But waves have one quite weird feature, and in La Jolla it was the pelicans that made it obvious. Brown pelicans live all along that coast, and they look so ancient that you wonder whether they’ve just flown through a wormhole from a few million years ago. They have ridiculously long beaks that usually stay folded up against their bodies, and small groups of these curious birds are often seen gliding solemnly just above the waves parallel to the coast. Once in a while, they’d plonk themselves down unceremoniously onto the ocean surface. And this was the interesting bit. The waves that the birds were sitting on rolled endlessly toward the shore, but the pelicans didn’t go anywhere.
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.
Waves come in many different types, but there are some basic principles that apply to them all. The sound waves made by a dolphin, the water waves made by a pebble, and the light waves from a distant star have a lot in common. And these days, we don’t just respond to the waves that nature provides for us. We also make our own, very sophisticated, contribution to the flood, and it connects the scattered elements of our civilization. But humans consciously using waves to cement cultural bonds isn’t new. This story began centuries ago, in the middle of a gigantic ocean.
A king surfing the ocean waves probably sounds like a snapshot from a particularly weird dream. But 250 years ago in Hawaii every king, queen, chief, and chiefess owned a surfboard, and royal prowess at the national sport was a considerable source of pride. Special long, narrow “Olo” boards were reserved for the elite, while the commoners used the shorter and more maneuverable “Alaia” boards. Contests were common, and provided the central drama for many Hawaiian stories and legends.? When you live on a stunning tropical island surrounded by deep blue ocean, building a culture around playing in the sea sounds perfectly sensible. But the Hawaiian surf pioneers had something else going for them: the right sort of waves. Their small island nation in the middle of a vast ocean was perfectly placed. Hawaiian geography and physics filtered the complexity of the ocean, and kings and queens surfed on the consequences.
While the Hawaiians were chanting to urge the flat, windless sea to rise into ready-to-surf swell, the ocean thousands of miles away could have looked very different. The winds in massive storms shove on the ocean surface, dumping energy by forcing the water up into waves. But the waves in storms are confused mixtures of short and long waves traveling in different directions, breaking and rebuilding and clashing. Winter storms are common at a latitude of about 45°, so the storms would be to the north of Hawaii in the northern hemisphere winter, and to the south of Hawaii in the southern hemisphere winter. But waves have to travel. Even as the storm winds were dying down, the patch of ruffled ocean would have been expanding out past the edges of the storm and into undisturbed water. Out here, a sorting process could take place. The true nature of the confused mess would be revealed—not jumbled chaos, but a crowd of different wave types all sitting right on top of each other. Water waves that have a longer wavelength (that’s the distance between peaks) travel faster than those with a shorter wavelength. So the first waves to escape would be the longest, racing outward ahead of their shorter cousins. But there is a price to pay as a water wave travels. Energy will gradually be stolen by the surroundings, and the price per mile is higher for the shortest waves. Not only are they losing the race, they’re losing their power as well, and it doesn’t take too long for them to vanish. Thousands of miles from the storm and days later, all that remains are the longest waves, a smooth regular swell, radiating out across the planet.
So Hawaii’s first advantage is being in a spot far enough away from the massive storms to experience them only in the form of that residual smooth, tidy, long-wavelength swell. Its second advantage is that the Pacific Ocean is very deep and islands’ volcanic sides are steep. Waves travel across the ocean surface undisturbed until they suddenly meet a steep slope. Then all the energy that was spread over a huge depth has to become more concentrated in the shallows, so the height of the waves must increase. And very close in to shore, the Hawaiians were waiting for the last gasp of these slow monsters, as the waves became so steep that they had to break over the perfect beaches of the islands. And as they broke, the kings and queens were ready with their surfboards.
Water waves are probably the first waves that most people are aware of. Something that a duck can bob about on is easy to imagine and to understand. But waves come in lots of different types, and many of the same principles apply to them all. All waves have a wavelength, a measurable distance between one peak and the next. Because they’re moving, all of them also have a frequency, the number of times they go through a cycle (peak to trough and back to peak again) in one second. All waves have a speed, too, but some of them (like the water waves) travel at different speeds depending on their wavelength. The problem with most waves is that we can’t see what’s doing the waving. Sound waves travel through air, and they’re compression waves; instead of a moving shape, what’s passed along is a push. The hardest waves to imagine are the most common of all: light waves, which move through electric and magnetic fields. But even though we can’t see electricity, we can see the effects of light being a wave all around us.§
One of the main reasons that waves are interesting and useful is that the environment they’re passing through often changes them. By the time a wave is seen or heard or detected, it’s a treasure trove of information because it carries the signature of where it’s been. But that signature is only stamped in relatively simple ways. There are three main things that can happen to a wave: It can be reflected, it can be refracted, or it can be absorbed.