# News this Week

Science  14 Sep 2012:
Vol. 337, Issue 6100, pp. 1276
1. # Around the World

1 - Parma, Italy
Report: Europe's Food Watchdog Is Independent
2 - Canary Islands
Island Hopping
3 - Sabah, Malaysia
Evolutionary Expedition Scales Borneo's Highest Peak
4 - Kyoto, Japan
Mathematical Gold?

## Parma, Italy

### Report: Europe's Food Watchdog Is Independent

The European Food Safety Authority (EFSA) is sufficiently independent from the food industry it oversees, according to an external review issued on 5 September. Lately, EFSA has come under fire from advocacy groups and members of the European Parliament who claimed board members and experts sitting on EFSA scientific panels sometimes have undisclosed ties to industry. But the report, written by auditors from Ernst & Young, says that EFSA has done more to protect the independence of its scientific opinions than required by its founding regulations. It says tightening conflict of interest rules further might make outside experts hesitant to sit on EFSA panels. However, the report recommends that EFSA become more transparent and explain its decisions better to a broader audience.

Critics aren't satisfied. “EFSA's conflict of interest policy has improved, but not enough,” says Nina Holland, a campaigner at Corporate Europe Observatory. EFSA's board says it will discuss the findings at its October meeting. http://scim.ag/_EFSA

## Canary Islands

### Island Hopping

Physicists have demonstrated “quantum teleportation” over a distance of 143 kilometers, besting the previous record of 97 kilometers by researchers from China. Instead of making an object disappear in one place and reappear in another, this technique transfers the delicate quantum state of one photon to another photon some distance away. Now, Anton Zeilinger of the University of Vienna and colleagues have teleported the states of photons between mountaintop observatories on the Canary Islands of La Palma and Tenerife (pictured below), they reported online on 5 September in Nature.

“Just showing that you can do it over such very long distances is a major step forward,” says Richard Hughes, a physicist at Los Alamos National Laboratory in New Mexico who was not involved in the work. Rupert Ursin, a member of Zeilinger's team from the Austrian Academy of Sciences in Vienna, says the advance points the way to teleportation between Earth and a satellite and, ultimately, to a quantum-mechanical Internet. The team worked on islands for several reasons, Ursin says, but “the unofficial reason is that the beach is super nice.”

## Sabah, Malaysia

### Evolutionary Expedition Scales Borneo's Highest Peak

Following in the footsteps of Alfred Russel Wallace, a contemporary of Charles Darwin, this week 40 Dutch and Malaysian scientists will ascend Borneo's 4000-meter Mount Kinabalu—the tallest peak in Southeast Asia—to study the region's world-famous biodiversity. Menno Schilthuizen of the Naturalis Biodiversity Center in Leiden, the Netherlands, has spent 7 years documenting unknown species in the region, such as the land snail Everettia layanglayang (pictured above). On this expedition, he and his colleagues will spend 2 weeks collecting DNA from plants, animals, and fungi from both the mountaintop and surrounding lowlands with the goal of comparing closely related species from the two environments. They hope to determine which species on Mount Kinabalu are ancient relics from cooler times, and which recently moved from the hot, humid lowlands to the summit's alpine climate. Starting with Wallace, “there is a long history of research on evolution [on the mountain],” Schilthuizen says. “But no one has taken a large-scale approach.”

## Kyoto, Japan

### Mathematical Gold?

In 1897, newspaper reports of gold in Alaska triggered a rush of nearly 100,000 adventurers willing to brave an arduous journey and miserable conditions in order to make their fortune. Recent buzz on the Internet may set off something similar, albeit on a smaller, more intellectual scale, in the world of mathematics. For the last few years, Shinichi Mochizuki of Kyoto University in Japan has issued progress reports on a new field of mathematics that he has been developing called Inter-universal Teichmüller theory. His fourth report, posted at the end of August, stakes a claim to a potential gold mine: Mochizuki announced he has solved a famous problem in number theory called the abc conjecture.

The abc conjecture is concerned with solutions to the seemingly trivial equation a + b = c. The technicalities involved in the conjecture's precise statement are familiar ones, number theorists note. But Mochizuki's theory is based on very new, highly technical math explored so far only by a very few. If initial assessments of Mochizuki's claim hold up, there'll be an influx of mathematical prospectors primed to use his proof to mine their own intellectual gold.

http://scim.ag/_conjecture

2. # Newsmakers

Philip Diamond, a British astronomer working in Australia, has landed perhaps the biggest job in astronomy: leading the design and preparing for construction of a €1.5 billion radio telescope that comprises thousands of dishes and spans two continents.

The Square Kilometre Array (SKA) aims to peer back in time to the universe's earliest stars and galaxies, study gravity, and look for signs of extraterrestrial life. The task requires dishes spread over continental distances with a combined collecting area of 1 square kilometer. Project leaders recently decided to split the array between two sites, centered in Australia and South Africa, each handling different frequencies (Science, 1 June, p. 1085). The plan is to start building the array in 2016 and finish by 2024.

Diamond has held senior positions at astronomy organizations in the United Kingdom, Sweden, Germany, and the United States and is currently head of astronomy and space science at Australia's research organization CSIRO. He is also a longtime member of SKA's scientific steering committee. “He's an excellent choice,” says Michael Garrett, director of ASTRON, the Netherlands Institute for Radio Astronomy.

## Golden Goose Awards Celebrate Basic Research

What do lasers, coral, and glowing jellyfish have in common? Research on these initially obscure subjects eventually led to important scientific advances in technology and health, including two Nobel Prizes. On 13 September, the scientists whose basic research paved the way for useful products and techniques—including laser technology, safe bone grafts, and green florescent protein—will receive the first Golden Goose Awards. Organized by U.S. Representative Jim Cooper (D–TN) and a coalition of leaders in education, business, and science, including AAAS (the publisher of Science), the awards are a playful rejoinder to those who criticize basic research as a waste of money. At first, recipient Martin Chalfie of Columbia University thought the Golden Goose Award “was a hoax.” But Chalfie, who shared the 2008 Nobel Prize in chemistry for developing green florescent protein from bioluminescent jellyfish, says he's delighted to receive the prize. He hopes the awards will serve as a reminder that many of the biggest discoveries in science are joyful surprises. “We shouldn't be so narrow in our seeking.”

http://scim.ag/_goose

## Lasker Awards for Molecular Motors, Liver Transplantation

This year's Lasker Awards go to researchers whose work unraveled how molecular motors work and others who made liver transplants possible.

Michael Sheetz of Columbia University, James Spudich of Stanford University, and Ronald Vale of the University of California, San Francisco, won for basic medical research. They used in vitro assays to discover how cytoskeletal motor proteins move material within cells. The motors also allow cells to move and muscles to contract.

Roy Calne of the University of Cambridge and Thomas Starzl of the University of Pittburgh will receive the Lasker clinical award for their studies of liver transplantation. Working first with dogs, they developed strategies surgeons could use to deal with the liver's complex system of blood vessels and with immune system rejection. In 1983, liver transplantation became an accepted medical procedure.

A third prize for special achievement in medical science goes to geneticists Donald Brown of the Carnegie Institution for Science in Baltimore and Tom Maniatis of Columbia University. The two are honored for their research and leadership in promoting technology and supporting young scientists.

## ScienceLIVE

Join us on Thursday, 20 September, 3 p.m. EDT for a live chat with experts on whether a restricted diet prolongs life.

http://scim.ag/science-live

4. Particle Physics

# Who Invented the Higgs Boson?

Five living theorists have claims to having dreamed up the most famous subatomic particle in physics. But what did they really do?

Now that the Higgs Boson—or something much like it—is in the bag, the question on many people's minds is who gets the Nobel Prize for the discovery.

If you go by the pop history, the answer is obvious. In 1964, Peter Higgs, a mild-mannered theorist from the University of Edinburgh in the United Kingdom, dreamed up the particle to explain the origins of mass. He completed physicists' standard model of fundamental particles and forces. Experimenters working with the world's largest atom smasher, the Large Hadron Collider (LHC) at the European particle physics laboratory, CERN, in Switzerland, have now seen that particle (Science, 13 July, p. 141). So Higgs gets the glory.

Only that's not exactly what happened. In fact, theorists say, Higgs made a fairly narrow and esoteric advance in mathematical physics. Several other physicists made the same advance at the same time. Their intellectual leap was essential to the development of the standard model, perhaps the most elaborate and precise theory in all of science. But their papers didn't even mention the most important problem their work helped to solve. Other scientists did that later—but their contribution (which won Nobel laurels in 1979) still doesn't explain the origins of all mass.

Even the famous particle, the Higgs boson, doesn't quite live up to its legendary status. Often portrayed as the engine that drives the standard model, the Higgs boson itself is in a way the byproduct of more important underlying physics. Instead of the boiler on a steam locomotive, it's more like the whistle: Its toot proves that the boiler is there and working, but it doesn't turn the wheels.

As for whether the work of Higgs and colleagues merits a Nobel Prize, opinions vary. “Certainly, yes, I think it is at least as profound as other things that have been given the Nobel in the past,” says Frank Close, a theorist at the University of Oxford in the United Kingdom. Others question whether the advance was a big enough step beyond previous work to merit science's biggest prize.

In any case, says Chris Quigg, a theorist at Fermi National Accelerator Laboratory (Fermilab) in Batavia, Illinois, historians and prize committees must be careful to give credit precisely where and for what it is due: “If these people receive their rewards, either in heaven or before, it would be nice if it was for something they actually did and not for what people say they did.”

## The problem

What Higgs and company did, albeit unwittingly, was to dynamite a huge boulder that was blocking progress on the standard model of particle physics. The standard model is a quantum field theory, so it focuses on quantum waves or “fields” that describe the probability of finding various particles here and there. It contains fields for the dozen types of matter particles—including electrons, the up quarks and down quarks that make up protons and neutrons, and the heavier analogs of those particles that emerge in high-energy particle collisions.

These particles interact through three forces: the electromagnetic force that binds the atom, the strong nuclear force that binds quarks into protons and neutrons, and the weak nuclear force, which produces a kind of radioactivity. (The standard model does not include gravity.) The forces are conveyed by particles of their own, known collectively as “gauge bosons.”

The whole kit and caboodle is encoded mathematically in one master function called the Lagrangian, which describes everything physicists know about how particles and their force fields behave (see sidebar, p. 1288). Here's the most important point in the whole theory: The standard model Lagrangian possesses three different mathematical symmetries called “local gauge symmetries,” which predict the existence of the three forces in the theory: weak, strong, and electromagnetic. For example, the simplest local gauge symmetry generates the quantum field for the photon, the gauge boson that conveys the electromagnetic force.

The connection between local gauge symmetries and forces is so strong that it defines the standard model, says Fermilab's Quigg. “I don't know that it's a miracle, but it's a wonderful thing,” he says. To construct the standard model, theorists had to find the Lagrangian with the right gauge symmetries to explain the observed forces.

In the early 1960s, however, physicists were just beginning to appreciate the importance of gauge symmetry. In 1961, Sheldon Glashow, now at Boston University, developed a model based on two gauge symmetries that described both the electromagnetic force and the weak force, which is carried by particles now known as the W boson and the Z boson. There was a hitch, however: Because the weak force acts at extremely short range—far shorter than the width of an atomic nucleus—theorists knew the bosons that convey it must be massive, as the more massive a gauge boson is, the shorter its range. But simply tweaking the Lagrangian to give the W and Z particles mass spoiled the very gauge symmetry that predicted their existence.

To salvage gauge symmetry as the origin of forces, theorists needed to find a way to give force-carrying particles mass without wrecking the symmetry.

## The solution

That's exactly what Higgs and five others did, although they weren't particularly thinking about the W and Z bosons. Instead, they were toying with a concept called “spontaneous symmetry breaking,” a process that occurs whenever the inner workings of a system possess a symmetry that gets lost as the system settles into its lowest energy state. For example, a marble in a round-bottomed bowl settles in the middle, the point of greatest symmetry. But if the center of the bowl has a hump like the “punt” in a wine bottle, the marble won't stay in the middle but will run downhill in some random direction. The symmetry of the bowl remains in the setup, but the marble's “choice” of direction makes it harder to see.

Spontaneous symmetry breaking had already been used to describe magnetism, superconductivity, and the formation of crystals. Years before the discovery of quarks, a pair of theorists had even developed a rough theory of the interactions of protons and neutrons through the strong force. Particle theorists hoped the concept would illuminate other issues, too.

But there was a snag, as Jeffrey Goldstone, now at the Massachusetts Institute of Technology in Cambridge, pointed out in 1961. He considered the simplest example, a quantum field that interacts with itself to produce an energy landscape or “potential” much like the wine-bottle bottom (see sidebar, p. 1289). In that case, the field can minimize its energy not in the usual way by vanishing but rather by taking on a nonzero strength in the vacuum. Some theorists speculated that the vacuum might not be as bland as they had assumed and might contain a hidden quantum field instead.

Unfortunately, Goldstone proved, any such field should produce massless particles known generally as Goldstone bosons. Such massless particles aren't seen flitting about. So Goldstone's theorem suggested that spontaneous symmetry breaking just doesn't apply to real-world particle physics.

Then Higgs and two groups of other theorists independently found a way out of this particular jam. “The Goldstone theorem was a definite setback, so it was natural that people would try to find a way around it,” says Tom Kibble of Imperial College London. Goldstone, the theorists realized, had considered a quantum field that interacts only with itself, and he didn't include local gauge symmetry or force-carrying gauge bosons. So they mixed those things into Goldstone's model, with two striking results. The pesky Goldstone bosons disappeared, and the force-carrying particles became massive.

Why does this happen? Physically, the force-carrying particles interacted with the new “Higgs field” produced by the spontaneous symmetry breaking to acquire energy and mass, in keeping with Albert Einstein's dictum that energy equals mass. Crucially, that happens without ruining the gauge symmetry, which is built into the theory from the start. The Higgs boson is a byproduct of the process. The Higgs field itself must consist of massive quantum particles lurking “virtually” in the vacuum, and those particles are Higgs bosons.

The theorists reported their solution in a string of papers in Physical Review Letters in 1964. Free University of Brussels researchers Francois Englert and Robert Brout, who died in 2011, reported their work on 31 August 1964. Higgs published 7 weeks later. Gerald Guralnik, now at Brown University; Carl Hagen, now at the University of Rochester in New York; and Kibble followed suit on 16 November. The papers made scarcely a ripple in the pond of theoretical physics. “Nobody took any notice of it at all,” says Oxford's Close. The authors suggested that their mechanism might help explain strong interactions, but they didn't follow up on that possibility.

In fact, this “Higgs mechanism” was just the thing theorists needed to give mass to the W and the Z bosons that carry the weak force. That didn't occur to its inventors, however. “One of the puzzles is why somebody didn't get the idea to put these two ideas together immediately in 1964,” Kibble says. “All the material was there.” Instead, the seminal application was made in 1967 by Steven Weinberg, a theorist now at the University of Texas, Austin, and independently in 1968 by Abdus Salam, a Pakistani theorist who died in 1996 (see sidebar, p. 1287). “We gave them the tool they had to have,” Guralnik says. Glashow, Weinberg, and Salam would share the Nobel Prize in 1979 for discovering the theory of the “electroweak force” and giving birth to the standard model.

## Big deal?

Given that complicated history, some theorists question whether the advance made by Higgs and his cohort really merits science's highest honor. They cite several possible arguments against it.

The Higgs mechanism didn't push far enough past earlier work. Several other physicists applied spontaneous symmetry breaking to particle theory before Higgs and company did, and some got close to the idea of the Higgs mechanism, says Michael Peskin, a theorist at SLAC National Accelerator Laboratory in Menlo Park, California. Goldstone was one such pioneer; another was Yoichiro Nambu of the University of Chicago in Illinois, who shared the Nobel Prize in 2008. Peskin acknowledges that the mechanism was controversial when first published in 1964. Even so, he says, “as someone who was educated in particle physics after 1972, it's hard for me to figure out what Higgs et al. did that was nontrivial.”

In fact, Philip Anderson, a condensed matter theorist now at Princeton University, sketched out the basic idea very roughly in 1963. Goldstone says he came up with the same scheme in 1962, but senior colleagues convinced him that he was on the wrong track. “So I lost my nerve,” he says. “The only evidence for this story is that I've told it many times over the years. I don't even have a scrap of paper. And it only proves that I wasn't thinking clearly.” If at least eight people have the same idea, how brilliant can it be? “That's a fair question,” acknowledges Close, who supports a Nobel for the work.

Higgs and company did not predict the standard model Higgs boson in the sense that physicists understand it today. It's true that a massive new particle is a byproduct of the physics described in the 1964 papers. And the observation of that particle is vital, as it confirms that nature really is using the Higgs mechanism, says Gordon Kane, a theorist at the University of Michigan, Ann Arbor: “Otherwise, the whole theory is bullshit.”

But the specific particle that researchers at CERN apparently discovered this summer, with all its predicted properties, emerged only later, during the construction of the actual standard model. “The Higgs field of the weak interactions—the real Higgs field, in other words—was the idea of Weinberg and Salam,” Peskin says.

Higgs didn't explain the origin of mass. Despite breathless headlines to the contrary, even the standard model Higgs mechanism does not explain the existence of all mass in the universe. The Higgs mechanism does give mass to the W and Z bosons. And Weinberg showed how it could give mass to other fundamental particles such as electrons and quarks. But most of the visible mass in the universe resides in protons and neutrons, which are not fundamental particles. And most of their mass comes from the binding energy among their component quarks.

## Favorites and long shots

Caveats aside, many physicists say that the advance Higgs and colleagues made—finding a way to give mass to force-carrying particles without screwing up the whole theory—definitely merits a Nobel Prize. The Higgs mechanism implies that the empty space is threaded by a new type of quantum field, Kane says, so its confirmation at CERN revolutionizes physicists' understanding of the universe. “I would say it's the most exciting thing in particle physics ever—no qualification,” he says.

If the Nobel committee agrees, its members will decide who should get the prize. That's a tricky question, as at most three people, still living, can share the Nobel. At first blush the answer might seem obvious: Englert and Brout published first; Higgs, second; and Guralnik, Hagen, and Kibble, third. And in science, the race goes to the swiftest.

But the contents of the papers, none more than three pages long, make matters less clear. Englert and Brout present only an approximate “first order” calculation. Higgs presents only a classical field theory argument and states in a footnote that “nothing is proved about the quantized theory.” Guralnik, Hagen, and Kibble present an analysis that other physicists say is more complete.

Some say the issue comes down to who predicted the existence of the Higgs boson itself. “Higgs has an unassailable case because he is the guy who realized there would be a massive boson,” says John Ellis, a theorist at King's College London.

However, in his 1964 paper, Higgs's discussion of the new particle consists of just one sentence—“Equation (2b) describes waves whose quanta have (bare) mass 2θ0{V″(θ0)}1/2”—and it clearly wasn't the focus of his work. And the fact that a quantum field consists of quantum particles goes without saying, physicists point out, so it hardly counts as a mark against the other theorists if they didn't mention it explicitly.

Asked to prophesy, Ellis, Close, and Kane all say that Higgs is a shoo-in for the Nobel and that Englert has a strong case for priority. Guralnik, Hagen, and Kibble are likely to get left out. “They were scooped, and that's a fact of life,” Close says—although he and the others agree that Kibble might get the nod for applying the mechanism to more complex gauge symmetries and paving the way for Weinberg and Salam.

Some theorists say a Nobel Prize should go to the experimenters who discovered the new particle. That may seem ludicrous, as the two teams that spotted it comprise 3000 members each. But “choosing one out of [each] 3000 might be easier than choosing three out of six,” Quigg says. Peskin says Lyndon Evans, the accelerator physicist at CERN who led the construction of LHC, clearly deserves the prize.

Nominations for this year's prizes closed in February, so a Nobel for the discovery of the Higgs probably won't come until 2013 at the earliest. That leaves plenty of time to place your bets.

5. Particle Physics

# Why the 'Higgs'?

Mistaken citations could be the reason the Higgs boson is named after Peter Higgs even though others reported the physics behind it first.

The physics behind the Higgs boson was first reported in August 1964 by Francois Englert and the late Robert Brout of the Free University of Brussels. Yet the particle bears the name of Peter Higgs of the University of Edinburgh in the United Kingdom. Why? Mistaken citations could be at fault, Frank Close of the University of Oxford in the United Kingdom wrote in his book The Infinity Puzzle.

Benjamin Lee, a Korean-American theorist who died in 1977, apparently used the term “Higgs boson” as early as 1966. But what made the term stick may have been a seminal paper Steven Weinberg, now at the University of Texas, Austin, published in 1967. In it, Weinberg cited a paper of Higgs's from Physics Letters, volume 12, and his key paper from Physical Review Letters, volume 13, before the paper by Englert and Brout from Physical Review Letters, volume 13. In fact, Higgs's first paper appeared 2 weeks after Englert and Brout's paper, and his key paper 5 weeks later still. Weinberg cemented the error in 1971 by mistakenly citing Higgs's earlier paper as being in volume 12 of Physical Review Letters, making it appear that he had clearly been first. That error propagated through the literature for decades, appearing in the 2010 version of the Review of Particle Physics, the standard reference in the field. Weinberg acknowledged the mix-up in an essay in The New York Review of Books in May 2012.

6. Particle Physics

# Symmetries and Forces

In the standard model, physicists roll all the fields that describe the distribution of the various particles into a single mathematical function called the Lagrangian that encodes all possible particle interactions.

Particle theory is a model of efficiency. The standard model focuses on quantum fields that describe the distribution of the various particles in the model, and physicists roll all those fields into a single mathematical function called the Lagrangian that encodes all possible particle interactions. The Lagrangian possesses certain mathematical symmetries called local gauge symmetries that determine the exact nature of the forces between particles. That is, you can mix up the quantum fields in the Lagrangian in certain ways that leave the function looking exactly the same, and those symmetries predict the number and nature of the forces in the model.

The connection between symmetries and forces stems from a theorem published by the German mathematician Emmy Noether in 1918. She proved that if the Lagrangian describing a physical system—be it a molecule or a solar system—possesses a symmetry, then some overall aspect of the system must remain constant, or be “conserved.” For example, if the Lagrangian is symmetrical with regard to position—meaning you can take the whole system and move it in any direction without changing its behavior—then momentum must be conserved. If the Lagrangian is symmetrical with regard to time—meaning that you can slide the whole works forward or backward in time without affecting its behavior—then energy is conserved.

Gauge symmetries are more complicated, but they, too, lead to conservation laws. In this case the conserved quantities are charges like the electric charge. The standard model possesses three distinct gauge symmetries, which define the charges for the electromagnetic, weak, and strong forces. The characteristics of the charges then determine the characteristics of the forces and the quantum particles that convey them. For example, there is one type of electric charge, and the electromagnetic force is carried by uncharged photons. The strong force has three types of charges—red, blue, and green—and is conveyed by particles called gluons, which themselves are colored with those charges.

7. Particle Physics

# Spontaneous Symmetry Breaking Decanted

To minimize its energy, a quantum field must take on a nonzero strength and choose a direction, breaking the symmetry of the situation and causing particles to emerge, including the Higgs boson.

Ordinarily, a quantum field reaches its lowest energy when it vanishes (see figure, left). But the field can interact with itself to produce an energy landscape resembling a wine-bottle bottom, with a hump in the middle and a circular trough surrounding it. The field can then minimize its energy by rolling downhill, just as a marble placed in the wine bottle would (see figure, right). To do so, the field must take on a nonzero strength and randomly choose a direction in an abstract two-dimensional “phase space,” breaking the symmetry of the situation.

When such spontaneous symmetry breaking occurs, different kinds of particles emerge, as can be seen by pushing the marble analogy further. Suppose the marble jiggles; such jiggling corresponds to the existence of particles in the quantum field theory. Jiggling along the trough costs no energy and corresponds to massless particles, known as Goldstone bosons. Jiggling across the trough and uphill in the energy landscape costs energy and corresponds to the existence of massive particles.

In the so-called Higgs mechanism, the massless Goldstone bosons meld with other massless force-carrying particles to make the force-carrying particles massive. The weighty particle corresponding to the uphill jiggling remains. It is the Higgs boson.

8. Bioacoustics

# The Sound in the Silence: Discovering a Fish's Soundscape

1. Jane J. Lee*

Bioacoustics pioneer Arthur Popper is getting ready to retire, but his work on how fish perceive sound isn't fading away.

As an undergraduate more than 40 years ago, Arthur Popper took a detour on his way to a class on New York University's campus in the Bronx that set him on a course to become the godfather of fish hearing. Popper decided to visit a new pet shop, where he spied a fish without eyes. He began thinking about how it lived guided by its other senses. The encounter eventually led Popper, now a bioacoustician at the University of Maryland, College Park, to become one of the world's pioneers in understanding how fish perceive and respond to sound. “If I hadn't walked by that shop that day,” he says, “I'd have a different life.”

Today, Popper's professional life is defined by sound. Among bioacoustics researchers, he's widely known for the classic drawings of fish ear anatomy he produced as a young scientist and for co-editing a series of influential books that colleagues say has helped shape the growing field. Popper has also conducted innovative studies that have documented the effects of human-generated sound on fish and raised questions about the science underpinning government regulations designed to protect sea life from industrial noise. “I knew he was going to be successful as a scientist,” says sensory biologist William Tavolga of the Mote Marine Laboratory in Sarasota, Florida, who oversaw Popper's doctoral work. “But there was no predicting the huge amount of work he's done and the quality of work.”

And now that the irrepressible 69-year-old researcher is preparing for retirement, colleagues are wondering if anyone can take Popper's place—and whether he'll actually slow down. “I'm amazed at the energy of the guy,” says marine biologist Robert Gisiner of the U.S. Navy's Energy and Environmental Readiness Division in Washington, D.C. “He could just run me into the ground and I'm 10 years younger.”

When Popper was growing up in New York City in the 1950s, many people still shared the notion of a silent ocean, popularized by the explorer Jacques Cousteau. That view has profoundly changed. We now know that many marine animals use sound to find food, avoid predators, and communicate. And humans have added their own cacophony: the thrum of ship screws, the blast of seismic air guns for oil exploration, and the concussive force of pile drivers used to build docks and bridges. Popper was one of the first to make the scientific community aware that humanmade noise could affect the behavior and health of animals other than marine mammals, says neuroethologist Darlene Ketten, who holds a joint appointment with the Woods Hole Oceanographic Institution and Harvard Medical School, both in Massachusetts.

As a graduate student at the City University of New York in the late 1960s, Popper initially wanted to focus on how blind fish determined where sound came from. “[It's] called sound-source localization,” and the ability is considered to be one of the most powerful forces driving the evolution of hearing, Popper says. “Because if you just hear a sound and don't know where it's coming from, it's not worth hearing.”

But sound bounced around in the fish tanks available to Popper at the time, making experiments impossible and forcing him to abandon his localization project. Even today, the question is hard to study, he says. “We know [fish] can localize sound, but how well and how they do it is still a mystery.” Instead, Popper moved on to studying the hearing capabilities of Mexican blind cavefish (Astyanax jordani) and its eyed ancestor (Astyanax mexicanus). He discovered that these species had the widest hearing range yet measured in fish, and that blind cavefish didn't necessarily sense pressure stimuli better than their eyed relatives. After earning his doctorate, Popper ultimately landed jobs at the University of Hawaii, Manoa, and then at the Georgetown University School of Medicine in Washington, D.C., where he taught neuroanatomy.

In 1975, Popper learned scanning electron microscopy during a sabbatical, opening a new window into fish hearing. He used the skill to delve into the form and function of a fish's inner ear, mapping the orientation of hair cells and showing that fish can actually regenerate damaged ones.

“One of Art's biggest contributions was the anatomy he did on fish hearing,” says longtime collaborator Anthony Hawkins, a bioacoustician and former head of fisheries research for Scotland. Researchers still use some of Popper's elegant, detailed drawings, he says: “We still don't know how it all works. But we have a lot of information on their anatomy.”

Then, in the early 1990s, Popper began co-editing a series of books—called the Springer Handbook of Auditory Research (SHAR)—with his longtime friend and collaborator, fish-hearing specialist Richard Fay. There are now 45 volumes, and each is meant to aid investigators in understanding an area of hearing research they aren't necessarily experts in. Popper and Fay enlist specialists to cover topics as diverse as hearing in bats and music perception. “Hearing research has been changed by [the SHAR] series,” Ketten says.

## A hissy fit

In the last few decades, Popper has become known for figuring out how to conduct difficult experiments that examine how fish respond to sound both in the field and in the laboratory. One focus is understanding how the noise produced by pile drivers—widely used machines that pound supports for bridges and docks into bottom sediments—affect fish and other aquatic creatures that are protected by environmental regulations.

“When people do experiments with very loud sounds, [they] usually have to do it in the field because you can't simulate loud sounds in the laboratory,” Popper says. That's because the volume is just too intense: For pile drivers, the sound can be louder than turning on a jet engine in a room.

But field experiments aren't easy. Piggybacking on construction projects while the crew tries to stay on schedule, for example, is less than ideal. And workers are not going to stop and wait while you get your fish into place, Popper says. As a result, past field trials had been “very weakly done, poorly controlled, by people who really don't understand how to evaluate the results of these experiments,” he laments.

In 2004, he decided to see if he could bring the studies into a controlled lab setting after a frustrating consulting experience trying to determine safe noise thresholds for fish during pile-driving operations on the San Francisco-Oakland Bay Bridge in California. The trick was finding a device that produced the needed racket without deafening researchers.

The solution came from a colleague, mechanical engineer Peter Rogers of the Georgia Institute of Technology in Atlanta. As part of a Navy study of the possible health effects of loud underwater noise on divers, Rogers had built a machine that allowed scientists to study how high-intensity sounds affected the lungs of submerged rats outfitted with a kind of rodent scuba gear. Rogers modified the machine for use with fish, producing what Popper affectionately refers to as the “hissy fit,” short for high intensity controlled impedance fluid-filled wave tube (HICI-FT).

It took about 2 years for Popper's lab to work out the kinks, but the machine now presides over a small room at the University of Maryland. A red metal frame supports a steel cylinder with 8.9-centimeter-thick walls, centered between two large shakers that vibrate, generating pressure waves akin to those produced by a pile driver. Tubes surrounding the HICI-FT draw away the enormous amount of heat generated by the shakers, and it perches on vibration isolation mounts to prevent it from shaking the entire building. Fish placed inside the chamber are exposed to sound levels they would experience if they were swimming up to 18 meters away from a pile-driving operation.

Several years ago, Popper and colleagues at the University of Maryland and the Pacific Northwest National Laboratory in Richland, Washington, started by giving juvenile Chinook salmon (Oncorhynchus tshawytscha) a hissy fit; regulators were interested in the experiments because the fish is an endangered species. They've since repeated the process with other species, including striped bass (Morone saxatilis) and lake sturgeon (Acipenser fulvescens).

The HICI-FT results, parts of which were published online June 2012 in PLoS ONE, show that the physiological effects experienced by the fish depend on the sound intensity and accumulated exposure. At lower sound levels, the pressure shifts caused by pile driving might cause minor blood vessels in fins to break and leak. Fish exposed to higher intensity sounds, however, could experience lethal and deafening injuries such as hemorrhaging of the heart and deflated or ruptured swim bladders. In some species, swim bladders both help fish regulate their buoyancy and conduct sound into the ear. Damaging the swim bladder could essentially render species such as catfish hard of hearing. Popper and his colleagues also found that the sound thresholds needed to induce such trauma were higher than what people had previously thought. The take-home message, he says, is that the sound levels that regulatory agencies have been using as safety limits for fish are lower than necessary.

## A working retirement

Although Popper would love to test other anthropogenic sounds fish encounter using the HICI-FT, it is headed back to the Transportation Research Board of the U.S. National Academies, which funded the device. It's just one loose end he's tying up as he prepares to retire in June 2013.

But even after taking his leave, Popper will have projects bubbling. This past June, for instance, he flew out to California to check on work he's started with tuna researcher Barbara Block of Stanford University in Palo Alto. Popper is helping train bluefin tuna (Thunnus thynnus) to respond to different sound levels in a bid to elucidate what the marine predators can hear. “It's the old operant-conditioning paradigm where the animal works for a food reward,” he explains. The sleek animals have taken to the task, Popper hints, although he is cagey about the details since it's a work in progress. He's also helping plan a third international conference on the effects of noise on aquatic life, set for Budapest in August 2013. (He helped kick off the meetings in 2007.)

First, however, many of Popper's students and colleagues will gather in Florida next year to honor the researcher some call the “godfather” of their field. “Art is an amazing person all around and an excellent role model for anyone in science,” Ketten says. Former students say that although Popper expected members of his lab to work hard, he also knew how to have fun, teasing lab members and colleagues. A few turn the tables: “Every now and then I threaten to take his Ph.D. away from him,” says Tavolga, who was Popper's dissertation adviser. “But he says I can't do that because there's a statute of limitations.”

• * Jane J. Lee is a writer in Washington, D.C.