I can be terse

There is a deeper nothing in which even the laws of physics are absent. Where do the laws come from? Are they born with the universe, or is the universe born in accordance with them? Here Dr. Krauss, unhappily in my view, resorts to the newest and most controversial toy in the cosmologist’s toolbox: the multiverse, a nearly infinite assemblage of universes, each with its own randomly determined rules, particles and forces, that represent solutions to the basic equations of string theory — the alleged theory of everything, or perhaps, as wags say, anything.

This is deeply unsatisfying, for reasons I'll get to in a minute. Dr. Krauss is following in the tradition of Pierre-Simon Laplace:

Laplace went in state to Napoleon to present a copy of his work, and the following account of the interview is well authenticated, and so characteristic of all the parties concerned that I quote it in full. Someone had told Napoleon that the book contained no mention of the name of God; Napoleon, who was fond of putting embarrassing questions, received it with the remark, 'M. Laplace, they tell me you have written this large book on the system of the universe, and have never even mentioned its Creator.' Laplace, who, though the most supple of politicians, was as stiff as a martyr on every point of his philosophy, drew himself up and answered bluntly, Je n'avais pas besoin de cette hypothèse-là. ("I had no need of that hypothesis.") Napoleon, greatly amused, told this reply to Lagrange, who exclaimed, Ah! c'est une belle hypothèse; ça explique beaucoup de choses. ("Ah, it is a fine hypothesis; it explains many things.")

The deeply unsatisfying part is hinted at in the NYT article: "But even the multiverse is not totally lawless, as Dr. Krauss acknowledged. We are not quite there yet. At the very least, there would still be the string equations and those quantum principles that undergird them."

Ah yes, because if we have nothing at all, we have nothing at all. Nothing that can fluctuate, nothing that describes strings, not even the abstract entities of mathematics, such as randomness. We just have... nothing. No existence of any kind, abstract or concrete. How can existence emerge from nonexistence? This puzzle is in fact a riddle wrapped in an mystery inside an enigma. Lengthening the chain from the Multiverse of today to Nothing At All doesn't remove the paradox.

Roses are red.
Violets are approximately blue.
A paracompact manifold with a Lorentzian metric can be a spacetime,
if it has dimension greater than or equal to two.

S. C. Kavassalis

My personal favorite is the Serpenski heart card pop-up.

Today, Juhan Kim at the Korea Institute for Advanced Study in Seoul, and a few pals, show just how far this technique has come. These guys have carried out the largest simulation of the universe ever undertaken, consisting of 374 billion particles in a box some 10 gigaparsecs across. That's roughly equivalent to about two thirds the size of the observable universe.

This took some 20 days of computing time on the Tachyonii supercomputer in Korea, the 26th fastest in the world in the last set of rankings.

They are looking for the signature of Cold Dark Matter in the evolution of the Universe.

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.

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.