Last September the OPERA collaboration posted a preprint whose main finding, if corroborated, would necessitate rebuilding one of the foundations of modern physics: that nothing travels faster than light. Derived by timing muon neutrinos on a 732-km journey from CERN in Geneva, Switzerland, to Gran Sasso, Italy, the result provoked a range of reactions and a flurry of media coverage.
Although I can’t be sure, I think most physicists were skeptical of the OPERA result. Other physicists leapt at the chance to apply their imaginations to deriving theoretical explanations for the anomalously speedy particles. As for the general public, how they reacted probably depended on their source of news. Britain’s BBC Radio 4 was careful to emphasize the provisional nature of scientific findings. The New York Times, however, was more excitable. Under the title “Tiny neutrinos may have broken cosmic speed limit,” Dennis Overbye’s story began:
Roll over Einstein?
The physics world is abuzz with news that a group of European physicists plans to announce Friday that it has clocked a burst of subatomic particles known as neutrinos breaking the cosmic speed limit—the speed of light—that was set by Albert Einstein in 1905.
If true, it is a result that would change the world. But that “if” is enormous.
On Wednesday the world learned that the OPERA result could well be spurious. Among the possible explanations for the neutrinos’ early arrival at the end of their journey is an improperly screwed-in fiber optic cable that connects a GPS receiver and a computer.
In retrospect, it looks as though the OPERA researchers posted their results prematurely—that is, before they’d thoroughly checked their equipment. After all, it was the OPERA team that discovered and disclosed the possible problem with the loose cable. Some particle physicists now worry that their field appears ridiculous. If only the OPERA team had waited, they say.
I first heard of the OPERA results when I was on vacation in Northern England. My reaction was complete skepticism. I’m not a particle physicist, but I do know that neutrinos are hard to detect and that the precision needed to time their flight is high. What’s more, Albert Einstein’s theory of special relativity, which sets the ceiling on a particle’s speed at c, has passed every experimental test.
My initial skepticism appears vindicated in the light of yesterday’s revelation, but was it entirely justified? The news about the faulty cable broke on the 380th anniversary of the publication in Florence of Galileo Galilei’s Dialogue Concerning the Two Chief World Systems. The title’s two systems are the Copernican and Ptolemaic models of the solar system. In the book, characters called Salviati and Simplicio make the case, respectively, for Copernicus and Ptolemy before a character called Sagredo.
Salviati wins over Sagredo to the Copernican camp on the strength of his appeal to observational evidence and reason. But Salviati also argues in favor of Galileo’s physically erroneous explanation for Earth’s tides. Presumably, Galileo hoped the readers of his Dialogue would be open to both ideas: the Copernican system, which turned out to be right, and his tidal theory, which turned out to be wrong.
Physicists should be skeptical of grand claims that overturn established and sometimes cherished notions. But they should also be open-minded enough to recognize the possibility that they might be wrong. In “The Nobel laureate versus the graduate student” (Physics Today, July 2001, page 46), Donald McDonald recounted John Bardeen’s opposition to then graduate student Brian Josephson’s prediction that a supercurrent could tunnel through a thin layer of insulating material. Bardeen’s objections hinged on Josephson’s treatment of electron–electron correlations in the insulator. He withdrew them graciously when experiments vindicated his former adversary.