Friday, October 07, 2011

An Ugly Little Fact

The great tragedy of science—the slaying of a beautiful hypothesis by an ugly fact.

attributed to Thomas Henry Huxley (1825 - 1895)
A group of scientists from Italy and Switzerland have reported that neutrinos can travel a bit faster than the speed of light [Measurement of the neutrino velocity with the OPERA detector in the CNGS beam]. If true, it will change our understanding of general relativity.

So how do the knowledgeable scientists deal with this ugly little fact"? Are they ready to abandon general relativity? No, they aren't. The typical response is skepticism combined with a "wait and see" attitude while the result is confirmed. Chad Orzel of Uncertain Principles has a nice analysis of the experiment: Faster Than a Speeding Photon: "Measurement of the neutrino velocity with the OPERA detector in the CNGS beam". Chad concludes with,
So, if you had money to bet on it, bet that this result is wrong. But these guys aren't complete chumps, and if something is wrong with their experiment, it's something pretty subtle, because they've checked all the obvious problem areas carefully.
Victor Stenger expresses similar skepticism in an article published on Huff Post [No Cause to Dispute Einstein].
As someone who worked in neutrino physics for thirty years before retiring from research in 2000, I should be more excited than most by the report from CERN that neutrinos have been observed moving faster than light. And I am. The experiment looks very well done and the scientists involved are saying all the right things -- that their result is very preliminary and must be independently replicated before accepting it as scientific fact. If the observation is confirmed, it may be the most important discovery in science in the last 100 years.

However, a big fly in the ointment is the supernova in the Large Magellanic Cloud, which sits just outside our galaxy 168,000 light-years from Earth. It was first seen by the naked eye on February 24, 1987. Three hours before the visible light reached Earth, a handful of neutrinos were detected in three independent underground detectors. If the CERN result is correct, they should have arrived in 1982. So, if I were a wagering man, I would bet the effect will go away because of some systematic error no one has yet been able to think of.
These responses are typical. Instead of immediately rewriting the textbooks in light of a new discovery, scientists initially express skepticism of results that conflict with well-established models. They do this because history has convinced them that most of those discoveries will never be confirmed and the standard model remains intact. [See alos Sean Carroll: Can Neutrinos Kill Their Own Grandfathers?]

Thomas Huxley was wrong. That's not how science works.

Stenger's response is informative because he gives us an example of how the new result conflicts with data from other experiments. Those conflicts aren't usually reported in the press releases so the general public is unaware of the true nature of the scientific conflict. In this case, it's not only the model of general relativity that's being challenged but also several decades of scientific data that conflict with the new result.

It's very difficult for the general public to appreciate how science is done. Just the other morning, for example, my local radio station announced that drinking red wine may cure breast cancer. The public is used to hearing of scientific breakthroughs that overthrow existing "theories"—it happens every week. What they're not used to is hearing from those who urge skepticism concerning the latest "breakthrough" and they're certainly not used to hearing about the follow-up studies that fail to substantiate the "breakthrough."

This false view of science, which I blame on scientists and science journalists, plays right into the hands of kooks and quacks who are only too eager to point out the fallibility of modern scientific reasoning. It should come as no surprise to you to learn that the Intelligent Design Creationists are exploiting the neutrino result to discredit science. After all, if general relativity can be overthrown by a simple experiment then why should we believe an even more outlandish "theory" like evolution?

Here's an example from David Klinghoffer: Another One Bites the Dust.
If you think Darwin's theory of evolution is as secure as Einstein's theory of special relativity, well...maybe you're right.
The creationists are quite fond of quoting every science paper that raises questions about how we interpret evolution. In some cases, they publish whole books with long lists of such papers (e.g. The Myth of Junk DNA). They never make any attempt to inform their audience about how science actually works and they never mention that most of these papers turn out to be wrong or irrelevant. In most cases those "breakthrough" papers are never heard from again.

On the other hand, as soon as there's a paper or a blog posting that criticizes creationism, the IDiots close ranks and tell their followers that most scientific papers are wrong and, besides, the scientists have ulterior motives. Isn't that strange behavior? I think so.


  1. Re: "Thomas Huxley was wrong. That's not how science works."

    I don't read Huxley's quote the way you seem to. I believe his meaning was that we can come up with elegant theories that explain a whole lot of things, and it's just beautiful, everyone loves it. And then an ugly little data point shows that's not right. Well, science accepts that, it doesn't fall in love with its own theories so much that it rejects conflicting data.

    So yeah, you're right, it won't throw out the elegant theory, perhaps it'll be used in a limited context, but science knows that just because something is beautiful doesn't make it true.

  2. Stenger said:

    Three hours before the visible light reached Earth, a handful of neutrinos were detected in three independent underground detectors.

    This sort of says that the neutrinos arrived before the light. They were were not quite as fast as the CERN neutrinos, but still faster than light. Isn't that what Stenger's words say?

  3. Anon2, actually, the difference between the light and the neutrinos from 1987A is due to the fact that it takes photons from the inside of a star some time to "diffuse" to the surface; they have a relatively short average path length in the electromagnetically thick environment of a star's interior (even when its exploding).

    Neutrinos, on the other hand, interact so weakly with matter than the star is effectively transparent, so the neutrinos radiate from the explosion immediately.

    For this reason it is expected that the neutrinos would be detected first, and the difference observed with 1987A is consistent with models of stellar interiors.

    (This is kind of an exciting problem for me as I was briefly associated with the SuperK collaboration as a grad student, when they started fooling with GPS timing for the K2K experiment.)

  4. The neutrinos arrive first exactly as predicted. In a supernova the core of a massive star 'explodes' creating a burst of neutrinos and photons. The neutrinos escape from the star immediately but it takes about tree hours for the photons to reach the surface. The neutrinos arrive first because they have a head start.

  5. Stenger went on to say that the neutrinos interact very weakly with matter so are not impeded by the solar mass where as the photons don't escape until most of the solar material has blown away in the super nova some time later.

    So the neutrinos start their journey earlier than the photons and both types of particle seem to be travelling at the same speed.

  6. The light from the supernova was delayed because it had to get through the remnants of the stellar explosion.

    As an example: The photons in our solar core take many years to escape to the surface while the sun is almost transparent to neutrinos. Neutrinos can pass through LIGHTYEARS of lead. This is why only a very tiny % of neutrinos are detected in experiments.

  7. Re neutrinos arriving earlier than light.

    According to Wikipedia, during a supernova neutrinos are emitted while the core of the star collapses. Light is emitted later when the shock wave of the collapse hits the stellar surface.

  8. I think Huxley was right. An ugly fact can slay a beautiful hypothesis. An ugly interpretation of an observation cannot destroy established scientific consensus, though. Not without friends. (It's not yet a fact that neutrinos can travel faster than light, and I think it's a little unfair on general relativity to equate it with "a beautiful hypothesis".)

    I don't know that many of them were "beautiful" but I've had many a reasonable hypothesis killed by the reality of the data.

  9. An ugly interpretation of an observation cannot destroy established scientific consensus, though. Not without friends.

    Ooh, I like this, especially the "Not without friends" part. One of these days I may steal it, with your kind permission.

  10. @Jud: knock yourself out - it's in the public domain now, anyway!