New device explores frontiers of the universe and the brain
By Steven Schultz
Princeton NJ -- Physicist Michael Romalis has invented a device that not only could help discover hidden properties of the universe but also probe the workings of the human brain.
The device measures magnetic signals with a sensitivity greater than any current apparatus, opening windows into a remarkable range of scientific disciplines. In physics, scientists believe some of the deepest mysteries of the universe may be revealed in signals that are very much like magnetic fields and pervade all space. In neuroscience, reading weak magnetic signals is an important method for detecting and mapping brain activity.
Romalis said his sensor may one day find even more uses, such as detecting flaws in microchips or performing military surveillance, but his real motivation for building it was simple curiosity.
"Deep down I am really interested in the fundamental questions," said Romalis. The best, he said, are questions so far outside the mainstream experience that their answers cannot be predicted with any confidence. The possibility of undiscovered fields of energy in the universe, only hinted at in the most advanced theories, is that kind of question. "You just have to go measure and find out," he said. "At the same time, I feel good that we now have this technology and can get something useful out of it."
New realm of understanding
Romalis received his Ph.D. in physics from Princeton in 1997 and went to the University of Washington as a postdoctoral researcher and then faculty member. In Washington, he became interested in a possible aberration in known physical laws, a hypothetical idea called CPT violation.
Most laws of physics have a kind of symmetry. A collision between two billiard balls, for example, is effectively the same whether it runs backwards or forwards in time. It also looks the same if viewed in a mirror or if all positive and negative charges are exchanged. However, physicists have found subtle, but profound exceptions to this idea, such as particles and anti-particles that obey slightly different rules. They even have observed instances when two forms of asymmetry occur simultaneously. (This discovery earned Princeton physicist Val Fitch a 1980 Nobel Prize.) CPT violation, which would involve the loss of three fundamental forms of symmetry at once, has never been observed. However, according to a cutting-edge branch of physics known as string theory, it could exist.
If CPT violation were shown to exist, the discovery would be a major boost to string theory, which deals mostly with phenomena that are too small to measure. String theory seeks to unify branches of physics that have seemed irreconcilable since the days of Einstein, so the discovery of CPT violation could become a major advance in physics. Detecting this effect, however, is not easy.
Romalis focused his attention on magnetism because, if CPT violation ever occurs, it would infuse the universe with a faint field of energy that interacts with ordinary atoms in a way similar to the effect of magnetic fields. This CPT field would give the universe a "preferred direction," like north on a compass. A very sensitive magnetometer might pick up the CPT effect, becoming a kind of universal compass.
The idea behind Romalis' device is the fact that every atom can be viewed as a tiny bar magnet, and that even the tiniest magnetic field will tend to push that bar around. The apparatus contains a vapor of potassium and helium atoms and uses a laser to line up all these atomic magnets. Another laser then "reads" the atoms and measures how far they've been twisted out of line by external magnetic fields. While other magnetometers contain materials that function only at temperatures approaching absolute zero, Romalis' device works at near room temperature and is much more sensitive.
After coming to Princeton in 2002, Romalis and colleagues refined the device and published a description last year in Nature magazine. By summer, Romalis and graduate student Tom Kornack plan to begin their search for CPT violation. While searches for other quirks of particle physics require enormous atom smashers, their test will take place on a table in Romalis' lab. He and Kornack will take measurements throughout the year and look for signals that change as the Earth goes around the sun.
If a pattern emerged, it would "open up a door to a whole new realm of understanding the universe," said Ron Walsworth, a physicist at the Harvard-Smithsonian Center for Astrophysics. And if not, the test would set an important new limit on how strong CPT violation could possibly be if it still somehow existed. "The limits they are trying to best are the ones we set," said Walsworth. "In the long term, his test has the potential for much more dramatic improvements than our technology."
Better images, lower cost
Romalis' device also could yield dramatic improvements in cognitive neuroscience, said James Haxby, professor in the Department of Psychology and the Center for the Study of Brain, Mind and Behavior. In this field, the goal is to see how parts of the brain interact to produce behaviors, thoughts, emotions and consciousness itself.
Neuroscientists have various machines that show which parts of the brain "light up" as people undergo tests. Some, such as "functional MRI," which tracks blood flow, are able to pinpoint brain activity to an area as small as 1 millimeter, but have a long lag between when the brain activity occurs and the signal shows up. Other machines, such as magnetoencephalo-graphy, respond directly to electrical activity in the brain, which also produces tiny magnetic fields. These machines detect changes almost instantly, but are not good at finding the exact location of the activity. Romalis' device could combine the best of both technologies -- instant response with accurate localization.
At the same time, Romalis' device would eliminate the supercooled magnets that are required for MRI and for some of the electromagnetic tests, making the equipment much less expensive and more versatile. Laid out around a person's head, current supercooled magnetic detectors take readings about every 2 centimeters along the scalp. Romalis' magnetometers could measure signals every 2 millimeters or so. And while a current state-of-the-art magnetoen-cephalography machine costs $2 million, Romalis is building his prototype for $200,000.
"If we have more information -- more measurements from more points in space around a person's head -- we should be able to get much better localization at a much lower cost," said Haxby. "So it's really exciting."
With a grant from the National Institutes of Health, Romalis already has begun building a human-sized metal tube made of three layers of an alloy that blocks the magnetic field from the Earth and other sources. If all goes well, Romalis and colleagues hope to put a volunteer into the tube and begin taking measurements during the summer.
In the meantime, Romalis continues to think about further uses for his magnetometer in medicine, physics and other fields. But in the end, he said, he prefers not to work on too many projects. "We've done some experiments in the lab and we're still at the drawing board. Over the next few years, we'll see which ones look most promising," he said. "If we have a few applications that would be good, and then I am always most excited to focus on the fundamental physics."