Faster Than Light Particles? Not So Fast, Some Say

The Gran Sasso National Laboratory of the Italian Institute of Nuclear Physics, located nearly a mile below the surface of the Gran Sasso mountain about 60 miles outside of Rome, detects tiny particles called neutrinos.

(Image credit: Paolo Lombardi INFN-MI)

Three weeks ago, a group of Italian scientists announced that they had measured objects moving faster than light, violating the fundamental laws of physics. Since then, their work has been met by a barrage of criticism. Physicists claim to have found flaws in the group's method of recording the speed of the neutrinos, and they say that correcting for these flaws slows the neutrinos to less astonishing speeds.

The researchers who conducted the OPERA experiment (Oscillation Project with Emulsion-tracking Apparatus) stand by their work, which found neutrinos to be traveling from Switzerland to Italy at 1.000025 times the speed of light. They invited the rest of the scientific community to scrutinize their startling finding, and that is exactly what has happened — a classic example of science in action, shouldering its way toward a consensus one way or the other on a controversial topic.

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In a paper posted to the physics pre-print website arXiv.org, van Elburg argues that the Italian scientists failed to account for the fact that the GPS satellite they used as their timekeeping device is moving. If they had corrected for the motion of the satellite as Einstein's theory of special relativity requires, they would not have measured the neutrinos traveling at a superluminal speed, van Elburg asserts.

But their timekeeping was flawed, van Elburg says, because the GPS clock was moving along its orbit from west to east above CERN and Gran Sasso, roughly parallel to the west-east line between them, and special relativity shows that this motion of the clock ever-so-slightly changes the distance between it and each of the two ground locations. When radio signals from the GPS are detected and recorded at each location to mark the neutrino departure and arrival times, the OPERA scientists needed to subtract the time it took for the signals to travel that distance. Van Elburg said they weren’t using the right measure of the distance, because they weren't considering the distance-shortening effect of the GPS clock's motion.

If they had applied the right correction to the neutrino departure time at CERN, the OPERA scientists would have recorded it as being 32 nanoseconds earlier, van Elburg said. Similarly, they would have calculated the neutrino arrival time at Gran Sasso as being 32 nanoseconds later. Adding up these changes, the neutrinos' travel time was actually 64 nanoseconds longer than the scientists thought it was, van Elburg said, making the particles 4 nanoseconds slower than light.

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Natalie Wolchover was a staff writer for Live Science from 2010 to 2012 and is currently a senior physics writer and editor for Quanta Magazine. She holds a bachelor's degree in physics from Tufts University and has studied physics at the University of California, Berkeley. Along with the staff of Quanta, Wolchover won the 2022 Pulitzer Prize for explanatory writing for her work on the building of the James Webb Space Telescope. Her work has also appeared in the The Best American Science and Nature Writing and The Best Writing on Mathematics, Nature, The New Yorker and Popular Science. She was the 2016 winner of the Evert Clark/Seth Payne Award, an annual prize for young science journalists, as well as the winner of the 2017 Science Communication Award for the American Institute of Physics.