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 no matter how much we scratch the surface of these scientific foundations, we can go even deeper, focusing that microscope further and uncovering even more forces that drive our world.
In his new book “ACCUSATION: Why does gravity rule?“, theoretical physicist Frank Close explores the fundamental forces that govern our world, posing questions along the way that seek to explain how the delicate balance of positive and negative charges gave way to gravity to shape our universe.
In this addition, he explains how magnetism, the most tangible of fundamental forces, was discovered, where it comes from, and how it got its name.
The strength within
Magnetism is a manifestation of electricity, and vice versa. Electricity and magnetism were embedded in our environment 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 magma cooled to form what is today the world’s solid outer crust, magnetism it was locked in minerals containing iron, such as magnetite.
Today, you Earth’s liquid core it is still a terpsichorean frenzy of electric currents, which generate a magnetic field. This extends into the atmosphere and far beyond, invisible to our normal senses. But spreading from its source in the molten core in the heavens above, it first penetrates the Earth’s crust. This is where it leaves a tangible imprint, evidence that there is a force more powerful than gravity at work within the Earth, whose influence extends far and wide.
From the earliest Precambrian period, four billion years ago, as the surface cooled, atomic elements accumulated in layers. The most stable of these, iron, is today one of the most abundant elements in the 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 has been exploited in popular demonstrations where the magnetic field of a bar magnet can be made visible.
Small iron filings are first spread on the surface of a 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 is properly oriented in the magnetic field, revealing how the direction of the magnetic force varies from place to place.
Connected: Why do magnets have north and south poles?
The bar magnet is a simple model that illustrates 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 extending far into space. There are no iron strands in space, but there are large amounts of iron ore in the hills, rocks and mountains on Earth. In some places, incidentally, these magnetic clusters are quite extensive, as on Elba Island and Mount Ida in Asia Minor, where large outcrops preserve the magnetic imprint in rocks historically known as lodestone, now called magnetite.
There are legends of how thousands of years ago in ancient Greece, a shepherd wearing leather shoes held in place with iron nails stumbled – literally – through magnetite when powerful magnetism stuck the nails in his shoes. Whether or not a shepherd named Magnes discovered the rock of the same name, and if so, whether it was at Magnesia, north of Athens, or on Mount Ida in Asia Minor, or even another Mount Ida in Crete, there is much it is likely that such experiences, if less dramatic than in history, would have occurred on different occasions.
Certainly, the power of magnetism would have been evident since the Iron Age. Lightning is a flash of electric current which generates intense magnetic fields and magnetizes iron rocks. Smelting to extract pure iron metal from these sources would have revealed their magnetic attraction. So, the phenomenon has been known for about 3000 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. In the sixteenth century, travelers recorded the best examples, from the East Indies and the Chinese coast: “Very massive and weighty, [the stone] will draw or lift its fair 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 morphed into ‘magnes rock’ or ‘magnet’.
© [Oxford University Press]
Excerpt from CHARGE: Why Does Gravity Rule? by Frank Close, published by Oxford University Press, available in both paperback and eBook formats
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