God, Physics and the Natural-Computer Natural Algorithms Joshua Arulanandham Computer Science

The wonders of the world come in two flavours!

How water “finds” the average Water finds the same level in all limbs due to atmospheric pressure. l1l1 l2l2 l3l3 (l 1 + l 2 + l 3 ) / 3

How to make a “computer” with beads, rods and gravity ++=

A “computer” that runs on gravity

Sorting {3, 1, 2} 2. Drop 1 bead 3. Drop 2 beads 1. Drop 3 beads (Remember, always from left-to-right) A “computer” that runs on gravity

Sorting {2, 4, 3, 2} 2. Drop 4 beads 3. Drop 3 beads 1. Drop 2 beads (Remember, always from left-to-right) 4. Drop 2 beads A “computer” that runs on gravity

90 0 The bead-sort computer The “tilt” operation

Calculating shortest path using strings and beads A B (Source) C D E (Destination) E (Destination)Shortestpath As the source, destination nodes in the physical graph-model are stretched apart, the shortest path forms a straight line between them.

A computer made of pipes and pistons Is (~a + b)(a + b) satisfiable? a b (~a + b) (a + b) (~a + b) (a + b) ab (a + b) ~ab (~a + b)

“Physics is like sex. Sure, it may give some practical results, but that's not why we do it.” Why natural algorithms?

Which is easier: flipping a coin or its numerical simulation?

Given a linear sequence of amino acids, into what three dimensional configuration will the sequence fold? Which is faster: protein folding or its numerical simulation?

A new vocabulary Boolean logic, automata theory, etc. Natural physical processes

“It’s not that the bear dances so well, it’s that he dances at all.” My Natural-Computer versus your PC !