Storm in a Teacup: The Physics of Everyday Life(44)

So we live our lives bathed in waves, and not just the ones we can see, the ones that might catch our eye if we look in the right direction. The Sun, our own bodies, the world around us, and also the technology we create are constantly making light waves. And the same goes for sound waves—high notes, low notes, the ultrasound that bats use to hunt, and the infrasound that elephants use to follow the weather. The amazing thing is that all of these waves can be traveling through the same room, and none of them will interfere with any of the others. The sound waves are the same whether a room is completely dark or full of disco lights. The light waves aren’t affected by piano concertos or screaming babies. All of this is what we tap into when we open our eyes and use our ears. We’re just siphoning off some of the useful bits from the flood, selecting the waves that send us the most useful information.

But which ones do you choose? The answer will be different for the newest self-driving cars and for an animal that needs to survive in a forest. There’s a huge richness of information out there, and you can pick and choose which of the waves will help you most. That is why blue whales and bottle-nosed dolphins can hardly hear each other, and also why neither of them gives a hoot about the color of your wetsuit.


THE GULF OF CALIFORNIA stretches along the western coast of Mexico, a narrow ocean haven 700 miles long that opens into the Pacific at its southern end. The blue water of the channel is protected by dark, raw mountain peaks that poke into the sky from both shores. Marine species migrate vast distances across the oceans to feed and to rest here. Bobbing about in a small boat in the middle of the channel, a fisherman can appreciate the peace. And what peace means is that the flood of waves that bathe that fisherman is low-key and relatively uncomplicated. Light streams from the Sun during daytime, reflected only by blue water and burnished rock. The lapping waves and the creaking of the boat send out the only sound waves. A lone dolphin leaps out of the water, briefly a part of this calm world, and then splashes back down into a completely different world and one that certainly isn’t calm. Down below is the loud, bustling hubbub of an ecosystem at work and play.

The dolphin sends out a high-pitched whistle as it dives downward, communicating to the rest of the pod following on behind. And as the pod catches up, the water is filled with clicks, short sharp waves sent out from the forehead of each dolphin that bounce off the surroundings. Those that make it back to the dolphin are transmitted through its jawbone to its ear, letting each animal build up a picture in sound of what’s nearby. The whistles and squeaks and clicks make this sound like a busy street. These are the sound waves of a community on the move. After spending a while at the surface, breathing and playing, the pod turns downward toward the deepest, darkest blue, on a mission: the hunt. The light waves that were so common above the surface are much less common down here. Light waves are absorbed by water very quickly, so information from light is scarce. The dolphins have eyes that can cope both above and below water, but the measure of light’s usefulness to them is shown in how that eye has evolved. They have no ability to distinguish color at all—why would you need it to when there’s hardly any variety in the color of your world? Their world is blue, but they will never know that. A dolphin can’t see the color blue, so their watery world looks black. But they can see the bright glints of passing silvery fish, so they can see what they need.

The ocean surface is like an Alice-in-Wonderland mirror, separating two worlds but easy to step through. Waves tend to bounce off the interface, so sound from the air stays in the air, and sound from the ocean stays in the ocean. In air, light travels very easily, and sound travels reasonably well. In the ocean, light waves are absorbed very quickly, but sound waves pass through quickly and efficiently. If you want to learn about your environment in the ocean, you need to detect sound waves. Light waves are often of little use unless you’re looking at something very close to you and near the surface.

But there’s more to the world of sound down here. Dolphins use very high-pitched sounds, some with wavelengths ten times shorter than anything we can hear. These short wavelengths mean that their echolocation mechanism can pick up on even tiny details of the shape of what’s in front of them. But high-pitched sounds don’t travel very far, so the noisy pod of dolphins can’t be heard from the other side of the channel. On top of the dolphin chatter are other sounds that travel much farther. There’s the deep hum of a distant ship, the tinkling of bubbles from surface splashes, the quiet popcorn-like crackling of snapping shrimp, and then a deep groaning noise, so low that the dolphins can’t hear it. The groan is repeated. Ten miles away, a blue whale is calling and the sound is echoing up the channel. The whale doesn’t use echolocation, so it doesn’t need a high-pitched wave. But it needs the sound to travel a long way, and that means using a low pitch (a long wavelength). A sound wave with a long wavelength can travel for huge distances, and the baleen whales—blue, fin, and minke whales, among others—need to communicate over huge distances. The whales can’t hear the dolphin clicks and the dolphins can’t hear the whale song. But the water carries it all, a vast flood of information for whichever creatures choose to tune in.

So the ocean has its own flood of light waves and sound waves, but in a completely different way from the air. Sound is king down there, and whales and dolphins are color-blind because the details of the light waves aren’t worth paying attention to.

There are some similarities between the atmosphere and the ocean, though. Just as the longest sound wavelengths travel farthest underwater, the longest light wavelengths travel farthest in the air. Just over a century ago, humans also learned to communicate over thousands of miles. Because we live in air, we don’t do it using sound waves. Our long-distance communication uses light waves. When light waves have wavelengths that long, we call them radio waves. But the most important early use of this technology was also to send information across oceans. And if her crew had really taken in the information carried by these new communication systems, the Titanic might never have sunk.