mean and short biographies of those who developed them. Applications of these laws are also described, even recent ones. The laws are all from the physical sciences, but I think it is a pity that, say, Mendel’s laws of genetics or Crick’s “central dogma” (another interesting word there) about the flow of information in molecular biology have been excluded.

The list starts with Archimedes and Kepler, whose three laws of planetary motion were not, incidentally, called “laws” by either him or Newton. The 19th century provides 25 laws and the 20th century only four, with the last being Hubble’s law in 1929. After that the flow dries up. Is this because of a different theological view, or because scientists became more modest (for example, naming particle physics’ most successful theory the Standard Model)?

The book ends with short sections on 47 “great contenders” — a sort of reserve list. However, I think that some of these deserve a place in the original selection. Pauli’s exclusion principle might have been called a law (and Heisenberg’s principle did indeed get picked), and either Maupertuis’ rule of least action or Hamilton’s related principle are surely as important as they come.

Stephen Hawking only gets in as a great contender, although the laws of black-hole thermodynamics that he helped formulate are nice examples of late 20th-century laws. Another possibility from the second half of the 20th century might have been the “CPT theorem”, which asserts, roughly, that every charged particle has an oppositely charged mirror antiparticle with otherwise identical properties.

The laws in the book could be classified into two sorts: those (like Boyle’s law) that are consequences of some more general theory; and those that have not been explained in this way (or at least not yet). I am not sure that any of the laws in the main list are of this second type, but some of the great contenders are and the latter sort perhaps have more claim to be “fundamental”.

Pickover’s book contains all sorts of interesting information and asides. For example, David Brewster (of the law of reflection of polarized light) invented the kaleidoscope, but he failed to benefit from its wide popularity because his patent was faulty. There are also many quotations and some, which are of a philosophical nature, are used as “conversation starters” between the chapters. The reader might well get interested in either the science or the history, and there are plenty of references for further reading. However, some line diagrams might have helped explain the more mathematical laws.

A question that often came to my mind as I read the book, and which I did not always find answered, is whether a law was first derived in just an empirical way, and if so, whether it was later derived from a bigger theory. I notice that many of the laws state just a proportionality between two quantities, which suggests that their inventors were attracted by simplicity. Poiseuille’s law about fluid flow through a tube is an exception, with a fourth-power dependence on the radius.

With such a wide range, this book cannot be expected to be equally authoritative about everything that it covers. However, like some of the quotations given, it is an excellent conversation starter.

Once a physicist: Subhankar Banerjee

Why did you originally choose to study engineering and physics?

I was born in Berhampore, a small town in West Bengal, India. I was immersed in literature and cinema from early in my life, and at 13 my great uncle introduced me to painting. But growing up in a middle-income family, art was not something I could pursue as a career. I chose science and engineering as a practical option.

How much did you enjoy the subject?

I studied electrical engineering as an undergraduate in India before doing physics and computer science as a graduate student in the US. However, it was always physics that intrigued and challenged me the most. I got bored with computer science so I switched to theoretical physics with a focus on particle physics and field theory. I immensely enjoyed theoretical physics as I could immerse myself in thought. I have difficulty memorizing things, so I found refuge in physics, where I could survive with thought rather than memory. Also, with physics, I felt closer to poetry and philosophy. During this time I attempted to continue in the arts by taking classes in painting and photography, only to abandon them due to the extreme pressure of studying physics.

What did you do when you left university?

After I got my Masters degrees in physics and computer science from New Mexico State University in 1994, I was offered a wonderful research position at the Advanced Computing Laboratory of the Los Alamos National Laboratory. The work involved using high-performance computers to solve problems in energy research. Later, I accepted a research position at the mathematics and computing technology division of Boeing in Seattle, Washington.

How did you get into photography?

During graduate studies in New Mexico, I fell in love with the wide open spaces of the desert. At the same time I started learning about land conservation through the Sierra Club, which is a grass-roots environmental organization. As outings chair of my local club, I led outdoor trips for students and community members. During this time I had an SLR Minolta camera and I took photos on trips across the American southwest.

What made you decide to become a full-time artist?

In Seattle I joined photography clubs at Boeing and also got involved in mountaineering. I started thinking about combining my passion for art and my concerns for disappearing land, wildlife and indigenous cultures. I left Boeing in 2000 to become a full-time artist, educator and activist.

Why did you choose to focus on the Arctic?

It was serendipitous. In late 2000 I went to Churchill in Manitoba, Canada, where most photographers go to see polar bears. I came back with decent photographs but having had a very disappointing experience — I would see a bear, and then eight large vehicles would converge on it with everyone happily snapping pictures. I wanted to find a place untrammelled by tourism or industry, and this eventually led me to the Alaskan Arctic. Also, I suppose opposites attract — coming from a tropical land, the Arctic had always intrigued me.

What are you working on at the moment?

Much of my work as a photographer and environmental activist is with the Inupiat people of Alaska and the Gwich’in people of Alaska and the Canadian Yukon. Most recently I started working with the Yukaghir and the Even people in the Siberian Arctic. Contrary to its established position as the “last frontier”, in my mind the Arctic is the most connected land on Earth. Hundreds of millions of birds migrate from every corner of the globe to the Arctic each spring to nest and rear their young — a planetary celebration on an epic scale that connects the Arctic to every land and ocean of the planet. On the other hand, climate change, toxin migration and resource wars connect the lives of Northern people and animals to the lives of people in faraway lands in a tragic manner.

Does your scientific background influence how you work now?

My scientific background has helped me immensely in understanding the Arctic ecology and preparing for harsh Arctic climates — both for personal survival and for photography in such conditions. But my Arctic work is also deeply influenced by philosophy, history and literature, including Rabindranath Tagore, Mahasweta Devi and other prominent writers from India, and films by Satyajit Ray, Mrinal Sen and Hrittik Ghatak. I approach the Arctic simply from the experience of “land as home” — a place that supports communities of our species and many other species with whom we share this planet.

Do you still keep up to date with physics?

I wish I could, but time is so limited. My only contact with physical theories is when I am trying to understand some aspect of a climatic theory or how toxins migrate from all over the world to the Arctic.

• To see some of Banerjee’s photographs, visit his website www.subhankarbanerjee.org

One year left to go

The final year of university is a time of transitions. After years of lectures and formal laboratory sessions, many physics undergraduates will spend a significant chunk of this period doing real research for the first time, as part of an honours thesis, MSci degree, Diploma or other “capstone” course. Some will apply to do a PhD as a result of this experience. Others will be inspired to seek a career tackling problems in industry, or to share their knowledge with the next generation of physicists, as teachers. Some (as our regular Once A Physicist column proves) will go off in entirely new directions, bringing their skills and mindsets to areas outside the traditional physics strongholds.

Regardless of their decisions, this is the year when career plans start to become reality — and when many students grow thoroughly sick of the question “What will you do next year?”. Physics World joins the legion of well-meaning inquisitors by asking final-year students — from the UK, US and Europe — to reflect on how their courses have gone so far, their plans for the future, and their advice for students who are just starting out.

Astronaut dreams

Jessica Snyder

Name: Jessica Snyder
Course: BS in engineering physics with an aerospace focus and BS in astronomy at the University of Kansas, US
Originally from: Clearwater, Kansas, US

My mother teaches high-school physics, so I was encouraged early on to take physics-oriented classes. I started out at Kansas University doing a purely engineering degree, but the people and atmosphere in the physics department were very inviting, which was part of the reason that I switched courses. The engineering-physics major gave me exposure to both the conceptual background and some practical applications of the principles used to understand and interact with the physical world.

Right now I’m looking at graduate schools with some sort of energy-systems engineering programme. I’ve known since childhood that I wanted to be an astronaut, but in this past year, many of my long-term goals have shifted and my career path has diverged from my childhood dream to a more “practical” direction. I guess that I have made a distinction between my ideal job and my dream job: my ideal job would be as an engineer designing and implementing systems involving renewable-energy technologies; but in my dream job, I’d walk in space.

My advice for first-year students is to make sure that you get started on the right foot. I did not take my freshman year nearly as seriously as I should have. And get involved early! Join clubs and groups to make an impact on your environment.

On course for teaching

Carole Kenrick

Name: Carole Kenrick
Course: BSc in physics at Bristol University, UK
Originally from: London, UK

I decided to study physics because it challenged and fascinated me. The best part has been finally getting my head round some difficult concepts in quantum mechanics. I enjoyed this so much that I am taking a module on the philosophical foundations of physics, which explores topics that physicists usually ignore so that they can focus on calculations. I’ve come to understand far more physics than I ever expected to, and discovered that doing physics is actually quite tricky!

Along the way, I’ve also learned some Spanish, thanks to Bristol University’s policy of allowing first-year students to take modules in other subjects. Given how international the scientific community has become, it might come in handy. If I could give any advice to first-year students, it would be to do as much maths as you possibly can, because it will eventually be useful. My only regret is not being involved in more societies in my first year, although it does take time to settle in.

My dream job is to be an ethical fashion designer who writes and illustrates children’s books about science on the side. My love of working with children is part of the reason that I decided to take up a place with Teach First next year. Teach First is a charity that encourages graduates who might not have otherwise considered teaching to spend at least two years in challenging schools. It will probably be the most demanding experience of my life, but I know it will be worth it.

Robots and research

Scott Watson

Name: Scott Watson
Course: BS in physics at College of William & Mary in Williamsburg, Virginia, US
Originally from: Reston, Virginia, US

I enjoy mathematics, and being able to apply mathematical concepts to understand the world around us fascinates me. Plus, as we learn more about how the world works, we can find ways to improve it, which I feel is very important.

My course offered me a wide variety of physics topics to study. I have also had a taste of doing real scientific research when working with one of my lecturers on interpreting sensor data for robotics. My professors are all interesting people, and very fun to get to know and talk to. They also love working with us, and talking to us about what they do.

My advice for students in the early years of their course is to find friends in your subject in order to work on coursework problems together. That way, you can get help from others when you run into trouble or they can explain things that you did not understand in class. Plus, it helps make the work less stressful.

I plan to go on to graduate school to do research in either physics or applied science. Eventually, I’d like to become a professor. I enjoy doing research, as I love the idea of exploring the topics I’m interested in and contributing the knowledge I gain to the community as a whole. I also enjoy working with other people, and being able to explain my work to them.

Super furry physics

Nia Bell

Name: Nia Bell
Course: MSci in theoretical physics at Durham University, UK
Originally from: Narberth, Pembrokeshire, UK

I decided to study physics after completing a year in industry, where I worked in a civil-engineering company. I would really recommend a placement year to younger students, as it is a great opportunity to get some quality experience, earn some money and grow up a little before university. There is no real rush to graduate, and I think the year off helped me feel confident in my choice of degree from the beginning. Although I enjoyed my placement, I soon realized that engineering was not for me. I felt that a more hi-tech, cutting-edge field would have greater appeal. The most advanced, groundbreaking form of engineering is, of course, physics.

The best part of my degree so far has been my decision to take a maths workshop suitable for theoretical physicists in my third year instead of the usual laboratory module that most people choose. I found the maths extremely difficult and I struggled with it for the entire year, but I am glad that I chose to take this module because it has given me some useful mathematical tools and, probably more importantly, the confidence to use them.

I did not realize until my third year at university that the concepts we had learned in previous years all had important applications in research and new technologies. This appreciation has reinvigorated my interest in physics and made me seriously consider a career related to it. In the coming year, I plan to produce a thesis of which I can be truly proud. I also intend to make the most of student life. Durham University is a very friendly place with a vast number of extracurricular activities, making it difficult to claim that there is nothing to do here.

As for the future, my dream job would be to play saxophone with the band Super Furry Animals, or to invent something amazing that I could put into production in a factory by the seaside where I grew up in Pembrokeshire. More realistically, I would like to do something I care about and can get excited about for many, many years. I hope to spend next summer in the most exotic place I can afford, but after that I would love to return to physics as a PhD student. I am still undecided about what to specialize in, but I would like to continue my studies abroad. I am also interested in possible industrial positions in which physics could be applicable.

Three paths

Balazs Karcsai

Name: Balazs Karcsai
Course: Degree in physics with astrophysics at Eotvos Lorand University, Hungary
Originally from: Budapest, Hungary

When I was a secondary-school student, my physics teacher asked me to give a lecture about particle physics, so I read Leon Lederman’s book The God Particle. My lecture ended up being five hours long, and it inspired me to be a physicist! At university I found out that particle physics is very hard, and so I started my student research in material physics. But when I selected my specialization, I chose astrophysics.

The best part of my course is that I have learned a lot about things beyond just the laws of physics. For example, I have learned how to give talks and write articles, how to simplify problems, and how to convince people. I got involved in my physics student association, organizing scientific and social programmes and finding sponsors to fund the society. I edited the weekly paper of the science faculty, and I have written articles in Hungarian scientific magazines about high-energy astrophysics. These skills and experiences have helped me both in and outside of science. For me, one downside of being a physics student in Hungary is that fewer than 10% of the students in my year are women, but I solved this problem by getting to know people in the humanities departments as well.

When I started my course, I had different conceptions about studying physics. At first, I was sure that I would eventually want to work as a researcher. But now I can see many other interesting possibilities, too. I have three different plans for the next year. The first is an astrophysics PhD somewhere in western Europe, the second is to work for a multinational company and earn some money, and the third is to be a science writer or a journalist.

Ideally, I would get a job where I am always with people and I need to use my brain and be creative. It is important to manage my own time, because I do not like getting up early and I am more effective in the evening. But I know the real world is usually different from dreams.

My advice for first-year students is to learn computer-programming languages as soon as you start your degree. I had many problems with programming when I started research on my thesis. And, have a good social life, go abroad as often as you can and be open to new things.

Calculations and more

Konstantin Ottnad

Name: Konstantin Ottnad
Course: Diploma in physics at the University of Bonn, Germany
Originally from: Freiburg, Germany

I decided to study physics because I was interested in how things work. I was also good at mathematics in school, so I never had to think much about what to study — it was pretty clear that it would be either maths or physics. In fact, I started studying maths — there was a project at my school that allowed you to attend courses at university during your final three years — but then I decided that physics was more interesting. Now I am working on my final thesis about chiral perturbation theory, a topic in quantum chromodynamics.

In Germany, after the first two years of study, the course is flexible. There is a big selection of lectures and seminars that you can choose from, with very few restrictions. Personally, I did not like most of the lab courses (which are obligatory) because I am more interested in theoretical physics. From my point of view, the lab sessions just created a lot of work without giving me the feeling of learning something I would need later.

The best parts have been the lectures and seminars during my third and fourth years that I chose on my own and that have dealt mainly with theoretical particle physics and quantum field theory. If I could do it over again, though, I would probably try to be a bit more careful about which lectures I attended. That probably could have saved me a semester.

I did one semester abroad at the University of Glasgow in the UK, which was great fun. In addition to going to lots of parties, I also did a Masters project there for about four months. This helped me to decide which field I should pick for my final thesis, and I even won a prize for it, which was nice.

I will be working on my thesis for the next 12 months. After this I am probably going to do a doctorate, which will take at least three more years. Ideally, I would like a job where I could do calculations and programming all day long, and get paid lots of money for doing so.

My advice for new students is simple: as someone once said, shut up and calculate! It really helps in most cases, believe me. I think it is extremely important to work hard right from the beginning of your studies. Otherwise you are likely to lose a lot of time just trying to catch up with the subsequent lectures.

Physics in action

Name: Julie Feldt
Course: BS in astronomy and physics, University of Kansas, US
Originally from: St Louis, Missouri, US

My high school physics teacher sparked my interest in physics. She was a great teacher. She would talk with me about what was going on in physics in the real world and encouraged me to go to lectures at the universities in St Louis. She showed me how cool physics really is.

The best part of my degree has been getting to do a lot of the experiments that we learned about in lectures, like Faraday rotation and the Michelson interferometer. We have measured the speed of light, the temperature of the Sun and the lifetime of muons. It was so much fun to actually see the experiments in action. I have also had really good professors. One major downside has been working with students who do not really care about understanding the subject — they just want to get the answers right and be done with it. Working with those students can be draining.

In my degree, I have taken several field-specific courses like nanotechnology, and next semester I will take space plasma physics and molecular biophysics. After that, I want to go to graduate school to get a Master’s degree in space physics and planetary science. I am not completely sure yet what I would like to do after that, but I would like it to involve research — maybe at a place like the National Oceanic and Atmospheric Administration or the Laboratory for Atmospheric and Space Physics.

I would really encourage students to get involved in research as soon as they know they are interested in the field. Research will tell you more about what things are really like, and then even if some of the classes seem hard they end up feeling more worth it. I have had a lot of research experience through the National Science Foundation’s Research Experience for Undergraduates (REU) programme, as well as undergraduate research courses. So when I have had a class that I was not as excited about, I just concentrated on how much I love working in my field and told myself that this was just one step out of many that I had to get through to reach my goals.

Love life, love physics

Name: Jelmer Renema
Course: MSc in experimental physics, specializing in quantum optics and quantum information, Leiden University, Netherlands

I always knew I was going to study a “hard science,” but I settled on physics only in my last year of high school, partially because the physics teacher that I had then was very enthusiastic about his subject. The strange thing was that he was not a very good teacher — he once had to suspend a lecture because he couldn’t find a sign error when he was deriving the of equation of motion of the simple harmonic oscillator — but his enthusiasm shone through and convinced me that physics was worth spending time on.

The best part of my course so far has been the theoretical course on quantum computing, which introduced a lot of concepts very quickly but has given me a broad grounding in the subject. It also provided a good overview of current research on the subject. I constantly draw on my knowledge from this course at conferences or when listening to colloquia.

I really like the academic atmosphere of openness and accessibility at the Leiden Institute of Physics, and I hope to make a career in academia. Barring that, a job as a science communicator or journalist would be nice.

I would advise first-year students to get involved in many associations, projects, etc. Now is the time of your life when you discover what you’re good at and what you like, and there is no better way to do this than to immerse yourself in as many different activities as possible. After a while, you are going to have to narrow it down a bit and get to work on graduating, but do not worry too much about that when you start.