The image of an atom with electrons swarming around a central nucleus bulging with protons and neutrons is as iconic to our understanding 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, focus the microscope further, and discover even more of the forces that govern our world.
In his new bookCHARGE: Why does gravity rule?“, theoretical physicist Frank Close explores the fundamental forces that govern our world, asking questions that try to explain how the delicate balance of positive and negative charges paved the way for gravity to shape our universe.
In addition, he explains how magnetism, the most tangible of fundamental forces, 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 embedded in our surroundings since 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, Earth’s liquid core is still a terpsichorean frenzy of electric currents that generate magnetic fields. This extends into the atmosphere and far beyond, invisible to our normal senses. But 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, evidence that there is a force stronger than gravity at work on Earth, whose influence extends far and wide.
As the surface cooled, in the earliest Precambrian, four billion years ago, atomic elements accumulated in layers. The most stable of these, iron, is one of the most abundant elements in the crust today. 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 become magnetic themselves. This is used in popular demonstrations where the magnetic field of a bar magnet can be made visible.
Small iron filings are first scattered on the surface of the table, and then a magnet is carefully placed between them. Its magnetic field induces magnetism in iron filings, turning them into thousands of miniature magnets. Each of them properly orients itself in the magnetic field and reveals how the direction of the magnetic force changes from place to place.
Related: Why do magnets have a north and south pole?
A bar magnet is a simple model illustrating what happens for 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 amounts of iron ore in the hills, cliffs, and mountains of Earth. In some places these magnetic clusters happen to be quite extensive, as on the island of Elba and Mount Ida in Asia Minor, where large outcrops preserve a magnetic imprint in rocks historically known as magnetite, now called magnetite.
There are legends of how thousands of years ago in ancient Greece, a shepherd with leather shoes held in place by iron nails stumbled upon magnetite—literally—when strong magnetism gripped the nails in his shoes. Whether the shepherd named Magnes discovered the rock of the same name or not, and if so, whether it was at Magnesia, north of Athens, or on Mount Ida in Asia Minor, or even on another Mount Ida in Crete, it is very likely that such experiences , if less dramatic than in the story, would happen on various occasions.
The power of magnetism would certainly have been evident since the Iron Age. Lightning is a flash of electrical current that creates intense magnetic fields and magnetizes ferrous rocks. Smelting to obtain pure metallic iron from these sources would reveal their magnetic attraction. This phenomenon has probably been known for some 3000 years. Like the discovery of fire, the discovery of magnetism probably arose in several places independently, all inspired by the natural magnetization of iron in rocks.
Magnetic rocks are ubiquitous. In the sixteenth century travelers noted 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 on to English, the names changed to “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 eBook format