Imagine looking down on a busy city. A man walking down the street pulls a phone from his pocket, taps at the touchscreen, and holds the phone to his ear. Now, add a superpower to your sight, the ability to see radio waves of different wavelengths as different colors. Green waves ripple outward in all directions from the man’s phone, brightest and strongest at the phone itself, but dimming as they travel away. There’s a mobile phone base station 100 yards away, and it detects the green waves and decodes the message, identifying the number he wants to contact. Then the base station sends out its own signal back to the man’s phone, another green ripple, but the color of this new signal is fractionally different from the original green. This is the first trick of modern telecommunications. Whereas the Titanic could only send a signal that was a mixture of lots of different wavelengths, our technology is now incredibly precise about which wavelengths are sent and received. The wavelength of the original signal from the phone was 13.412 inches, and the wavelength used to send the return signal was 13.409 inches. The phone and the base station can listen and talk on channels with wavelengths that are different by only a tiny fraction. Our eyes can’t distinguish color with anywhere near the same precision. But like the red and blue ink on my white paper, those waves are separate and don’t interfere with each other. As the man walks down the street, the green waves rippling out from his phone carry a pattern, the message that is being relayed on. A woman across the street is also talking on the phone, using a fractionally different wavelength again. But the base station can distinguish between the two. This is why the government sells bandwidth as a range; if your phone network is using that range, you’re free to make the differences between channels as tiny as you like, as long as the hardware can separate them out. So as we look down on this section of the city, we see lots of bright spots, as phones send out their signals. The signals are bouncing off buildings and slowly being absorbed by the surroundings, but most of them reach a base station before they get too weak.
As the man we were watching walks down the street, away from the base station, we start to see new colors. The streets ahead of him are full of red radio splotches, all centered on the next base station, which is sending out many shades of red to the phones around it. As the strong green signal from the first base station fades, the man’s phone detects the new frequencies and starts communicating with the new base station. He has no idea he’s reaching the edge of the “green” section, but as he does so his phone switches wavelengths so that it’s now sending out shades of red. These aren’t picked up by the original green base station, but they are relayed on by the new red one. If he keeps walking, he might walk into areas where the radio waves look like green or yellow or blue to us, with our superhero radio vision. No two patches of the same color touch; but if he walks even farther, he might walk into a new green area. This is the second trick of our mobile phone networks. By keeping the signal strength very low, we make sure that the signals can only reach the nearest base station. That means that a little way farther on, you can have a new station, using the same green frequencies. But the signals from the two green stations are too weak ever to reach each other, so there’s no problem with interference. Information flows to and from the center of each cell (that’s what the patches around each base station are called),?? but doesn’t interfere with the information from other cells. It doesn’t matter that everyone is talking at once, because they’re all talking using slightly different waves. And the technology can separate out all these conversations by tuning its receivers with incredible precision. If your phone sends signals at a wavelength that’s wrong by a tiny fraction, the message will never get through. But the incredible precision of modern technology means that the tiniest subtleties are enough to tell the waves apart.
And this is what we walk around in every day. Zooming past our heads are overlapping ripples from phones, Wi-Fi networks, radio stations, the Sun, heaters, and remote controls. And those are just the light waves. On top of that is the sound: the deep rumbles of the Earth, jazz music, dog whistles, and the ultrasound being used to clean the instruments in a local dentist’s office. And then the ripples on the cup of tea as we blow on it to cool it, ocean waves, and the undulations of the surface of the Earth itself from the occasional earthquake. And more. We’re filling our world with more waves all the time, as we use them to detect and connect the details of our lives. But they all behave in basically the same way. They all have a wavelength. They can all be reflected and refracted and absorbed. Once you understand the basics of waves, the trick of sending energy and information without sending stuff, you’ve got a huge grasp on one of the major tools of our civilization.
In 2002, I was working in New Zealand at a horse-trekking center near Christchurch. One evening, the phone rang and, to my astonishment, it was for me. The phone had a cordless handset, so I could take it outside and sit on the hillside, looking out through the dusk over the New Zealand countryside. It was Nana. She had decided to call me (I’d been away from the UK for about six months by that time, and I hadn’t spoken to my family at all), and so she pressed the right numbers on her phone and there I was, on the other end. As her familiar Lancashire accent asked about the food and the horses and the work, I was completely distracted by the weirdness of the situation. I was on the other side of a gigantic planet, as far from my family as it was possible to be while still on Earth (7,918 miles in a straight line, and 12,400 miles as a very enthusiastic crow flies), and here was Nana on the phone. Just . . . talking. Chatting. But there was a whole planet in the way. I’ve never quite got over how disconcerting those ten minutes were. These days, our planet is connected by waves. We all talk to each other, all the time, via waves that we can’t see. It’s such a gigantic achievement, and so fundamentally odd. The work of inventors like Marconi and events like the sinking of the Titanic pointed the way toward the world of today where we take these connections for granted. I feel very grateful that I was born just early enough to experience the astonishment that this particular achievement deserves. Our eyes can’t detect these waves, and it’s always hard to appreciate the invisible. But next time you make a phone call, give it a thought. A wave is really a very simple thing. But if you’re clever about how you use it, it can shrink the world.
* One of the unintentional discoveries from my time at sea is that the best way to provoke a bird enthusiast is to casually ask about seagulls. There are gulls (lots of different types), and some of them live in or on or near the sea. But there is no such thing as a seagull. Bird enthusiasts will either spend hours explaining this to you or leave in a huff.
? If you get the chance to see them from the side, you’ll see that they’re actually going around in small circles. The point is that they’re not traveling with the wave.
? Other Pacific Islanders, most notably the Tahitians, also had surfboards. However, it seems that they only lay or sat on them. The Hawaiians pioneered the idea of standing up on the board, and so “surfing” as we understand it today.
§ Experiments showing that light behaves like a wave were relatively straightforward. It took an extremely clever experiment the size of the Earth’s orbit around the sun to reveal the most counterintuitive thing about light: There isn’t any “stuff” that’s doing the waving. Instead, the waves travel as disturbances in electric and magnetic fields. The test became known as the Michelson–Morley experiment, and it’s one of my favorites of all time, because it’s simple to understand, it’s extremely elegant, and it used our whole planet as a vehicle to test their hypothesis.
? Like many materials, diamond slows down different colors of light—different wavelengths—by different amounts. So part of the sparkle comes from the diamond separating out the colors, as well as bouncing them back at you.