Flogging a dead horse

No, not the latest Ebay scam, just me banging on about the sensational reporting of science again.

I wasn't the only person blogging about so-called Boltzman Brains (see, for example, John Ratcliff's blog), and they are the subject of continuing correspondence in New Scientist. Here are two more examples of what I was talking about. Both are research findings reported in New Scientist, although it should be said that in both cases the articles included a less sensational interpretation of the results than that implied by the headline, suggesting that the reader should have a large pinch of salt to hand while reading them. However, the experiments were also widely reported, salt-free, in other media.

In an article in the 18th August issue, headlined "Light seems to defy its own speed limit" [my emphasis], New Scientist reported an experiment by Günter Nimtz and Alfons Stahlhofen which they (the experimenters) say shows faster-than-light-speed (superluminary) travel. When the experiment was reported later on BBC radio's 5Live, it had become a "scientists say time-travel is possible" story. It's not easy to describe the experiment without a diagram (there's one at Wikipedia here), but the superluminary claim is made because light appears to be travelling via paths of different lengths to arrive at a detector in the same time. Hence the light taking the longer path must have travelled faster than the light on the shorter path, which is assumed to be travelling at light speed. The important point is the nature of the extra distance that the light on the longer path is supposed to travel. This 'distance' was inserted into the path as a 1 metre long opaque barrier. The only way for light to penetrate such a barrier is by an effect called quantum tunnelling, whereby, as a consequence of Heisenberg's Uncertainty Principle, a photon has a (slim) chance of disappearing from one end of the barrier and reappearing at the other. This effect has been known about for 80 years, and isn't just theoretical (it's how transistors work). In the experiment, the time between the disappearance and reappearance didn't significantly contribute to the overall journey time for the light, hence the claims for superluminarity: the light going through the barrier travelled 1 metre further, in the same time, as the unimpeded light.

I'm a scientific layman and so not qualified to criticise the experiment (others are - see, for example, this from Chris Lee at Ars Technica). The results speak for themselves, but interpretations differ. Nimtz boldly says: "For the time being this is the only violation [of special relativity] that I know of". But then he made similar assertions nearly 8 years ago (see this paper from 2000, where he described a very similar experiment and claimed that "Photonic tunnelling violates Einstein causality"). Now where did I put that salt?

The second example of cosmic hype is in an article I read in the current (8th September) issue of New Scientist. A long time ago, in a galaxy far, far away... well, half a billion light years away, and the galaxy is called Markarian 501... anyway, the galaxy flared up, sending out a burst of gamma rays (very high frequency light) across intergalactic space until, half a billion years later, it eventually arrived here and was detected by the aptly-named MAGIC gamma-ray telescope on La Palma in the Canary Islands. That, in itself, is amazing; observing an event today that took place in Mkn501 at about the time that the Coelacanth first appeared on Earth. However, on examining the received signal, the MAGIC team saw that it could be interpreted as showing the high frequency component of the signal arriving 4 minutes behind the lower frequency components. Four minutes in half a billion years might seem close enough for jazz, but, if this interpretation of the measurements were shown to be feasible, (although, of course, it could just be that the higher frequencies were emitted later in the Mkn501 event, or that there could be another, simpler, explanation for the delay), it would pose some serious difficulties for Special Relativity, which says that (and explains why) all the components of the signal should arrive together (light of whatever frequency travels at the same speed). Not only would SR be violated by such a result, it would also (so the researchers say) throw a spanner into the works of the string theorists.

Again, I'm only a layman and not qualified to comment on the science of this. For a more informed view, see Peter Woit's blog entry here. (Woit is a critic of String Theory, mentioned in my previous post). However, even to the layman, it's interesting that, in both these cases, it seems as if a scientific version of cultural relativism is at work, and that Relativity is seen as a valid target, one among many theories, and ripe for toppling. Which strictly it is, of course; I know that any theory can be disproved, but Relativity has passed all its tests with flying colours so far. It seems to me that both sets of researchers have forgotten that one of the guiding principles of science is (or should be) Occam's Razor: "Entities should not be multiplied beyond necessity". In other words, consider the simplest explanation first. Otherwise... well, watch out for my forthcoming paper: "Were MAGIC delays caused by a mischievous Boltzmann Brain?".