What is measured

The teaching

As the science of the body's electricity teaches it.

Charge, voltage and field

Everything in this teaching rests on three ideas. Electric charge comes in two kinds, positive and negative: charges of the same kind push each other apart, and opposite kinds pull together. A voltage is a difference of electrical pressure between two places, measured in volts, which drives charge from one to the other, and moving charge is a current. A field is the region around charges in which their push and pull can be felt. Charges at rest make an electric field; charges in motion, currents, make a magnetic field as well. Magnetic fields are measured in teslas, and a tesla is a great deal: the field of the Earth, which turns a compass needle, is about fifty millionths of one.

How the heart makes its current

Every living cell keeps a small voltage across its outer membrane, the inside negative to the outside, by pumping charged atoms of sodium and potassium across it. In a resting heart muscle cell the difference is about nine hundredths of a volt. When the cell fires, channels in the membrane open, sodium rushes in, and the voltage swings briefly the other way before it recovers. That swing passes from cell to cell like a wave.

The heartbeat begins in a small knot of pacing cells in the wall of the right atrium, the sinoatrial node, which fires of its own accord sixty to a hundred times a minute at rest. The wave spreads across the two atria, which contract; pauses for a moment at a second node between the atria and the ventricles; then races down special fibres and spreads through the ventricles, which contract and drive the blood out. Last, the ventricles recover, ready for the next beat.

The electrocardiogram

Because millions of cells change their voltage together, the whole heart acts for a moment like a small battery whose poles swing round as the wave travels. The currents spread through the body's salty tissues, so electrodes on the wrists, the ankles and the chest pick up the changing differences between them. The trace has a shape every doctor knows: a small P wave as the atria fire, a tall, sharp QRS as the ventricles fire, and a rounded T wave as they recover. Its largest swing on the skin is about a thousandth of a volt.

How the brain makes its current

Nerve cells signal in the same way, by brief swings of voltage that travel along their fibres, and by passing chemical messages across the gaps between cells, which open channels and send small currents through the receiving cell. The signal of a single nerve cell is far too small to detect through the skull. What electrodes on the scalp record is the sum of slow currents in many thousands of cells of the brain's outer layer, lying side by side and acting together.

That recording, the electroencephalogram, measures millionths of a volt, typically ten to a hundred of them, and it shows rhythms whose speed changes with the state of the mind. Delta, below four cycles a second, belongs to deep sleep. Theta, from four to eight, comes with drowsiness. Alpha, from about eight to twelve, appears when a person rests awake with the eyes closed, and fades when they open. Beta, faster, goes with active thinking, and gamma, faster still, with close attention. These rhythms are often called brainwaves. They are the rise and fall of voltage in the brain's own tissue, counted in cycles per second; they are not waves that leave the head.

The magnetic fields

Currents make magnetic fields, so the heart and the brain have them too, and they can be measured without touching the body. The heart's, at the surface of the chest, is about a ten-billionth of a tesla, roughly a millionth of the Earth's field. The brain's is a hundred to a thousand times weaker again. To detect them, physicists use the most sensitive magnetometers there are: SQUIDs, superconducting rings cooled by liquid helium to a few degrees above absolute zero, inside rooms shielded against the magnetism of the world outside. Newer sensors, which watch the effect of a field on a vapour of atoms lit by a laser, can be worn close to the head.

Here is the one place where quantum physics truly meets the body's fields. A SQUID works by a quantum effect in superconductors, and without it the brain's magnetism could hardly be recorded at all. The meeting is in the instrument, not in the body.

How fast a field fades

A field like the heart's weakens steeply with distance. Seen from far enough away it behaves like the field of a small magnet, which falls to an eighth each time the distance doubles. A few centimetres from the chest it is already a small part of what it is at the skin, and long before it reaches a person across a room it is buried, thousands of times over, under the magnetism of the Earth, the wiring in the walls and the traffic in the street. That is why measuring it at any distance needs a shielded room.

The heart's field, as some teach it

The HeartMath Institute in California teaches that the heart's magnetic field is about a hundred times stronger than the brain's, that it can be detected several feet from the body, and that it carries the rhythm of the heart, and with it the emotional state of its owner, to the people nearby. With this goes a practice of heart coherence: slow, even breathing, attention resting on the area of the heart, and a feeling of appreciation or care, which makes the heart's rhythm smooth and regular.

The physics beside it confirms the first claim and qualifies the rest. The heart's field is indeed far stronger than the brain's. It can be picked up some distance away, but only by a SQUID in a shielded room. No sense organ in the human body is known that could register so small a field against the Earth's, so another person cannot feel it by magnetism. What slow, even breathing does to the heart's rhythm is real and can be measured in the one who breathes; it reaches others, as moods do, through the face, the voice and touch.

The biofield, as healers teach it

In energy healing the biofield is a field of energy and information said to surround and pass through the body, which a trained hand can feel and smooth. In Therapeutic Touch, for example, the practitioner first centres themselves, then moves the hands a few inches above the body to sense differences of warmth, tingling or pressure, then sweeps through the field to clear it, and directs energy where it is felt to be lacking.

Beside this stand the fields the body is known to make: the electric and magnetic fields of heart, brain and muscle, all tiny outside the skin, and its heat. A resting body gives off about as much heat as a bright old lamp bulb, much of it as infrared light, and a hand held close to skin feels that warmth and the warmed air rising from it. The sensations in a healer's hands are real sensations; instruments have found no other field for them to be sensing.

The quieter signals

Muscles fire with the same kind of electrical change as the heart, and electrodes over a working muscle record it. The eyes carry a steady voltage between front and back, so their movements can be traced from the skin beside them. The skin's resistance to a tiny current falls when its sweat glands open in a moment of feeling, which is what lie detectors and some meters used in religious counselling register. All of these are real, and all are small, local and read by contact.