Deep inside the Earth, a thick layer of molten magma churns round and round the core. Packed into that magma are tonnes of iron and other metals, and as they swirl they generate a dynamo effect. That effect throws up a magnetic field that wraps the whole planet and stretches far out into space — a shield against solar storms and the dangerous radiation streaming in from the cosmos, and the reason Earth gets to keep an atmosphere at all. Mars, by contrast, has no molten core, so no strong magnetic field, and no liveable atmosphere either. Down here, that powerful field may be tugging at us more directly than you'd think. Recent research looked at how the Earth's magnetic field affects people while they sleep. Because it turns out we have a magnetic field of our own: the neurons in our brains fire off electromagnetic pulses, and those pulses, the researchers say, can be swayed by the planet's field — especially when we're asleep. They tested which direction you sleep in — north–south versus east–west — against your brainwaves through the night. And sleeping east–west had a real, measurable effect, disrupting people's rest, compared with lying north–south. So it isn't only war and climate change keeping us up at night. Our beloved phone — with all its entertainment and advertising, engineered down to the pixel to hijack our attention — is quietly robbing us of sleep too. Inside that phone sits a bit of electromagnetic battery technology we take completely for granted and probably assume is brand new. But the battery is no modern invention. The oldest one in the world was dug up in ancient Baghdad and is around two thousand years old: a clay jar with a copper cylinder and an iron rod tucked inside. Pour in a bit of acid — olive oil or lemon juice will do — and it works as a battery. We have no idea what they used it for. Only that they had it. There are two main kinds of electricity: direct current and alternating current. A battery runs on direct current to power machines and gadgets — and direct current was exactly what the world-famous inventor Thomas Edison wanted to light up our cities with. It had just one flaw: it works fine over short distances (perfect for a battery), but the power fades after a couple of hundred metres. So the fix was to build a power station on every other street corner to cover a whole city. Expensive, clunky, and not very clever. Nikola Tesla, who was working for Edison at the time, begged him to switch to alternating current — far stronger, and able to send electricity as far as you liked. Edison refused, convinced the technology was lethally dangerous. Tesla never got the pay he'd been promised. And so the two turned bitter enemies, clawing at each other to become the go-to supplier of power to the cities. Tesla won in the end, and lit up our streets. That was the starting gun for the second industrial revolution — society got electrified, and the age of machines could truly begin. Electrifying the world handed us all sorts of marvels: cinema, computers, mobile phones. They've enriched our lives — and quite possibly made it even harder to sleep. By now the cinema and the computer have both squeezed themselves inside the phone! And here you might think: surely the computer, at least, is a modern invention? Nope! The oldest computer ever found comes from ancient Greece, around 80 BC. Granted, it's an analogue one — a set of gears that could predict lunar and solar eclipses, and trace the planets' paths across the night sky, Mars included. The technology hasn't slowed down, and one of the people gunning hardest to be today's Tesla — while actually looking a lot more like Edison — is Elon Musk. His grand vision: that one day we'll all own a Tesla bot to run the house and do everything we can't be bothered to do ourselves. And that's not all — he'd also love us to slot a chip into our heads! Which, understandably, a lot of people aren't wild about. Plenty are afraid we'll turn into machines, cyborgs. The famous author and philosopher Yuval Noah Harari, on the other hand, reckons we already ARE cyborgs — the phone has quietly taken over so many of our mental jobs that popping the chip and the computer inside our skulls isn't really that big a leap. The chip would probably leave us even more exposed to advertising and entertainment than we already are, and make a good night's sleep harder still. But it would also let us gather and share information far more efficiently. And maybe that's how we finally crack the problems the industrial revolutions saddled us with — global warming among them — so we don't have to tag along with Musk to Mars, and can find our way back to sleeping soundly here on Earth.
