The image of an atom with electrons swarming around a central nucleus bulging with protons and neutrons is as iconic in our perception of science as the helix of DNA or the rings of Saturn. But as much as we scratch the surface of these scientific foundations, we can go even deeper, focusing that microscope further and discovering even more forces that govern our world.
In his new book “CHARGE: Why does gravity rule?,” theoretical physicist Frank Close explores the fundamental forces that govern our world, asking questions along the way that seek to explain how the delicate balance of positive and negative charges paved the way for gravity to shape our universe.
In this exception, he explains how magnetism, the most tangible fundamental force, was discovered, where it came from, and how it got its name.
The power within
Magnetism is a manifestation of electricity and vice versa. Electricity and magnetism have been sealed into our surroundings from the beginning. Five billion years ago, when the newborn Earth was a hot plasma of swirling electric currents, these currents created magnetic fields. As the magma cooled to form what is today the world’s solid outer crust, magnetism it was locked in iron-bearing minerals such as magnetite.
Today, on Earth’s liquid core it is still a terpsichoric frenzy of electric currents that generate a magnetic field. This extends into the atmosphere and far beyond, invisible to our normal senses. But in spreading from its source in the molten core to the heavens above, it first penetrates the earth’s crust. This is where it leaves a tangible imprint, proof that there is a force more powerful than gravity operating within the Earth, whose influence extends far and wide.
As early as the earliest Precambrian, four billion years ago, as the surface cooled, atomic elements accumulated in the layers. The most stable of these, iron, is today one of the most abundant elements in the earth’s crust. Igneous rocks formed from volcanic lava. These rocks have the property that, in the presence of a magnetic field, their iron atoms act like soldiers on parade, as they themselves become magnetic. This is used in popular demonstrations where the magnetic field of a bar magnet can be made visible.
Small iron filings are first spread over the surface of the table and then a magnet is carefully placed among them. Its magnetic field induces magnetism in the iron filings, turning them into thousands of miniature magnets. Each one orients itself correctly in the magnetic field, revealing how the direction of the magnetic force varies from place to place.
Connected: Why do magnets have a north and a south pole?
A bar magnet is a simple model illustrating what happens to the magnetic Earth itself. Earth’s North and South Magnetic Poles are analogous to those of a bar magnet, our planet’s magnetic field extends far into space. There is no iron filings in space, but there are large quantities of iron ore on Earth’s hills, rocks, and mountains. In some places, by chance, these magnetic clusters are quite extensive, as on the island of Elba and Mount Ida in Asia Minor, where large outcrops preserve the magnetic imprint in rocks historically known as magnetic pillar, now called magnetite.
There are legends of how thousands of years ago in ancient Greece, a shepherd wearing leather shoes fastened with iron nails came across magnetite—literally—when the powerful magnetism gripped the nails in his shoes. Whether a shepherd named Magnes discovered the eponymous rock or not, and if so whether it was in Magnesia, north of Athens, or on Mount Ida in Asia Minor, or even another Mount Ida in Crete, similar experiences are very likely if -less dramatic than in the story would happen on different occasions.
Certainly the power of magnetism would have been evident since the Iron Age. Lightning is a flash of electric current that generates intense magnetic fields and magnetizes iron rocks. Smelting to extract the pure iron from these sources would reveal their magnetic attraction. So the phenomenon has probably been known for about 3,000 years. Like the discovery of fire, that of magnetism probably arose in several places independently, all inspired by the natural magnetization of iron in rocks.
Because magnetic rocks are ubiquitous. By the sixteenth century, travelers recorded the best examples from the East Indies and the Chinese coast: “Very massive and heavy, [the stone] will draw or lift its just weight in iron or steel” [Robert Norman, The Newe Attractive, 1581]. As knowledge of the phenomenon spread from Greek myth to Latin and into English, the names became “Magnes rock” or “magnet”.
© [Oxford University Press]
Excerpted from CHARGE: Why Does Gravity Rule? by Frank Close, published by Oxford University Press, available in hardcover and e-book formats
