Murphy's lab - combatting obstacles in researching for new data

Science News, April 25, 1992 by Ivars Peterson

The minute you think everything is under control, beware. Murphy lurks nearby, ready to meddle.

That's the moment when a sensor that has performed reliably through innumerable experiments will suddenly malfunction. When spurious electrical signals will surreptitiously creep into a stream of hard-won data. When a long-overlooked hardware quirk or software glitch will triumphantly proclaim its presence.

Such are the perils of experimental and observational science. Each measurement, dutifully recorded and elegantly displayed by a diligent computer, serves not only as a probe of the unknown but also as a testament to Murphy's ubiquity.

"I and my colleagues have been implacable foes of Mr. Murphy," says physicist Lawrence G. Rubin of the National Magnet Laboratory at the Massachusetts Institute of Technology.

But decades of experience suggest that no matter how much care someone may take to avoid Murphy's meddling, Murphy will find a way. "He's always going to win in some cases," Rubin insists. "All you can do is hope it doesn't happen too often."

And, as instruments become more sophisticated and technology more complicated, Murphy finds new playgrounds in which to show off his ingenuity and exercise his unique skills. "It gives him the chance to dream up things that we never knew about before," Rubin says.

Alas, too many researchers - both novice and experienced -- no longer appreciate well enough the numerous ways in which data can be corrupted as signals pass from sensor to meter to computer. The crisp displays of digital electronic instruments and the breathtaking number-crunching, data-manipulating capabilities of computers distract them from questions about the quality of the original signals.

Many researchers no longer have first-hand knowledge of when to be skeptical of their measurements and when to trust them. Not so long ago, a scientist or technician would sit in front of a meter, patiently recording sequences of numbers in a notebook (or on the indispensable scrap of paper towel). It was possible to see directly when the meter had settled down, whether the signals made sense, whether any glitches or unexpected events occurred. Nowadays, inscrutable electronic boxes automatically convert analog signals into sequences of digits and send them to computers -- with nary a researcher in sight.

And it is at the frontiers of research -- at millikelvin temperatures, nanometer dimensions, kilogauss magnetic fields and giga-electron-volt energies -- that it's easiest to fall into Murphy's traps. In these situations, experience gained at less extreme conditions may no longer apply.

Concerns that physics students and others no longer take Murphy seriously enough prompted Rubin, Scott T. Hannahs of MIT and Bruce L. Brandt, now at Florida State University in Tallahassee, to develop a tutorial on measurement technology in the laboratory. Presented last month at an American Physical Society meeting in Indianapolis, their tutorial carried the subtitle, "How to Give Murphy a Run for His Money."

Rubin and his colleagues belong to a group within the American Physical Society dedicated to promoting the cause of careful measurement in physics.

Switch on a power supply, and the momentary electrical surge that results can show up in a nearby data-conveying cable. Operate a television camera, and its characteristic frequencies can leak into electrical leads. The inevitable result of a highly electrified world, electromagnetic interference caused by alternating or fluctuating currents creates one woe after another.

Such problems are nothing new to experienced experimenters. Over the years, they have developed sophisticated means of filtering out unwanted signals, or they have learned to avoid making measurements when and where certain types of interference are likely to occur.

"It's always there, and we're always trying to beat it," Rubin says. "Murphy comes in by producing interfering signals that happen to arrive at the same time or at the same frequency as what you're looking for."

A classic example of what can go wrong occurred in early 1989, when astronomers thought they had detected the precisely timed flashes of light coming from a rapidly rotating neutron star in the remnant of supernova 1987 A. To identify the pulsar's minute fluctuations in brightness, the astronomers used a sensitive, telescope-mounted detector to collect visible and infrared light from the supernova. The brightness data, recorded on magnetic tape, were then analyzed with a supercomputer at the Los Alamos (N.M.) National Laboratory.

The researchers focused their attention on extracting any faint signals that occurred at a fixed frequency -- the output expected from a pulsar. In this way, they could eliminate any interfering sources of electrical noise, generally characterized by erratic or varying signals. Among the more notorious culprits were television cameras used to monitor telescope operations.

"[Electromagnetic interference' is a common problem and always a considerable worry," says team member Jerome Kristian of The Observatories of the Carnegie Institution of Washington, based in Pasadena, Calif.