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A Mystery, Locked in Timeless Embrace
By JOHN NOBLE WILFORD, The New York Times, December 20, 2005
When Egyptologists entered the tomb for the first time more than four decades ago, they expected to be surprised. Explorers of newly exposed tombs always expect that, and this time they were not disappointed - they were confounded.
It was back in 1964, outside Cairo, near the famous Step Pyramid in the necropolis of Saqqara and a short drive from the Sphinx and the breathtaking pyramids at Giza. The newfound tomb yielded no royal mummies or dazzling jewels. But the explorers stopped in their tracks when the light of their kerosene lamp shined on the wall art in the most sacred chamber.
There, carved in stone, were the images of two men embracing. Their names were inscribed above: Niankhkhnum and Khnumhotep. Though not of the nobility, they were highly esteemed in the palace as the chief manicurists of the king, sometime from 2380 to 2320 B.C., in the time known as the fifth dynasty of the Old Kingdom. Grooming the king was an honored occupation.
Archaeologists were taken aback. It was extremely rare in ancient Egypt for an elite tomb to be shared by two men of apparently equal standing. The usual practice was for such mortuary temples to be the resting place of one prominent man, his wife and children.
And it was most unusual for a couple of the same sex to be depicted locked in an embrace. In other scenes, they are also shown holding hands and nose-kissing, the favored form of kissing in ancient Egypt. What were scholars to make of their intimate relationship?
Over the years, the tomb's wall art has been subjected to learned analysis, inspiring considerable speculation. One interpretation is that the two men are brothers, probably identical twins, and this may be the earliest known depiction of twins. Another is that the men had a homosexual relationship, a more recent view that has gained support among gay advocates.
Now, an Egyptologist at New York University has stepped into the debate with a third interpretation. He has marshaled circumstantial evidence that the two menmay have been conjoined twins, popularly known as Siamese twins. The expert, David O'Connor, a professor of ancient Egyptian art at the N.Y.U. Institute of Fine Arts, said: "My suggestion is that Niankhkhnum and Khnumhotep were indeed twins, but of a very special sort. They were conjoined twins, and it was this physical peculiarity that prompted the many depictions of them hand-holding or embracing in their tomb-chapel."
Dr. O'Connor elaborated on his hypothesis in a recent lecture and in an interview in New York. He is describing and defending the idea before scholarly peers at a conference, "Sex and Gender in Ancient Egypt," this week at the University of Wales in Swansea.
Opposition to his proposal promises to be spirited. Most Egyptologists accept the normal-twins interpretation advanced most prominently by John Baines, an archaeologist at the University of Oxford in England.
"It's a very persuasive case Baines makes," Dr. O'Connor acknowledged.
And he noted that the gay-couple hypothesis had become the popular idea in the last decade. A leading proponent is Greg Reeder, an independent scholar in San Francisco and a contributing editor of KMT, a magazine of Egyptian art and history. The most Google references to the tomb, archaeologists say, concern the homosexual idea.
The gay argument leans on the analogy with depictions of married heterosexual couples in Egyptian art, which was first suggested by Nadine Cherpion, a French archaeologist.
Because the embraces of heterosexual couples in the tomb art convey an implicit erotic and sexual relationship, and perhaps the belief of its continuation in the afterlife, Mr. Reeder and his allies contend that similar scenes involving the two men have the same significance, that they presumably are gay partners.
Calling attention to the most intimate scene of the two embracing men, Mr. Reeder said: "They are so close together here that not only are they face to face and nose to nose, but so close that the knots on their belts are touching, linking their lower torsos. If this scene were composed of a male-female couple instead of the same-sex couple we have here, there would be little question concerning what it is we are seeing."
In an interview last week, Mr. Reeder said Dr. O'Connor's new interpretation was fascinating, but added, "It's the most extreme and unnecessary theory."
Dr. Baines, in an e-mail message from Oxford, said that he "would stick with my own interpretation, because it seems to me to require the smallest amount of 'exceptionalism' and to fit reasonably well with other patterns."
As for the sexual implications of the embracing poses, Dr. Baines has suggested that they could signify the "socially and emotionally linked roles" of two men who probably were twins.
Or they could symbolize "protection or close identification and reciprocity" between the two.
Ancient Egyptian art, experts say, is not meant always to be taken literally.
James Allen, an Egyptologist at the Metropolitan Museum of Art who is not involved in the research, called the twins hypothesis probable and the conjoined-twins idea "an interesting wrinkle." The least likely, he said, was the homosexual-relationship proposal.
Dr. Baines said, "The gay-couple idea is essentially derived from imposing modern preoccupations on ancient materials and not attending to the cultural context."
If Dr. O'Connor is correct, the tomb holds a rare example of documented conjoined twins that early in history, he said, and thus an insight into ancient Egyptian attitudes toward disabilities. He cited other records, and art of the dwarf Seneb, who in a somewhat later court was "overseer of dwarfs in charge of dressing" the king and a tutor of the royal sons, both positions of elite status. Egyptians appear to have viewed such people as auspicious figures, not freaks.
"The creator gods had made everything, dwarfs, two-headed calves and conjoined twins," Dr. O'Connor said. "A king felt more elevated for having these singular creatures to serve him as manicurists."
Like most elite tombs, this one was built of stone masonry and had several chambers, the most sacred the chapel or cult room. Here, survivors of the deceased brought offerings and paid homage. Beneath the room was the burial chamber. The remains of the two men were not found.
Egyptian tombs typically represent the lives of the departed in art and script. Images of the two men and hieroglyphic inscriptions about them and their families are everywhere, in corridors and in the chapel. The two men had wives who are named and represented in the art. Yet there are no scenes of them embracing their wives.
Their apparently close relationship and equal standing are illustrated not only in images of them together, either holding hands or embracing. In other instances, Dr. O'Connor said, one man appears alone on a wall face, and the other on the opposing wall. Their stature and pose are identical, and they are performing similar acts. While one fishes in the marshes, for example, the other hunts birds in the same setting.
These scenes and the ones of intimate embraces led to the speculation, initially by Mounir Basta, the Egyptian archaeologist who first explored the tomb, that Niankhkhnum and Khnumhotep were brothers, probably twins. Dr. Baines developed the idea in a seminal study in the 1980's, and others took up the gay-couple idea.
When Dr. O'Connor looked into the matter, he was struck by a comparison of the images of the two men with pictures of Chang and Eng, the famous conjoined twins born in 1811 in Siam. They were seen close together, arm in arm. They and a number of documented conjoined twins also had wives and children and engaged in strenuous activities, much like the hunting and fishing of the two Egyptians.
Their names, Niankhkhnum and Khnumhotep suggest another clue, Dr. O'Connor said. Both names refer to the god Khnum, the deity who fashions the form of a child in the womb. Though not an uncommon part of Egyptian names, in this case it might be a play on words to signify their paired lives.
David Silverman, an Egyptologist at the University of Pennsylvania, and his student Joshua Robinson pointed out to Dr. O'Connor that the name Khnum was also similar to the ancient Egyptian word khenem, which means "to unite" or "be united."
One problem, however, is that none of the tomb art shows a physical link between the two men, as in some pictures of Chang and Eng.
Egyptian mortuary art, Dr. O'Connor said, "operates in terms of idealized types, not actual figures."
"It's not photographic art," he added.
Dr. Allen of the Metropolitan Museum agreed, saying, "Egyptian art was symbolic, and it is doubtful the Egyptians would have tried to represent realistically the join between these twins."
Whether the two men were normal twins, conjoined twins or a gay couple, the speculation highlights a problem and an opportunity for scholars.
"We don't have a lot of information about how twins were viewed in ancient Egypt or how gay life was perceived," Dr. Allen said.
Few accounts refer to twins of any kind in the civilization, and an honored role for conjoined twins, if that is what they were, would be even stronger evidence of Egyptian attitudes toward people with physical disabilities.
"Such attributes were often seen as fabulous rather than monstrous, and positive rather than negative," Dr. O'Connor said. "They attested the creator god's ability, if he wished, to bring wondrous changes upon the norms he himself had established."
Besides, Dr. O'Connor pointed out, "The fact that they could have worked simultaneously on the grooming of the king's two hands might have been seen as especially appropriate and desirable."
Homosexuality was only occasionally referred to in Egyptian documents, sometimes in myths of certain gods, implying that it was not considered a normal relationship. The prevailing attitude, scholars say, was not antigay, though probably negative, and certainly not as accepting of homosexual activity it was in classical Greece.
If the tomb of the two men was indeed a public profession of their emotional and sexual attachment, scholars say, it could inspire a reassessment of the place of homosexuals in Egyptian culture.
Defending his interpretation, Mr. Reeder said the similarity of the embracing scenes with those of husbands and wives should not be dismissed. He further noted, in his lecture in Wales, new evidence that he said suggested that one of the men died well before the other. Khnumhotep was described in one place as being honored by a great god, possibly meaning he had by then entered the afterlife, while in a corresponding scene Niankhkhnum had only official titles of his career in life.
If, then, Niankhkhnum was the one who finished decorating the tomb, Mr. Reeder said, it was unlikely that they were conjoined twins. "They would have had to be surgically separated," he said in an interview. "The Egyptians had surgical knowledge. But separating such twins would be expecting too much."
The fact that the two men had families is not seen as contradicting the gay hypothesis, Egyptologists said. Like others of the time, the two men would presumably have sired children to carry on after them and maintain the cult dedicated to their well-being through eternity.
Mr. Reeder said his hypothesis "resonates in the gay community because it shows two historical men being intimate with each other, and this was something that could be shown in an ancient culture."
Dr. O'Connor acknowledged the interpretation's appeal. "Gays and lesbians still experience a great deal of prejudice and discrimination, and these two ancient Egyptians are yet further proof that homosexuality goes far back in history," he said.
"The semipublic nature of their tomb chapel," he added, "suggests their gay relationship was accepted as normative by the elite of a particularly famous and illustrious civilization."
Finally, Dr. O'Connor conceded that the conjoined-twins hypothesis, like the other two, is not "fully supported by conclusive evidence."
Findings: Is That a Finger or a Jell-O Mold?
By ERIC DASH, The New York Times, December 20, 2005
Identity thieves are always looking for new ways to pry out personal information, from trolling through trash cans to phishing for bank accounts online. But here is one method they may not have tried: using fake fingers made from Play-Doh and gelatin, or taking digits from a cadaver's hand.
In a study, researchers at Clarkson University in Potsdam, N.Y., tested 66 fake fingers to see if they could outwit biometric devices, which identify individuals based on the physiological properties of their fingerprints or other body parts. The fake fingers went undetected more than half the time.
"Even if it comes from Play-Doh, the scanner has no way of knowing that. It is just taking a picture of an image," said Stephanie C. Schuckers, a Clarkson electrical and computer engineering professor who helped lead the research. "People in the industry are aware this is an issue."
The results, published this year in the IEEE: Transactions on Systems, Man, and Cybernetics journal, highlight a potentially huge vulnerability. Many hospitals and federal agencies use it for tracking people and restricting access. More than a million I.B.M. laptops have print-based safeguards built-in. Even some supermarkets allow their customers to swipe a finger instead of a credit card.
Biometric devices generally work by converting a fingerprint image into a series of numbers, just as a checkout-counter scanner reads a bar code. They do not capture so-called "liveness" characteristics, like the blood oxygen content or sweat.
To be sure, some biometric devices rely on an additional form of identification, like a PIN, to guard against fraud. But Dr. Schuckers hopes to introduce new technology that can detect pore perspiration patterns to prevent the biometric devices from being fooled. She has started a company, NexID Biometrics, to start licensing it next year.
Dr. Schuckers conceded it would take determined handiwork to pull off such a fraud. Besides lifting the latent fingerprint off a glass like a forensics specialist on the TV hit "C.S.I.," a thief would need to scan, flip and then use ultraviolet light to etch the image onto printed circuit board before transferring it to the Play-Doh or gummy finger cast.
Global Trend: More Science, More Fraud
By LAWRENCE K. ALTMAN and WILLIAM J. BROAD, The New York Times, December 20, 2005
The South Korean scandal that shook the world of science last week is just one sign of a global explosion in research that is outstripping the mechanisms meant to guard against error and fraud.
Experts say the problem is only getting worse, as research projects, and the journals that publish the findings, soar.
Science is often said to bar dishonesty and bad research with a triple safety net. The first is peer review, in which experts advise governments about what research to finance. The second is the referee system, which has journals ask reviewers to judge if manuscripts merit publication. The last is replication, whereby independent scientists see if the work holds up.
But a series of scientific scandals in the 1970's and 1980's challenged the scientific community's faith in these mechanisms to root out malfeasance. In response the United States has over the last two decades added extra protections, including new laws and government investigative bodies.
And as research around the globe has increased, most without the benefit of such safeguards, so have the cases of scientific misconduct. Most recently, suspicions have swirled around a dazzling series of cloning advances by a South Korean scientist, Dr. Hwang Woo Suk.
Dr. Hwang's research made him a national hero. His team outdid rivals by claiming to have extracted stem cells from cloned human embryos and to have cloned a dog, an extraordinary feat. Some observers hailed the breakthroughs as worthy of a Nobel Prize.
Last month, critics charged that Dr. Hwang's published findings hid ethical lapses. And last week, collaborators accused the researcher of fabricating results in one of his landmark human cloning studies, published in Science last spring.
Dr. Hwang has insisted on his innocence but said he would retract the Science paper. Now questions are growing about his earlier work, including Snuppy, the dog he claims to have cloned. Yesterday, news agencies reported that Seoul National University officials investigating Dr. Hwang's claims locked down his laboratory, impounded his computer and interviewed his colleagues, among other actions.
"The Korean case shows us that we should be a lot more cautious," Marcel C. LaFollette, the author of "Stealing Into Print: Fraud, Plagiarism, and Misconduct in Scientific Publishing," said in an interview. "We have been unwilling to ask tough questions of people who are from other countries and whose systems are different because we were attempting to be polite."
To be sure, most scientists resist pressures to cut corners and adhere to the canons of science, honoring the truth above all else. But surveys suggest that there are powerful undercurrents of misbehavior and, in some cases, outright fakery.
In June, a survey of 3,427 scientists by the University of Minnesota and the HealthPartners Research Foundation reported that up to a third of the respondents had engaged in ethically questionable practices, from ignoring contradictory facts to falsifying data.
Scientific fraud as a public danger burst into public view in the 1970's and 1980's, when major cases of misconduct shook a number of elite publications and institutions, including Yale, Harvard and Columbia.
In 1981, Dr. Donald Fredrickson, then the director of the National Institutes of Health, defended the standard view of science as a self-correcting enterprise. "We deliberately have a very small police force because we know that poor currency will automatically be discovered and cast out," he said.
But fraud after fraud made the weaknesses of that system impossible to ignore. In the early 1980's, a young cardiology researcher, Dr. John R. Darsee, was found to have fabricated much data for more than 100 papers he wrote while working at Harvard and Emory Universities. His work appeared in The New England Journal of Medicine, The Proceedings of the National Academy of Sciences and The American Journal of Cardiology, among other top publications.
Startled, the federal government, beginning in 1985, took steps to augment the existing safeguards. For instance, Congress passed a law requiring public and private institutions to establish formal ways to investigate charges of fraud, in theory helping to assess damage, clear the air and protect the innocent. Eventually, the federal government established its own investigative body, now known by the Orwellian title of the Office of Research Integrity.
Journal editors, at the center of the storm, also took collective action to enhance their credibility. In 1997, they founded the Committee on Publication Ethics, or COPE, "to provide a sounding board for editors who are struggling with how to best deal with possible breaches in research and publication ethics," according to the group's Web site.
Consisting mostly of editors of medical journals, the committee now has more than 300 members in Europe, Asia and the United States.
Still, the frauds kept coming. In 1999, federal investigators found that a scientist at the Lawrence Berkeley Laboratory in Berkeley, Calif., faked what had been hailed as crucial evidence linking power lines to cancer. He published his research in The Annals of the New York Academy of Sciences and F.E.B.S. Letters, a journal of the Federation of European Biochemical Societies.
The year 2002 proved especially bleak. At Bell Labs, a series of extraordinary claims that seemed destined to win a Nobel Prize, including the creation of molecular-scale transistors, suddenly collapsed. Two of the world's most prestigious journals, Science and Nature, had published many of the fraudulent papers, underscoring the need for better safeguards despite two decades of attempted repairs.
Experts now say that the explosive growth of science around the globe has made the problem far worse, because most countries have yet to institute the extra measures that the United States has put in place. That imbalance is at least partly responsible for a rise in scientific scandals in other countries, they say.
Dr. Richard S. Smith, a former editor of The British Medical Journal (now BMJ) and the co-founder of the Committee on Publication Ethics, a group of journal editors, said in an interview that fraud was becoming increasingly difficult to root out because most countries' protective measures were either patchy or altogether absent. "It's hard enough to do something nationally, and to do it internationally is still harder," he said. "But that's what is needed."
Contributing to the problem is a drastic rise in the number of scientific journals published around the world: more than 54,000, according to Ulrich's Periodicals Directory. This glut can confuse researchers, overwhelm quality-control systems, encourage fraud and distort the public perception of findings.
"Foreign scientific journals have gone through the roof," said Shawn Chen, a senior associate editor at Ulrich's, nearly doubling to 29,098 in 2005 from 15,300 in 1980. "We're having a hard time keeping up."
While millions of articles are never read or cited - and some are written simply to pad résumés - others enter the pressure cooker of scientific and biomedical promotion, becoming lucrative elements of companies' business strategies.
Until now, cases of questionable research in other countries have gotten little attention in the United States. But international editors, shaken by scandal, are now publicizing them and expressing concern. This year, the July 30 issue of BMJ devoted four articles to the subject, asking on its cover: "Suspicions of fraud in medical research: Who should investigate?"
The articles discussed cases in which several publications, including BMJ, had stumbled in resolving serious doubts about the truthfulness of published studies done in Canada and India. The Canadian research claimed that a patented mix of multivitamins improved brain function in older people, and the Indian study said that low-fat, high-fiber diets cut by nearly half the risk of death from heart disease.
The BMJ said that it published its own version of the Indian research in April 1992 and that it had later investigated serious questions about the validity of the research for more than a decade before speaking out.
The difficulty, the editors said, was that journals could go only so far in fraud inquiries before needing the aid of national investigative bodies and professional associations that oversee scientific research. But in the Indian and Canadian cases, they added, such bodies either did not exist or refused to help, so "the doubts are unresolved."
The journal's editors, Dr. Fiona Godlee and Dr. Jane Smith, noted that the United States and Scandinavian countries had adopted institutional defenses and that Britain was considering such safeguards. Journals have an obligation to help the process, they concluded, by publicizing their difficulties and doubts.
Most recently, the South Korean uproar illustrates the tangle of publishing and policing issues that can arise as science becomes increasingly competitive and international.
"Now we're in a situation where we have these alliances between university researchers in countries and between institutions that really weren't working together before," said Dr. LaFollette, author of "Stealing Into Print."
The journal Science, owned by the American Association for the Advancement of Science, published the research of Dr. Hwang of Seoul National University and his colleagues in March 2004 and June 2005, hailing it as pathbreaking.
On Dec. 14, the magazine noted in a statement how fraud charges about the 2005 research had led to two investigations - one in South Korea and the other at the University of Pittsburgh, home to one of the article's 25 co-authors. "The journal itself is not an investigative body," Donald Kennedy, the magazine's editor, argued. "We await answers from the authors, as well as official conclusions, before we come to any ourselves."
On Friday in a news conference, Dr. Kennedy emphasized that the magazine had made no accusations of fraud against Dr. Hwang. "As of now we can't reach any conclusions with respect to misconduct issues," he said.
Independent scientists said it remained to be seen how thoroughly authorities in South Korea, where Dr. Hwang is a celebrity, would investigate the case and resolve knotty issues in what amounts to a highly public test of institutional maturity.
Seoul National University is leading the inquiry. Its committee, which apparently has the authority to examine Dr. Hwang's raw data and to question his colleagues, may have the best chance of discovering how much of his work remains valid.
But experts also cautioned that the committee's credibility requires the addition of outsiders, and perhaps scientists from other countries, who know the field and can help ensure that the investigation will retain its objectivity.
"Unfortunately, individual institutions have an enormous conflict of interest," said Dr. Smith, the former editor of The British Medical Journal. "It's a lot easier," he said, for such bodies when examining an allegation of fraud on their own, "to slide someone out of the organization or to suppress it altogether."
Old Curative Gets New Life at Tiny Scale
By BARNABY J. FEDER, The New York Times, December 20, 2005
Silver, one of humankind's first weapons against bacteria, is receiving new respect for its antiseptic powers, thanks to the growing ability of researchers to tinker with its molecular structure.
Doctors prescribed silver to fight infections at least as far back as the days of ancient Greece and Egypt. Their knowledge was absorbed by Rome, where historians like Pliny the Elder reported that silver plasters caused wounds to close rapidly. More recently, in 1884, a German doctor named C. S. F. Crede demonstrated that a putting a few drops of silver nitrate into the eyes of babies born to women with venereal disease virtually eliminated the high rates of blindness among such infants.
But silver's time-tested - if poorly understood - versatility as a disinfectant was overshadowed in the latter half of the 20th century by the rise of antibiotics.
Now, with more and more bacteria developing resistance to antibiotic drugs, some researchers and health care entrepreneurs have returned to silver for another look. This time around, they are armed with nanotechnology, a fast-developing collection of products and skills that helps researchers deploy silver compounds in ways that maximize the availability of silver ions - the element's most potent form. Scientists also now have a better understanding of the weaknesses of their microbial adversaries.
One of the urgent goals is to prevent bacterial infections that each year strike 2 million hospital patients and kill 90,000, according to the Centers for Disease Control and Prevention. Such infections are usually treated with large doses of antibiotics and sometimes with repeat surgeries. They cost the health care system roughly $4.5 billion annually, and the challenge is growing with the spread of drug-resistant microbes.
The latest advance for silver therapy comes from AcryMed, a small company in Portland, Ore., that has invented a process to deposit silver particles averaging about 10 nanometers - less than a thousandth the diameter of a human a hair - on medical devices. AcryMed's first customer, I-Flow, makes a silver-coated catheter that pumps painkillers into the wounds created by surgery.
I-Flow got federal regulatory clearance on Dec. 2 to sell the device and has already begun shipping them to customers. The nanoscale particles have so much surface area to react with the microbes, in relation to their volume, that small concentrations are effective antiseptics.
"The equivalent of a teaspoon of silver in a seven-lane Olympic-size swimming pool is enough to do the job," said Bruce Gibbons, the microbiologist who is AcryMed's founder and chief executive.
AcryMed hopes to reach agreements with catheter companies larger than I-Flow, including the makers of urinary catheters, the most common breeding ground for hospital infections. Nano-scale silver could also eventually make its way onto permanently implanted devices like silicone breasts, artificial hips and knees and pacemakers.
The term nanotechnology is derived from the nanometer, one-billionth of a meter. Nanoscale materials often exhibit unusual structures and behaviors compared with bulkier quantities of the same material.
AcryMed began developing wound dressings with large-scale silver particles in the 1990's. It adapted its process to make smaller and smaller particles when medical-device makers asked it for silver coatings. As the particles shrank to nanoscale dimensions, they became so highly reactive that AcryMed was able to bind them to virtually every glass and plastic material it tested.
As has often been the case in nanotechnology, AcryMed is rushing to get products into the market long before the nano-scale phenomena it is exploiting are fully understood. It is not entirely clear, for example, how silver kills many bacteria at the diluted concentrations considered safe for medical use.
AcryMed also admits that it cannot fully explain the forces that produce the surface-binding performance of its particles. It is a crucial trait, though, because surface coverage that is even and thorough blocks the formation of a thick carpet of bacteria known as biofilm.
Preventing the build up of biofilms, which eventually release large masses of free-floating bacteria, is in turn a key to avoiding infections, according to Dr. Dennis Maki, a professor of medicine and the head of infectious diseases at the University of Wisconsin Medical School and Pubic Health.
What a Pool Table Can Teach You About Unstirring the Coffee
By KENNETH CHANG, The New York Times, December 20, 2005
When cream is stirred into coffee, it is no surprise to see the swirls of white and brown become tan. It would be a shock if stirring in the opposite direction separated the liquid back to the original brown and white swirls.
Physicists describe the stirring of coffee, as well as the billowing of smoke, the flow of heat, the decay of buildings and many other phenomena as "irreversible."
The second law of thermodynamics essentially says that disorder increases. In the long term, this means that the universe will inevitably fall apart. In the short term, it means that you cannot unstir your coffee.
Yet the basic physics of the universe does not demand the second law; it includes no such notion of irreversibility. And an experiment, described in the current issue of the journal Nature, shows that stirred liquids can be unstirred in some cases.
Two physicists, David J. Pine of New York University and Jerry P. Gollub of Haverford College in Pennsylvania set up a device consisting of two concentric cylinders. In the gap, about a tenth of an inch wide, they poured a liquid with the viscosity of honey and hundreds of thousands of tiny beads of the same density as the liquid, so that they floated within in the liquid without rising or falling. The researchers traced the motion of about 60 of the balls that were dyed black.
The researchers turned the inner cylinder clockwise - dragging along the liquid and the balls - and then turned it counterclockwise back to its original position. When the amount of turning was small, the balls all returned to virtually the same positions where they started. This behavior occurred only because the fluid was viscous.
For a slightly greater degree of turning, then the balls started jostling around instead of ending up back at their starting positions. "The particles move all over the place," Dr. Pine said.
The stirring had become irreversible.
"What it implies is there is a sharp transition" between reversible and irreversible flows, said Troy Shinbrot, a professor of biomedical engineering at Rutgers University who was not involved in the research but did write an accompanying commentary in Nature.
Dr. Pine and Dr. Gollub enlisted two other scientists, John F. Brady of the California Institute of Technology in Pasadena, Calif., and Alexander M. Leshansky at the Technion-Israel Institute of Technology, to help explain what was going on.
Dr. Pine said they believed that the stirring became irreversible when the balls were significantly affected by more than one of their neighbors.
For example, if the cue ball bounces off only one other ball, it is easy to imagine a pool shark making the reverse shot. But if the cue ball bounces off more than one other ball, then the shot becomes much more difficult to reverse.
Stirring is not just a theoretical interest, either. The same phenomenon is important in manufacturing drugs, refining oil and understanding the movement of the Earth's interior.
