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Asteroids, Dinosaurs, and the History of Physics

There is nothing like a “close encounter of the asteroid kind” to captivate the public. The resulting effect is what yields profit for Hollywood studios that make movies of the sort where brave Americans take a space ship to an interloping rock, and plant explosives to blow the thing up just seconds before it reaches dear old Earth. (At least with the old Star Trek series the crew on such death-defying missions was international, if not the Captain.) It is part of why we find it easy to neglect planning for less exotic natural disasters, such as the destruction in Russia caused by a meteor the other day (granted that that one was both big and hard to anticipate).

Stories for another day, those. Here I want to focus on another aspect of the fascination, and one that has been resurrected in recent media coverage such as WaPo’s of the asteroid 2012 DA214 that flew by yesterday: the disappearance of the dinosaurs.

In 1980 the Nobel Laureate physicist Luis Alvarez, his geologist son Walter, and some others announced that there was a high concentration of the element Iridium, rare on earth but plentiful in celestial bodies like meteorites and asteroids, at the boundary between the Cretaceous and Paleogene geological periods in an area of central Italy, which boundary is precisely the time when some paleontologists believed the dinosaurs went extinct. The natural inference from this discovery, suitably buttressed by some peripheral considerations that need not detain us, was that an asteroid hit the earth at that time, some 65 million years ago, in a catastrophic collision that wiped out the giant reptiles and a good deal else. The elder Alvarez then ran with this hypothesis in a big way.

Now Alvarez was a big shot well before 1980, and even before his Nobel in 1968. I was familiar with his presence as a graduate student working at Berkeley’s Lawrence Radiation Laboratory in the late 1950s, where he was a leading figure, indeed, a person with a reputation in the back corridors as an “operator.” He led the group of physicists associated with the 72 inch liquid hydrogen bubble chamber, the sexiest of elementary particle detectors of the era, which leadership is what would get him (never mind the other physicists) his Nobel. That is to say, he was a pioneer in the development of Big Physics, where experiments are now carried out by dozens of people (so many that sometimes the Physical Review articles that report their results list their names in a footnote rather than in the byline).

I worked in the Lofgren group, which was responsible for operating the lab’s then principal atom smasher, the Bevatron machine (pictures), which supplied beams of particles for the benefit of the bubble chamber and the apparati of other groups. My mentors were William Wenzel and Bruce Cork, who had recently been part of the team that isolated the antineutron, and I also got to work with the eventual Nobel winner James Cronin for a time, while he was visiting from Princeton. Apart from physics proper, in the area of instrumentation we worked on developing the elementary particle detection device called the spark chamber, and constructed some of the first of such devices. [cont'd.]