YSM Issue 96.4

FASTER THAN
Physics
FEATURE
LIGHTSPEED
THESE NEUTRINOS WERE FASTER THAN THE SPEED OF LIGHT—
UNTIL THEY WEREN’T
Physics-bending findings. Irreproducible results. In 2011,
news of neutrinos, neutral particles with infinitesimal
mass, traveling faster than the speed of light topped science
headlines, prompting widespread debate about the truth of these
findings. The debate stemmed from the fact that Einstein’s theory
of special relativity says nothing can travel faster than light. But the
Oscillation Project with Emulsion-tRacking Apparatus (OPERA)
experiment at the underground Gran Sasso Lab (LNGS), had
measured the velocity of neutrinos to be 0.0024 percent faster than
lightspeed, contradicting Einstein. If OPERA’s results were true, a
core theory of physics would be shaken.
The premise of this measurement was simple: send a beam of
neutrinos 730 kilometers from the European Organization for
Nuclear Research (CERN) to the OPERA detector at LNGS and
measure their time of flight. Yet, OPERA’s primary goal was not
to measure neutrinos’ speed. The researchers conducted the
additional measurement because OPERA was well suited to
accurately determine neutrino velocity. The OPERA experiment
had primarily been designed to test the phenomenon of neutrino
oscillations, which occur when neutrinos oscillate between three
known “flavors”: electron, muon, and tau. Located at the LNGS, the
OPERA system aimed to be the first to detect the
appearance of tau-neutrinos from the oscillation of
muon-neutrinos during the 2.4-millisecond trip
from CERN to Gran Sasso.
The researchers exhaustively checked every part of
the experiment that could have caused the unexpectedly
fast neutrino speed. They debated whether the research
should be made public. Some didn’t think the checks and
tests on the equipment and experimental methods had
been exhaustive enough. “I was skeptical—almost sure
it was wrong,” said Laura Patrizii, a member of
the OPERA Collaboration. Putting it to
a vote, the researchers who pushed
for sharing their potentially
revolutionary findings won out.
However, since many
working on the project
maintained that something had
gone wrong, the Collaboration
www.yalescientific.org
BACKGROUND IMAGE COURTESY OF BERKELEY LAB
BY GENEVIEVE KIM
didn’t submit for publication in a scientific journal and instead posted
to arXiv.org, a non-peer-reviewed open-access archive. Meanwhile,
the OPERA researchers continued to investigate still-unknown
systematic effects that could explain the anomalous result.
“Exceptional results require exceptional checks,” Patrizii
said, paraphrasing Carl Sagan, astronomer and famous science
communicator. OPERA’s error-searching efforts proceeded in tandem
with labs across the world that tried to replicate the results—to no avail.
Other research groups noted that if the neutrinos were truly traveling
at light-surpassing speed, they should have also been releasing energy.
But no trace of this energy was seen in the experiment, increasing doubt
about the measurements.
In 2012, OPERA finally disproved its own findings. The Collaboration
found that there were two sources of error that had caused the observed
relativity-defying speed. First, a connector measuring the time delay
from a GPS receiver to the OPERA Master Clock was faulty, and
second, the frequency of the Master Clock was out of specification. The
researchers had calibrated the connector when it was securely plugged
in, but during the experiment it had been partially disconnected,
resulting in a distortion and delay of the signal. After the time delay was
calculated and accounted for, the neutrino interactions with OPERA
lagged by sixty nanoseconds. The neutrinos hadn’t actually traveled
faster than the speed of light—the timing itself was incorrect. The search
for an explanation was finally over.
In 2014 and 2015, OPERA papers shared the neutrino oscillation
data. Like all other findings from CERN, they underwent multiple
reviews and screenings before being released to the public. Today,
the common worldwide policy for peer review even bans graduate
students conducting research at CERN from including figures made
for their own research in any university papers if the figures involve
CERN projects that have not been finalized. Any results they do share
from a non-finalized project leave CERN marked as “preliminary.”
This rigorous peer-review process reflects how the scientific process
preserves scientists’ credibility, just as researchers around the world
constructively critiqued the neutrino speed findings.
“The ‘case’ of superluminal neutrinos is frequently referenced as an
example of how science operates, highlighting the effectiveness of the
scientific method and its provando e riprovando (trying and trying again)
approach,” Patrizii said. “Science is not a belief system; it operates without
dogma.” The researchers’ desire to ensure their findings’ validity, even
if it would negate what would otherwise be a groundbreaking finding,
shows the scientific community’s dedication to better understanding the
universe. This case of the too-fast neutrinos, rather than being a scientific
failure, was actually an example of the success of the scientific process. ■
December 2023 Yale Scientific Magazine 25