Einstein Avenged: Neutrinos Bow to Light Speed Laws
CERN has disclosed results of experiments undertaken after previous tests seemed to indicate subatomic particles called "neutrinos" were capable of traveling faster than the speed of light. The original results caused a stir several months ago and threatened to upend several well-established theories, but the subsequent experiments indicate neutrinos do indeed obey the universal speed limit.
Jun 8, 2012 11:51 AM PT
Eight months after the multinational Opera research team caused an uproar among physicists with its findings that some neutrinos appeared to travel faster than light, its findings have been officially refuted.
CERN, the European Organization for Nuclear Research, on Friday said that four experiments have found that neutrinos actually travel no faster than the speed of light.
Opera's original measurements can be attributed to a faulty element of its experiment's fiber optic timing system, CERN said.
The findings were announced at the 25th International Conference on Neutrino Physics and Astrophysics in Kyoto, Japan, by CERN research director Sergio Bertolucci.
Life in the Fast Neutrino Lane
Opera's initial findings, announced in September, triggered skepticism among the scientific community because, if validated, they could have meant that Einstein's theory of special relativity was wrong. Special relativity will only hold true when space-time is flat, and if the theory is wrong, it could mean that the curvature of space is hidden somehow.
Another possibility suggested by faster-than-light neutrinos was that special relativity doesn't apply to neutrinos. That would have impacted quantum theory because it's based on the balance between quantum behavior and special relativity.
A neutrino is an electrically neutral elementary subatomic particle with a small mass that usually travels close to the speed of light.
The Opera Experiment
The Opera team shot a high-intensity, high-energy beam of muon neutrinos produced at the CERN SPS accelerator in Geneva at the LNGS underground laboratory at Gran Sasso in Italy, 730 km (454 miles) away and measured the speed at which the neutrinos emitted traveled.
Preparations for the experiment were apparently meticulous. The Opera team worked with experts in metrology, or the science of measurement, from CERN and other institutions to measure the distance between CERN SPS and LNGS with an uncertainty of 20 cm (7.9 inches) over 730 km. Advanced GPS systems, atomic clocks and other sophisticated instruments were used to ensure the scientists could measure the neutrinos' time of flight to within less than 10 nanoseconds of accuracy.
The neutrinos' velocity was determined using high-statistics data collated by the Opera neutrino detector at LNGS from 2009. This detector consists of two identical Super Modules, each being an instrumented target section with a mass of about 625 tons followed by a magnetic muon spectrometer.
It took the neutrinos about three milliseconds to travel the 730 km. This is a measure of the time distribution of protons each time the beam was fired, aggregated and normalized. It's not possible to precisely measure the time of flight of any single neutrino because any proton might produce the neutrino detected by the Opera detector.
"Each experiment necessarily has its own timing system to record the time of its events," Michael Witherell, vice chancellor for research at the University of California Santa Barbara's physics department, told TechNewsWorld.
Opera's discovery of problems with its timing system was announced on Feb. 23, Witherell said. "At that time, CERN said that Opera would have their first neutrino run with the repaired timing system in May. Apparently, all four experiments ran in that May run, and all say transit times were consistent with the speed of light."
Into the Sun
In October, an experiment by Icarus contradicted Opera's findings, according to physicist Tommaso Dorigo in the Science 2.0 blog.
Icarus officially announced its findings in March.
What took CERN so long to announce its findings then?
Icarus's earlier experiment "was a quick result based on a small number of events, but [CERN] were being very careful and accumulating more data," James Brau, professor of physics at the University of Oregon, told TechNewsWorld. "This is the way things tend to work."
CERN did not respond to our request for further details.