Einstein, relativity, and much of 20th-century physics have come under assault from an esoteric but far-reaching experiment. A collaboration of 174 physicists fired bursts of neutrinos from the headquarters of CERN, the European Organization for Nuclear Research, in Geneva, Switzerland, to a detector in Gran Sasso, Italy. They tracked 16,111 of the ghostlike particles and measured how long they took to complete the trip. After three years of experiments and intense analysis, the team reported in September that the neutrinos were arriving one 17-millionth of a second early.
The minuscule discrepancy revealed by the experiment, dubbed OPERA (Oscillation Project with Emulsion-tRacking Apparatus), has staggering implications. It seems to indicate that the neutrinos were traveling faster than light, violating what has long been regarded as an ironclad cosmic law. If neutrinos really can do that, then Einstein’s theory of relativity, the backbone of modern physics, could break down. Time could flow in reverse. Neutrino-based messages could reach recipients before they were sent. An effect could precede its cause, which would explode our entire way of thinking about the universe.
The result was so peculiar that the CERN physicists encouraged other scientists to look for design errors in their experiment. Many quickly obliged, but physicist and Opera spokesman Antonio Ereditato says that a lot of the critiques have been overly simplistic: “We are not so stupid, ok? These are mistakes we don’t do.” The group did receive some good ideas and suggestions, he adds, but found no smoking guns. Even the most skeptical scientists agree that the experiment was carefully performed and analyzed.
That credibility has led some brave physicists to confront a question both daunting and electrifying: What if the Opera results are correct and neutrinos really are thumbing their noses at Einstein? Relativity has been experimentally validated so many times over the past century that no respectable physicists are calling for its death. Instead, when the neutrino results emerged, theorists rushed to propose addenda, including grand visions of new forces and extra dimensions, that could account for the Opera findings and keep relativity intact—much as relativity elaborated on Isaac Newton’s model of physics but did not invalidate it.
One of the most intriguing ideas comes from Jarah Evslin, Emilio Ciuffoli, and Xinmin Zhang of the Chinese Academy of Sciences in Beijing, who are using one unexplained phenomenon to account for another. Dark energy is a mysterious kind of antigravity thought to operate on a cosmological scale, pushing galaxies apart and causing the universe to expand ever-more quickly. Evslin and colleagues propose that dark energy changes its behavior in the presence of large masses like Earth. It could be scrunching space-time together near the planet so that the neutrinos’ route becomes slightly shorter—20 meters shorter, to be exact—than the measured value of 730,534.61 meters. “It creates a shortcut,” Evslin says. “The neutrinos see the distance between CERN and Gran Sasso as being less than we do.” If the particle is traversing a smaller distance (from the neutrino’s perspective) in the same amount of time, its speed dips below that of light, preserving relativity.
Particle physicist Argyris Nicolaidis of the University of Thessaloniki in Greece suggests that neutrinos might take another kind of shortcut, one that passes through an extra, hidden dimension. Some versions of string theory, an all-encompassing theory of particle physics, suggest that our three-dimensional universe could exist within a four-dimensional sheet called a brane. (By analogy, think of the universe as a picture imprinted on an enormous piece of paper.) This brane may, in turn, occupy a higher-dimensional space known as the bulk. Most of the particles in our universe stick within the brane, but theorists have proposed that some neutrinos might be able to travel through the bulk as well. If our brane is folded over itself, then passing between the folds could offer a shorter path between two points. By taking an excursion through the bulk, Nicolaidis explains, the neutrinos do not have to travel as far to get from Switzerland to Italy. “That gives you an effective speed which appears faster than the speed of light,” he says.