https://ntrs.nasa.gov/search.jsp?R=19940022864 2018-09-18T22:10:35+00:00Z

N94- 27367

UTILITY FOG: A UNIVERSAL PHYSICAL SUBSTANCE

J. Storm Hall Rutgers University New Brunswick, New Jersey

Abstract tern of , which vary their properties according to which part of the object they are representing at Active, polymorphic material ("Utility Fog") can the time. An object can then move across a cloud of be designed as a conglomeration of 100-micron robotic robots without the individual robots moving, just as cells (_foglets'). Such robots could be built with the pixels on a CRT remain stationary while pictures the techniques of molecular [18]. Con- move around on the screen. trollers with processing capabilities of 1000 MIPS per The Utility Fog which is simulating air needs to be cubic micron, and electric motors with power densities impalpable. One would like to be able to walk through of one milliwatt per cubic micron are assumed. Util- a Fog-filled room without the feeling of having been ity Fog should be capable of simulating most everyday cast into a block of solid Lucite. It is also desire- materials, dynamically changing its form and proper- able to be able to breathe while using the Fog in this ties, and forms a substrate for an integrated virtual way! To this end, the robots representing empty space reality said telerobotics. constantly run a fluid-flow simulation of what the air would be doing if the robots weren't there. Then each does what the air it displaces would do in its 1 Introduction absence. How can one breathe when the air is a solid mass of Imagine a microscopic robot. It has a body about machines? Actually, it isn't really solid: the Foglets the size of a human cell and 12 arms sticking out in all only occupy about I0_ of the actual volume of the directions. A bucketful of such robots might form a air (they need lots of "elbow room" to move around "robot crystal" by linking their arms up into a lattice easily). There's plenty of air left to breathe. As far as structure. Now take a room, with people, furniture, physically breathing it, we set up a pressure-sensitive and other objects in it- it's still mostly empty air. Fill boundary which translates air motions on one side to tile air completely full of robots. Fog motions on the other. It might even be possible With the right programming, the robots can ex- to have the Fog continue the air simulation all the way ert any force in any direction on the surface of any into the lungs. object. They can support the object, so that it ap- To understand why we want to fill the air with mi- parently floats in tile air. They can support a person, croscopic robots only to go to so much trouble to make applying tile same pressures to the seat of the pants it seem as if they weren't there, consider the advan- that a chair would. They can exert the same resisting tages of a TV or computer screen over an ordinary forces that elbows and fingertips would receive from picture. Objects on the screen can appear and dis- the arms and back of the chair. A program running appear at will; they are not constrained by the laws in the Utility Fog can thus simulate the physical exis- of physics. The whole scene can shift instantly from tence of an object. one apparent locale to another. Completely imaginary The Utility Fog operates in two modes: First, the constructions, not possible to build in physical reality, "naive" mode where the robots act much like cells, and could be commonplace. Virtually anything imagin- each robot occupies a particular position and does a able could be given tangible reality in a Utility Fog particular function in a given object. The second, or environment. "Fog" mode, has the robots acting more like the pixels Why not, instead, build a virtual reality machine on a TV screen. The object is then formed of a pat- that produces a purely sensory (but indistinguishable)

115 versionof the same apparent world? The Fog actsas a - Anything requiringhard metal (coldsteel?).For continuousbridge between actualphysicalrealityand example, Fog couldn't simulate a drillbit cuttiag virtualreality.The Fog is universaleffectoras well through hardwood. It would be able to cut the hole, as a universalsensor. Any (real)object in the Fog but the process would be better describedas intelli- environment can be manipulated with an extremely gent sandpaper. wide array of patternsof pressure,force,and support; - Anything requiringboth high strength and low measured; analyzed;weighed; cut;reassembled;or re- volume. A parachute could not be made of Fog (un- duced to bacteria-sizedpiecesand sortedforrecycling. less,ofcourse,allthe airwere filledwith Fog,in which caseone could simply fly). - Anything requiringhigh heat.A Fog fireblazing 2 General Properties and Uses merrilyaway on Fog logsin a fireplacewould feelwarm on the skin a few feetaway; itwould feelthe same to As well as forming an extensionof the senses and a hand insertedintothe "flame". muscles of individualpeople, the Fog can act as a - Anything requiringmolecular manipulation or generalizedinfrastructurefor society at large. Fog chemical transformation. Fogletsare simply on the City need have no permanent buildingsof concrete, wrong scaleto play with atoms. In particular,they no roads of asphalt,no cars,trucks,or busses. Itcan cannot reproduce themselves.On theotherhand, they looklikea park,or a forest,or ifthe populationissuffi- can do things likeprepare food the same way a hu- cientlywhimsical,ancientRome one day and Emerald man cook does-by mixing, stirring,and usingspecial- City the next. purpose devicesthat were designed for them to use. Itwillbe more efficientto builddedicatedmachines - Fog cannot simulatefood, or anything elsetheft forlong distanceenergy and informationpropagation, is destinedto be broken down chemically. Eating it and physicaltransport.For localuse,and interfaceto would be likeeatingthe same amount of sand or saw- tileworldwide networks,the Fog isidealforallofthese dust. functions.It can act as shelter,clothing,telephone, - Fog can simulateair to the touch but not to the computer, and automobih. Itwillbe almost any com- eyes.The best indicationsare that itwould look like mon household object,appearing from nowhere when heavy fog. Thus the Fog would need to support a needed (and disappearingafterwards).It gainsa cer- pair of holographic gogglesin frontof the eyes of an tain efficiencyfrom this extreme of polymorphism; embedded user. Such goggles are clearlywithin the considerthe number of hardcopy photographs neces- capabilitiesof the same levelof nanotechnology as is sary to storeallthe images one seeson a televisionor needed for the Fog, but are beyond the scope of this computer screen. With UtilityFog we can have one paper. "display"and keep allour physicalpossesionson disk. Another item of infrastructurethat willbecome in- 2.2 Other Desirable Limitations creasinglyimportant in the futureisinformationpro- ceasing.Nanotechnology willallow us to buildsome In 1611,William Shakespeare wrote his finalplay, reallymonster computers. Although each Foglet will "The Tempest." 445 years later,an obscure science possess a comparatively small processor-which is to fictionwriter named W. J. Stuart updated the Tern- say the power of a current-daysupercomputer-there pest'splotintoa storycalled"Forbidden Planet,"and are about 16 millionFoglets to a cubic inch. When createda modern myth. those Fogletsare not doing anything else,i.e.when Forbidden Planet,more preciselythe movie version, they are simulatingthe interiorof a solidobjector air has become the classiccautionarytalcforany scenario that nothing ispassing through at the moment, they in which people become too powerfuland controltheir can be used as a computing resource(with the caveats environment too easily.In the story,the Krellare an below). ancient,wise,and highlyadvanced civilization.They perfect an enormous and powerful machine, capable of 2.1 The Limits of Utility Fog Capability projecting objects and forces anywhere in any form, upon the mental commands of any Krell. The ma- When discussing something as far outside of every- chine works "not wisely but too well," manifesting all day experience as the Utility Fog, it is a good idea the deeply buried subconscious desires of the Krell to to delineate both sides of the boundary. The Fog is destroy each other. capable of so lnany literally amazing things, we will Utility Fog will provide humans with powers that point out a few of the things it isn't capable of: approximate those of the fictional Krell machine.

116 Luckily,we have centuriesofliterarytraditionto guide concept of hierarchicalcontrolwith human oversight us around the pitfallsof hubrismade reality.We must can be seen to be hopelesslyinadequate. Agoric dis- study thistradition,or we may be doomed to repeat tributedcontrolalgorithmsofferone possiblesolution. it-a truth that isby no means limitedto the Utility Fog, or indeed to nanotechnology in general. 2.3 Advantages of a Utility Fog Environ- Tile firstthing we can do is to requirefullycon- ment scious,unequivocalcommands forthe Fog to take any action. Beyond that,we can try to suggest some of Another major advantage for space-fillingFog is the protocolsthat may be usefulin managing the Fog safety.In a car (oritsnanotech descendant) Fog forms in a situationwhere humans are interactingin close a dynamic form-fittingcushion that protectsbetter physicalproximity.Even ifwe have solved the prob- than any seatbeltof nylon fibers.An appropriately lem of translatingone'sindividualwishes,however ex- builthouse filledwith Fog couldeven protectitsinhab- pressed,intothe quadrillionsof setsof instructionsto itantsfrom the (physical)effectsof a nuclear weapon within 95% or so of itslethalblastarea. individualFogletsto accomplish what one desired,the problem of who gets to controlwhich Fogletsisprob- There are many more mundane ways the Fog can ably a much more contentiousone. protect itsoccupants, not the leastbeing physically to remove bacteria,mites, pollen,and so forth,from We can physicalizethe psychologicalconcept of the air. A Fog-filledhome would no longer be the "personalspace". The Fogletswithin some distance placethat most accidentshappen. First,by perform- of each person would be under that person'sexclu- ing most household tasks using Fog as an instrumen- sivecontrol;personal spaces could not merge except tality,the cuts and fallsthat accompany the use of by mutual consent.This singleprotocolcould prevent knives,power tools,ladders,and so forth,can be elim- most crimes of violencein our hypotheticalFog City. inated. A corollarypoint is that physicallyperpetrated Secondly, the other major classof household ac- theftwould be impossible in a Fog world. It would cidents,young childrenwho injurethenmelves out of still be possible by informational means, i.e. fraud, ignorance,can be avoided by a number of means. A hacking, etc; but the Fog could be programmed to put childwho climbed over a stairrailwould floatharm- ownership on the level of a physical law. -Not that it lesslyto the floor. A child could not pull a book- really makes any sense to think of stealing a fog-mode case over on itself;fallingover would not be among object, anyway. Ownership and control of the Fog the bookcase's repertoire. Power tools, kitchen im- need not be any more complex than the bundles of plements, and cleaning chemicals would not normally rights currently associated with everything from land exist; they or their analogues would be called into ex- to corporate stock. istence when needed and vanish instead of having to Indeed, much of the programming of the Fog will be cleaned and put away. need to have the characterof physicallaws. In order Outside the home, the possibilities are, if any- forthe enormous potentialcomplexity to be compre- thing, greater. One can easily imagine "industrial hensibleand thus usable to human beings,itneeds to Fog" which forms a factory. It would consist of be organizedby simple but powerful principles,which larger robots. Unlike domestic Fog, which would have must be consonant with the huge amount of hard- the density and strength of balsa wood, industrial wired information processing our sensory systems per- Fog could have bulk properties resembling hardwood form. For example, it would be easy to move furni- or aluminum. A nanotechnology- age factory would ture (or buildings)by manipulating an appropriately probably consist of a mass of Fog with special-purpose sizedscalemodel, and easy to observe the effectsby reactors embedded in it, where high-energy chemical watching the model. However, the Fog could just as transformations could take place. All the physical ma- easilyhave flooded the room with 100 kHs sound, and nipulation, transport, assembly, and so forth would be frequency-scaledthe echoes clown intothe human au- done by the Fog. ditory range. A bat would have no trouble with this kind of "scalemodel", but to humans it'sjustnoise. 2.4 Applications in Space Exploration It will be necessary, in general, to arrange the over- all control of the Fog to be extremely distributed, as The major systems of spaceships will need to be localas possible,robust in the presence of failure. made with special- purpose nanotechnological mecha- When we realizethat a singlecubicinch of Fog repre- nisms, and indeed with such mechanisms pushed much sentsa computer network of 16 millionprocessors,the closer to their true capacities than anything we have

117 talkedaboutheretofore.In the spaceship's cabin, mechanical design allows us to have an evacuated in- however, will be an acceleration couch. When not terior in which more sensitive nanomechanical compo- accelerating, which is most of the time, we'd prefer nents can operate. Of course, any macroscopic ignition something useful, like empty space, there. The Utility source would vaporize the entire Foglet; but as long as Fog makes a better acceleration couch, anyway. more energy is used vaporizing the exoskeleton than is Fill the cabin with Utility Fog and never worry gained burning the carbon-based components inside, about floating out of reach of a handhold. Instru- the reaction cannot spread. ments, consoles, and cabinets for equipment and sup- Each Foglet has twelve arms, arranged as the faces plies are not needed. Non-simulable items can be em- of a dodecahedron. The arms telescope rather than bedded in the fog in what are apparently bulkheads. having joints. The arms swivel on a universal joint at The Fog can add great structural strength to the the hase, and the gripper at the end can rotate about ship itself; the rest of the structure need be not much the arm's axis. Each arm thus has four degrees of more than a balloon. The same is true for spacesuits: freedom, plus opening and closing the gripper. The Fog inside the suit manages the air pressure and makes only load-carrying motor on each axis is the exten- motion easy; Fog outside gives extremely fine manip- sion/retraction motor. The swivel and rotate axes are ulating ability for various tasks. Of course, like the weakly driven, able to position the arm in free air but ship, the suit contains many special purpose non-Fog not drive any kind of load; however, there are load- mechanisms. holding brakes on these axes. Surround the space station with Fog. It needs ra- The gripper is a hexagonal structure with three fin- diation shielding anyway (if the occupants are long- gers, mounted on alternating faces of the hexagon. term); use big industrial Foglets with lots of redun- Two Foglets "grasp hands" in an interleaved six-finger dancy in the mechanism; even so they may get re- grip. Since the fingers are designed to match the end cycled fairly often. All the stock problems from SF of the other arm, this provides a relatively rigid con- movies go away: humans never need go outside merely nection; forces are only transmitted axially through to fix something; when EVA is desired for transfer or the grip. recreation, outside Fog provides complete safety and When at rest, the Foglets form a regular lattice motion control. It also makes a good tugboat for dock- structure. If the bodies of the Foglets are thought of as ing spaceships. atoms, it is a "face-centered cubic" crystal formation, Homesteaders on the Moon could bring along a where each atom touches 12 other atoms. Consider batch of heavy duty Fog as well as the special-purpose the arms of the Foglets as the girders of the trusswork nanotech power generation and waste recycling equip- of a bridge: they form the configuration known as ment. There will be a million and one things, of the the "octet truss" invented by Buckminster Fuller in ordinary yet arduous physical task kind, that must be 1956. The spaces bounded by the arms form alternate done to set up and maintain a self- sufficient house- tetrahedrons and octahedrons, both of which are rigid hold. shapes. The Fog may be thought of as consisting of layers of 3 Physical Properties of Utility Fog Foglets. The layers, and the shear planes they define, lie at 4 major angles (corresponding to the faces of the Most currently proposed nanotechnological designs tetrahedrons and octahedrons) and 3 minor ones (cor- are based on carbon. Carbon is a maxvelous atom responding to the face-centered cube faces). In each for structural purposes, forming a crystal () of the 4 major orientations, each Foglet uses six arms which is very stiff and strong. However, a Fog built of to hold its neighbors in the layer; layers are thus a 2- diamond would have a problem which nanomechanical dimensionally rigid fabric of equilateral triangles. In designs of a more conventional form do not pose: the face-centered mode, the layers work out to be square Fog has so much surface area exposed to the air that grids, and are thus not rigid, a slight disadvantage. if it were largely diamond, especially on the surface, Most Fog motion is organized in layers; layers slide it would amount to a "fuel-air explosive". by passing each other down hand-over-hand in bucket Therefore the Foglet is designed so that its struc- brigade fashion. At any instant, roughly half the arnls tural elements, fornfing the major component of its will be linked between layers when they are in motion. mass, are made of aluminum oxide, a refractory com- The Fog moves an object by setting up a seed- pound using common elements. The structural ele- shaped zone around it. The Foglets in the zone move ments form an exoskeleton, which besides being a good with the object, forming a fairing which makes the

118 motionsaround it smoother. If the object is moving 3.1 Foglets in Detail fast, the Fog around its path will compress to let it go by. The air does not have time to move in the Fog Foglets run on electricity, but they store hydrogen matrix and so the motion is fairly efficient. For slower as an energy buffer. We pick hydrogen in part because motions, effÉciency is not so important, but if we wish it's almost certain to be a fuel of choice in the nanotech to prevent slow-moving high-pressure areas from in- world, and thus we can be sure that the process of terfering with other airflow operations, we can enclose converting hydrogen and oxygen to water and energy, the object's zone in a self-contained convection cell as well as the process of converting energy mid water to which moves Foglets from in front to behind it. hydrogen and oxygen, will be well understood. That means we'll be able to do them efficiently, which is of Each moving layer of robots is similarly passing the prime importance. next layer along, So each layer adds another increment Suppose that the Fog is flowing, layers sliding of the velocity difference of adjacent layers. Motors for against each other, and some force is being transmit- arm extension can run at a gigahertz, and be geared ted through the flow. This would happen any time the down by a factor of 100 to the main screw in the arm. Fog moved some non-Fog object, for example. Just as This will have a pitch of about a micron, giving a lin- human muscles oppose each other when holding some- ear extension/retraction rate of about 10 meters per thing tightly, opposing forces along different Foglet second. We can estimate the inter-layer shear rate at arms act to hold the Fog's shape and supply the re- this velocity; the foglets are essentially pulling them- quired motion. selves along. Thus for a 100-micron interlayer distance When two layers of Fog move past each other, the Fog can sustain a 100 meter-per-second shear per mil- limeter of thickness. arms between may need to move as many as 100 thou- sand times per second. Now if each of those motions The atomically-precise crystals of the Foglets' were dissipative, and the fog were under full load, it structural members will have a tensile strength of at would need to consume 700 kilowatts per cubic cen- least 100,000 psi (i.e. high for steel but low for the ma- timeter. This is roughly the power dissipation in a .45 terials, including some fairly refractory ceramics, used caliber cartridge in the millisecond after the trigger is in modern "high-tech" composites). At arms length of pulled; i.e. it just won't do. 100 microns, the Fog will occupy 10% of the volume But nowhere near this amount of energy is being of the air but has structural efficiency of only about used; the pushing arms are supplying this nmch but 1% ill ally given direction. the arms being pushed are receipting almost tile same amount, minus the work being done on the object be- Thus Utility Fog as a bulk material will have a ing moved. So if the motors can act as generators density (specific gravity) of 0.2; for comparison, balsa when they're being pushed, each Foglet's energy bud- wood is about 0.15 and cork is about 0.25. Fog will get is nearly balanced. Because these are arnm instead have a tensile strength of only 1000 psi; this is about of wheels, the intake and outflow do not match at any the same as low-density polyethylene (solid, not foam). given instant, even though they average out the same The material properties arising from the lattice struc- over time (measured in tens of microseconds). Some ture are more or less isotropic; the one exception is buffering is needed. Hence the hydrogen. that when Fog is flowing, tensile strength perpendic- I should hasten to add that almost never would one ular to the shear plane is cut roughly in half. expect the Fog to move actively at 1000 psi; the pres- Without altering the lattice connectivity, Fog can sure in the column of Fog beneath, say, a "levitated" contract by up to about 40% in any linear dimension, human body is less than one thousandth of that. The reducing its overall volume (and increasing its density) 1000 psi capability is to allow the Fog can simulate by a factor of five. (This is of course done by retracting hard objects, where forces can be concentrated into all arms but not letting go.) In this state the fog has very small areas. Even so, current exploratory engi- the density of water. An even denser state can be neering designs for electric motors have power conver- attained by forming two interpenetrating lattices and sion densities up to a billion watts per cubic centime- retracting; at this point its density and strength would ter, and dissipative inefficiencies in the 10 parts per both be similar to ivory or Corian structural plastic, million range. This means that if the Empire State at specific gravity of 2 and about 6000 psi. Such high- Building were being floated around on a cohmm of density Fog would have the useful property of being Fog, the Fog would dissipate less than a watt per cu- waterproof (which ordinary Fog is not), but it cannot bic centimeter. flow and takes much longer to change configuration. Moving Fog will dissipate energy by air turbulence

I19 and viscous drag. In the large, air will be entrained Each Foglet is going to have 12 arms with three in the layers of moving Fog and forced into laminar axis control each. In current technology it isn't un- flow. Energy consumed in this regime may be prop- common to have a processor per azis; we could fit 36 erly thought of as necessary for the desired motion no processors into the Foglet but it isn't necessary. The matter how it was done. As for the waving of the tradeoffs in macroscopic today are such that arms between layers, the Reynolds number decreases processors are cheap; in the Foglet things are different. linearly with the size of the arm. Since the absolute The control of the arms is actually much simpler than velocity of the arms is low, i.e. 1 m/s, the Reynolds control of a macroscopic robot. They can be managed number should be well below the "lower critical" value, by much simpler controllers that take commands like and the arms should be operating in a perfectly viscous "Move to point X at speed y." Using a R.ISC design regime with no turbulence. The remaining effect, vis- allows a single processor to control a 100 kHz arm; cous drag (on the waving arms) comes to a few watts using auxilliary controllers will let it do all 12 easily. per square meter of shear plane per layer. But there is still a problem: Each computer, even There will certainly be some waste heat generated with the power-reducing reversible logic designs es- by Fog at work that will need to be dissipated. This poused by Drexler, Merkle, and this author, is going and other applications for heat pumps, such as heating to dissipate a few nanowatts. At a trillion foglets per or cooling people (no need to heat the whole house, cubic meter, this is a few kilowatts per cubic meter. especially since some people prefer different tempera- Cooling for such a dissipation must needs be some- lures), can be done simply by running a flow of Fog where between substantialand heroic.As long as the through a pipe-like volume which changes in area, computers can go intoa standby mode when the Fog compressing and expanding the entrained air at the isstandingstill,however, thisisquiteworkable. Con- appropriate places. centrationsof heavy work, mechanical or computing, would stillrequirecoolingcirculationto some degree, 3.2 Communications and Control but, as we have seen,the Fog is perfectlycapable of doing that. In the macroscopic world, microcomputer-based What about allthe other computing overhead for controllers (e.g. the widely used Intel 8051 series rai- the Fog? Besides the individualcontrolof itsrobotic crocontrollers) typically run on a dock speed of about self,each Foglet willhave to run a portion of the 10 MHz. They emit control signals, at most, on the overalldistributedcontroland communications algo- order of 10 KHz (usually less), and control motions in rithms. We can do another clock-speedto capability robots that are at most 10 Hz, i.e. a complete motion analogy from currentcomputers regardingcommuni- taking one tenth of a second. This million-clocks-per- cations.Megahertz-speed computers findthemselves action is not strictly necessary, of course; but it gives well employed managing a handful of megabit data us some concept of the action rate we might expect for lines.Again we are forced to abandon the engineer- a given computer clock rate in a digitally controlled ing tradeoffsof the macroscopic world: routing of a nanorobot. message through any given node need theoretically Drexler's carefully detailed analysis shows that it consume only a handful of thermodynamically irre- is possible to build mechanical nanocomputers with versiblebit operations;typicalcommunications con- gigahertz clock rates. Thus we can immediately ex- trollerstakemillions.Special-purposemessage routers pect to build a nanocontroller which can direct a 10 designed with thesefactsin mind must be a part of kilohertz robot. However, we can do better. the Foglet. Since the early microcontrollers were developed, If the Fog were configuredas a store-and-forward computer architecture has advanced. The 8051's do 1 network, packetswith an average length of 100 bytes instruction per 6, 12, or 18 clock cycles; modern R.ISC and a 1000-instructionoverhead, information would architectures execute 1 instruction per cycle. So far, move through the Fog at 50 meters/second,i.e.110 nobody has bothered to builda RISC microcontroller, mph. It represents a highly inefficient use of com- sincethey already have more computing power than putation even with special-purpose hardware. It will they need. Furthermore, RISC designsare efficientin be necessary to design a more efficient communica- hardware as well as time;one earlyRISC was imple- tion protocol. Setting up "virtual circuits" in the Fog mented on a 10,000-gategate array.This designcouhl and using optical repeaters (or simply mechanically be translatedintorod logicin lessthan one tenth of switching the optical waveguides) should help consid- one percent of a cubic micron. erably.

120 3.3 Synergistic Combination with Other Fog for a house, or building-sized machines filling cities Technologies with Fog. The Fog itself, of course, conveys raw ma- terials back to the machine. The counterintuitive inefficiency in communica- tions is an example, possibly the most extreme one, Acknowledgements of a case where macroscopic mechanisms outperform the Fog at some specific task. This will be even more Many thanks to Carl Feynman who analyzed the true when we consider nano-engineered macroscopic Fog and made numerous suggestions. mechanisms. We could imagine a robot, human-sized, that was formed of a collection of nano-engineered parts References held together by a mass of Utility Fog. The parts might include "bones", perhaps diamond-fiber com- posites, having great structural strength; motors, [1] by K. Eric Drexler, Anchor power sources, and so forth. The parts would form Press, 1986. a sort of erector set that the surrounding Fog would assemble to perform the task at hand. The Fog could [2]"Nanotechnology: wherein molecular comput- do directly all subtasks not requiring the excessive ers control tiny circulatorysubmarines", by A. strength, power, and so forth that the special-purpose K. Dewdney, Scientific American, January 1988, parts would supply. pages 100 to 103. The Fog house, or city, would resemble the Fog "There's Plenty of Room at the Bottom" a talk robot in that regard. The roof of a house might well be [3] specially engineered for qualities of waterproofness, so- by Richard Feynman (awarded the Nobel Prize in Physics in 1965) at an annum meeting of the lar energy collection, and resistance to general abuse, American PhysicalSocietygivenon December 29, far exceeding that which ordinary general purpose Fog would have. (On the other hand, the Fog could, if de- 1959. Reprinted in Miniaturization, edited by H. sired, have excellent insulating properties.) Of course D. Gilbert (Reinhold, New York, 1961) pages 282- tile roof need not be one piece-it might be inch-square 296. tiles held in place by the supporting Fog, and thus be [4] "Molecular manipulation using a tunnelling micro- quite amenable to rearrangement at the owner's whim, scope," by J. S. Foster, J. E. Frommer and P. C. incremental repair and replacement, and all the other Arnett. Nature, Vol. 331 28 January 1988, pages advantages we expect from a Fog house. 324-328. Another major component that would be special- purpose would be power and communications. Work- [5]"Molecular Engineering: An Approach to the De- ing on more-efficient protocols such as suggested velopment of General Capabilities for Molecular above, the Fog would form an acceptable communica- Manipulation," by K. Eric Drexler, Proceedings of tions link from a person to some terminal in the same the National Academt/ of Sciences (USA), Vol 78, building; but it would be extremely inefficient for long- pp 5275- 78, 1981. haul, high bandwidth connections such as that needed for telepresence. [6] "Tiny surgical robot being developed'. San ,lose Power is also almost certainly the domain of special- Mercury News, Feb. 18, 1989, page 26A purpose nano-engineered mechanisms. Power trans- mission ill the Fog is likely to be limited, although for [7]"Rod Logic and Thermal Noise in the Mechanical differentreasons data transmission.Nanotech- from Nanocomputer', by K. Eric Drexler, Proceedings uology willgiveus allamazing arrayof power gener- of the Third International Symposium on Molecu- ation and distributionpossibilities,and the Fog can lar Electronic Devices, F. Carter ed., Elsevier 1988. use most of them. The criticalheterogeneous component of Fog is [8]"Submarines small enough to cruise the blood- the Fog-producing machine. Foglets are not self- stream", in Business Week, March 27 1989, page reproducing; there is no need for them to be, and 64. it would complicate theirdesign enormously to give them fineatom-manipulating capability.One imag- [9] The Tomorrow Makers, Grant Fjermedal, MacMil- inesa Fog machine the sizeof a breadbox producing lan 1986.

121 [10] "Machines of Inner Space" by K. Eric Drexler, 1990 Yearbook of Science and the Future, pages 160-177, published by Encyclopedia Britannica, Chicago 1989.

[11] Theory of Self Reproducing Automata by John Von Neumann, edited by Arthur W. Burks, Uni- versity of Illinois Press, 1966.

[12]"The Childrenof the STM" by Robert Pool,Sci- ence,Feb. 9, 1990,pages 634-636.

[13] "A Small Revolution Gets Under Way, _ by Robert Pool,Science,Jan. 5 1990.

[14] Advanced Automation for Space Mission.s, Pro- ceedings of the 1980 NASA/ASEE Summer Study, edited by Robert A. Freitas, Jr. and William P. Gilbreath. Available from NTIS, U.S. Department of Commerce, National Technical Information Ser- vice, Springfield, VA 22161; telephone 703-487- 4650, order no. N83-15348

[15] "Positioning Single Atoms with a Scanning Tun- nelling Microscope," by D. M. Eigler and E. K. Schweizer, Nature Vol 344, April 5 1990, page 524- 526.

[16] Mind Children by Hans Moravec, Harvard Uni- versity Press, 1988.

[17] "Tile Invisible Factory," The Economist, Decem- ber 9, 1989, page 91.

[18] Nanosysten_s: Molecular Machinery, Manufac- turing and Computation, by K. Eric Drex]er, John Wiley 1992.

[19] "MITI heads for inner space s by David Swin- banks, Nature, Vol 346, August 23 1990, page 688- 689.

[20] The CRC Handbook of Chemistry and Physics, CRC Press (any year)

[21] Molecular Mechanics by U. Burkert and N. L. Allinger, American Chemical Society Monograph 177 (1982).

[22] "Atom by Atom, Scientists build 'Invisible' Ma- chines of the Future," Andrew Pollack, The New York Times, Science section, Tuesday November 26, 1991, page B7.

122 A Foglet

Arms in dodecahedral configuration

Grippers

socket

The Grip

@

Optical waveguide for communications

g gripper Power (electric) transmission line Couplers for comm. and power

123 Foglet Internals -- schematic (more or less to scale)

Computer Fuel tank (hydrogen) (rod logic) ! Fu, line Scale (microns) -0 Control lines u (electric) I Oxygen ftlter

m

m m motor/generator

,Communications lines - 10 :guiSes)

20 !:::::::::::i.::: ! !

| 30 / i

m

m

i (electric)

I 40 Motors

i Optical switch (For inter-foglet communicaticqas)

Arm extension (detail)

Fixed to Counter-threaded screws gripper mounted here • structural bearings _ I /

I

With atomically-precise surfaces the screws should be almost completely frictionless.

124 Three layers of Foglets Shear planes for moving layers

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This shows the lattice structure assumed by a mass of Foglets. Only three of the Foglets in this picture are shown with all their arms. Grippers are not shown at all.

3 of the 4 major shear planes and the 3 minor ones. The other major (triangular) plane is parallel to the page. There is no rectangular shear plane parallel to the page.

125 The flow of Fog around a moving object

In this region, layers of Foglets merge and accelerate backward.

The fast-moving "Venturi" path conveys The junction point moves forward Fog back around the object with the same speed as the object.

These arrows represent the velocity of the Fog and object at the corresponding point The boundary layers in the diagram.

match the speed of ,ID, the object to that of the surrounding Fog. In the boundary layer, single layers ,ID, of Foglets double up to allow forward motion. Again, the junction points are moving forward.

IP

126