(For previous posts in this series, see here.)

A lot of things need to happen before the extraordinary claims of faster-than-light neutrinos are accepted as true. As Carl Sagan once said, “Extraordinary claims require extraordinary evidence.” The required evidence needs to take many forms: the results should be consistent and reproducible, corroborating evidence will have to be found, consistency with other phenomena will have to established, and alternative explanations for the phenomenon based on traditional physics will have to be ruled out. All this is going to take some time.

But if the result seems to hold up, even then it is not usually the case that scientists completely discard a highly respected old theory and start from scratch. While a few bolder scientists may take this opportunity to try and create a completely new theory, the majority of them usually seek to find minimal changes in the existing theory that would accommodate the new result.

As physicist Heinrich Pas says:

Even if true, this result neither proves Einstein wrong nor implies that causality has to be violated and time travel is possible. Things can move faster than the speed of light without violating Einstein if either the speed of light is not the limiting velocity as one can observe it for light propagation in media such as, for example, water. This can be modeled with background fields in the vacuum as has been proposed by [Indiana University physicist] Alan Kostelecky.

Or spacetime could be warped in a way so that neutrinos can take a shortcut without really being faster than the speed of light. As our three space plus one time dimensions look pretty flat, this would require an extra dimension (as proposed by [University of Hawaii at Manoa physicist] Sandip Pakvasa, [Vanderbilt University physicist] Tom Weiler and myself).

It was Einstein who suggested in 1905 that there is a limiting speed in nature and that this is the speed of light in a vacuum. I have already discussed in connection with Cherenkov radiation that when traveling in a medium such as water or glass or even air, the speed of light is reduced and it is possible to have other particles travel at speeds greater than light in that medium.

So one possible explanation for the OPERA neutrino results is to decouple the speed of light with the limiting speed. Perhaps what we call the vacuum has properties that slows down light from this potentially larger limiting value, and that this new upper limit is what should appear in the theory of relativity. If so, then having neutrinos travel faster than the speed of light in the vacuum would simply mean that neutrinos are slowed down less than light by the vacuum, similar to what happens in other media like the Sun or water or glass. This would require some additional adjustments to theory. Einstein said that the limiting speed must be an invariant for all observers and equated this limiting speed to the speed of light because it overcame some problems of consistency with Maxwell’s electromagnetic theory. Decoupling those two speeds may require us to refine Maxwell’s laws as well, at the very minimum. As is well known, there is no free lunch in science. You cannot make changes in one scientific theory without having to make adjustments in other theories so that they all fit together again.

This series has tried to explain why the proper scientific response to reports of a major discovery is skepticism. This should not be equated with dogmatic obstructionism because in the case of dogma, one starts with a belief that cannot be changed whatever the evidence. Skepticism, on the other hard, is merely resistance that can be overcome with sufficient evidence and reason.

Major theories in science are rarely overthrown on the basis of a single experimental result, though textbooks sometimes tend to give that erroneous image of scientific progress. Usually what happens when a surprising result crops up is that a few people start to look at it closely to see if the results can be replicated by other people in different contexts, and if the ancillary consequences of the new result are also seen.

If none of these pans out, then the original result is deemed to be due to an error (usually a subtle one in the case of careful scientists) or to some factor that was overlooked in the data collection or analysis. The latter is often referred to as a systematic error and is more common because it is hard to be sure that you have accounted for all the possible factors that can influence an experiment, especially if you are working at the frontiers of knowledge, pushing the limits. Sometimes, as in the case of cold fusion, an adequate explanation of the phenomenon within the standard framework is not discovered for a long time and a few scientists believe they do have a new effect and continue to work on it. Such theories die only when their advocates die out.

I doubt that the faster-than-light neutrino story will remain similarly ambiguous for too long but it is a difficult experiment and so may take years to sort out. The quickest resolution to such controversies is when the original experimenters find some error that causes them to withdraw their claim. The OPERA team already has plans to repeat the neutrino experiment with modifications designed to address at least a few of the concerns expressed so far. Another group known as MINOS also plans to repeat the experiment but at locations in the US, with neutrinos produced at Fermilab near Chicago and detectors in northern Minnesota or even South Dakota, the latter being a longer distance than that between CERN and Gran Sasso,

Whatever the final outcome, the faster-than-light neutrino reports have shone a light onto how science really works and that is always a good thing.

Just for the fun, I am ending this series with a word cloud made out of this series of posts. (Ignore the href and em items since these are merely html tags and have nothing to do with the content.)