New constraints on the physics of OPERA FTL neutrinos

What Cohen and Glashow did last week was to generalize this idea to point out a new physical phenomenon (new at least to me) and use it to argue that OPERA’s result is self-inconsistent. They argue that the very effect of faster-than-light travel that OPERA claims to observe would have caused distortions in its neutrino beam that clearly were not observed. Moreover, Cohen and Glashow also pointed out that at least two other experiments studying higher energy neutrinos put even stronger constraints on the possibility of anything similar to what OPERA observed.

The article is fascinating, so read the whole thing. Dr. Strassler describes an elegant approach to constraining the types of modifications to Relativity that are consistent with the OPERA data. This approach was developed by Andrew Cohen and Sheldon Glashow.

Cerenkov radiation is emitted by electrically charged particles moving faster than light in a medium. Relativity says we shouldn’t see Cerenkov radiation in a vacuum, but it is an important effect in materials where light slows down, such as water, and particles can exceed the local speed of light. You may have seen that blue glow around a submerged reactor; that’s Cerenkov radiation, and the effect takes energy from the emitting particle.


Neutrinos have no charge, so they would not emit Cerenkov radiation (well, they have a very, very tiny type of charge so they can emit a very, very dim form of Cerenkov radiation). But neutrinos interact via the weak force, and what Cohen and Glashow did was show that such particles can emit an analogous type of radiation if they exceed the speed at which electrons can travel in a medium. This radiation would remove energy from the neutrino beam in a way that would be very easy for the OPERA experiment to see. But OPERA’s results do not show the energy removal signature of Cohen-Glashow radiation.

Observations of neutrinos from a distant supernova have put strong constraints on neutrino speed for lower energies than OPERA. Two other experiments have observed neutrinos 100 to 1000 times more energetic than OPERA’s neutrinos, and they do not see the Cohen-Glashow radiation energy loss.

So, we must choose between OPERA’s FTL neutrinos or Cohen and Glashow’s weak force radiation effect. It is not impossible that both could be true, but if so, it will place strong constraints on the kind of modifications that can be made to Special Relativity.

In short, OPERA’s FTL results became more unlikely, but have not yet been ruled out. I was struck by the elegance of the Cerenkov radiation analogy involving the weak force to put tighter constraints on the physics of FTL neutrinos, if they exist.

Why Skepticism in Science isn’t just Politics

The reasons for the intense scepticism about OPERA are both general and specific.  The general reasons stem from the track record of experiments on the frontiers of science, which is pretty dismal.  This is not because experimentalists are careless or foolhardy (well, occasionally this happens) but because doing first-of-a-kind experiments, using new and clever methods and the latest technology, is extremely difficult, and prone to unforeseen problems.  And statistical flukes can always happen, too.  Everyone who has worked in high-energy physics for a while knows that the vast majority of exciting results, even from the best experimentalists, simply don’t hold up over time.  I made an informal list over the weekend of false alarms that have occurred during the nearly 30 years that I’ve been following or actually doing high-energy physics, and came up with nearly two dozen separate incidents — and I keep thinking of new ones.  [I may do some writing later this week about how some of these “discoveries” went awry.]  Meanwhile I can think of only three actual discoveries that survived, one of which (the top quark) was expected, one of which (neutrino oscillations) was pretty exciting but not unexpected, and only one of which really violated the prejudices of my field.  The last — the only real shocker to occur during my career — won this year’s Nobel Prize: the discovery that the universe’s expansion is accelerating instead of decelerating.

First, read the whole article by Dr. Strassler. I’ll wait.

OK. Prof. Strassler is exactly correct; whenever interesting results come out in physics, it pays to be skeptical. This isn’t because physicists want to protect the current paradigm, but a response born of long experience. Most interesting results have a good chance of being wrong. Nature always has the last say, and if an interesting result can be replicated, well, everyone wants to be part of a physics revolution. But if a result cannot be reproduced… it doesn’t matter how beautiful the math or how much explanatory power a theory has, at the end of the day, we can only accept those explanations that match up with the behavior of Nature. Feynman said it best: “It doesn’t matter how beautiful your theory is or how smart you are, if it doesn’t agree with experiment, it is wrong.”

Natural science has this wonderful property that an objective standard exists for judging the correctness of explanations. The behavior of Nature cannot be dismissed.

Siri has a sense of humor


The 2011 Nobel Prize in Physics

For almost a century, the Universe has been known to be expanding as a consequence of the Big Bang about 14 billion years ago. However, the discovery that this expansion is accelerating is astounding. If the expansion will continue to speed up the Universe will end in ice.

The acceleration is thought to be driven by dark energy, but what that dark energy is remains an enigma – perhaps the greatest in physics today. What is known is that dark energy constitutes about three quarters of the Universe. Therefore the findings of the 2011 Nobel Laureates in Physics have helped to unveil a Universe that to a large extent is unknown to science. And everything is possible again.

This year’s Nobel in Physics goes to Saul Perlmutter, Brian Schmidt, and Adam Riess for their discovery that the expansion of the Universe is accelerating, not decelerating as expected. This result came from an examination of distant supernova, and has been confirmed by an examination of the cosmic microwave background and the dynamics of galaxy clusters.

Dr. Perlmutter led a team studying distant type Ia supernova occurring in binary star systems in which a white dwarf accretes matter from the evolving companion. As the white dwarf’s mass grows, it becomes unstable, and eventually destroys itself in a huge blaze of energy which can be seen across the Universe. These explosions are amazingly uniform and consistent in energy, which enable astronomers to use them as “standard candles”, or objects of known absolute brightness. By measuring the observed peak brightness, the distance to the supernova can be computed.

Drs. Schmidt and Riess started a second search for high-z, or distant, supernova a few years later. Both teams came to similar but astonishing conclusions; the Universe’s expansion is not decelerating, but rather is speeding up over time.

The Jobs minimalist esthetic

What makes Steve’s methodology different from everyone else’s is that he always believed the most important decisions you make are not the things you do – but the things that you decide not to do. He’s a minimalist.

Deciding what to leave out is so very hard to do. I know it is a weak area for me. I’m going to work much harder on minimalism in my designs.

already initialized constant WFKV_

Arrrgh. Squashing a DOS bug in Rack 1.3.4 was done by lifting some code from Ruby. But if you use Rack in your rails app, you’ll get a warning to the effect of “already initialized constant WFKV_”. To fix this, just revent back to Rack 1.3.3. I reverted back because this message is so darn annoying.

Of course, if you need the DOS protection in a production app, you’ll have to put up with Rack 1.3.4 in Production mode.