This glossary contains terms used in describing matters related to advanced technology. It was compiled by the MIT Nanotechnology Study Group, with special help from David Darrow of Indiana University.

ACTIVE SHIELD: A defensive system with built-in constraints to limit or prevent its offensive use.

AMINO ACIDS: Organic molecules that are the building blocks of proteins. There are some two hundred known amino acids, of which twenty are used extensively in living organisms.

ANTIOXIDANTS: Chemicals that protect against oxidation, which causes rancidity in fats and damage to DNA.

ARTIFICIAL INTELLIGENCE (AI): A field of research that aims to understand and build intelligent machines; this term may also refer to an intelligent machine itself.

ASSEMBLER: A molecular machine that can be programmed to build virtually any molecular structure or device from simpler chemical building blocks. Analogous to a computer-driven machine shop. (See Replicator.)

ATOM: The smallest particle of a chemical element (about three ten-billionths of a meter in diameter). Atoms are the building blocks of molecules and solid objects; they consist of a cloud of electrons surrounding a dense nucleus a hundred thousand times smaller than the atom itself. Nanomachines will work with atoms, not nuclei.

AUTOMATED ENGINEERING: The use of computers to perform engineering design, ultimately generating detailed designs from broad specifications with little or no human help. Automated engineering is a specialized form of artificial intelligence.

BACTERIA: One-celled living organisms, typically about one micron in diameter. Bacteria are among the oldest, simplest, and smallest types of cells.

BIOCHAUVINISM: The prejudice that biological systems have an intrinsic superiority that will always give them a monopoly on self-reproduction and intelligence.

BIOSTASIS: A condition in which an organism's cell and tissue structures are preserved, allowing later restoration by cell repair machines.

BULK TECHNOLOGY: Technology based on the manipulation of atoms and molecules in bulk, rather than individually; most present technology falls in this category.

CAPILLARIES: Microscopic blood vessels that carry oxygenated blond to tissues.

CELL: A membrane-bound unit, typically microns in diameter. All plants and animals are made up of one or more cells (trillions, in the case of human beings). In general, each cell of a multicellular organism contains a nucleus holding all of the genetic information of the organism.

CELL REPAIR MACHINE: A system including nanocomputers and molecular scale sensors and tools, programmed to repair damage to cells and tissues.

CHIP: See Integrated circuit.

CROSS-LINKING: A process forming chemical bonds between two separate molecular chains.

CRYOBIOLOGY: The science of biology at low temperatures; research in cryobiology has made possible the freezing and storing of sperm and blood for later use.

CRYSTAL LATTICE: The regular three-dimensional pattern of atoms in a crystal.

DESIGN AHEAD: The use of known principles of science and engineering to design systems that can only be built with tools not yet available; this permits faster exploitation of the abilities of new tools.

DESIGN DIVERSITY: A form of redundancy in which components of different design serve the same purpose; this can enable systems to function properly despite design flaws.

DISASSEMBLER: A system of nanomachines able to take an object apart a few atoms at a time, while recording its structure at the molecular level.

DISSOLUTION: Deterioration in an organism such that its original structure cannot be determined from its current state.

DNA (DEOXYRIBONUCLEIC ACID): DNA molecules are long chains consisting of four kinds of nucleotides; the order of these nucleotides encodes the information needed to construct protein molecules. These in turn make up much of the molecular machinery of the cell. DNA is the genetic material of cells. (See also RNA.)

ENGINEERING: The use of scientific knowledge and trial-and-error to design systems. (See Science.)

ENTROPY: A measure of the disorder of a physical system.

ENZYME: A protein that acts as a catalyst in a biochemical reaction.

EURISKO: A computer program developed by Professor Douglas Lenat which is able to apply heuristic rules for performing various tasks, including the invention of new heuristic rules.

EVOLUTION: A process in which a population of self-replicating entities undergoes variation, with successful variants spreading and becoming the basis for further variation.

EXPONENTIAL GROWTH: Growth that proceeds in a manner characterized by periodic doublings.

FACT FORUM: A procedure for seeking facts through a structured, arbitrated debate between experts.

FREE RADICAL: A molecule containing an unpaired electron, typically highly unstable and reactive. Free radicals can damage the molecular machinery of biological systems, leading to cross-linking and mutation.

HEISENBERG UNCERTAINTY PRINCIPLE: A quantum-mechanical principle with the consequence that the position and momentum of an object cannot be precisely determined. The Heisenberg principle helps determine the size of electron clouds, and hence the size of atoms.

HEURISTICS: Rules of thumb used to guide one in the direction of probable solutions to a problem.

HYPERTEXT: A computer-based system for linking text and other information with cross-references, making access fast and criticisms easy to publish and find.

INTEGRATED CIRCUIT (IC): An electronic circuit consisting of many interconnected devices on one piece of semiconductor, typically into 10 millimeters on a side. ICs are the major building blocks of today's computers.

ION: An atom with more or fewer electrons than those needed to cancel the electronic charge of the nucleus. An ion is an atom with a net electric charge.

KEVLAR (TM): A synthetic fiber made by E. I. du Pont de Nemours & Co., Inc. Stronger than most steels, Kevlar is among the strongest commercially available materials and is used in aerospace construction, bulletproof vests, and other applications requiring a high strength-to-weight ratio.

LIGHTSAIL: A spacecraft propulsion system that gains thrust from the pressure of light striking a thin metal film.

LIMITED ASSEMBLER: An assembler with built-in limits that constrain its use (for example, to make hazardous uses difficult or impossible, or to build just one thing).

MEME: An idea that, like a gene, can replicate and evolve. Examples of memes (and meme systems) include political theories, proselytizing religions, and the idea of memes itself.

MOLECULAR TECHNOLOGY: See Nanotechnology.

MOLECULE: The smallest particle of a chemical substance; typically a group of atoms held together in a particular patter, by chemical bonds.

MUTATION: An inheritable modification in a genetic molecule, such as DNA. Mutations may be good, bad, or neutral in their effects on an organism; competition weeds out the bad, leaving the good and the neutral.

NANO-: A prefix meaning ten to the minus ninth power, or one billionth.

NANOCOMPUTER: A computer made from components (mechanical, electronic, or otherwise) on a nanometer scale.

NANOTECHNOLOGY: Technology based on the manipulation of individual atoms and molecules to build structures to complex, atomic specifications.

NEURAL SIMULATION: Imitating the functions of a neural system - such as the brain - by simulating the function of each cell.

NEURON: A nerve cell, such as those found in the brain.

NUCLEOTIDE: A small molecule composed of three parts: a nitrogen base (a purine or pyrimidine), a sugar (ribose or deoxyribose), and phosphate. Nucleotides serve as the building blocks of nucleic acids (DNA and RNA).

NUCLEUS: In biology, a structure in advanced cells that contains the chromosomes and apparatus to transcribe DNA into RNA. In physics, the small, dense core of an atom.

ORGANIC MOLECULE: A molecule containing carbon; the complex molecules in living systems are all organic molecules in this sense.

POLYMER: A molecule made up of smaller units bonded to form a chain.

POSITIVE SUM: A term used to describe a situation in which one or more entities can gain without other entities suffering an equal loss - for example, a growing economy. (See Zero Sum.)

REDUNDANCY: The use of more components than are needed to perform a function; this can enable a system to operate properly despite failed components.

REPLICATOR: In discussions of evolution, a replicator is an entity (such as a gene, a meme, or the contents of a computer memory disk) which can get itself copied, including any changes it may have undergone. In a broader sense, a replicator is a system which can make a copy of itself, not necessarily copying any changes it may have undergone. A rabbit's genes are replicators in the first sense (a change in a gene can be inherited); the rabbit itself is a replicator only in the second sense (a notch made in its ear can't be inherited).

RESTRICTION ENZYME: An enzyme that cuts DNA at a specific site, allowing biologists to insert or delete genetic material.

RIBONUCLEASE: An enzyme that cuts RNA molecules into smaller pieces.

RIBOSOME: A molecular machine, found in all cells, which builds protein molecules according to instructions read from RNA molecules. Ribosomes are complex structures built of protein and RNA molecules.

RNA: Ribonucleic acid; a molecule similar to DNA. In cells, the information in DNA is transcribed to RNA, which in turn is "read" to direct protein construction. Some viruses use RNA as their genetic material.

SCIENCE: The process of developing a systematized knowledge of the world through the variation and testing of hypotheses. (See Engineering.)

SCIENCE COURT: A name (originally applied by the media) for a government-conducted fact forum.

SEALED ASSEMBLER LABORATORY: A work space, containing assemblers, encapsulated in a way that allows information to flow in and out but does not allow the escape of assemblers or their products.

SYNAPSE: A structure that transmits signals from a neuron to an adjacent neuron (or other cell).

VIRUS: A small replicator consisting of little but a package of DNA or RNA which, when injected into a host cell, can direct the cell's molecular machinery to make more viruses.

ZERO SUM: A term used to describe a situation in which one entity can gain only if other entities suffer an equal loss; for example, a private poker game. (See Positive Sum.)