Computronium
Computronium is a material hypothesized by  Norman Margolus and Tommaso Toffoli of the Massachusetts Institute of Technology in 1991 to be used as "programmable matter", a substrate for computer modeling of virtually any real object.

It also refers to a theoretical arrangement of matter that is the best possible form of computing device for that amount of matter.

In the 2010 film The Singularity Is Near: A True Story About the Future, American futurist Ray Kurzweil discusses a universe filled with computronium. He believes this could be possible until the late 22nd century by sending intelligent nanobots through the universe faster than light, e.g. by using wormholes. According to him, such an endeavor would have the potential to prevent the natural ending of the universe.

See also
 Limits of computation
 Molecular scale electronics
 Molecular electronics
 Unobtainium
 Computon

References

Fictional computers
Hypothetical technology