A canna’ change the laws of physics

Scotty, The Naked Time, stardate 1704.3, Episode 7

Dowsing For Answers

Posted by apgaylard on October 4, 2007

Listening to the BBC Radio 4 programme Questions, Questions today I was interested to hear a discussion on dowsing .  Disappointingly for a “factual” programme the piece was outrageously biased towards dowsing.

The pitch was very much “science doesn’t know how this works”, rather than the truth: science knows how this doesn’t work!

Various dowsers aired their views, with anecdotes masquerading as data.

To answer the question “How can this be explained scientifically?” the audience were subject to pseudo-physics babble from Michael Guest, introduced as the Vice President of the British Society of Dowsers.  To summarise he contended that it was explained by “… the Earths’ magnetism and our reaction to it  …” he elaborated that an underground stream effects the magnetic background.  This can be detected by human beings.  How?  Dowsers’ tensed muscles are relaxed by passing over the “reaction” of the magnetic field to the water.  This causes the rod reaction.

Scientifically this is utter, utter nonsense. I’ll just take one part of this nonsense to task.  Muscle reaction (contraction) is stimulated by electrical impulses transmitted by the nerves.   The only way a magnetic field could cause a muscular reaction is by inducing a similar electrical signal.  Faraday’s Law of Induction tells us that, in the Earth’s steady magnetic field, a voltage (emf) can only be induced by moving a conductor through it and hoping for a changing magnetic flux (dFB/dt); perhaps due to some local anomaly.  IF a conducting rod (not wood!) is used and IF the motion could induce a suitable electric current this could, assuming conduction into appropriate nerves, induce muscle tension (contraction).  The latter IF, as we shall see, is a mammoth IF.

What we are being asked to swallow is that this actually happens in the presence of an underground stream.  How realistic is that? Could the effect be strong enough to cause some sort of muscle reaction? 

 Taking some generic data we can make some very charitable estimates.  At its strongest (the poles) the earth’s magnetic field is around 60μT. Using Faraday’s Law of Induction: If a 1m long conductive rod was swept at 90 degrees to the magnetic field at 1 m/s the induced voltage could be no more than 60μV (0.00006 Volts), assuming the dowser completes the electrical circuit and we have a changing magnetic flux (dFB/dt) due to the motion.  (Please note that this is very much a estimate of maximum magnitude.  There are lots of assumptions here, but for the purposes of the argument they are made to increase the size of the estimated voltage). 

The typical action potential required for muscle contraction is 15 mV (0.015 Volts).  The upshot is that the induced voltage is at least 250 times too small to trigger muscle contraction.  So there is no possibility of magnetically induced muscle reaction.  The presence of an underground stream will not induce much of an anomaly, let alone negate the background magnetic field entirely!

Other points to note are this would only work with a conducting rod.  Dowsers often use wood!  The induced voltage is also proportional to both the length of the rod and the speed at which it moves; double the size or speed and the effect is still at least 125 times too small.

Of course, it is worse than this.  Moving a conductor through a uniform, steady magnetic field would not generate the changing flux (dFB/dt) required to induce the voltage.  So, I have assumed that the magnetic anomaly is the same size as the earth’s magnetic field at its strongest.  Finally, the motion required is at 90 degrees to the magnetic field lines.  Only at the poles would this be motion parallel to the ground.

This physical nonsense was accepted without challenge; hardly the stuff of “factual” broadcasting.

Guest then moved on to “… areas we simply don’t understand scientifically”.  What are these? Dowsing for depth information, from a map and at a distance.  We were blithely informed that: “skilled dowsers do it all the time”  No evidence is asked for or offered.  Of course, there is no sound evidence for “standard” dowsing being more than luck or intuition, let alone these more speculative forms.

One sceptical voice was heard.  Terrence Hines, introduced as a New York Psychologist.   It was claimed, on his behalf, that he thought dowsing could never be authenticated because of lack of evidence as to how exactly it works!  No, it has never been authenticated because it does not work. 

Randi states that: By far the most common claim made for the Million Dollar Challenge offered by the James Randi Educational Foundation (JREF) is dowsing”.  Yet the million dollar prize is still unclaimed!  If dowsing worked then Randi would have lost his money years ago! (This is borne out by the evidence discussed in wikipedia and the Encyclopaedia Britannica’s description of it as “occultism”)

Hines’ explanation for the movement of the dowsing rods is small unconscious muscle twitches.  (Randi offers the same explanation).

It was also said of Hines that he: “… Refuses to accept anecdotal reports, claiming they are unreliable.”  The implication of this is that he is being unfair, instead of absolutely right.  To have a factual programme inferring that anecdotes are data is very irresponsible.

We were then introduced to Tony Faulkner, apparently an electrical engineer, who was claimed to have conducted controlled experiments to try “… to substantiate why the dowsing he had seen could have worked.”  More nonsense.  That is the path to self-deception.  Good science is about trying to falsify your hypothesis, not confirm it. 

His defence: “… people who are trained in a western way find it hard to accept …” When “western” is used as a pejorative against the scientific method, then we have a sure sign that we are in the presence of quackery.

The show did mention that sceptics point out that if you dig virtually anywhere in the UK, at random, you will hit water eventually.  It’s a shame that the programme makers did not think the implications of this one through.

Instead we closed on the delusional conclusion from the journalist “responsible”: “… In my own brief experience I and many like me have seen the rods work.”

In the words of Homer Simpson: D’Oh!

[Edit.  I came across this and this on dowsing for explosives]

4 Responses to “Dowsing For Answers”

  1. “the induced voltage could be no more than 60mV” – you mean 60μV, right?

    Anyway, they probably thought they were being balanced by giving just as much time to a worthless and incorrect viewpoint as to a valid and correct one – what a load of nonsense that is.

  2. apgaylard said

    Absolutely. I get the mu symbol on my screen, perhaps there’s a bit of a glitch.

    If only they had given the same time to the bonkers and sensible bits!

    The piece seemed to be not much more than a sales pitch for dowsing courses! Who said the BBC can’t take advertising.

    Thanks for stopping by.

  3. “I get the mu symbol on my screen, perhaps there’s a bit of a glitch.”

    Use the html entity: μ

  4. apgaylard said

    Thanks. My html is very rusty.

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