tion better。〃 Having watched Julia's demo tape； I was immensely curious to see what he showed me next。 Because many people I respected thought molecular manufacturing was impossible。 One of the major theoretical objections was the time it would take to build a working molecule。 To work at all； the nanoassembly line would have to be far more efficient than anything previously known in human manufacturing。 Basically； all man…made assembly lines ran at roughly the same speed： they could add one part per second。 An automobile； for example； had a few thousand parts。 You could build a car in a matter of hours。 A mercial aircraft had six million parts； and took several months to build。
But a typical manufactured molecule consisted of 1025 parts。 That was 10；000；000；000；000；000；000；000；000 parts。 As a practical matter； this number was unimaginably large。 The human brain couldn't prehend it。 But calculations showed that even if you could assemble at the rate of a million parts per second； the time to plete one molecule would still be 3；000 trillion years…longer than the known age of the universe。 And that was a problem。 It was known as the build…time problem。
I said to Ricky； 〃If you're doing industrial manufacturing 。。。〃
〃We are。〃
〃Then you must have solved the build…time problem。〃
〃We have。〃
〃How？〃
〃Just wait。〃
Most scientists assumed this problem would be solved by building from larger subunits； molecular fragments consisting of billions of atoms。 That would cut the assembly time down to a couple of years。 Then； with partial self…assembly； you might get the time down to several hours； perhaps even one hour。 But even with further refinements； it remained a theoretical challenge to produce mercial quantities of product。 Because the goal was not to manufacture a single molecule in an hour。 The goal was to manufacture several pounds of molecules in an hour。 No one had ever figured out how to do that。
We passed a couple of laboratories； including one that looked like a standard microbiology lab； or a genetics lab。 I saw Mae standing in that lab； puttering around。 I started to ask Ricky why he had a microbiology lab here； but he brushed my question aside。 He was impatient now； in a hurry。 I saw him glance at his watch。 Directly ahead was a final glass airlock。 Stenciled on the glass door was MicroFabrication。 Ricky waved me in。 〃One at a time；〃 he said。 〃That's all the system allows。〃
I stepped in。 The doors hissed shut behind me； the pressure pads again thunking shut。 Another blast of air： from below； from the sides； from above。 By now I was getting used to it。 The second door opened； and I walked forward down another short corridor； opening into a large room beyond。 I saw bright； shining white light…so bright it hurt my eyes。 Ricky came after me； talking as we walked； but I don't remember what he said。 I couldn't focus on his words。 I just stared。 Because by now I was inside the main fab building…a huge windowless space； like a giant hangar three stories high。 And within this hangar stood a structure of immense plexity that seemed to hang in midair； glowing like a jewel。
DAY 6
9：12 A。M。
At first； it was hard to understand what I was seeing…it looked like an enormous glowing octopus rising above me； with glinting； faceted arms extending outward in all directions； throwing plex reflections and bands of color onto the outer walls。 Except this octopus had multiple layers of arms。 One layer was low； just a foot above the floor。 A second was at chest…level； the third and fourth layers were higher； above my head。 And they all glowed； sparkled brilliantly。
I blinked； dazzled。 I began to make out the details。 The octopus was contained within an irregular three…story framework built entirely of modular glass cubes。 Floors； walls； ceilings； staircases…everything was cubes。 But the arrangement was haphazard； as if someone had dumped a mound of giant transparent sugar cubes in the center of the room。 Within this cluster of cubes the arms of the octopus snaked off in all directions。 The whole thing was held up by a web of black anodized struts and connectors； but they were obscured by the reflections； which is why the octopus seemed to hang in midair。
Ricky grinned。 〃Convergent assembly。 The architecture is fractal。 Neat； huh？〃 I nodded slowly。 I was seeing more details。 What I had seen as an octopus was actually a branching tree structure。 A central square conduit ran vertically through the center of the room； with smaller pipes branching off on all sides。 From these branches； even smaller pipes branched off in turn； and smaller ones still。 The smallest of the pipes were pencil…thin。 Everything gleamed as if it were mirrored。
〃Why is it so bright？〃
〃The glass has diamondoid coating；〃 he said。 〃At the molecular level； glass is like Swiss cheese； full of holes。 And of course it's a liquid； so atoms just pass right through it。〃
〃So you coat the glass。〃
〃Right。 Have to。〃
Within this shining forest of branching glass； David and Rosie moved； making notes； adjusting valves； consulting handheld puters。 I understood that I was looking at a massively parallel assembly line。 Small fragments of molecules were introduced into the smallest pipes； and atoms were added to them。 When that was finished； they moved into the next largest pipes； where more atoms were added。 In this way； molecules moved progressively toward the center of the structure； until assembly was pleted； and they were discharged into the central pipe。 〃Exactly right；〃 Ricky said。 〃This is just the same as an automobile assembly line； except that it's on a molecular scale。 Molecules start at the ends； and e down the line to the center。 We stick on a protein sequence here； a methyl group there； just the way they stick doors and wheels on a car。 At the end of the line； off rolls a new； custom…made molecular structure。 Built to our specifications。〃
〃And the different arms？〃
〃Make different molecules。 That's why the arms look different。〃 In several places； the octopus arm passed through a steel tunnel reinforced with heavy bolts； for vacuum ducting。 In other places； a cube was covered with quilted silver insulation； and I saw liquid nitrogen tanks nearby； extremely low temperatures were generated in that section。
〃Those're our cryogenic rooms；〃 Ricky said。 〃We don't go very low； maybe …70 Centigrade； max。 e on； I'll show you。〃 He led me through the plex； following glass walkways that threaded among the arms。 In some places； a short staircase enabled us to step over the lowest arms。
Ricky chatted continuously about technical details： vacuum…jacketed hoses； metal phase separators； globe check valves。 When we reached the insulated cube； he opened the heavy door to reveal a small room； with a second room adjacent。 It looked like a pair of meat lockers。 Small glass windows were set in each door。 At the moment； everything was at room temperature。 〃You can have two different temps here；〃 he said。 〃Run one from the other； if you want； but it's usually automated。〃
Ricky led me back outside； glancing at his watch as he did so。 I said； 〃Are we late for an appointment？〃
〃What？ No； no。 Nothing like that。〃 Nearby two cubes were actually solid metal rooms； with thick electrical cables running inside。 I said； 〃Those your magnet rooms？〃
〃That's right；〃 Ricky said。 〃We've got pulsed field magnets generating 33 Tesla in the core。 That's something like a million times the magnetic field of the earth。〃 With a grunt； he pushed open the steel door to the nearest magnet room。 I saw a large doughnut…shaped object； about six feet in diameter； with a hole in the center about an inch wide。 The doughnut was pletely encased in tubing and plastic insulation。 Heavy steel bolts running from top to bottom held the jacketing in place。
〃Lot of cooling for this puppy； I can tell you。 And a lot of power： fifteen kilovolts。 Takes a full…minute load time for the capacitors。 And of course we can only pulse it。 If we turned it on continuously； it'd explode…ripped apart by the field it generates。〃 He pointed to the base of the magnet； where there was a round push button at knee level。 〃That's the safety cutoff there；〃 he said。 〃Just in case。 Hit it with your knee if your hands are full。〃
I said； 〃So you use high magnetic fields to do part of your assemb…〃
But Ricky had already turned and headed out the door； again glancing at his watch。 I hurried after him。
〃Ricky 。。。〃
〃I have more to show you；〃 he said。 〃We're getting to the end。〃
〃Ricky； this is all very impressive；〃 I said； gesturing to the glowing arms。 〃But most of your assembly line is running at room temperature…no vacuum； no cryo； no mag field。〃
〃Right。 No special conditions。〃
〃How is that possible？〃
He shrugged。 〃The assemblers don't need it。〃
〃The assemblers？〃 I said。 〃Are you telling me you've got molecular assemblers on this line？〃
〃Yes。 Of course。〃
〃Assemblers are doing your fabrication for you？〃
〃Of course。 I thought you understood that。〃
〃No； Ricky；〃 I said； 〃I didn't understand that at all。 And I don't like to be lied to。〃
He got a wounded look on his face。 〃I'm not lying。〃
But I was certain that he was。
One of the first things scientists learned about m