Beyond reality and imagination

The Book of Imaginary Beings is a compendium of extraordinary fictions of the human brain.

The Book of Barely Imagined Beings celebrates a few of the real creatures that are stranger and more astonishing than most of the ones that humans have imagined.

Nils Aall Barricelli was, perhaps, the first to explore another category altogether -- entities that are neither 'real' in the sense that most of us customarily use that term nor fictional -- when, in the early 1950s, he created numeric organisms based on Darwinian principles.

These organisms and the universes they inhabited existed purely as mathematical values. In Barricelli's mind, however, they were true organisms, not simply mathematical models of life.

Max Tegmark believes that physical existence and mathematical existence are the same, so any structure that exists mathematically is also real.

(see also Turing's Cathedral.)