If you have used a compass, you will know our planet has a magnetic North and South pole. You might even be aware that the geographical and magnetic poles are not exactly in the same location. The magnetic poles have a tendency to wander with time. They can even swap places, and we have evidence of a long history of such geomagnetic reversals in the rock record. But how does this happen? And what would the consequences be if this happened today? Earth’s magnetic field offers protection against radiation from outer space, primarily from the sun, so if this field weakens or changes, what will happen to us and our electrical infrastructure? Join science journalist Alanna Mitchell as she explores this topic and delves into the history of electromagnetism.

Before we can understand geomagnetic reversal and its consequences, we first need to understand magnetism and electricity, which requires understanding the fabric of the universe: atoms, subatomic particles, and the fields that permeate everything. Mitchell has travelled the world to meet with key scientists who can explain the long and chequered history of our understanding of these phenomena.

We meet Jacques Kornprobst, the man who is fighting to preserve the intellectual legacy of the French physicist Bernhard Brunhes who first discovered evidence for geomagnetic reversals (the most recent one is fittingly known as the Brunhes–Matuyama reversal). We ponder the ideas of Greek philosophers as they tried to explain magnetism. Some of this ground has been covered in North Pole, South Pole: The Epic Quest to Solve the Mystery of Earth’s Magnetism. And once Western sailors started exploring the globe, precise navigation became vital, spurring a race to study the Earth’s magnetic field (see also Earth’s Magnetism in the Age of Sail and The Illustrated Longitude: The True Story of the Lone Genius Who Solved the Greatest Scientific Problem of His Time). Discoveries in this field often flew in the face of dominant theological ideas of the day, which hampered progress in our understanding.

In comparison, research on electricity did not really take off until the middle of the 18th century, and in the book’s second part Mitchell visit museums and talks to scientists who introduce her to Benjamin Franklin (you may remember him for letting up kites in a thunderstorm to attract lightning), Michael Faraday, the forgotten Hans Christian Ørsted, Luigi Galvani, Alessandro Volta, André-Marie Ampère, Charles-Augustin de Coulomb, etc. If you remember your physics classes, some of these last names should look familiar, as SI units were named in their honour.

“[…] our magnetic field is not a simple two-poled entity like that of a magnet, but a complex phenomenon with independently wandering poles, magnetic anomalies and incomplete reversals”

Having covered the groundwork and history of both magnetism and electricity, and reminding us that we nowadays understand them to be part of the phenomenon of electromagnetism, it is back to the geophysicists and their long and winding path to understanding Earth’s magnetic field. This part of her narrative takes in findings from astrophysics, seismology (the study of earthquakes), stratigraphy (the study of rock layers), and plate tectonics. The fascinating picture that starts to emerge in this third part of the book is that our magnetic field is not a simple two-poled entity like that of a magnet. It is a complex phenomenon, with the two poles wandering independently of each other, with magnetic anomalies in other parts that form minor, secondary poles, and with incomplete reversals known as geomagnetic excursions where the strength of the field drops to as little as 5%. And all of it is changing relatively rapidly, shifting and moving over the course of decades. Geophysicists are still puzzling over it.

Finally, then, Mitchell can start discussing geomagnetic reversal in earnesty in the fourth and final part of the book. The problem is that the last known reversal happened 780,000 years ago, so it is hard to know what the impact will be. As Mitchell discovers, the geophysical community is quite reticent about making grand statements, knowing full well how hard it is to make predictions on how the Earth’s magnetic field will change in the future, and whether or not a reversal is imminent.

“Although the topic of geomagnetic reversals sounds like fodder for a Hollywood disaster movie, this book is far from sensationalist”

Astrophysicists, it turns out, are far keener to talk and speculate. They are, quite literally, looking at it from the other side, researching the impact of radiation from space as it bombards the Earth from above. Solar flares, cosmic radiation, coronal mass ejections – especially the Sun is constantly throwing radiation and charged particles our way, something the Earth’s magnetic field protects us from. But astronomers have also spotted the weaknesses and the gaps in the field. Data from manned spaceflights and the study of our planetary neighbours have taught us quite a bit about what happens next. Furthermore, the insurance industry has thought about the potential damage from this so-called space weather and has made projections and assessments, allowing Mitchell educated guesses and informed speculation about the potential consequences. We know that our satellites and ground-based electrical infrastructure of power lines, transformers and power stations are sensitive to radiation from space, and if the Earth’s magnetic field weakens, it could cause blackouts and damage on a very large scale.

With The Spinning Magnet, Mitchell has written an engrossing scientific detective story. Although the topic of geomagnetic reversals sounds like fodder for a Hollywood disaster movie, this book is far from sensationalist. It is a perfect mix of reportage, scientific history, and lively portrayals of academics current and past, revealing as much about electromagnetism and geophysics as it does about the process of scientific discovery.

The book has just one drawback: its complete lack of illustrations. It discusses many abstract topics: our understanding of what atoms look like, the discovery of the zebra-skin-like pattern of past magnetic polarity stored in spreading seabed, also known as magnetic striping, which was further proof towards Alfred Wegener’s idea of plate tectonics and became known as the Vine–Matthews–Morley hypothesis (the map Lawrence Morley examined was illustrated in Four Revolutions in the Earth Sciences: From Heresy to Truth), or the Van Allen radiation belts – the banks of radiation trapped by the Earth’s magnetic field around its magnetic equator. Mitchell does a good job describing these concepts in words, or have scientists explain them to her in clear terms, but how much clearer they would have been if drawings and photos had been included. That, for me, was the only blemish in an otherwise fascinating and superbly readable piece of popular science.

Disclosure: The publisher provided a review copy of this book. The opinion expressed here is my own, however.

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