||This article possibly contains original research. (October 2007)|
A chemical computer, also called reaction-diffusion computer, BZ computer (stands for Belousov–Zhabotinsky computer) or gooware computer is an unconventional computer based on a semi-solid chemical "soup" where data is represented by varying concentrations of chemicals. The computations are performed by naturally occurring chemical reactions. So far it is still in a very early experimental stage, but may have great potential for the computer industry.
Chemical computing in today's world mainly refers to the BZ reaction-diffusion model. That said, chemical computing is playing an increasingly important role in areas of biochemical computing, biocomputing, organic computing, and quantum computing.
Chemical computing can contain elements of quantum computing, but is not necessarily quantum computing.
A chemical computer is different from a molecular logic gate.
The simplicity of this technology is one of the main reasons why it could in the future be turned into a serious competitor to machines based on conventional solid-state electronic hardware. A modern microprocessor is an incredibly complicated device that can be destroyed during production by no more than a single airborne microscopic particle.
In a conventional microprocessor the bits behave much like cars in city traffic; they can only use certain roads, they have to slow down and wait for each other in crossing traffic, and only one driving field at once can be used. In a BZ solution the waves are moving in all thinkable directions in all dimensions, across, away and against each other. These properties might make a chemical computer able to handle billions of times more data than a traditional computer.
Originally chemical reactions were seen as a simple move towards a stable equilibrium which was not very promising for computation. This was changed by a discovery made by Boris Belousov, a Soviet scientist, in the 1950s. He created a chemical reaction between different salts and acids that swing back and forth between being yellow and clear because the concentration of the different components changes up and down in a cyclic way. At the time this was considered impossible because it seemed to go against the second law of thermodynamics, which says that in a closed system the entropy will only increase over time, causing the components in the mixture to distribute themselves till equilibrium is gained and making any changes in the concentration impossible. But modern theoretical analyses shows sufficiently complicated reactions can indeed comprise wave phenomena without breaking the laws of nature.  (A convincing directly visible demonstration was achieved by Anatol Zhabotinsky with the Belousov-Zhabotinsky reaction showing spiraling colored waves.)
The wave properties of the BZ reaction means it can move information in the same way as all other waves. This still leaves the need for computation, performed by conventional microchips using the binary code transmitting and changing ones and zeros through a complicated system of logic gates. To perform any conceivable computation it is sufficient to have NAND gates. (A NAND gate has two bits input. Its output is 0 if both bits are 1, otherwise it's 1). In the chemical computer version logic gates are implemented by concentration waves blocking or amplifying each other in different ways.
In 1989 it was demonstrated how light-sensitive chemical reactions could perform image processing. This led to an upsurge in the field of chemical computing. Andrew Adamatzky at the University of the West of England has demonstrated simple logic gates using reaction-diffusion processes. Furthermore, he has theoretically shown how a hypothetical "2+ medium" modelled as a cellular automaton can perform computation.
The breakthrough came when he read a theoretical article of two scientists who illustrated how to make logic gates to a computer by using the balls on a billiard table as an example. Like in the case with the AND-gate, two balls represents two different bits. If a single ball shoots towards a common colliding point, the bit is 1. If not, it is 0. A collision will only occur if both balls are sent toward the point, which then is registered in the same way as when two electronic 1's gives a new and single 1. In this way the balls work together like an AND-gate. Adamatzkys' great achievement was to transfer this principle to the BZ-chemicale and replace the billiard balls with waves. If it occurs two waves in the solution, they will meet and create as a third wave which is registered as a 1. He has tested the theory in practice and has already documented that it works. For the moment he is cooperating with some other scientists in producing some thousand chemical versions of logic gates that is going to become a form of chemical pocket calculator. One of the problems with the present version of this technology is the speed of the waves; they only spread at a rate of a few millimeters per minute. According to Adamatzky, this problem can be eliminated by placing the gates very close to each other, to make sure the signals are transferred quickly. Another possibility could be new chemical reactions where waves propagate much faster. If these teething problems are overcome, a chemical computer will offer clear advantages over an electronic computer.
In 2015, Stanford University graduate students created a computer using magnetic fields and water droplets infused with magnetic nanoparticles, illustrating some of the basic principles behind a chemical computer. 
An increasing number of individuals in the computer industry are starting to realize the potential of this technology. IBM is at the moment testing out new ideas in the field of microprocessing with many similarities to the basic principles of a chemical computer. 
Timeline of Chemical Computing
- Soviet scientist Vladimir Lukyanov builds an analog water computer for solving differential equations 
- Boris Belousav pioneers reaction-diffusion research
- Anatol Zhabotinsky publishes additional work on reaction-diffusion
- Adamatzky begins performing research in chemical computing
- A chemical computing system is developed by an international team headed by the Swiss Federal Laboratories for Materials Science and Technology (Empa). The chemical computer used surface tension calculations derived from the Marangoni Effect to find the most efficient route between points A and B, outpacing a conventional Satellite Navigation system attempting to calculate the same route. 
- Stanford graduate students create a computer demonstrating some basic concepts behind a chemical computer
- University of Washington students create a programming language for chemical reactions (originally developed for DNA analysis).
- Molecular logic gate
- Quantum Computing
- DNA computer
- Organic Computing
- water integrator
- history of computing hardware
- fluid dynamics
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