Book examines the ups and downs of waves of every kind

“There’s a regular rhythm to waves that calms us,” says British author Gavin Pretor-Pinney, explaining how he came to be fascinated by the science behind the movement of the ocean. In “The Wave Watcher’s Companion: From Ocean Waves to Light Waves via Shock Waves, Stadium Waves, and All the Rest of Life’s Undulations,” he stares down the physics behind waves of all stripes (Perigee Books, July 2010).

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FOR THE RECORD:
Waves: An interview in Saturday’s Section A with British author Gavin Pretor-Pinney on his new book, “The Wave Watcher’s Companion,” incorrectly referred to oceanographer Walter Munk as Walter Munch. —

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The quaint book is part hard science, part friendly explanation. Pretor-Pinney talked with the Los Angeles Times about waves of sea and sand; how bees and hippos do “the wave,” and more.

You write, “There’s no such thing as a wave-free sea.” Can you explain?

There’s always movement in the sea, even if there is no wind.

As wind blows over the surface of the water, it causes tiny ripples, less than an inch in height, that roughen the surface, increasing the friction between wind and water, giving it more purchase and helping it lift the surface. In this way, the wind’s energy is transferred to the water.

The stronger the wind, the greater the area over which it blows and the longer its duration, the higher the waves will grow. But when the storm dissipates and the wind dies down, the waves that it caused roll on of their own accord. The train of waves is known as a swell, and can travel over huge distances.

In the 1950s and 1960s, the great oceanographer Walter Munch measured how far ocean waves travel from the storm that created them. He found that waves created in storms off Antarctica could be tracked right up through the Pacific to the coast of Alaska. It took about two weeks for them to make this epic 7,000-mile journey, at the end of which they were far too feeble to be detected by anything but the most sensitive recording equipment.

What are the three forms of waves?

The three kinds of waves are transverse, longitudinal and torsional waves. It kind of worried me that these sound sort of dull. So I described these waves as animals.

A transverse wave is sort of like the serpentine movements of a snake. When you send a wave down the length of your garden hose to unhitch it from the fence post, you are creating a snake wave — sorry, a transverse wave.

A longitudinal wave is more like the way an earthworm moves. The worm grips the earth around it by bunching up its body to make it thicker and sending the muscular contraction down its length to propel it forward through the ground. Here the movements of the worm are not from side to side but forward and backward. Sound waves are examples of longitudinal waves. The sound from a speaker travels towards you on account of the air molecules vibrating forwards and backwards to produce traveling regions of higher and lower air pressure.

Torsional waves move in a twisting motion. You don’t tend to come across torsional waves much — not unless you work in the drilling industry. Nor do you come across many animals that use torsional waves to get around. In fact, I found it impossible to come up with any animal at all.

What are sand waves?

The dunes of the “sand seas” of the Sahara certainly look like waves, and they even travel along gradually in the wind. But I soon found out from an aeolian geomorphologist — a dune expert, to you and me — that they result from fundamentally different physical processes than actual waves.

Talk about your trip to Hawaii.

The main reason for writing the book was to go on vacation — sorry, I mean on a research trip — to Hawaii. The swells there arrive unimpeded from the winter storms tracking across the North Pacific. I was transfixed by the immense power and beauty of the breakers along the North Shore. There, more than anywhere, you get a true understanding of the energy that waves can contain.

When the ocean swells reach the lava reefs, bunching up into peaks and peeling forwards into an explosion of white water, you can feel the energy that originated from the storm as it is finally released. This energy doesn’t disappear — energy can only change from one form to another. Some of it changes into the crashing sound of the waves — and sound is a form of wave, isn’t it? Some of it travels on through the ground as vibrations — which are known as ‘microseisms’ and are like mini seismic waves. And some ends up heating up the water and shore slightly. This heat, too, travels on as waves — infrared waves. It was a huge revelation for me to realize that ocean wave energy just keeps on traveling as other types of waves.

What about stadium waves?

We all love performing The Wave — especially when there is not much going on on the pitch. But I was intrigued to learn that a Hungarian professor had made two studies into the science of stadium waves. He told me that the critical number of people needed to get a wave started is 25. Also, the waves typically travel around the stadiums at 27 mph.

I was amazed to learn that Apis dorsata, the giant Asian honeybee, also performs The Wave. The bees do it not for fun but for defense, for they build their hives out in the open, protecting them with just a wriggling mass of bees. Hippopotamuses have been known to produce a sound version of a crowd wave. This involves the males in one group, or pod, making bellowing calls which then cause those in the next pod along the river to do the same, who then set the next pod calling. Known as chain chorusing, this wave of hippo calls can travel for several miles along the river. It is probably to do with establishing satisfactory distances between the groups.

Let’s talk about traffic.

Professor Yuki Sugiyama [who runs the Mathematical Society of Traffic Flow at Japan’s Nagoya University] demonstrated that traffic jams can be a sort of wave — known as a “stop-and-go-wave.” Like stadium waves, these are not like the usual sort of waves that physicists study. But they do appear like a sort of density wave within the flow of traffic as cars join the jam at the back and others pull away at the front. Sugiyama found that the critical number of cars on the road [for these waves to form] is 40 per mile. When the weight of traffic is more than this, the flow becomes “unstable” and the natural fluctuation in our driving style is enough to cause these waves to start up. No obstruction is needed — it is just a matter of time before a traffic wave will form.

Other fun facts?

Mariners used to dangle rags and sacks filled with fish oil over the sides of their ships when the sea was particularly rough in order to calm the waves. As an extremely thin film of oil spreads over the surface of the water, it reduces the wind’s grip on the surface, and so makes the waves less likely to break onto a ship, bringing hundreds of tons of water down onto the deck.

Waves are essential to the transport systems of your body. For your heart to pump the 4,300 gallons of blood it does in any 24-hour period, it has to beat 100,000 times. Each and every one of those beats takes the form of a coordinated muscular wave.

Different states of relaxation or arousal are associated with different frequencies of brain wave: the slowest frequencies in deep sleep, the highest when concentrating hard on a difficult task. There is even a medical treatment, known as neurofeedback, in which patients are taught to change the speed of their brain waves as they play a computer game.

lori.kozlowski@latimes.com