Here There Be Dragons
Illustration by Dana Collins
MEN OF THE MIDDLE AGES SADLY REALIZED THAT the great dragons were long since gone from European soil. Only feeble remnants remained, paltry debased descendants of the grand saurians of the past: frilled snakes and lizards, and small, feathered, scaly-headed beasts not much bigger than a pheasant. The latter bore an uncanny resemblance to roosters, which had recently been imported from China and were still a bizarrity to European eyes. If the fearsome fire-breathing creatures of legend existed anywhere, it was in far-off lands at the edges of the known world. "Here there be dragons," the maps optimistically declared.
Historians Lorraine Daston and Katherine Park (authors of Wonders and the Order of Nature) alert us to a perverse tendency of wonders to congregate at the outer reaches of our cartographic knowledge. Throughout history, distant lands have beckoned with the promise of marvels: unicorns and elephants; giants, Cyclopes and races of dog-headed men; miraculous healing springs and trees whose gourds enclose, like fruits, miniature fleecy lambs. Distance loosens the mind, freeing the imagination from the restraints of common knowledge and opening the doors of perception to strange and unlikely counterintuitive phenomena.
Adventurous persons, from Marco Polo to Neil Armstrong, have always been willing to travel immense distances to experience wonders for themselves -- expeditions have been mounted, novel conveyances constructed and fortunes expended. Today, of course, cartographic knowledge exceeds the bounds of our planet, and the domain of the marvelous has retreated, as it always will, to even farther fringes. These days, those in search of the preternatural look not across the Atlantic but beyond the horizons of geography itself, to what Kant called the "island universes" of distant galaxies. Ever since Galileo pointed his "optick tube" to the heavens and discovered mountains on the moon and "satellites" orbiting Jupiter, outer space has become our chief domain of marvels. Here there be dragons indeed: quasars spitting the energy of entire galaxies, cosmic strings thrumming with the original Primal Force, neutron stars so dense a teaspoon weighs as much as Everest, and black holes so powerful they could shred a spaceship into strings of spaghetti.
The ties that bind matter to space prevent us from voyaging in person to this fabulous frontier; absent a revolution in physics and a radical new form of propulsion, humanity seems destined to remain on our ancestral cosmic home. Miraculously, however, light is exempted from Einstein's laws, confirming perhaps the great physicist's belief that if "God is subtle, he is not malicious." Ephemeral and immaterial, light bears witness across the universe. Where adventurers past were propelled on ocean waves toward the lands of their dreams, so the phantasms of distant cosmic landscapes are borne to us across oceans of space on waves of light. Here, the wonders come to us, though again, Herculean effort is required for proper apprehension of the magical phenomena -- which is why astronomers build telescopes.
Sometimes, bigger really is better. The speed and power of sailing ships depended on the size of their sails; so, the bigger the telescope mirror, the more light waves you can catch. Translating this into the metric of marvelousness, which, in opposition to gravity, increases with distance, the larger the mirror, the farther out into space you can see, and hence the more marvels you can behold. This tyranny of numbers was majestically brought home to me on a recent trip to the University of Arizona's Mirror Lab, where the world's largest telescope mirrors are made. There is nothing minimal about the place, which is in itself a haven of wonder.
Even before you enter the Mirror Lab, a touch of the surreal hovers about the enterprise, for it is bolted to the side of the university's sports stadium, the only structure on campus strong enough to support the huge machinery that casting requires. Inside it is more aerospace than bench top; the main workroom stretches three stories high and is half the size of a football field. Gigantic gantries crisscross the cavernous space, while massive cranes stand by with claws unclenched; they must be strong enough to heft 20 tons, yet gentle enough to handle crystal. The whole building is low-pressurized to protect the nascent mirrors from dust.
At the far end of the lab, some 50 yards away, an enormous mirror is being polished: 8.4 meters in diameter, it seems impossibly big yet indescribably delicate. With its deep concave surface smooth and glistening, and bathed in water to aid the buffing, it resembles nothing so much as a vast contact lens. Telescope mirrors are augmented eyes, and this one has 12 times the light-gathering surface of the Hubble Space Telescope. It is one of a pair intended for the Large Binocular Telescope currently being constructed on Mount Graham, in the Quinlan Range west of Tucson, which will soon be the world's most powerful optical instrument. Maximal vision demands that no bump on the mirror surface be larger than 100 nanometers (about 500 times narrower than a human hair): If the giant mirror being polished here were expanded to the size of North America, there would be no protrusion higher than 4 inches. The custom-designed robotic polisher crawling over the surface acts like a mechanical caterpillar nibbling away atoms at a time. Amazingly, it will be at its task 24 hours a day, seven days a week, for eight to 10 months.
Where conventional telescope mirrors are spherical, the Mirror Lab's are parabolic, the most efficient shape for focusing light. As early as the 17th century, Johannes Kepler perceived that one way to make a parabola was to rotate a bowl of liquid -- under the force of gravity, spinning liquid naturally configures itself to this unique mathematical form. A few telescopes have employed this idea using rotating bowls of mercury, but that's a toxic way to view the stars. In 1980, Mirror Lab founder Roger Angel realized that Kepler's insight could be implemented with molten glass, if only you could keep the whole apparatus spinning while the glass cooled and set.
A physicist by training, Angel tells me that when insight struck, his understanding of the chemistry of glass was nil. Though English by birth, he repaired immediately to that great American laboratory, the back yard, where in a homemade kiln he fused together a couple of Pyrex custard cups -- enriching both the future of astronomy and the noble tradition of domestic science.
ON THE DAY I VISITED THE LAB, A RARE TREAT awaited. A brand-new mirror had just been taken out of the colossal new oven and was sitting on its pallet like a gigantic freshly baked cookie. Most of the glass is in a honeycomb structure, with just a thin layer on top that will be polished to form the actual mirror surface. Angel explains that the honeycombing gives the mirror strength while radically reducing the weight. Still, we're talking 21 tons of ultrapure borosilicate glass. The oven itself is a gargantuan steel contraption, bristling with bolts and snaking tubes 10 meters in diameter and 2.5 meters high. This apparatus rests on a base 3.5 meters high that spins the entire construction seven times a minute. In flight it resembles a giant whirling pressure cooker. Normally, thermal expansion would tear the mirror apart, and to guard against that catastrophe, the floor is lined with aluminum plates sitting on a bed of steel ball bearings that allow the mold to expand and contract as the glass heats and cools. When it's cooking, the oven reaches 2,120 degrees Fahrenheit, the heat of the Earth's mantle 50 miles down, and hot enough to melt rock into magma.
In the Age of Sony, when the little black box is king, there is something tremendously comforting about Large Scale Engineering, which reminds us, as we seem to need reminding, that there is (still) a physical world beyond the virtual flicker of our screens. Extending our vision monstrously, Angel's mirrors take us to the far edges of material awareness, to those distant domains where the cosmos dreams, and where matter and space disport themselves in contradiction to natural law. As always on the periphery, the real becomes marvelous and the marvelous becomes real.
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