Twistor (7 page)

'Vickie, if I'd wanted to work with a mother hen, I'd have gone into zoology,' said David, slightly annoyed. 'I'm well aware that I can't work much longer. That damned eight-thirty lecture is only about eight hours away now.

'But speaking of mother hens, how are you doing with Flash?' asked David, seeking to change the subject. Vickie's sixteen-year-old brother was now living in her rooming house. He had come to Seattle at Vickie's widower father's request after a brush with the law in
southern
California. Last month Sarah and David had gone with Vickie to SeaTac Airport when young William Gordon arrived. He was a tall scrawny kid with acne and Vickie's red hair. They'd had a nice dinner at David's apartment that evening, and David had tried to interest him in physics. But William, or 'Flash,' as he had insisted on being called, seemed more interested in David's new portable Macintosh III computer and his collection of science fiction hardbacks. He had told David that if they ever let him out of high school he was going to get a fast degree in computer science and make lots of money.

Victoria shrugged on her jacket and her backpack. She frowned and said, 'William is doing OK, I guess. He just started as a senior at Roosevelt High School, and he got into the classes he wanted. His teachers say he's turning in assignments on time and doing well in class. And the Seattle police, unlike the L.A.P.D., don't pay him a visit every time some hacker cracks a bank machine.'

'So he's reformed?' David asked.

'I've got my fingers crossed,' she answered. 'William claims to have learned his lesson, and he gives the appearance of being a serious student. I haven't the time to watch him continuously, of course, any more than Dad could in Santa Monica.'

He nodded, waiting.

'David,' she said, 'I don't think William has completely given up hacking.'

'Why?' he asked.

'Because last night when I got home I noticed that my modem was still warm,' she said. 'He may have just been dialing into bulletin boards, but he might be trying to crack commercial systems again. I'm worried.'

She looked at her watch, frowned, waved at David, and left. For a minute David looked unseeing at the closed door, musing over how cold and empty the room suddenly felt with Vickie not in it.

Then
he turned his thoughts back to the present problem, the glitch in their experiment. He seated himself at the experimental console and moused up the control program. Scanning several of the new parameter files that Vickie had generated, he selected one and tried it. He didn't have to look at the vacuum gauge to know that the problem was still there. He could hear the reed relay click as the automatic mechanism changed vacuum scales. He began to experiment. He tried changing the field in the superconducting magnet; he tried altering the rotation rate of the field precession system; he tried playing with the relative phases of the electric-mode and magnetic-mode driving fields. Nothing helped.

He'd been working for about an hour when he noticed one peculiarity. Watching a field pickup with an oscilloscope, he saw with surprise that the field was not making a single 'twist' as it was programmed to do. Instead it was 'tumbling,' repeating the rotation cycle over and over again. He'd found a bug! Backtracking the symptom, he discovered that it originated not in the electronics but in the programming. A few days earlier he'd made a small 'improvement' in the control program. Apparently this change had brought with it an unwanted side effect: instead of making a single twistor rotation pass, the field rotation was cycling again and again.

Relieved that he had at last found a fixable problem, David corrected and recompiled the program, then activated the field cycle. The result was a disappointment. While the vacuum excursion was now much reduced, it was still there. And the strange loss of RF power was now bigger than before. The program bug had not created the problem, it had only aggravated some other glitch that was still present. It just didn't make any sense.

David, feeling frustrated, got up from the console and walked around the room, topping off the liquid nitrogen and liquid helium reservoirs inside the apparatus and
tightening
a brace to reduce vibrations from the mechanical first-stage vacuum pump. As his hands worked automatically, he had an idea: if you can't twiddle parameters to make things better, why not see what it takes to make them worse? The rotating field volume of the system was carefully adjusted to be well inside the boundaries of the sample holder and the magnetic guide field. But suppose the problem was coming from some stray field getting where it didn't belong. By readjusting a few currents he could make the field volume bigger – much bigger, in fact. There was plenty of drive power for that. They had been quite conservative in estimating the power needed, and as a result the driver units were considerably overdesigned. If he could make the problem worse, then perhaps its source would become more apparent.

He returned to the control console and moused up the program that he and Vickie had developed to design and model the unusual coil configuration of the apparatus. He set the nonlinear least-squares search feature of the program to find settings that duplicated the same twistor field shape but with a diameter that was, say, eight times larger.

The computer settled into its search procedure. It took a while. It usually needed about twenty minutes for its central processor to search out optimum parameters in the complex parameter space of possibilities. While the search code wandered about in its arcane way, mapping the parameter space and seeking a minimum in the chi-squared goodness-of-fit value, the system's powerful display processor had nothing to do. So, for the user's amusement, Vickie had arranged the program to produce a perspective view of the chi-squared space being searched, a spectacularly colored graphical representation showing a mathematical terrain of tall mountains, rolling foothills, and broad deep valleys. The colors of the surfaces were selected using an algorithm that, on a
blue-
washed background, mapped mathematical mountains with white tops, brown central regions, and green bases.

As the lengthy search proceeded and the contours of the terrain were filled in, David settled back to wait for the result. He realized that the emerging scene with its snowy mountain summits, brown slopes, and green valleys looked very much like the Cascades he had explored the previous summer. He remembered his first climb. The winter snows of the central Cascade Range near Seattle had melted enough for safe mountaineering, and Paul had invited him along on 'an easy Class Three climb.' He remembered it well . . .

The four of them had been climbing Kaleetan, a minor two-thousand-meter peak in the Central Cascades. Paul had been in the lead; David was second, in the novice position; followed by Rudi Baumann and George Williams, both quantum-gravity theorists.

The monotony of the uphill plodding had lulled David into daydreaming. He was just fitting his boot into the next step that Paul had provided when he heard a shout. Back along the white slope marked with dark footsteps he saw George, last on the rope and heaviest of the party, momentarily frozen in the act of losing his footing as a snow step crumbled away. As David watched, George flailed, pivoted, and toppled into a downward slide, head first on his side. He twisted, pivoting on an elbow as he planted the short wide blade of his ice axe in the snow to halt his fall. That, it seemed, was a mistake; George was falling too fast for that maneuver. The broad blade bit out a shower of snow, and the ice axe jerked and was wrenched from George's grip, his acceleration continuing unchecked. A clearly enunciated 'Shit!' echoed resoundingly from the nearby rock walls.

David felt his heart speed up from an involuntary adrenaline spurt. He watched as George's red-clad figure
moved
leisurely down the slope, trailing the dark rope, moving toward the jagged rockfall below, twisting as he maneuvered into a stomach-down, head-up position. George was trying without much effect to slow his fall by digging toes and elbows into the snow. The rope straightened, stretched, and stiffened, shedding snow and moisture as it became a vibrating line. George was slowed momentarily as the impact hit Rudi, now kneeling in the snow, the narrow spike of his ice axe planted about halfway up the blade.

But David could see a problem developing. The climbing rope, which should have absorbed the shock at Rudi's waist, well centered on his braced position, had somehow become draped over his shoulder instead. The impact levered him up and backward, and now he was sliding down the snow slope head down on his back, his axe blade pointing uselessly toward the sky.

I'm next, thought David. We're like dominoes. Those two falling now are both heavier than I am. George must mass about one-hundred-twenty kilos, and Rudi perhaps ninety. When that quarter ton of meat hits the end of the rope, I'll never be able to stop them. They'll drag me off too, and then there will be three of us falling. We'll pull Paul off, and that will make four. We're going to end in a pile of broken bodies on those sharp rocks down there. In a day or so maybe someone will find what's left of us. We're going to die right here, right now. And this was only supposed to be a Class Three climb!

Somehow the thoughts racing through his head seemed to calm David, as if someone else was about to die as he observed remotely. With control and precision he kicked deep toeholds in the snow and then nudged out depressions for his knees. He made sure that the rope was positioned correctly, then chopped the long thin blade of the ice axe into the grainy snow, his right hand gripping its top at the cross of the tee while his left held the handle so that it passed under his right arm, adjusting
the
stance until it felt right. It all seemed to be taking quite a long time.

The impact, when it came, was not the sudden crushing blow that David had anticipated. The climbing rope was surprisingly flexible, like a rubber band. He could feel it stretch as the force built and the rope cut deeper into his waist. He was slowing them! He had the brief illusion that his braced position would hold, that the two would stop. But then the rough snow crumbled beneath his left foot and he too was falling, the rubber-band effect now accelerating him to join his comrades in their tumble to the rocks.

He was sliding on his stomach, feet down. His axe blade was cutting through the crusted snow like a knife, a plume of frosty fragments streaming out behind him as he slid. In his right hand the ice axe pulled with a force that was close to the limit of his strength. But he found that by levering back to reduce the axe blade's bite in the snow he could bring the force down a bit. He slid on, cursing and working to dig in his toes.

This must be using up a lot of the available gravitational energy, a detached corner of his mind murmured. Energy-in is energy-out is force times distance:
E = mgh = f F. dl.
A big force over a long distance might just do the trick. Hell, maybe I can stop them! With new optimism he gritted his teeth and dug in the blade deeper, until he was straining with all his strength against an enormous force. He couldn't do this for long. Was it his imagination, or were they slowing down? He became more certain that they were slowing, that the drag on his arms and the pull of the rope on his waist were diminishing.
Maybe,
he thought,
may-be
. . . Then, quite unexpectedly, he stopped.

David looked back up the steep slope at his track. He had traveled about forty meters down the incline, his trail through the snow delineated by grooves from his boots and the jewel-edged black line cut by his axe blade. He
looked
up to where Paul was set and ready, face down in the snow, feet, knees and ice axe braced for the impact that now would not come. There was still a little slack in the rope.

David exhaled a laugh, jerked twice on the rope as a signal, and stood up shakily. Downslope, Rudi was still lying on his back, head downhill, his ice axe blade still pointing at the zenith. Farther down, George was getting slowly to his feet and cursing fluently in several languages as he combed snow and ice from his bushy beard.

The blood still singing in his ears, David inhaled deeply, brushed himself off, and looked around at the snowcapped peaks and the green valleys far below. It's wonderful to be alive, he thought. It wouldn't do to die just now, when things have been going so well at the lab. He grinned.

The computer made a beeping noise, signaling that it had found a steep descent trajectory. David shook himself. The view of the Cascades on the display screen shifted back to a representation of a mathematical surface.

The calculation was nearing completion. The program had found a deep minimum groove in the chi-squared surface and was sliding along a channel that headed downhill at an increasingly steep angle. Like a slide down a snow field, David thought. The search code raced along this 'creek bed' until it emptied into a broad green valley with a deep blue depression at one end. It targeted on the depression, dived into it, and settled, rocking back and forth at its very bottom. Then it registered success by playing a few bars from The Ride of the Valkyries,' a feature that Vickie in a moment of CalTechie exuberance had added. David smiled.

He moused the packet of final fit parameters that the search code had generated into the control program and configured it for a count-down-to-run of five seconds. He moused the cursor to the
control on the computer
screen
and clicked. The settings were fed to the driving circuits, and there was a brief wait while the static fields and power levels stabilized. Then the computer's synthesized 'voice' produced by the control program counted in the usual way:
'Five!
. . .
Four!
. . .
Three!
. . .
Two!
. . .
One!'
and finally,
'Activating!'