PROGRAMMABLE MATTER

'Programmable matter' is a term originally coined in 1991 by Toffoli and
Margolus to refer to an ensemble of fine-grained computing elements
arranged in space . In this
context, programmable matter refers to compute models similar to
cellular automata and
lattice gas automata . The CAM-8 architecture is an example hardware realization of this model.
The main application of programmable matter, as envisioned by this
community, is to use the spatial nature of the computing medium to
simulate physical systems.
As semiconductor technology and nanotechnology have advanced the use
of the term programmable matter has changed to reflect the fact that
it is possible to build an ensemble of elements which can be
"programmed" to change their physical properties in reality not just
in simulation. Thus, programmable matter has come to mean "any bulk
substance which can be programmed to change its physical properties."
In one school of thought the programming could be external to the
material and might be achieved by the "application of light, voltage,
electric or magnetic fields, etc." . For
example, in this school of thought an LCD display is a form of
programmable matter. A second school of thought is that the
individual units of the ensemble can compute and the result of their
computation is a change in the ensembles physical properties. An
example of this more ambitious form of programmable matter is
claytronics, where the units in the ensemble "compute"
and the result is a change in the shape of the ensemble. .
There are many proposed instantiations of programmable matter. Scale
is one key differentiator between different forms of programmable
matter. At one end of the spectrum reconfigurable modular robotics
pursues a form of programmable matter where the individual units are
in the centimeter size range (E.g.,
[1][2][3]).
At the nanoscale end of the spectrum there are a tremendous number of
different basis for programmable matter, ranging from shape changing
molecules (E.g., [4]) to
quantum dots. Quantum dots are in fact often
referred to as artificial atoms. In the micron to sub-millimeter
range examples include: claytronics, currently working on MEMS-based
units, cells created using synthetic biology,
and the utility fog concept.

History

In 1991, Toffoli and Margolus the first paper to describe a
programmable matter system . Their paper describes a computing
substrate that is composed of fine-grained compute nodes distributed
throughout space which communicate using only nearest neighbor
interactions.
In the early 1990s there was a significant amount of work in
reconfigurable modular robotics with a philosophy similar to
programmable matter.
In the summer of 1998, In a discussion on artificial atoms and
programmable matter, Wil McCarthy and Gary E. Snyder of Pioneer
Astronautics coined the term "quantum wellstone" (or simply
"wellstone") to describe this hypothetical but plausible form of
programmable matter. Wil McCarthy has used the term in his fiction.
In 2002, Seth Goldstein and
Todd Mowry started the
claytronics project at Carnegie
Mellon University to investigate the underlying hardware and software
mechanisms necessary to realize programmable matter.

Examples of Programmable matter

Below are some specific examples of programmable matter. (This needs
to be filled out.)

Complex fluids

The physical properties of several complex fluids can be modified by
applying a current or voltage, as is the case with liquid crystals.

Quantum wells

Quantum wells can hold one or more electrons. Those
electrons behave like an artificial atom, which like real atoms
can form covalent bonds. Because of their larger sizes, other
properties are widely different.

Metamaterials

Metamaterials are artificial composites that can be controlled to
react in ways that do not occur in nature. One example developed by
David Smith and then by John Pendry and David Schuri is of a material
that can have its index of refraction tuned so that it can have a
different index of refraction at different points in the material. If
tuned properly this could result in an "invisibility cloak." For more see Metamaterial

Cellular Automata

See Cellular Automata.

Shape Changing Molecules

An active area of research is in molecules that can change their
shape, as well as other properties, in response to external stimuli.
These molecules can be used individually or en masse to form new kinds
of materials. For example, J Fraser Stoddart's group at UCLA has been developing molecules that can
change their electrical properties.

Claytronics

See Claytronics.

Reconfigurable Modular Robotics

Self-Reconfiguring Modular Robotics is a field of robotics in
which a group of usually identical robots work together to dynamically
form shapes suitable for each task. See for an overview of recent work and challenges.

Synthetic Biology

Synthetic biology is a field that aims to engineer cells with
"novel biological functions." Such cells are usually used to create
larger systems (e.g., biofilms) which can be "programmed" to change
their color, shape, etc.