Origins ANTARCTICA, Scientific Journeys from McMurdo to the Pole
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  © Per Olof Hulth
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A literary essay about AMANDA by Francis Halzen
page 2

The end result, abstracted on a computer screen, would have seemed unremarkable to most people. But to us it was the sole trace of a particle that had traversed vast distances to reach us, perhaps a remnant of one of the most spectacular events in the universe. More to the point, it was the first concrete proof that AMANDA worked—that it could help map the distant depths of space, thereby perhaps resolving some of the most heated controversies in physics. Later, when I E-mailed the diagram to our collaborators, one of them wrote back: "This is why I’ve spent five years of my life on this project."

"NEUTRINOS, THEY ARE VERY SMALL," John Updike wrote, famously. "They have no charge and have no mass / And do not interact at all." As it turns out, Updike was wrong on two counts, but he got the spirit right, anyway. Neutrinos are so small and slippery that they pass through the Earth (and stars and cities and most everything else) like a bullet through a rainstorm. Unfazed by magnetic fields or the strong nuclear force, they have to make a direct hit on a proton to be stopped at all—a highly unlikely event. At the same time, neutrinos are about as plentiful in the universe as the photons that constitute light: 3 x 1016 of them pass through our bodies every second.

That combination of factors makes neutrinos the best focus for deep-space astronomy. Most photons cannot reach us from the most distant points in the universe (the most energetic ones cannot even make it from the edge of the galaxy: they crash into microwave background radiation along the way). And though radio waves routinely travel as far as neutrinos, they are emitted even by rather mundane astronomical objects—the moon, for instance. Neutrinos, on the other hand, not only travel long distances, they are easy to categorize: low-energy neutrinos are generated by the sun, by cosmic-ray collisions in the upper atmosphere, and by other nearby phenomena; high-energy neutrinos only reach the earth from distant, supremely violent events—gamma-ray bursts, for instance, or black holes at the center of new galaxies. By focusing on high-energy neutrinos alone, a telescope can naturally filter out all but the most interesting things in the sky.

But there is no free lunch. If neutrinos can fly through planets without stopping, they hardly brake for your average telescope mirror. In fact, neutrinos are so hard to detect that for decades they existed only in theory. The Swiss theoretical physicist Wolfgang Pauli "invented" them in 1930 to balance out the energy apparently lost when radioactive matter decays. ("I have done a terrible thing," he told the German astronomer Walter Baade. "I have postulated a particle that cannot be detected.") It was not until twenty-six years later, when the physicists Frederick Reines and Clyde L. Cowan built a neutrino detector near the Savannah River nuclear plant in South Carolina, that the existence of the particle was confirmed.

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