The OPERA experiment that caused such a flurry of interest with its reports of faster-than-light neutrinos has been repeated to take into account one of the criticisms and they find that the neutrinos still seem to be traveling faster than the speed of light. You can read the paper on the revised experiment here. (For previous posts in this topic, see sere.)

In the earlier experiments, the neutrinos were sent in clusters that spanned 10 microseconds, much longer than the 60 nanoseconds time difference that signaled the faster-than-light effect, and thus the experimenters had to do some fancy statistical analyses to extract the time of flight of each neutrino. Some skeptics had suggested that those statistical analyses were flawed. The new experiment has clusters that last only 3 nanoseconds, thus ruling out that particular source of systematic error.

The other potential sources of error will take longer to check out.

(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.)

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

Suppose that the claim that neutrinos can travel faster than light holds up. What are the implications?

As I said earlier in the series, this does not mean that Einstein’s theory of relativity is overthrown, since it always allowed for faster than light particles, though we had never observed them. But it does mean that Einstein causality, the idea that if two events are causally connected by a signal that travels from one event to the other, then all observers’ clocks will agree that the signal left the source before it arrived at the other end, will have to go.
[Read more…]

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

The ‘cold fusion’ episode from back in 1989 illustrates the danger with issuing press releases announcing a major scientific discovery before the scientific community has had a chance to weigh in and sift through the evidence. Two respected scientists Stanley Pons and Martin Fleischmann at the University of Utah discovered reactions producing enormous amounts of heat when the metal palladium was immersed in what is known as ‘heavy water’, which contains a large fraction of water molecules in which the ordinary hydrogen atom has been replaced by the heavier isotope deuterium. The experimenters thought that chemical reactions could not account for the scale of the energy release and were convinced that they had discovered a way to produce nuclear fusion reactions at room temperature, thus opening the way to a vast, cheap, and clean new energy source. Needless to say, this would be a revolutionary discovery, both scientifically and practically.

In March 1989 they announced their results at a press conference to loud fanfare. I remember hearing the announcement on BBC news over my short-wave radio and thinking “Wow! This is huge.” As in the current case of faster-than-light neutrinos, the initial surprise was quickly followed by considerable skepticism within the scientific community because cold fusion went completely against all that we thought we knew about nuclear fusion. For two nuclei to come close enough to fuse, they have to overcome the strong repulsive forces due to both having positive charges. For the nuclei to overcome this ‘Coulomb barrier’, they have to have high energies that are associated with high temperatures as found in the Sun and other stars, which is what enables fusion to be their energy source. What Pons and Fleischmann were suggesting would require some new mechanism to overcome the well-known and well-understood obstacles to low-temperature fusion.

Other scientists pointed out that even if we ignored the Coulomb problem, the byproducts of fusion, which should have been copiously produced, were not observed either, throwing doubt on whether fusion was actually occurring. This objection was countered by claiming that perhaps this was a new form of nuclear reaction that did not produce those specific byproducts. As I pointed out in my series on the logic of science, almost any theory can be salvaged by the introduction of such auxiliary hypotheses. But adopting such stratagems tends to weaken the case for a new theory unless they too can be corroborated with other evidence.

If the claims of Pons and Fleischmann were true, the practical benefits and the revolutionary science they spawned were enormous and this persuaded enough scientists to take the cold fusion claims seriously enough to spend considerable time and effort and money to investigate them. As far as I am aware, over two decades later, though some scientists still continue to work on it, there is still no consistency about the cold fusion reactions, despite periodic resurgences of enthusiasm, enough that the Pentagon is funding further studies. In 2009, the program 60 Minutes did a program giving the history of cold fusion and some new developments.

One problem with cold fusion is that the heat reactions cannot be reliably reproduced. “The experiments produce excess heat at best 70 percent of the time; it can take days or weeks for the excess heat to show up. And it’s never the same amount of energy twice.” This is always a troubling sign. Scientific laws are not idiosyncratic. If they work, they should work all the time in the same way with no exceptions. If there are exceptions, these should also be law-like in that you should be able to predict exactly under what conditions they will or will not occur. Results that occur sometimes with no understanding why are signs that there are some unknown factors at work that are skewing the results.

So what has all this history to do with the recent neutrino story? The fact that this result was also announced via what was essentially a press release and not at a scientific meeting or in a peer-reviewed journal article aroused some concern. Press releases do not face the same degree of scrutiny as a journal article, where a sensational claim of this sort would be subject to close scrutiny before being approved for publication. In the above video, Fleischmann recognized this mistake, saying that he had two regrets: “calling the nuclear effect “fusion,” a name coined by a competitor, and having that news conference, something he says the University of Utah wanted.”

It is not the case that scientists are hidebound dogmatists, determined to cling on to old ideas, as is sometimes claimed by non-scientists when their pet theories (such as intelligent design) are rejected. As I said before, part of the strength of science is that because scientific knowledge is the product of a consensus-building process, it does not get easily swayed by each and every claim of a big discovery. It initially views reports of revolutionary developments with skepticism, waiting to see if the results hold up and corroborating evidence is produced. If so, the community can and does accept the new idea. For example, this year’s award of the Nobel prize for physics was for the discovery that distant galaxies are not only moving away from us (which agreed with existing theories) but are actually accelerating (which flatly contradicted everything we had thought and has led to the highly counter-intuitive idea of so-called ‘dark energy’ permeating and dominating all of space) shows that the community can change its collective mind and accept radically new ideas, and fairly quickly. But the reason such a seemingly outlandish result as dark energy became the conventional wisdom within the short space of less than two decades is because the proponents were able to marshal the evidence in favor of it that survived close scrutiny and was corroborated.

The history of cold fusion, despite not becoming mainstream, also puts the lie to the claims of the so-called intelligent design movement that scientists conspire to suppress those ideas that challenge conventional wisdom. Despite the fact that most of the scientific community is highly skeptical of it being a real effect, cold fusion advocates actually do have a research program in which they do experiments, produce data, and publicize their results. All that members of the intelligent design community do is write books and articles and give talks whining that the scientific community refuses to give them a platform to promote their ideas and that this is because the community is hidebound and refuses to even consider their bold new idea that challenges the accepted ‘dogma’ of evolution.

The actual explanation for why the scientific community rejects intelligent design is simple and mundane. More that two decades after the idea was first proposed, intelligent design advocates still have not done a single experiment or have even a research program to do any.

Next: What if Einstein causality has to be abandoned?