Skeptophilia (skep-to-fil-i-a) (n.) - the love of logical thought, skepticism, and thinking critically. Being an exploration of the applications of skeptical thinking to the world at large, with periodic excursions into linguistics, music, politics, cryptozoology, and why people keep seeing the face of Jesus on grilled cheese sandwiches.

Saturday, February 18, 2012

Stonehenge and the sound of silence

Scientists understand the world through the use of models.  These models, most often mathematical systems, are an attempt to describe how the world works, and (with luck) make predictions that then can be supported (or not) by experimental data.

It is an all too common error, however, to then decide that the model is the reality.  We see this in the realm of simple analogy, where the analogy is substituted for the real phenomenon (as in my student who began one of her AP exam essays with the sentence, "Antibodies are trash tags.").  On a more sophisticated level, we have people like Stephen Wolfram, the iconoclastic mathematician and theorist whose book A New Kind of Science (2002) makes the claim that because some processes in the universe resemble a mathematical construct called a "cellular automaton," the universe is, in fact, just a bunch of interacting, interlocking cellular automata.  This conjecture led Nobel-prize-winning physicist Steven Weinberg to state, "It's possible, but I can't see any motivation for these speculations, except that this is the sort of system that Wolfram and others have become used to in their work on computers.  So might a carpenter, looking at the moon, suppose that it is made of wood."

An interesting example of mistaking the model for the reality was just published recently, and was the subject of a talk at a meeting of the American Association for the Advancement of Science.  Archaeologist Steven Waller has proposed, apparently seriously, that Stonehenge was built to resemble the interference pattern that develops when two nearby instruments play the same note continuously.

He studied the phenomenon of acoustic interference by connecting two flutes to air pumps so that they played the same note, and then observing the areas of reinforcement (where the sound waves add together, resulting a louder tone) and interfere (where the waves cancel out, resulting in silence).  He took blindfolded volunteers, and had them walk around the room, and then draw what they experienced -- and came up with a pattern that looked a little like Stonehenge.

"If these people in the past were dancing in a circle around two pipers and were experiencing the loud and soft and loud and soft regions that happen when an interference pattern is set up, they would have felt there were these massive objects arranged in a ring," Waller stated.  "It would have been this completely baffling experience, and anything that was mysterious like that in the past was considered to be magic and supernatural.  I think that was what motivated them to build the actual structure that matched this virtual impression.  It was like a vision that they received from the other world.  The design of Stonehenge matches this interference pattern auditory illusion."

Well.  I have a variety of objections to this conjecture, and I have to hope that someone in at the AAAS meeting brought them up as well (the article describing Waller's findings doesn't mention any questions asked after Waller's talk).   The first one is that the position of the "nodes" (places where interference causes sound cancellation) depends on the pitch being played.  It's interesting that he chose an instrument in his experiment (the flute) and in his talk (the pipes) that are both instruments I play, because I happen to know a bit about those instruments and how they produce sound.  The flute was a convenient choice for his experiment, because it produces fairly pure tones, with few overtones, and therefore a pair of flutes playing the same note would create a simple, stable interference pattern.  The bagpipes, however -- being a double-reed instrument, it has lots of overtones (resulting in the, shall we say, distinctness of its sound).  This would make any perfect cancellation and resulting "areas of silence" a near impossibility, crushing any hopes you may have if you ever happen to be unfortunate enough to be trapped between two bagpipers.

There's also the problem that no musicians, either then or now, are going to simply stand there and play the same note for hours on end.  They were presumably playing an actual tune, which means that the pitches would be shifting all over the place -- shifting any nodes produced all over the place, as well.

But the fundamental problem is one of mistaking appearance for reality.  Stonehenge might very well look like the pattern of nodes in an acoustic interference pattern, but that doesn't mean that it is one, any more than antibodies are trash tags or the universe is a cellular automaton.  I find it interesting that this research even made it past the peer review stage, especially given Waller's seemingly incessant focus on sound as a motivator for prehistoric art and architecture (his website, for example, describes his conjecture that sound echoes were the motivators for cave paintings -- notwithstanding that most cave paintings are representational, depicting ordinary things like horses, cattle, bears, and people).  It's possible, of course, that the acoustic characteristics of a particular place may have led prehistoric people to attribute magical properties to the locale; but to go from there to the conjecture that Stonehenge was built to mimic an acoustic interference pattern is a stretch indeed.

Of course, given that the whole thing centers around Stonehenge, I'm sure there will be a lot of buzz surrounding this paper for some time to come.  If you want to get attention from the woo-woo crowd, Stonehenge is a sure-fire winner.  But as far as scientific validity goes -- I'm afraid I'm not convinced.

1 comment:

  1. One of the curious things I noticed when visiting Stonehenge for the first time aged 16 (oh golly, that's almost 30 years ago) was that there was something distinctly unusual about the acoustics of the site. Sound is VERY flat. That visit was on a rainy day but each time I've been back since, I noticed the same thing. There's a deadening of all sound. I have no way of knowing if this existed BEFORE the stones were put up.
    I have a couple of cds of flute music played in the King's chamber of the Great Pyramid at Giza; the music takes on an unearthly, eerie beauty. I used to run a drumming group and we wanted to drum at Grimes' Graves, a neolithic flint mine not far from where we lived, but we never had the courage to ask for permission, or break in during darkness. It's amazing how different instruments sound in different places.