The image of the atom, with electrons crowded around a central nucleus bulging with protons and neutrons, is as iconic to our conception of science as the helix of DNA or the rings of Saturn. But no matter how much we scratch the surface of these scientific basics, we can go deeper than that, by focusing this microscope further and discovering 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 universe, 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 installment, he explains how magnetism, the fundamental, tangible force, was discovered, where it came from and how it got its name.
The power is within
Magnetism is a manifestation of electricity, and vice versa. Electricity and magnetism have been imprinted in our surroundings from the beginning. Five billion years ago, when the nascent Earth was a hot plasma of eddy electric currents, these flows created magnetic fields. When the magma cooled to form what is known today as the solid outer crust of the world, Magnetism It was trapped in minerals containing iron, such as magnetite.
today is Earth’s liquid core There is still a terpsichorean frenzy of electric currents, which generate a magnetic field. This extends into the atmosphere and far beyond, and is invisible to our natural senses. But as it spreads from its source in the molten core to the sky above, it first penetrates the Earth’s crust. Here it leaves a tangible imprint, evidence of the existence of a force stronger than gravity operating inside the Earth and whose influence extends to a very long distance.
Going back to the early Precambrian, four billion years ago, when the surface cooled, atomic elements accumulated in the layers. The most stable of these elements is iron, which today is one of the most abundant elements in the Earth’s crust. Igneous rocks formed from lava. These rocks have the property that in the presence of a magnetic field, their iron atoms act like soldiers in a parade, becoming magnetic themselves. This is exploited in popular demonstrations where the magnetic field of a bar magnet can be made visible.
Small pieces of iron are first scattered on the surface of the table and then a magnet is carefully placed between them. Its magnetic field stimulates the magnetism in the iron filings, turning them into thousands of miniature magnets. Each of these elements orients itself in the magnetic field, revealing how the direction of the magnetic force changes from one place to another.
Related: Why do magnets have north and south poles?
A bar magnet is a simple model that shows what happens to the magnetic earth itself. Earth’s north and south magnetic poles They resemble those of a bar magnet, our planet’s magnetic field that extends far into space. There are no iron filings in space, but large amounts of iron ore are found in hills, slopes and mountains on Earth. In some places, by chance, these magnetic assemblages are very 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 lodestone, and now called magnetite.
There are legends that say that thousands of years ago in ancient Greece, a shepherd wearing leather boots held in place with iron nails literally stumbled upon magnetite when strong magnetism captured the nails in his shoe. Whether or not a shepherd named Magnes discovered the rock of the same name, and if so whether in Magnesia, north of Athens, or on Mount Ida in Asia Minor, or even another Mount Ida on the island of Crete, it is very likely that such experiences , if less dramatic than in the story, could have happened on different occasions.
Certainly the power of magnetism has been evident since the Iron Age. Lightning is a flash of electric current that generates intense magnetic fields and magnetizes iron rock. Smelting to recover pure iron from these sources would reveal their magnetic attraction. So, this phenomenon has probably been known for about 3,000 years. Like the discovery of fire, magnetism may have arisen in several places independently, all inspired by the natural magnetization of iron in rocks.
Because magnetic rocks are everywhere. By the 16th century, travelers recorded the best examples, from eastern India and the Chinese coast: “Very large and heavy; [the stone] “He will pull or lift a fair weight for himself of iron or steel.” [Robert Norman, The Newe Attractive, 1581]. As knowledge of this phenomenon spread from Greek mythology to Latin, and then to English, the names changed to “magnes rock” or “magnet.”
© [Oxford University Press]
Excerpt from CHARGE: Why does gravity rule? Written by Frank Close, published by Oxford University Press, Available in hardcover and e-book formats
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