Absolute zero, as the name suggests, is as cold as it gets.
In 1848, Lord Kelvin, the great British physicist, pegged it at –273 °C. He thought that bringing something to this temperature would freeze electrons in their tracks, making what is normally a conductor into the perfect resistor. Others believed that electrical resistance would diminish gradually as a conductor cooled, so that by the time it reached absolute zero, all vestiges of resistance would disappear. It turns out that everybody was wrong.
Heike Kamerlingh Onnes, professor of physics at Leiden University, in the Netherlands, found the answer early in 1911 by measuring the resistance of mercury that was frozen solid and chilled to within a few degrees of absolute zero. He found that the resistance declined in proportion to the temperature all the way down to 4.3 kelvins (4.3 °C above absolute zero), at which point it fell abruptly to zero. Onnes first thought he had a short circuit. It took him a while to realize that what he had was, in fact, the makings of a Nobel Prize—the discovery of superconductivity.
Since then, physicists have sought to understand the quantum-mechanical origins of superconductivity, and engineers have tried to make use of it. While scientific efforts in this area have been rewarded by no fewer than seven Nobel prizes, all commercial applications of superconductivity have pretty much fizzled except one, which came out of the blue: magnetic resonance imaging (MRI).
Why did MRI alone pan out? Can we expect to see a second widespread application anytime soon? Without a crystal ball, it's hard to know, of course, but reviewing the evolution of superconductivity's first century offers some interesting clues about what we might expect for its second.
Onnes himself expected that superconductivity would be valuable because it would allow for the transmission of electrical power without a loss of energy in the wires. Those early hopes were, however, dashed by the observation that there were few materials that became superconducting at temperatures above 4 K and that those materials stop superconducting if you try to pass much current through them. This is why for the next five decades most of the research in this field was centered on finding materials that could remain superconducting while carrying appreciable amounts of current. But that was not the only requirement for practical devices. The people working on them also needed to find superconducting materials that weren't too expensive and that could be drawn into thin, reasonably strong wires.
In 1962 researchers at Westinghouse Research Laboratories, in Pennsylvania, developed the first commercial superconducting wire, an alloy of niobium and titanium. Soon after, other researchers, at the Rutherford Appleton Laboratory, in the United Kingdom, improved it by adding copper cladding. At the time, the most promising application appeared to be in the giant magnets physicists use for particle accelerators, as superconducting magnets were able to offer much higher magnetic fields than ones made from ordinary copper wire.
