Utility fog

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Utility fog is a hypothetical collection of tiny robots, envisioned by Dr. John Storrs Hall while he was thinking about a nanotechnological replacement for car seatbelts. The robots would be microscopic, with extending arms reaching in several different directions, and could perform lattice reconfiguration. Grabbers at the ends of the arms would allow the robots (or foglets) to mechanically link to one another and share both information and energy, enabling them to act as a continuous substance with mechanical and optical properties that could be varied over a wide range. Each foglet would have substantial computing power, and would be able to communicate with its neighbors.

The idea of nanobotic swarms was detailed as early as in 1964 by Stanislaw Lem in the novel The Invincible.

In the original application as a replacement for seatbelts, the swarm of robots would be widely spread-out, and the arms loose, allowing air flow between them. In the event of a collision the arms would lock into their current position, as if the air around the passengers had abruptly frozen solid. The result would be to spread any impact over the entire surface of the passenger's body. This is a concept similar to in function, though different in detail, to that of the "crash field" presented in Larry Niven's science fiction short story The Soft Weapon (1967), and is also similar in function to the inertial dampers of Star Trek and other science fiction series.

Utility fog is sometimes thought of as a nanotechnological version of the Swiss Army Knife.

While the foglets would be micro-scale, construction of the foglets would require full molecular nanotechnology. Each bot would be in the shape of a dodecahedron with 12 arms extending outwards. Each arm would have 4 degrees of freedom. When linked together the foglets would form an octet truss. The foglets' bodies would be made of aluminum oxide rather than combustible diamond to avoid creating a fuel air explosive.

In the postcyberpunk comic series Transmetropolitan, there are a race of beings known as foglets. Through a complicated technical process, their consciousness is transferred into a cloud of billions of foglet robots - a process they see as stripping away their biological limitations and leaving them with only personal amusement. The now-vacant body is then used as fuel to jump-start the foglet. They can spread themselves so thin they seem invisible, and come together as a pink cloud of dust with digital faces when they wish to be seen.

A suggestion was made by Jim Al-Khalili that the chameleonic external surface of a TARDIS could be composed of utility fog in the programme "How To Make A Tardis", broadcast as part of the nostalgic Doctor Who Night on BBC2 late in 1999.