Creeps to Leaps

July 20th, 2010

Most people think of technological advances in terms of some inventive genius coming up with a brilliant idea that conquers the world. This seldom happens; most technological advances arise from mundane causes. A British journalist, James Burke, created a wonderful television series back in the 1970s called “Connections” that showed how technological change can arise from all sorts of accidents. In this essay, I propose to explain a different factor in technological development: how slow incremental improvements can add up to a point where the technology suddenly opens up new possibilities.

My first example of this process concerns the power to weight ratio of engines. An engine is a device that converts energy from one form into mechanical energy. Waterwheels are a form of engine. Steam engines are a better example, because they convert the chemical energy of fuel into mechanical energy. However, steam engines are big and heavy for the amount of power they develop. This restricted their primary use to stationary applications. As they improved, they became smaller and lighter for the same amount of power output; this enabled them to be used in railroad engines and steamships. For example, the power-to-weight ratio for the first railroad steam engines was only 3.5 watts per kilogram (W/kg). These engines were still too big and bulky to be applied to personal transport -- what we now call automobiles. Steam engine designers steadily pushed up that ratio, but it was only around 1900 that steam engine technology had advanced far enough to get a power to weight ratio high enough to be practical for use in automobiles.

The internal combustion engine started off even weaker than steam engines: the earliest models had power-to-weight ratios of only 2.1 W/kg. However, the basic technology had greater potential, and within a few decades, that power-to-weight ratio had climbed impressively: the engine that powered the Wright brothers’ airplane had a power-to-weight ratio of 33 W/kg. This was an extraordinarily high ratio; at that time, most engines were still operating at about 10 W/kg. The Wright brothers had souped up their engine, sacrificing just about every other measure of performance to get that high power-to-weight ratio. But that was the trick to achieving flight -- all subsequent aircraft used engines generating power-to-weight ratios of greater than 50 W/kg. That was the crucial obstacle that had to be overcome to get an airplane into the air. It could not be achieved with steam engines, nor with early internal combustion engines. But the steady improvement of internal combustion engines eventually produced an engine adequate for the task.

Here’s another example: steel. People had been making steel for thousands of years, although they didn’t quite realize that it was adding the right amount of carbon to iron that yielded much stronger steel. With the Industrial Revolution, iron metal became readily available, but it was still not strong enough -- or cheap enough -- to be of use as a construction material. Steel was used only for blades and other small applications where its special strength was necessary. Then, in 1855, Henry Bessemer invented a new process for making steel that reduced the cost of steel by a factor of eight. I suppose that this wasn’t a creeping improvement -- it was by itself a leap. However, it took several decades for the kinks in the production process to be ironed out and for large-scale manufacturing of steel to begin. But the effects of this simple reduction in the cost of steel were stupendous. In 1902, the first skyscraper, the Flatiron Building, was constructed in New York City, using a steel skeleton for its structural support. It was 22 stories high. Buildings made of wood or stone could only reach about 3 stories because of the limitations of the materials; iron beams could get a building up to 7 stories. (The Eifel Tower is made of iron, not steel, but it is a light, open structure. A building as high as the Eifel Tower made of iron would collapse.) Thus, the Bessemer Process changed the skylines of cities all over the world, permitting the dense inner cores of modern cities.

Here’s another example: neodymium magnets. Magnets were always made of various alloys of iron until the 1970s, when research on rare-earth magnets began to yield impressive results. Over the next thirty years, extensive research produced steadily stronger and cheaper rare earth magnets; the neodymium magnet became available in quantity in the 1990s and is now a standard. These magnets are only about 3 times stronger than the old ferrite magnets, but that improvement has had profound results. For example, they have permitted hard disk drives to make a huge leap forward. In the 1980s, hard disk drives used worm drives to move the read/write heads over the disk surface. A small motor turned a long helical gear, on which rode the read/write heads. Because this process was mechanical, it was necessarily slow and noisy. You could really hear a hard drive working in those days. But then a new technology arrived: the “voice coil” technique. Instead of using a motor to move the read/write heads, the heads were mounted on a swiveling arm that had a coil of wire in its base. That coil of wire was placed directly over a powerful neodymium magnet; the current flowing through the coil of wire pulled the arm a precise distance. This technique was lightning fast. But it hinged on having powerful magnets; the old ferrite magnets were just too weak to permit precise positioning of the arm. Thus, a threefold improvement in the strength of permanent magnets led to a revolution in a completely different technology. These new magnets also made possible some interesting new technologies, such as the clever magnetic coupling used to connect the power cord to the Macintosh laptop computers. These magnets are strong enough to insure a solid connection, yet break away easily if the power cord is yanked. Another example, which inspired this essay, is the little magnet on my iPhone holster. I don’t need to snap the holster shut; the magnet secures it quite nicely yet yields readily under a short firm yank. Expect to see more such uses of magnets replacing snaps and other connectors.

Jet engines provide us with another example. They were not invented in a stroke of genius in 1940. The basic idea of an turbine engine goes back to 150 CE, with the Greek scientist Hero’s aeolipile. The idea was further developed by Leonardo da Vinci and advanced from there. The first true gas turbine was patented in 1791. Steam turbines advanced steadily all through the 19th century. The first jet engines -- turbines using a fuel that burned inside the engine -- were developed in the 1930s in England and Germany. The factor that really held up development was the burning of the turbine fan blades. These blades had to withstand the extremely high temperatures generated by the burning fuel, yet be strong enough to turn the turbine. Here is where the incremental development came into play: high-temperature metal alloys had been under development for many years, primarily for internal combustion engines, but in the 1930s there was nothing capable of meeting the requirements of a jet engine. Eventually, such alloys appeared, but it was the slow, incremental process of refinement that made these possible -- and they were the crucial limiting factor on jet engine design.

Over and over we see the same basic process: the slow, steady improvement of one technology can suddenly make possible a completely new technology that was previously beyond our reach.