We associate civilizations with cities, but they are always founded in the fields. It takes energy to build, to explore, to try and fail and try again, and so humans had to marshal the plants to harvest solar energy in order to fuel their efforts. Humans can move soil and water and seeds, but we need plants to convert light waves into sugar. We learned how to put our own green dam in place to divert a tiny part of the torrent of solar energy, and we reaped the rewards. As it trickled through Earth’s system, that temporarily diverted energy fed us, fed our animals, and gave us the capacity to alter our world.
We think of ourselves as living in a modern society, but that’s only partly true. We rely on infrastructure built by previous generations, sometimes decades ago, sometimes centuries ago, and sometimes millennia ago. Those roads and buildings and canals are still useful because they are the conduits that connect the distant and disparate parts of our society. Cooperation and trade bring enormous benefits, and these networks give each individual access to far more than their own solitary strength and intelligence could bring them.
A city is a forest of buildings, each with a different function and a different design. But underneath them all runs a huge web of thick copper cables. The copper tendrils branch as they run into individual buildings and then branch again and again, hidden in the walls and floors until the tip of one offshoot finally becomes visible at each power socket. As soon as something is plugged in, a loop is completed and electrons are free to shuffle around it, linking the outward-branching structure with the merging return structure. If you could see only the cables and not the city, you’d see the arteries of modern life, feeding us with energy from the massive power generation facilities elsewhere. The network extends across each country, a metal network of linked routes, connecting up the huge range of energy sources capable of collectively feeding the monster. We are surrounded by drifting electrons doing our bidding.
Overlaid on top of the power network there are other networks, also reaching up into the buildings and into our lives. Earth has its own planet-sized water cycle, linking oceans with rain and rivers and aquifers. Energy from the Sun provides the energy to evaporate water, to move it through our atmosphere, and to deposit it somewhere else. We humans build local diversions, funneling water out of the natural cycle and pumping it through our civilization before releasing it back to the world. Rain that has collected in a reservoir is held back, prevented from following gravity’s call directly into rivers and then the ocean. Shuffling electrons provide power to pumps that send water through pipes 3 feet in diameter, out from the reservoir, branching and branching as they travel out along our roads, into our buildings, and finally up to our taps. When we have used it, it travels back through drains and sewers, through pipes gradually increasing in size as they join together on their way to a water treatment plant or a river. When we turn on a tap, we see the tip of the network, a small link in a giant loop. Then the water runs away, out of our sight, back into the concealed tunnels. Gravity keeps it in check; as long as we do the initial work to lift it up, putting in the energy to push the water away from equilibrium, gravity will always take over to guide the onward flow down again. The drain is just the place where the resistance against gravity temporarily disappears.
A city is the place where these networks and others are all compressed together because in these places the humans are compressed together, relying on the networks to live. There are other networks overlaid on the familiar city scene: systems of food distribution, human transport, and trade to share resources. And these are just the ones that are visible if you know where to look.
Fire was the start of the human adventure with artificial light. Instead of relying on light waves from the Sun, we learned to make our own. Candles meant that we could see even when our side of the Earth had rotated around to face away from the Sun. A hundred and fifty years ago, a city at night was lit up by the light waves given out by burning candles, wood, coal, and oil. Today, the sky is filled by light that we can’t see, shining all day and all night. If we could see radio waves, we’d see that our planet hasn’t been dark at those wavelengths for a century. But these new waves are more than illumination. Radio waves, television broadcasts, Wi-Fi and phone signals form a tightly coordinated network of information, constantly rippling through our surroundings and ourselves. Anyone standing in the midst of our civilization with an electronic device that can listen in to precisely the right type of wave immediately has access to visual news broadcasts, shipping forecasts, reality TV shows, air traffic control, ham radio, and the voices of friends and family. The waves are streaming around us all the time, and the wonder of the modern world is that it’s so easy to listen in and to contribute. The flow of information ties our world together. Farmers can plan harvests based on what the supermarkets want this week. News of natural disasters touches the rest of the planet in real time. Planes can reroute to avoid bad weather up ahead. A trip to the shops can be postponed because the rainclouds will arrive overhead in ten minutes’ time. The system works because the waves are coordinated by humans cooperating with each other, because our species agreed on global rules for some waves and national rules for others. For most of human history, there were waves but no network. In only the past five generations, humans have constructed the wave-based information network that we now all find indispensable.