Science is always trying to prove itself wrong, because that’s the quickest route to finding out what’s actually going on.

They found that as the pressure on a pocket of air increased, its volume decreased. This is Boyle’s Law, and it says that gas pressure is inversely proportional to volume.

We do the same thing when we suck a drink up a straw.§ As we expand our lungs, the air inside is spread more thinly. There are fewer air molecules inside the straw to push on the water surface. And so the atmosphere pushing on the rest of the drink pushes the drink up the straw. We call this sucking, but we’re not pulling on the drink. The atmosphere is pushing it up the straw, doing the work for us. Even something as heavy as water can be shunted about if the hammering of the air molecules is harder on one side than the other.

This was the step taken by the great scientist Isaac Newton when he published his Law of Universal Gravitation in Philosophiae Naturalis Principia Mathematica—the famous Principia—in 1687. Using the rule that the gravitational force between two things is inversely proportional to the square of the distance separating them, he showed that if you added up the pull of every single bit of a planet, quite a lot of those sideways pulls cancelled each other out, and the result was a single downward force, pointing toward the center of the planet and proportional to the Earth’s mass and the mass of the thing being pulled. A mountain that’s twice as far away will only pull on you with a quarter of the force. So distant objects matter less. But they still count. Sitting looking out at the sunset, I was being pulled sideways to the north and a bit downward by Alaska and sideways to the south plus a bit downward by the Andes. But the pulls to the north and the south cancelled each other out, and what was left over was downward.

When we say “heat rises,” that’s not quite true. It’s more that “cooler fluid sinks as it wins the gravitational battle.” But no one thanks you for pointing that out.

Viscosity is just a measure of how hard it is for one layer of a fluid to slide over another layer.

There’s a word for the rapidly developing field of Lilliputian plumbing, the manipulation and control of fluids flowing through narrow channels: “microfluidics.” It’s not a familiar word to most of us now, but it’s going to have a huge impact on our lives in the future, especially when it comes to medicine.

If you can move a fluid through tiny tubes and filters, gather it in reservoirs, mix it with other chemicals along the way, and see the results, you have all the components of a chemistry lab. No need for glass test tubes, hand-held pipettes, and microscopes. This is the premise of the growing “lab-on-a-chip” industry, the development of tiny devices to carry out medical tests.

Considering how common life is on this planet, it’s surprising that no one can come up with a single definition of what it is. We know it when we see it, but the living world can usually provide an exception to any simple rule. One definition has to do with maintaining a non-equilibrium situation, and using that situation to build complex molecular factories that can reproduce themselves and evolve. Life is something that can control the speed at which energy flows through its system, manipulating the stream to maintain itself. Nothing that is in equilibrium can be alive. And this means that the concept of disequilibrium is fundamental to two of the great mysteries of our time. How did life start? And is there life anywhere else in the universe?

Scientists currently think that life may have started in deep-sea vents, 3.7 billion years ago. Inside the vents was warm alkaline water. Outside was cooler, slightly acid ocean water. As they mixed, at the surface of the vent, equilibrium was reached. It seems that early life may have started by standing in the middle of that path to equilibrium, and acting as a gatekeeper. The flow toward equilibrium was diverted to build the first biological molecules. That first tollgate may then have evolved into a cell membrane, the city wall around each cell that separates inside, where there is life, from outside, where there isn’t. The first cell was successful because it could hold back equilibrium, and that was the gateway to the beautiful complexity of our living world. The same is probably true for other worlds.

Next time you stand on the shore and watch waves rolling toward you, watch the seabirds sitting on the surface.* They’ll be parked quite happily, passengers being carried up and down as the waves go past, but they’re not going anywhere.† What this tells you is that the water isn’t going anywhere either. The waves move, but the thing that is “waving”— the water—doesn’t. The wave can’t be static; the whole thing only works if the shape is moving. So waves are always moving. They carry energy (because it takes energy to shift the water into the wave shape and back again), but they don’t carry “stuff”. A wave is a regular moving shape that transports energy. I think this is partly why I found sitting on the beach and looking out to sea so therapeutic. I could see how energy was continually carried toward the shore by the waves, and I could see that the water itself never changed.

There are three main things that can happen to a wave: It can be reflected, it can be refracted, or it can be absorbed.

Our long-distance communication uses light waves. When light waves have wavelengths that long, we call them radio waves.

An upper atmospheric layer (called the ionosphere) acts as a partial mirror for radio waves. So the radio signals from the Titanic weren’t just sweeping outward over the surface of the ocean; they were bouncing up into the atmosphere and then back down again. This is why radio waves can travel across oceans, even though the curvature of the Earth means that there’s no line of sight between sender and receiver. Reflecting waves can travel around a planet, because the reflections help them get around the curved surface. There’s no equivalent mirror in the sky for visible light.

This is what 100 percent humidity means: that every molecule that evaporates is replaced by another one condensing. If the humidity is lower than 100 percent, more molecules will leave the liquid than arrive. The bigger that difference is, the faster things dry.

The point at which more molecules are condensing than evaporating is called the dew point, and the liquid drops that form are dew.

As glaciers and ice sheets melt, water that was locked up on land is flowing back into the sea, so there’s more water in the global ocean. But that accounts for only approximately half of the current rise. The other half comes from thermal expansion. As the oceans warm, they take up more space. The current best estimate is that 90 percent of all the extra heat energy that the Earth has because of global warming has ended up in the oceans, and the extra sea-level rise is the consequence.

But because Sputnik had such a huge sideways speed, by the time it had fallen a little way down toward the Earth, it had gone so far forward that the Earth had curved away beneath it. And as it kept falling, so the Earth’s surface kept curving away. This is the beautiful balance of being in orbit. You’re going sideways so quickly that you fall toward the ground and miss. And because there’s almost no air resistance, you can just keep falling and missing, as you go around and around.

The direction of the Earth’s magnetic field seemed to reverse every few hundred thousand years. It completely flipped, so that south became north and north became south. It didn’t seem to matter too much, but it was very odd.

The blades are driving the magnets past the coils, and the rules of electromagnetic induction are creating a current in each coil. This is how electricity is born. The same principle operates in all our power stations, whether they’re producing coal, gas, nuclear, or wave energy. Magnets are pushed past wires, and so movement energy is transferred into electrical current. The beauty of a wind turbine is that this is as raw as it gets; the wind turns magnets which generate current. In a coal-fired plant, water is heated to turn a steam turbine, which turns magnets. The outcome is the same, but it takes a few extra stages to get there. Every time you plug anything in, you’re using energy that flowed into the grid as a magnet pushed on the electrons in a coiled copper wire. Electricity and magnets are inseparable. Our civilization relies on energy that is harvested and distributed using the dance between these two twins. We have done spectacularly well at hiding the dance away, trapping it in shielded wires and behind walls and in buried cables.

The shortest time that we can appreciate is approximately the blink of an eye (about a third of a second), but in that time millions of proteins have been built inside us and billions of ions have diffused across our nerve synapses, while the simpler world outside our bodies has just been getting on with things.

Water is the canvas for life, but only in the Goldilocks zone,* the energy range within which the molecules move about as a liquid. Give those molecules extra energy, and their vibrations will shake apart any complex molecules that they house. More energy still, and they will float away as a gas, useless for protecting fragile life. At the lower end of the Goldilocks range, as you reduce the energy, the vibrations slow until the molecules must slot themselves into an ice lattice. Immobility like that is the enemy of life. Even the process of building these inflexible ice crystals can burst any living cell that contains them. Our planet is special not just because it has water, but because that water is mostly liquid.

Our planet lives because of the constant injection of energy from above, feeding the engine and preventing Earth from winding down into stable, unchanging equilibrium.