One of my fascinations has to do with the many paranormal beliefs humans hold as true. I have done so myself at times. At least until science explained what was really going on. Scientific explanations are soooooo very much more fun than the paranormal one. In the case of the myth of water dowsing the scientific explanation could end up saving you a lot of money and perhaps even your life.
In the sense that it finds underground water, water dowsing does not work. Water dowsing involves the claim that a person can locate underground sources of water without using any scientific instruments. Typically, the person that is dowsing holds sticks or rods and walks around a property in the hopes that the rods will dip, twitch, or cross when he walks over the underground water. The dowsing rods do indeed move, but not in response to anything underground. They are simply responding to the random movements of the person holding the rods. The rods are typically held in a position of unstable equilibrium, so that a small movement gets amplified into a big movement. The movements of the rods do not seem like they are coming from the small vibrations in the dowser’s arms, since these vibrations are so small and the rod’s movements are so large. From the false assumption that the movements of the rods are not coming from the small random vibrations of the dowser’s arms, people then make the illogical leap that the movements must therefore be caused by something powerful that is out of sight, i.e. underground water. Since successfully locating underground water can save a farmer the trouble of digging several wells that end up dry, and since scientific approaches can be expensive, there is a strong incentive for people to want water dowsing to work.
Unstable equilibrium describes a state where all the forces on an object cancel out but the slightest deviation from the point of equilibrium causes the object to fly off. For instance, if you place a marble on exactly the top edge of a sharply-ridged roof, the marble will sit there motionless since the forces pulling it down either side of the roof cancel out. However, if the slightest breeze blows past the marble, it will give the marble a small bump toward one side of the roof. The forces will no longer cancel and the marble will shoot down one side of the roof. Since the marble was in a state of unstable equilibrium, gravity was able to amplify a small movement invisible to humans (the bump from the gentle breeze) into a large movement (the marble rolling down the side of the roof). To the naked human eye, it looks like a power agent exists only on one side of the house and is drawing the marble towards it. If we didn’t understand the concept of unstable equilibrium, we may be tempted to say that there is underground water only on the one side of the house which pulled the marble down that side. Belief in water dowsing operates on this type of misunderstanding.
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