The ulam Programming Language for Artificial Life.

Traditional digital computing demands perfectly reliable memory and processing, so programs can build structures once then use them forever-but such deterministic execution is becoming ever more costly in large-scale systems. By contrast, living systems, viewed as computations, naturally tolerate fallible hardware by repairing and rebuilding structures even while in use-and suggest ways to compute using massive amounts of unreliable, merely best-effort hardware. However, we currently know little about programming without deterministic execution, in architectures where traditional models of computation-and deterministic ALife models such as the Game of Life-need not apply. This expanded article presents ulam, a language designed to balance concurrency and programmability upon best-effort hardware, using lifelike strategies to achieve robust and scalable computations. The article reviews challenges for traditional architecture, introduces the active-media computational model for which ulam is designed, and then presents the language itself, touching on its nomenclature and surface appearance as well as some broader aspects of robust software engineering. Several ulam examples are presented; then the article concludes with a brief consideration of the couplings between a computational model and its physical implementation.

Bespoke physics for living technology.

In the physics of the natural world, basic tasks of life, such as homeostasis and reproduction, are extremely complex operations, requiring the coordination of billions of atoms even in simple cases. By contrast, artificial living organisms can be implemented in computers using relatively few bits, and copying a data structure is trivial. Of course, the physical overheads of the computers themselves are huge, but since their programmability allows digital "laws of physics" to be tailored like a custom suit, deploying living technology atop an engineered computational substrate might be as or more effective than building directly on the natural laws of physics, for a substantial range of desirable purposes. This article suggests basic criteria and metrics for bespoke physics computing architectures, describes one such architecture, and offers data and illustrations of custom living technology competing to reproduce while collaborating on an externally useful computation.