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by Hans Christian von Baeyer, College of William and Mary
(Photo from A Century of Physics Time Line Wall Chart)
The news of the fall of the Berlin Wall (1989), the re-unification of Germany (1990), and the disintegration of the Soviet Union (1991), rang out over an astonished world like so many peals of a great bell celebrating the end of the Cold War. As global tensions diminished and global trade flourished, the world seemed determined to make a fresh start.
Physics, too, entered a new phase. The headlong rush into new discoveries that had started after World War II was slowing down, mainly because over the years science had grown cumbersome. Theories were becoming so complex that even supercomputers couldn't keep up with the calculational demands made upon them. Experiments in some branches of physics took years to plan and carry out, simply because they required enormous research teams, scientific instruments, and financial resources. Physicists took advantage of the more measured pace by going back to take a second, harder look at what had been discovered earlier in the century - sometimes with surprising results.
Since 1925 quantum mechanics had been an infallible guide to the atomic world, universally accepted, but difficult to interpret. "Nobody understands quantum mechanics," grumbled Richard Feynman. The advent of lasers, computers, and fast electronics led to the substitution of real experiments for mere thought experiments. Observations of the behavior of individual photons and atoms brought about increasingly convincing proofs that nature really is as bizarre as quantum mechanics makes it appear.
To describe nuclear and particle physics, a consistent theory based on quantum mechanics, relativity, and quarks had in two decades been refined to such a degree that it acquired the name Standard Model. Although it left many questions unanswered, it successfully accounted for all known particles and forces except gravity. The Standard Model confidently predicted the existence of a sixth and last quark named "top." But when the top quark was finally found in 1995, its huge mass turned out to be so grotesquely out proportion with the others that it became a new enigma itself.
On the human scale, the phenomenon of superconductivity, which had been discovered in 1911 and explained in 1957, also produced a bombshell: the detection of superconductivity at much higher temperatures than had been thought possible. What's more, the old explanation did not fit the new observations, so theorists had to start all over again.
On the cosmic scale, new instruments mapped out the microwave background radiation (discovered in 1965) at an unprecedented level of detail. The new data encouraged cosmologists, including the British physicist Stephen Hawking, to tackle a theory of "quantum cosmology," which deals with the wave function of the entire universe, and the beginning of time. It will be the ultimate union of atomic and cosmic physics.
Editor's Note: A CENTURY OF PHYSICS, a dramatic illustrated timeline wallchart of over a hundred entries on eleven large posters is intended for high schools and colleges. Each poster covers about a decade and is introduced by a thumbnail essay to provide a glimpse of the historical and scientific context of the time. A Century of Physics will be on display at the Atlanta Centennial Meeting in March. In the February 1999 issue, APS News will feature the last introductory essay: 1995 - Prospect: Taking a Second Look.
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Editor: Barrett H. Ripin
Associate Editor: Jennifer Ouellette