When Cornell University physicist and atomic-bomb theorist Hans A. Bethe died last week at age 98, many obituaries portrayed him as a "titan" - the last giant of a "golden age" of physics that flowered between the world wars.
Those years of experimenting and theorizing about the fundamental nature of matter and energy built the science that made possible construction of the first atomic bomb.
The same years, and the rise of Nazi power in Germany, also provided the fear and rationale for building the bomb, and the brilliant corps of scientists - many of them refugees from Hitler's race laws - who did the work for the United States instead of the Fuehrer.
But scientists and historians insist that physics in the 1920s and 1930s was far more than a workshop for the fathers (and mothers) of the post-war atomic "Balance of Terror" that gripped the world for 45 years. It was, discoveries with profound and lasting implications for society far bigger than the bomb, and seminal to modern materials science, engineering, computers, medicine, astronomy, astrophysics and cosmology.
And the brilliant young minds, many of whom fled fascism with this new knowledge, became the post-war teachers and role models for a new generation of scientists.
Their critical mass gave the United States pre-eminence in post-war physics, and foreshadowed what some would argue has become a new "golden age" in the field.
The list of modern wonders that owe their existence to the discoveries of the 1920s and '30s seems endless. Jonathan Bagger, chairman of physics and astronomy at the Johns Hopkins University, notes especially computer engineering and medicine, including the development of MRI machines and CAT scanners, the decoding of the human genome and nanotechnology.
"This is a golden age of physics for many reasons: for its interconnectedness with biological and materials science and indeed for the convergence of physics and astronomy - for answering some of the deepest questions humans can imagine," he says.
At the turn of the 20th century, scientists had only barely established that matter was composed of atoms. X-rays and radioactivity had been discovered, but they were not well understood.
"There were only about 1,000 physicists in the world in 1900; and if you asked people on the street what they did, they wouldn't have a clue," said Richard Rhodes, the Pulitzer Prizewinning author of The Making of the Atomic Bomb.
Until 1926, scientists labored under the mistaken idea that electrons circle their atomic nuclei as planets do their sun. This notion, born in the old world of Newtonian mechanics, worked fine to predict things on the scale of baseballs or even planets. But it broke down when scientists applied it to atoms.
Then, physicists including Austrian Erwin Schroedinger, German Werner Heisenberg and Briton Paul Dirac produced seminal work that proposed a new kind of physics called "quantum" mechanics. It was weird, but it worked.
At the scale of atoms, "one enters a region where probabilities and uncertainties become the language of physics," says Bagger.
Fundamental to this new physics is that the act of observing a system actually changes it. "You can't study an atom without jiggling it, and those jiggles change what it's doing," he says. But the message was clear: "If you wish to make new materials with new properties, you need to understand quantum mechanics."
Long-standing problems in physics began to tumble, and the ferment attracted some of the best minds in Europe and America. "Everybody jumped in," says Jeremy Bernstein, physics professor emeritus at Stevens Institute of Technology.
Many were drawn to Germany, which had quite intentionally made itself a scientific magnet. At the end of the 19th century it was racing to catch up to the other industrial powers. "They had to beef up their scientific research and development capabilities," says physicist Nina Byers of the University of California Los Angeles, who studied under atomic pioneer Enrico Fermi.
The Germans invested heavily in their universities, which became leading centers for physics and math. Germany in 1933 had more Nobel laureates than any other nation.
Brilliant students arrived from Germany, Austria, Hungary and elsewhere, among them Jews excluded from other academic fields.
In the 1930s, they discovered how the atom worked. They found it had a tiny nucleus with enormous amounts of energy locked up inside. Lise Mietner, an Austrian Jew working in Berlin, was a co-discoverer of nuclear fission - the theoretical key to atomic weapons and ultimately nuclear power plants, Byers said.
American physicist Robert Oppenheimer, who later would lead the Manhattan Project, earned his doctorate in Berlin. Bethe and Arnold Sommerfeld solved the great puzzle of the thermal properties of metals.
But the scientific geniuses who produced such discoveries began to flee the country after the imposition of anti-Jewish race laws in 1933. Some scientists lost their jobs and fled because they were Jewish or were married or related to Jews; others followed because they were appalled by the Nazis, and saw the best in their field departing.
"Because of Hitler, the best talent was exploded around the world, landed in new pastures and ended up doing a lot of different things, but with the rigor of what had been the science capital of the world," says William Lanouette, a biographer of Manhattan Project physicist Leo Szilard.
They emigrated anywhere they could, especially to England and America. Albert Einstein, Bethe, Szilard, Edward Teller, Marietta Blau and others fled the Germans. Danish physicist Niels Bohr, whose mother was of Jewish ancestry, escaped when the Nazis occupied Denmark. Fermi, whose wife was Jewish, left fascist Italy for America.
Rhodes says the United States wasn't particularly excited about accepting a lot of Jewish professors, "but these people were so luminary they were able to find positions."
Their discoveries continued. At Cornell, Bethe worked out for the first time the thermonuclear cycle that fuses hydrogen nuclei to form helium and makes the sun and stars shine. The work later earned him a Nobel Prize. Oppenheimer and his students would describe what happens when large stars collapse, outlining the physics of what later became known as black holes.
When war broke out, and fears began to rise that the remaining German physicists would build an atom bomb first, many of the emigre physicists offered their services to America. They helped develop such things as radar and armor-piercing technology. In 1943, many joined the Manhattan Project.
Oppenheimer said later that their work at Los Alamos, N.M., produced very little new science. "It was the application of things already known," Rhodes says. "These people, who were superb theoretical and experimental physicists, turned to being superb engineers."
After the war, the same people turned back to science. "Nearly everybody who was working and important in the 1940s and '50s were refugees, and they were teachers," Byers says. "There was a great flowering of physics in the U.S."
The emigres and their new students brought the U.S. global pre-eminence in physics, aided by a government that had learned the importance of physics to national security and how to build and manage large national research projects.
"Lots of money flowed into physics, and that changed things a lot," Rhodes says. America built national laboratories and the particle accelerators that enabled even deeper study of the atom.
America's scientific strength continues to rely on its ability to attract talented students and teachers from abroad, physicists say. "We do not have enough home-grown scientists and engineers to support what we're doing in this country, and that's a huge problem," Bagger says.
A wariness of foreigners has appeared since the Sept. 11 terrorist attacks, and many have found it more difficult to obtain the visas they need, and have found the culture less hospitable.
A survey by the Council of Graduate Schools found a 28 percent decline last year in applications to U.S. schools. Visa delays are said to be easing, but the survey found a 5 percent decline in applications for the coming school year.
Scientists and students will find their opportunities in other countries or alternate fields, such as Wall Street or biotechnology. "It's especially poignant given that this is a golden age for physics," Bagger says.
Meanwhile, there is a universe of powerful questions still to be answered.
For example, Bagger says, "because we understand quantum mechanics, we can understand the evolution of the universe.
We now know the universe is 13.7 billion years old." But its composition remains mysterious. "We know that only 5 percent of the material in the universe is like the stuff that's here on Earth. Ninety-five percent is something else," Bagger says. We're calling it dark matter and dark energy, "but we don't have a clue what it is, and we don't know how to make it consistent with quantum mechanics."
Physicists today are searching for a new breakthrough - a "unified" theory that will do for today's physics what quantum theory did for the old Newtonian physics in 1926.
"One of the biggest puzzles in all of theoretical physics is the fact that Einsteins's theory of relativity is incompatible with quantum mechanics," he says. "How do you put them together?"
"The only way we know how to do it is to say that tiny elementary particles are actually vibrating strings. But the catch is the strings have to vibrate in 10 space-time dimensions. We know there are three spatial dimensions plus time. Where are the other six?" Bagger asks.
"If we discover those dimensions it will be an epochal event in the history of humanity," he says. Maybe even bigger than the discoveries in quantum physics, made 80 years ago during physics' last golden age.