Does a Pendulum Really Work? What the Tests Show

Two questions in one

When people ask whether a pendulum works, they usually mean one of two things. First: does the pendulum detect something outside me, like water underground, a hidden object or a future event? Second: is it any use to me when I pick it up?

The first question can be tested by experiment, and it has been, many times. The second is more personal, and the answer has to do with reflection, not detection. Keeping them apart protects you from both credulity and contempt.

How dowsing gets tested

A controlled dowsing test aims at one simple thing: making sure the person with the rod or pendulum can't be guided by any ordinary clue. Typically the target is hidden, say water flowing through a buried pipe or an object in one of several boxes, and neither the dowser nor anyone near them knows where it is.

Then the number of hits is compared with what chance alone would produce. If someone beats chance again and again under tight conditions, there's something to explain. If the hits hover around chance, the simplest explanation is that the instrument is responding to the person, not the target.

This kind of design is called double-blind, the same approach used to test medicines. It isn't a trap set for dowsers; it's the only way to tell a real ability from coincidence.

The Munich barn experiments

The most ambitious dowsing experiments took place in a barn near Munich in 1987 and 1988, funded by the German government and led by the physicists Hans-Dieter Betz and Herbert König with colleagues. On the ground floor, water ran through a pipe whose position was moved at random along a line; upstairs, each dowser had to mark where they thought it was.

About 500 people took part in the preliminary rounds. The final report, in 1990, analyzed 843 trials by 43 dowsers. The researchers concluded that a handful of participants had done better than chance, while acknowledging that the effect was very small.

The biologist James T. Enright of the Scripps Institution of Oceanography reexamined the data in Naturwissenschaften in 1995 and in Skeptical Inquirer in 1999. His critique: plot all the trials and there's no visible relationship between where the pipe was and where dowsers marked it; the best scores in one session weren't repeated in later ones; and the favorable analysis depended on choosing, after seeing the data, whom and what to count. Betz and his colleagues answered in 1996 and 1999, defending their analysis, and Enright stood by his conclusion. Today the case is cited mostly as an example of an effect that couldn't be replicated.

Other controlled tests

Controlled dowsing tests over the past several decades have, by a wide margin, produced results consistent with chance. In 1979 the skeptic James Randi tested four dowsers in a field near Rome, using buried pipes carrying running water, in a trial filmed by Italian television; none of them beat chance.

In Kassel, Germany, the German skeptics' society GWUP tested about thirty dowsers over three days: they had to say whether water was flowing through a plastic pipe buried about 20 inches deep. The participants had agreed beforehand that the test was fair and expected to succeed nearly every time; the results were what chance would predict.

These tests come mostly from skeptics' organizations, and dowsers sometimes object that the pressure of a test interferes. That's an understandable objection, but it's also the hard part: an ability that vanishes exactly when it can be checked is very hard to tell apart from one that isn't there.

Why a pendulum seems to get it right

A pendulum seems to get things right for several well-understood reasons, and none of them requires bad faith. The main one is the ideomotor effect: the hand makes tiny, unconscious movements in the direction the person expects, and the chain magnifies them.

Add to that the clues we pick up without noticing, like the lay of the land, the plants, or the face of whoever hid the object; selective memory, which keeps the hits and forgets the misses; and the fact that many questions have answers we already sensed. Strip all of that away in a double-blind test, and the hits drift toward chance.

Why so many people still find it useful

A pendulum that can't detect hidden things can still be useful. Many people use one precisely because it shows them something about themselves: if your hand leans toward an answer, some part of you was already leaning that way.

That's why the most valuable moment usually comes after the swing. Did you feel relief, disappointment, an urge to ask again until you got something else? That reaction is real information about what you want or fear, and the pendulum brings it into the open in a calm, concrete way.

Used like this, a pendulum is a lot like journaling, talking it through with a friend, or flipping a coin just to find out which side you were hoping for. You don't have to believe in hidden forces for it to help you think.

How to test it yourself

You can run your own test at home, and it's worth doing: knowing how your pendulum behaves helps you use it better. Write everything down, because memory tends to keep the hits.

On Paths you can also compare engines: with "your hand" your own micro-movements decide, and with "secure randomness" the device's randomness decides. Notice whether the answer feels different in each case; that difference tells you something too.

• Have someone hide a coin under one of three cups while you're not looking, then leave the room before you ask.
• Ask the pendulum which cup it's under and write down the answer. Repeat at least twenty times.
• Compare your hits with chance: with three cups, about one right answer in three is what you'd expect.
• Then use the pendulum for a personal question and notice how you feel about the answer. That's where its usefulness lies.

What a pendulum shouldn't decide

A pendulum shouldn't decide anything about your health, your money, your legal matters or other people's lives. The tests don't support the idea that it detects outside information, and in those areas a mistake can be costly.

If you have symptoms, see a doctor. If you're facing a big financial or legal decision, talk to someone who knows the field. Afterward, if you like, use the pendulum to notice how you feel about what you decided.