First Light: The Search for the Edge of the Universe (20 page)

Juan went downstairs to gather a midnight snack in the dome’s kitchen. He returned with a tray of steaming coffee mugs and cans of soda pop and plates holding toasted English muffin sandwiches packed with a yellow mucoid that the astronomers referred to as plastic cheese.

“
Doctor
Schmidt,” Juan said.

“Thank you, Juan.” Maarten took an English muffin and a mug of coffee and stood up. He said, “Some part of my record player at home needs to be repaired. I am looking forward tonight to some loud, flawless music,” and headed for the stereo. Fragments of rock music drifted through the data room as he scanned the dial, until
The Goldberg Variations
came up softly.

“Doctor Schneider,” Juan said.

Don took a can of Von’s Lemon-Lime soda and an English muffin with cheese. He did not touch coffee or alcohol, but his consumption of plastic cheese positively alarmed the cooks at the Monastery.

“Professor James E. Gunn,” Juan said.

“Thank you, Juanito.” Gunn accepted a can of Von’s and spritzed it without removing his eyes from the endless saraband of the galaxies. He took a long swig while groping through a pile of papers until he had located his personal jumbo value-pack of M&Ms, out of which he pulled a handful of chasers to the soda.

Juan sat down at his own television screen with a cup of coffee. He sipped it thoughtfully, looking into the universe.

Don leaned back in his chair with a huge grin on his face. “Well, what do you think of this, Juan? Is this any way to do astronomy?”

Juan took a moment to consider the question while he sipped his coffee. “Yes,” he said.

“All of us standing and gaping,” said Maarten. He pumped up the volume on the stereo, and
The Goldberg Variations
filled the data room, Maarten Schmidt conducting with a coffee mug. “Fantastic,” Maarten said. “Fantastic! It’s a Big Eye, by golly! Who cares about our own eyes when we’ve got a Big Eye!”

As an object in its own right, the universe resembles a sponge of rising dough, in which superclusters of galaxies interfinger around voids or cavities, as if the superclusters were the matrix of the sponge. As an object, the universe also looks remarkably like a swollen, pocked, filamentary cloud dissipating after an explosion—like something that began with a bang. Unlike a classical explosion, the Big Bang had no expansion center or point of origin. The explosion did not begin in any particular place. It happened everywhere out there. The prevailing theory of the Big Bang is called the inflation theory. According to this theory, at the moment of the Big Bang, the observable universe—all of the matter that makes all of the galaxies—occupied a volume of space smaller than a quark, which is the smallest known subatomic particle. The matter in the Milky Way occupied that space, along with the matter that makes up the most distant observable superclusters and quasars. During the Big Bang this microscopic, tightly compressed region of space smaller than a quark suddenly inflated into an unimaginably hot object the size of an apple, which has been expanding at a more leisurely rate ever since, until it has evolved into the present-day universe—a cold vacuum speckled with glowing floccules of matter. The universe may continue to expand or it may not. The galaxies may leave each other or they may not.

The explosion that created the universe happened somewhere between ten and twenty billion years ago. A radio telescope can hear a faint whisper of the creation. Radio telescopes can collect a signal from an event that occurred about 250,000 years after the Big Bang, when the universe consisted of a dense, hot gas. As the gas expanded and cooled, the entire universe released a sea of orange light. The light has not disappeared; it is still arriving at the earth, streaming out of the early universe from every direction in the sky. This orange light is now so deeply redshifted—coming from so far away—that it appears as the microwave background radiation, a surface of microwave emission visible all over the sky. It really is a surface: astronomers call it the surface of last scattering. The creation is visible out there. The distance from the Milky Way to the absolute horizon of our knowable universe is somewhere
between ten and twenty billion light-years, although nobody is sure of the precise distance. But somewhere out there lies an image of the beginning of time, beyond which nothing, in principle, can be seen. A telescope cannot look past the beginning.

Jim Gunn took me up to the top of the Hale Telescope’s dome one night, to inspect the universe. We climbed a ladder that curved up along the inner edge of the dome slit. Gunn pushed up a hatch and pulled himself through the hatchway. I followed; and we were standing on a small platform at the vertex of the Hale dome. The platform was plastered with ice, and a cold wind was blowing. “Don’t fall,” Gunn said, “it’s a long way down.” The view—pine-blanketed ridges, a yellow glow coming from Los Angeles over the horizon, the Big Dipper hanging upside down in the north—provoked thought. The earth seemed a solid place, not an oospore lost in the oceans of galaxies. I asked Gunn, “If the Milky Way were the size of a dime, how big would the universe be?”

“You mean, out to the horizon?” he asked. He was silent while he evidently calculated some numbers in his head. He said, “Incredible. On that scale the horizon of the universe would only be about four miles away. That’s not very far at all.” The wind picked up. His hair whipped around. He said, “It shows that the observable universe is a surprisingly small object. This universe—or at least the universe we can see—is a small object, something like a cloud of dimes four miles in radius.” He gripped a railing and raised his voice. He said, “Essentially we live in a small watering hole.”

The object of the quasar search was to learn something about the edge of the watering hole, and the tool to accomplish that was Gunn’s favorite gadget. Unfortunately, 4-shooter’s number-two camera broke down one night. Gunn happened to be in New Jersey at the time, and so he took a taxi to Newark Airport before sunrise. Don Schneider and I both went with Gunn in the taxi, and all I can remember of the ride is the two astronomers talking about cosmic strings and gravitational lenses while a brown sun rose over the oil tanks of Elizabeth, beside the New Jersey Turnpike. I didn’t take the same flight as Gunn and Schneider. By midafternoon I had arrived on Palomar Mountain in a rented car, where I found
Gunn already at work in a “garage” built into the wall of the dome beside the telescope, where 4-shooter sat prepped for surgery. It stood upright on a hydraulic cart, a white cylinder with a black lid. A scaffold surrounded it. Gunn paced underneath the scaffold, collecting tools. From his shirt pocket he removed a vinyl pouch stuffed with pens. He said, “It’s exceedingly dangerous to lean over 4-shooter with one of these pen things in your pocket. It could fall down in there.” He took surgical inventory. Crescent wrench. Multitest meter. Swiss officer’s knife. Eyeglasses—extra-magnifying, Woolworth-type. Bag of Allen wrenches. He tucked a roll of wiring diagrams under his arm and hauled a portable oscilloscope up a ladder onto the scaffold. He dropped the diagrams on the floor of the scaffold and never looked at them again.

Gunn inserted an Allen wrench into the camera’s black lid and twirled the wrench with his index finger. One by one he removed a set of Allen bolts around the top of the instrument. He said, “I need your help. We want to lift off this cover. Grab here. Pull straight up.” We lifted away a hood. “Careful,” he said, “we don’t want to hit the cameras.” We put the hood on the floor of the scaffold. Flaps and curls of Ensolite foam poked out from the interior of 4-shooter. Pipes snaked hither and thither, wrapped with foam. He said, “Are you familiar with Ensolite? It’s the stuff backpackers use for mattresses. It tends to crack at minus 193 Centigrade, but it does have the tremendous virtue of being
cheap
.” Some of the Ensolite-wrapped pipes delivered liquid nitrogen to the cameras, and other pipes sucked air out of the circuity—4-shooter’s light-sensor chips could operate only in the cold and vacuum of deep space.

He undid some screws and lifted a nitrogen tank away from the back of the broken number-two camera. Now we were looking inside the camera. It was a Schmidt telescope the size of a coffee can and packed with circuitry, a generous portion of which was of Gunnish design. He pointed to a small gold-plated can in the center of the camera and said, “The chip is sealed in there.”

The gold can contained a silicon chip known as a charge-coupled device—a CCD. An astronomical CCD is about one hundred times more sensitive to light than the most sensitive photographic film. Many CCDs are classified secret by the United States Department
of Defense, because they are used in spy satellites. The Keyhole-11 spy satellite uses a CCD; it apparently can resolve objects two to four inches across from more than one hundred miles away. CCDs will, presumably, be the primary sensors at the heart of any system of orbiting weapons. At Los Alamos National Laboratory, scientists were until recently building CCD cameras that had a working life span of a millisecond—the camera was vaporized while recording the infant face of a nuclear fireball. The CCDs inside 4-shooter can see light in the optical band; they are sensitive to the same wavelengths as the human eye, except that a CCD sees in black-and-white rather than in color. The human eye can discriminate among sixteen levels of gray. A CCD can discriminate among six thousand levels of gray. 4-shooter’s CCDs were made by the Texas Instruments Corporation, and although they are among the most sensitive CCDs in the world, they are not classified. Texas Instruments built them under a contract with the Jet Propulsion Laboratory, in Pasadena, to be the sensors inside the main imaging camera on the Hubble Space Telescope. This camera is called the Wide Field/Planetary Camera. It so happens that Jim Gunn is one of the principal designers of the Wide Field/Planetary Camera, which is why he was able to get his hands on four supersensitive CCD chips. Each chip is square, and 1.2 centimeters on one side. The chip is a pure, flawless, translucent crystal of silicon, and is extremely thin. Fifteen of these chips, if pressed together, would add up to the thickness of a piece of paper. If you blew a breath of air onto a CCD chip, it would shatter. The chip is covered with a grid of sensors that are known as pixels. The grid on the surface of a Texas Instruments CCD contains 640,000 pixels and no less than forty feet of microscopic wiring.

ACCD is difficult to manufacture. The sheet of crystalline silicon must be etched with acids to a thinness greatly exceeding that of sandwich wrap, and the crystal has to be perfect, because a single defect in the crystal will render the chip useless. The Texas Instruments CCD group, under the direction of a solid-state physicist named Morley Blouke, fabricated about twenty-five thousand of these chips in order to get about 125 chips that worked reasonably well, of which eight were selected for use in the Space Telescope’s Wide Field/Planetary Camera. Gunn’s Texas Instruments chips
might have cost fifty thousand dollars each if Gunn had paid for them, but he managed to scrounge his four chips for nothing. They had slight flaws. They were, in a word, surplus parts. The CCDs inside 4-shooter would never work inside the Space Telescope, but chilled with liquid nitrogen and encouraged by gobs of circuitry, they work nicely enough on earth. Coupled to the Hale Telescope, 4-shooter could see a lit cigarette seven hundred miles away.

Gunn put on his Woolworth glasses. He found a mechanical pencil. He pointed the pencil at a wire emerging from the gold can that held the CCD. “Can you see this wire?” he asked. The wire was as thin as a human hair. “That’s the video wire,” he said. “It brings the signal out of the chip and into the circuitry. The chip talks to the outside world through that wire.” He remarked that the video wire was brittle. “If you touch the video wire, you break it.”

The CCD was hermetically sealed inside the gold can. The can had a window through which the chip looked out at the universe. The liquid nitrogen tank on the camera had a cold finger that touched the can and cooled the chip down to nearly the temperature of liquid nitrogen, which made the chip exquisitely sensitive to light. A CCD chip collects light just as photographic film collects light. When 4-shooter’s four camera shutters are opened, starlight falls onto the four chips. The chips can be left exposed to the sky for several hours. During long, deep time exposures, light coming from a galaxy may arrive on the surface of a chip a single photon at a time, at a rate of one photon every few seconds. When photons impinge on the silicon crystal in a CCD, they knock electrons out of silicon atoms. The electrons collect in the grid of pixels on the surface of the chip. After an exposure, the camera shutters are closed. 4-shooter’s computer system then pumps the electrons from the pixels, causing the electrons to flow out of the chip, over the hairlike video wire, and into a set of amplifiers inside 4-shooter, where the electrons are counted and converted into digital numbers. From there, the numbers flow through cables into video monitors in the data room, which fill with wraiths of nameless galaxies, and finally onto computer tapes. Ever since Gunn had built the little blue kludge box, 4-shooter had been able to pump out unbroken rivers of electrons while the sky moved past the
mouth of the Hale Telescope and microscopic images of galaxies crept across the faces of the chips.