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My September 24 article 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 possible.
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 per hour.)
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.
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