'Faster-than-light' observations reined in
The same subatomic particles clocked going faster than light speed by European scientists show signs indicating they are moving at only the speed of light, says a group of Italian physicists.
The ICARUS collaboration based their conclusion on an independent analysis of particles known as neutrinos generated at CERN, the European Organization for Nuclear Research, and travelling to Gran Sasso, Italy.
The same particles from the same source were timed over the same path in two separate experiments by the OPERA collaboration, and found to be going faster than light. That appears to contradict Albert Einstein's 1905 special theory of relativity, which provides the basis for most of modern physics.
OPERA most recently announced this past Friday that it got the same results after revising the experiment to rule out a certain type of error. It has submitted the finding to the Journal of High Energy Physics for publication.
The ICARUS scientists didn't time the particles. Instead, they looked at the energy signature of the neutrinos in data from their own experiments in 2010, they said in a paper published online at the Arxiv scientific physics archive in October.
The ICARUS scientists pointed to calculations published online in September by Boston University physicists Andrew Cohen and Sheldon Glashow, which showed that theoretically, if the particles were travelling faster than light, they would lose a lot of energy on their journey.
That would generate an energy signature that was smaller and shaped differently than the one the ICARUS collaboration actually measured. The measured signature was consistent with particles moving at just the speed of light.
The ICARUS scientists went back and checked the signatures after hearing about the OPERA discovery. Their results have not been peer reviewed or published in a scientific journal.
In a blog posting last Friday, Tommaso Dorigo, a physicist with the Compact Muon Solenoid Experiment at CERN, called the ICARUS experiment "very simple yet definitive."
He considers the results to be a refutation of OPERA's findings.
Not a refutation
Rutgers University theoretical physicist Matt Strassler disagrees. He noted in his own blog post Monday that although theoretical calculations "provide a very strong constraint on any modification of relativity that could permit what OPERA observes, logically this does not, in my current view, constitute a refutation."
Instead of showing the OPERA results are wrong, the ICARUS results may just show that "there's a so-far unknown modification of relativity" that allows the particles to travel faster than light without losing energy as expected, Strassler wrote.
Regardless of the new finding, Dorigo wrote, other teams with neutrino detectors, such as the MINOS experiment at Chicago's Fermilab and the Borexino experiment, which is also based in Gran Sasso, Italy, are no doubt "already set up to produce an independent confirmation of the startling OPERA result."
The OPERA collaboration has been encouraging others to run experiments to confirm its results. In the meantime, it says it is in the process of discussing other checks for systematic errors in its experiment that it could run.
The group said its original result was surprising and it invited close scrutiny by other scientists. Many physicists greeted the original finding with skepticism, saying a very high standard of proof is needed for such an extraordinary result, which was more likely the result of an undiscovered error.