A little while back, I was put in touch with a Wall Street Journal writer who was looking into a new-ish health fad called "earthing," which involves people sleeping on special grounded mats and that sort of thing. The basis of this particular bit of quackery is the notion that spending time indoors, out of contact with the ground, allows us to pick up a net positive charge relative to the Earth, and this has negative health consequences. Walking barefoot on the ground, or sleeping on a pad that is electrically connected to ground via your house's wiring, allows you to replace your lost electrons with electrons from the Earth, curing all manner of ills.

I'm quoted briefly in a column about this, but in preparing to talk about the physics, I drew up a more extensive list of reasons why this "earthing" business is a bunch of crap than could really fit in a single column. Luckily, I have this blog where I can post this sort of thing; thus, a collection of physics reasons why this fad is nonsense.

Of course, like most health fads, there's a tiny grain of truth at the center of a giant ball of crap. It is, in fact, perfectly true that we can build up a potential difference between our bodies and the Earth, due to brushing against materials that tend to grab electrons. It's also true that contact with the Earth, or with grounded conductors, will equalize the potential by allowing electrons to flow between your body and the Earth. There's nothing particularly wrong about those two statements; it's just, you know, everything else that follows after them. They're true, but basically meaningless, for the following reasons, among others:

1) Electrons are electrons. The sites I looked at are full of talk about "beneficial electrons from the Earth" and that sort of thing, which is garbled nonsense. Electrons are electrons are electrons-- there's nothing that singles out or sets apart an electron from the Earth as opposed to from some synthetic material, or, for that matter, an electron that came blasting in from outer space.

How do we know this? Basically because chemistry works. The Periodic Table of the elements is set up the way it is because of the arrangement of electrons within atoms-- as you increase the number of electrons in a given atom, you "fill up" energy states, with the last electron added going into a particular state that determines the binding properties of the atom in question. That "filling up" is a consequence of the Pauli Exclusion Principle, which says that no two electrons can be found in exactly the same state. The Exclusion Principle, in turn, is a consequence of the indistinguishability of electrons-- two electrons aren't allowed to occupy the same state because electrons are perfectly indistinguishable, and that puts some constraints on their properties.

If there were a difference between electrons from the Earth and from other sources, then chemistry would be a mess. Electrons that originated in the ground would "fill up" one set of states, while electrons that originated somewhere else would "fill up" a different set of states. You'd end up with carbon atoms that could only form two chemical bonds, instead of the usual four, or solids that ought to be conductors but act as insulators, and all sorts of other screwy results. We don't see those things, which means that all electrons are truly identical to a very high degree.

2) Potential Differences Are Transient and Meaningless. Shuffle your feet across a carpet, and then touch a doorknob. Feel a spark? Congratulations, you've established a significant potential difference between yourself and the Earth, and then eliminated it.

It's perfectly true that ordinary interactions with many materials will strip electrons off your body. But that never lasts all that long, as the doorknob-spark illustrates. In the process of shuffling across a carpeted floor, you lose (or gain, depending on the materials involved) several billion electrons, but as soon as you touch a metal object, you get them all back (or give them all up).

It's simply not possible to build up and maintain a significant charge imbalance between your body and the rest of the world, because everything we interact with contains electrons, and they move back and forth between objects all the time. If nothing else, the charge on an object will eventually dissipate into the air-- back when I was doing sticky tape experiments, I had to periodically recharge the tapes, because the charge goes away over time. A net positive charge will attract negative ions from the air, and eventually neutralize, and the same thing happens to your body.

3) The Potential Measurements Made by "Earthing" Advocates Are Worthless. One of the many sites out there promoting this stuff (I'm not going to dignify them with a link) suggests that you can demonstrate the severity of the problem by getting a voltmeter from Radio Shack and putting one of the leads into the ground socket of an electrical outlet in your house. Then touch the other to your body, and you'll see a voltage reading that's a measure of how much your potential differs from that of the Earth.

That seems very convincing, as long as you've never been an easily bored physics major (as if there's any other kind). I was an easily bored physics major, though, so I've played with voltmeters lots of times in the past, and tried measuring the potential difference between myself and lots of things. As a result, I know that these results are gibberish.

But, just to be fair, I did what they suggested, and plugged the meter into the ground socket, then touched my thumb with the other lead. I measured a potential difference that fluctuated a bit, between about 0.03V and 0.15V. I then took the lead out of the electrical socket, and touched both leads to my left thumb, about an inch apart. Where I measured a potential difference that fluctuated between 0.03V and 0.15V. Those measurements are basically meaningless-- it's noise in the meter, fluctuating local fields, and other garbage effects.

Their literature talked about potential differences of multiple volts, which I didn't see, but have occasionally managed in past screwing around with voltmeters. But even that is completely insignificant-- if you shuffle your feet across the rug and then throw a spark touching a metal object, the potential difference between you and the metal thing was probably around 1,000V. It takes an electric field around 1,000,000 V/m to make a spark in air (give or take a factor of ten or so; the textbook we used to use had a long discussion of sparks), and a typical spark from everyday static electricity will jump around a millimeter. So, a potential difference across that gap of 1,000V will get the job done.

You build up and discharge potential differences of hundreds of volts all the time, without particularly noticing.

4) Their Own Safety Devices Undermine Their Claims. The literature I looked at reassured potential customers that there was no danger of electric shock from using their products, because the cord used to connect the "Earthing" mats to the ground of your house's electrical system contains a 100,000 Ω resistor as a precaution. That made me bust up laughing.

Why? Because the definition of a resistor is that it resists the flow of current. Which means it will impede the flow of harmful current from a faulty appliance of some sort, true, but it will also act to impede the flow of beneficial electrons from the Earth by exactly the same amount.

How big a difference are we talking? Well, the connection between the ground plug of your electrical system and actual ground (generally either a metal spike driven into the ground, or something like a metal water pipe coming into the house) should have a resistance of a few ohms (see, for example, this discussion). So if you drop a 100,000 Ω resistor in there, you're increasing the resistance by nearly a factor of 100,000, which reduces the rate at which electrons flow in from the Earth by the same factor.

What's that mean? Well, in order to get the same health benefit of one second of electron flow between you and the Earth due to direct contact-- standing barefoot on the ground, for example-- you would need to spend 100,000 seconds in contact with their mat. 100,000 seconds is about 27 hours, a bit more than a day. Their literature talks about the health benefits of multiple hours spent "Earthing" yourself, which would require hundreds of thousands of hours on the protected mat, and 100,000 hours is over 11 years.

And that, right there, ought to be enough to, well, bury this whole silly idea. Their "safety" precaution should obliterate the effectiveness of their devices. The fact that they advertise this as a positive feature indicates just how little real physics there is at work here.