Physics shocker! Neutrinos clocked faster than light

Tiny subatomic particles are challenging Einstein's decades-old conclusion that nothing can travel faster than light. Next up: intense scrutiny of the finding.

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Stephen Shankland
4 min read
As part of the OPERA experiment, physicists tracked how long it takes for neutrons generated at CERN to reach a detector 730km away in Italy.
As part of the OPERA experiment, physicists tracked how long it takes for neutrons generated at CERN to reach a detector 730km away in Italy. National Institute of Nuclear Physics (ITFN) in Italy

European physicists have measured tiny particles called neutrinos moving just faster than the speed of light--only a smidgen faster, but enough to raise a serious possibility that Einstein's physics need a major overhaul.

The scientists sent a beam of neutrinos from CERN, on the Swiss-French border near Geneva, to the INFN (Istituto Nazionale di Fisica Nucleare) Gran Sasso Laboratory in central Italy, 730 kilometers (454 miles) away, in a research project called OPERA. The physicists had planned to study a rare event, the transformation of the muon variety of neutrinos into the tau variety. Instead, they found the extraordinary result that the neutrinos appeared to travel faster than the speed of light.

Under Einsteinian physics, nothing can exceed the speed of light, and so far, nothing has challenged that conclusion. At particle accelerators over the decades, subatomic particles are pushed to ever-higher speeds, but it takes ever more energy to attain each new fractional step toward the speed of light. Instead of going faster when driven with higher-energy accelerators, the particles get heavier. That phenomenon is described by Einstein's famous equation linking energy (E), mass (m), and the square of the speed of light (c): E=mc2.

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But over the last three years, the OPERA experiment has gathered high-precision data on exactly how long it took for the neutrinos to make a journey that should last about 2.4 thousandths of a second. The neutrinos, though, arrived about 61 billionths of a second sooner than would light traveling in a vacuum, where its speed is at a maximum.

That's about 2 thousandths of a percent faster than the speed of light--not much, but more than enough to throw a major wrench into the workings of physics if the result is validated.

The dry language of a paper, written by 174 authors, describes the result this way: "We cannot explain the observed effect in terms of presently known systematic uncertainties," referring to factors within the equipment that generates and detects the neutrinos. "Therefore, the measurement indicates an early arrival time of...muon neutrinos with respect to the one computed assuming the speed of light in vacuum."

'A complete surprise'
In the official announcement comes the more human reaction from a profession for whom the speed of light's unbreakability has been a core belief for generations.

"This result comes as a complete surprise," said Antonio Ereditato, spokesman for OPERA and a professor a the University of Bern, in a statement.

But he didn't dwell on the research's implications: "The potential impact on science is too large to draw immediate conclusions or attempt physics interpretations."

No doubt plenty of speculation will begin. But first things first: it's time for other physicists to try to figure out if the measurements could have been wrong and to see if they can be reproduced.

If the results hold up, it won't be the first time scientific beliefs have been upended. But Einstein's work has held up superbly under decades of verification and challenge.

The researchers will detail their results today at CERN, and they've published the results in a paper at Arxiv, a site for research that's not yet passed the peer-review scrutiny required for publication in academic journals.

"After many months of studies and cross checks we have not found any instrumental effect that could explain the result of the measurement. While OPERA researchers will continue their studies, we are also looking forward to independent measurements to fully assess the nature of this observation," Ereditato said.

Neutrino behavior
It's another surprise from neutrinos, particles that lack any electrical charge and that interact only rarely with anything else. For decades, physicists thought neutrinos had no mass, but in the 1990s, research showed they actually are very light.

Neutrinos constantly stream through the earth, only rarely fazed by what they encounter. The sun produces them, but people also have figured out ways; CERN does so by smashing protons into a graphite target.

The rarity of neutrino interactions makes it hard to perform scientific experiments involving them. The physicists, though, measured 16,111 neutrino interactions over three years--enough to narrow the error bars that show the statistical uncertainties that plague smaller data sets.

Much of the paper, naturally, dwells on just exactly how the scientists measured the neutrinos' time of flight. To do so, they used very precise GPS measurements and atomic clocks to sychronize timing between the two facilities. Ultimately, the distance from the neutrino source to their detection was measured with an accuracy of 20cm.

Combining it all, the researchers concluded they had enough precision in their measurements. The ultimate finding was that the neutrinos arrived 60.7 nanoseconds faster than light in a vacuum would have, with a statistical uncertainty of only plus or minus 6.9 nanoseconds and measurement uncertainty of plus or minus 7.4 nanoseconds.

The researchers know their work isn't done when it comes to convincing the world that a supposedly unbreakable law has been broken.

"Despite the large significance of the measurement reported here and the stability of the analysis, the potentially great impact of the result motivates the continuation of our studies in order to investigate possible still unknown systematic effects that could explain the observed anomaly," the paper concludes. "We deliberately do not attempt any theoretical or phenomenological interpretation of the results."