Hall came up with idea for utility fogs when imagining what an advanced form of seat belt might look like.

"I came up with this vision of form fitting foam — one that could take on the shape of anything inside it and on the fly," he told io9, "which got me to wondering if we could ever possibly build something like that." The answer, says Hall, came to him by considering the nascent field of molecular nanotechnology. By designing and creating objects at the molecular scale, Hall envisioned a fog that could quickly morph along with the movements of anything around it — including the passengers of cars. In essence, the utility fog would be a polymorphic material comprised of trillions of interlinked microscopic ‘foglets', each equipped with a tiny computer. These nanobots would be capable of exerting force in all three dimensions, thus enabling the larger emergent object to take on various shapes and textures. So, instead of building an object atom by atom, these tiny robots would link their contractible arms together to form objects with varying properties, such as a fluid or solid mass. The Foglets

To make this work, each foglet would have to serve as a kind of pixel. They'd measure about 10 microns in diameter (about the size of a human cell), be powered by electricity, and have twelve arms that extrude outwards in the formation of a dodecahedron. The arms themselves would be 50 microns long and retractable. Each foglet would have a tiny computer inside to control its actions. "When two foglets link up they'll form a circuit between each them so that there will be a physical electrical network," said Hall, "that way they can distribute power and communications."

The arms themselves will swivel on a universal joint at the base, and feature a three-fingered gripper at the ends capable of rotating around the arm's axis. Each gripper will grasp the hands of another foglet to create an interleaved six-finger grip — what will be a rigid connection where forces can only be transmitted axially. The foglets themselves will not float like water fog, but will instead form a lattice by holding hands in 12 directions — what's called an octet truss (conceived by Buckminster Fuller in 1956). Because each foglet has a small body compared to its armspread, the telescoping action will provide the dynamics required for the entire fleet to give objects their shape and consistency. Applications

In terms of what it would look or feel like, Hall says it would probably resemble something like snow rather than fog. "In fact that's a better way of describing it," he told io9, "It would essentially approximate multi-branched snowflakes that are barely touching each other — and interacting with it would feel like standing or moving through packed snow." This programmable "snow", says Hall, could move around a person — and even move them around.

And indeed, utility fogs will be capable of some incredible things. They'll be able to make objects appear and disappear on command, and even make them hover and fly around. And through such forces as squeezing, hitting, and pulling, they'll also be able to manipulate objects in the environment. In his paper, "Aspects of Utility Fog," Hall elaborates: If you allow the sum of the arm extensions to vary with the sum of the forces on the arms, you have something that approximates a gas within a certain pressure range. Note that because the Foglets can use their own power to move or resist moving, the apparent density and viscosity of the fluid can be anything from molasses to near vacuum. Now you can begin to get cute. Run a distributed program that at a specified time, changes a certain volume from running water to running wood. A solid object would seem to appear in the midst of fluid. It can just as easily disappear. Now fill your entire house with the stuff, running air in background mode. Have an operating system that has a library of programs for simulating any object you may care to; by giving the proper command you can cause any object to appear anywhere at any time. You could carry a remote control, which might happen to be shaped like a wand with a star on the end... More ambitiously, since you're embedded in the Fog, it can sense every detail of your bodily position. It forms a "whole-body dataglove", and you can control it with extremely subtle gestures. At the ultimate extreme, the Foglets can carry various special sensors ranging from simple electrodes with voltmeters to SQIDs and form an extremely high bandwidth polygraph. With proper programming the Fog would almost be able to read your mind. This combination of extreme reactivity to control and virtually limitless creative and operational ability suggest a comparison with the Krell machine in "Forbidden Planet". But that's not where Hall sees its greatest potential. "You could actually push this technology to the point of creating a virtual world around you," he said. "You'd essentially get Star Trek's holodeck — one that could actually cut you and make you bleed." Hall foresees the day when utility fogs will blend seamlessly with the real and virtual worlds, creating a kind of hybrid reality in between. "You could put yourself in a virtual environment where you're interacting with something that leads to a real environment," he said, "and it's this interface between what's real and virtual that will prove to be the most important thing about it." But utility fogs may have an even more radical application than that — there's also the potential for people to upload their minds directly into this nano-infused cloud. "You could very realistically imagine uploading into it," he said, "and then you'd be this sort of formless data amoeba controlling this formless physical amoeba and take any size or form you wanted." This will work, says Hall, because any batch of fog will function as a discrete computer network. Each interlinked foglet will contribute to the overall processing requirements by working in a massively distributed way. As to whether Hall would ever hope to upload himself into the fog, Hall responded, "That would actually be my first choice." Limitations

As fantastic as this all sounds, there are some barriers to development, and some limitations to the utility fog itself.

The technology required to build utility fogs is contingent on the advent of fully mature molecular assembling nanotechnology, which is still several decades away. There's also the microscopic computers inside each foglet that needs to be considered, though they won't need to be that sophisticated.

But Hall believes there's another more daunting challenge: cost. And it's not just the expense of having to produce trillions upon trillions of foglets — it's the cost of developing the software to run the utility fog itself.

"The system will have to be capable of keeping track of any changes to the environment and to keep track of you — and this will require incredibly sophisticated simulation, sensing, and interfacing software," he said, "and that's going to be tremendously expensive." In Hall's mind, coming up with the hardware will be the easy part.

"To navigate that hairy interface between the continuous and the discreet — that's more difficult," said Hall, "the foglets will have to link up hands, let go, walk, crawl, and so forth — it'll be like a three dimensional square dance." Hall figures that it could take a team of experts as much as a half decade to come up with the first set of algorithms required for the most basic functions.

The utility fog will also be subject to physical limitations. At its strongest configuration, Hall predicts that it will be as tough as balsa wood. As an open lattice, the foglets will occupy only about 3% of the volume they encompass (hence the "fog" like appearance); locked in place, it will appear as a solid structure and exhibit a tensile strength of about 1,000 psi. And while the fog can be programmed to simulate most of the physical properties of any object, such as air and water, it won't be able to exhibit such characteristics as taste, smell, or complete transparency.

As for other limitations, Hall noted that the utility fog will be unable to take on the form of hard metals (like a drill bit), anything requiring both high strength and low volume (like a parachute), or anything exhibiting high heat (such as a flame). Additionally, the fog won't be able to simulate food (or anything else destined to be broken down chemically).

And in terms of when we can expect utility fogs to make their appearance, Hall says it should come about in the neighborhood of around 2030 — but no later than 2040. "Any later than that," said Hall, "and I would be profoundly disappointed."