My September 26 newsletter discussed a
recent experiment at the Italian “OPERA” neutrino detector. Physicists
there claimed to have observed neutrinos traveling faster than light
speed, arriving 61 billionths of a second before Einstein said was
While there are many possible technical
problems with the measurement, an October 17th paper by Dutch physicist
Ronald van Elburg raises a more profound issue. I thank my dear friend
Dr. Jerry Clifford for referring me to this insightful paper.
Elburg says the analysis was simply done
in the wrong reference frame, and if done properly, the experiment
proves Einstein was right, once again.
Einstein said space and time are relative,
meaning there is no single right answer to “how long is this distance?”
or “how much time did that take?” These answers depend on the observer,
and in particular on how fast the observer is moving relative to what
is being measured. If two observers moving at different speeds measure
the speed of a photon, a particle of light, they will measure different
values for the path length traveled by the photon and different values
for its transit time. But when each observer computes the photon’s speed
they’ll get the same result — the speed of light. If one observer
measures the path length being 10% more then he will necessarily measure
the transit time also being 10% more, thus measuring the same speed
(speed = distance / time).
Clearly this doesn’t work if we divide
one observer’s distance by a different observer’s time, which is what
Elburg said the OPERA physicists inadvertently did.
The clocks measuring neutrino arrival
times at OPERA (80 miles from Rome) and the clocks used to infer
neutrino departure times at CERN (near Geneva) were all synchronized to
clocks on GPS satellites. Thus the time measurements were really being
made in the satellite reference frame, the frame in which the satellites
are stationary and Earth is moving. To be consistent, the CERN-to-OPERA
distance must also be measured in the satellite frame. (The GPS
satellites are 12,000 miles above Earth and moving more than 8400 miles
As seen in the satellites’ frame, Elburg
states, while the neutrinos move toward OPERA at almost the speed of
light, the OPERA detector moves toward CERN at 8400 mph. This reduces
their effective path length so they arrive earlier than the physicists
expected. The distance traveled looks shorter in the GPS frame than it
looks to observers on Earth. Elburg estimates this effect could reduce
the neutrinos’ transit time by 64 billionths of a second, making the
experimental result consistent with Einstein’s theory that nothing
travels faster than light.
The exact value of Elburg’s correction
depends on precisely where the GPS satellites are during the neutrino
transit and how the synchronization is accomplished. Only the physicists
at OPERA have access to these details. It’s now up to them to apply
Elburg’s equations to precisely determine the correction.
My money’s still on Einstein.
November 9, 2011