his machine blatting away, the noise stinging Waterhouse's nose as he rides by. Waterhouse strides after him for some distance, but loses his trail after a hundred yards or so. That is acceptable; more of them will be along soon, as the Wehrmacht's nervous system awakens and its signals are picked up by the Y Service.
The motorcyclist went through a quaint little gate that joins two old buildings. The gate is topped by a tiny cupola with a weathervane and a clock. Waterhouse goes through it and finds himself in a little square that evidently dates back to when Bletchley Park was a precious Buckinghamshire farmstead. To the left, the line of stables continues. Small gables have been set into the roof, which is stained with bird shit. The building is quivering with pigeons. Directly in front of him is a nice little red brick Tudor farmhouse, the only thing he has seen so far that is not architecturally offensive. Off to his right is a one-story building. Strange information is coming out of this building: the hot-oil smell of teletypes, but no typing noises, just a high mechanical whine.
A door opens on the stable building and a man emerges carrying a large but evidently lightweight box with a handle on the top. Cooing noises come from the box and Waterhouse realizes that it contains pigeons. Those birds living up in the gables are not feral; they are homing pigeons. Carriers of information, strands of Bletchley Park's web.
He homes in on the building that smells of hot oil and gazes into a window. As evening falls, light has begun to leak out of it, betraying information to black German reconnaissance planes, so a porter is strutting about the courtyard slamming the black shutters closed.
Some information comes into Waterhouse's eyes at least: on the other side of that window, men are gathered around a machine. Most of them are wearing civilian clothes, and they have been too busy, for too long, to trifle much with combs and razors and shoe polish. The men are intensely focused upon their work, which all has to do with this large machine. The machine consists of a large framework of square steel tubing, like a bedstead set up on one end. Metal drums with the diameter of dinner plates, an inch or so thick, are mounted at several locations on this framework. Paper tape has been threaded in a bewilderingly loopy trajectory from drum to drum. It looks as if a dozen yards of tape are required to thread the machine.
One of the men has been working on a rubber drive belt that goes around one of the drums. He steps back from it and makes a gesture with his hand. Another man flips a switch and the drums all begin to spin at once. The tape begins to fly through the system. Holes punched in the tape carry data; it all blurs into a grey streak now, the speed creating an illusion in which the tape appears to dissolve into a ribbon of smoke.
No, it is not an illusion. Real smoke is curling up from the spinning drums. The tape is running through the machine so fast that it is catching fire before the eyes of Waterhouse and the men inside, who watch it calmly, as if it were smoking in an entirely new and interesting way.
If there is a machine in the world capable of reading data from a tape that fast, Waterhouse has never heard of it.
The black shutter slams home. Just as it does, Waterhouse gets one fragmentary glimpse of another object standing in the corner of the room: a steel rack in which a large number of grey cylindrical objects are stored in neat rows.
Two motorcyclists come through the courtyard at once, running in the darkness with their headlights off. Waterhouse jogs after them for a bit, leaving the picturesque old courtyard behind and entering into the world of the huts, the new structures thrown up in the last year or two. 'Hut' makes him think of a tiny thing, but these huts, taken together, are more like that new Pentagon thing that the War Department has been putting up across the river from D.C. They embody a blunt need for space unfiltered through any aesthetic or even human considerations.
Waterhouse walks to an intersection of roads where he thought he heard the motorcycles making a turn, and stops, hemmed in by blast walls. On an impulse, he clambers to the top of a wall and takes a seat. The view from here is no better. He knows that thousands of people are at work all around him in these huts, but he sees none of them, there are no signposts.
He is still trying to work out that business that he saw through the window.
The tape was running so fast that it
But why bother, if those impulses had nowhere to go? No human mind could deal with a stream of characters coming in at that speed. No teletype that Waterhouse knew of could even print them out.
It only makes sense if they are constructing a machine. A mechanical calculator of some sort that can absorb the data and then do something with it-perform some calculation-presumably a cipher-breaking type of calculation.
Then he remembers the rack he glimpsed in the corner, its many rows of identical grey cylinders. Viewed end-on, they looked like some kind of ammunition. But they are too smooth and glossy for that. Those cylinders, Waterhouse realizes, are made of blown glass.
They are vacuum tubes. Hundreds of them. More tubes in one place than Waterhouse has ever seen.
Those men in that room are building a Turing machine!
It is no wonder, then, that the men in the room accept the burning of the tape so calmly. That strip of paper, a technology as old as the pyramids, is merely a vessel for a stream of information. When it passes through the machine, the information is abstracted from it, transfigured into a pattern of pure binary data. That the mere vessel burns is of no consequence. Ashes to ashes, dust to dust-the data has passed out of the physical plane and into the mathematical, a higher and purer universe where different laws apply. Laws, a few of which are dimly and imperfectly known to Dr. Alan Mathison Turing and Dr. John von Neumann and Dr. Rudolf von Hacklheber and a few other people Waterhouse used to hang around with in Princeton. Laws about which Waterhouse himself knows a thing or two.
Once you have transfigured the data into the realm of pure information, all that is required is a tool. Carpenters work with wood and carry a box of technology for measuring it, cutting it, smoothing it, joining it. Mathematicians work with information and need a tool of their own.
They have been building these tools, one at a time, for years. There is, just to name one example, a cash register and typewriter company called the Electrical Till Corporation that makes a dandy punched-card machine for tabulating large quantities of data. Waterhouse's professor in Iowa was tired of solving differential equations one at a time and invented a machine to solve them automatically by storing the information on a capacitor-covered drum and cranking through a certain algorithm. Given enough time and enough vacuum tubes, a tool might be invented to sum a column of numbers, and another one to keep track of inventories, and another one to alphabetize lists of words. A well-equipped business would have one of each: gleaming cast-iron monsters with heat waves rising out of their grilles, emblazoned with logos like ETC and Siemens and Hollerith, each carrying out its own specialized task. Just as a carpenter had a miter box and a dovetail jig and a clawhammer in his box.
Turing figured out something entirely different, something unspeakably strange and radical.
He figured out that mathematicians, unlike carpenters, only needed to have one tool in their toolbox, if it were the right sort of tool. Turing realized that it should be possible to build a meta-machine that could be reconfigured in such a way that it would do any task you could conceivably do with information. It would be a protean device that could turn into any tool you could ever need. Like a pipe organ changing into a different instrument every time you hit a preset button.
The details were a bit hazy. This was not a blueprint for an actual machine, rather a thought experiment that Turing had dreamed up in order to resolve an abstract riddle from the completely impractical world of pure logic. Waterhouse knows this perfectly well. But he cannot get one thing out of his mind as he sits there atop the blast walls at the dark intersection in Bletchley Park: the Turing machine, if one really existed, would rely upon having a tape. The tape would pass through the machine. It would carry the information that the machine needed to do its work.
Waterhouse sits there staring off into the darkness and reconstructs Turing's machine in his mind. More of the details are coming back to him. The tape, he now recollects, would not move through the Turing machine in one direction; it would change direction frequently. And the Turing machine would not just read the tape; it would be able to erase marks or make new ones.
