https://news.ycombinator.com/item?id=30735397

DonHopkins on March 19, 2022 | parent | context | favorite | on: Ask HN: What book changed your life?

Cellular Automata Machines: A New Environment for Modeling
Published April 1987 by MIT Press. ISBN: 9780262200608.

http://mitpress.mit.edu/books/cellular-automata-machines

http://www.researchgate.net/publication/44522568_Cellular_au...

https://donhopkins.com/home/cam-book.pdf

https://github.com/SimHacker/CAM6/blob/master/javascript/CAM...

themodelplumber on March 20, 2022 | prev [–]

I'm curious, how did the book change your life? What kind of problems did the authors model using their approach? I'm new to the topic, thanks for any input.

DonHopkins on March 22, 2022 | parent [–]

It really helped me get my head around how to understand and program cellular automata rules, which is a kind of massively parallel distributed "Think Globally, Act Locally" approach that also applies to so many other aspects of life.

But by "life" I don't mean just the cellular automata rule "life"! Not to be all depressing like Marvin the Paranoid Android, but I happen to think "life" is overrated. ;) There are so many billions of other extremely interesting cellular automata rules besides "life" too, so don't stop once you get bored with life! ;)

https://www.youtube.com/watch?v=CAA67a2-Klk

For example, it's kind of like how the world wide web works: "Link Globally, Interact Locally":

https://donhopkins.medium.com/scriptx-and-the-world-wide-web...

It's also very useful for understanding other massively distributed locally interacting parallel systems, epidemiology, economics, morphogenesis (reaction-diffusion systems, like how a fertilized egg divides and specializes into an organism), GPU programming and optimization, neural networks and machine learning, information and chaos theory, and physics itself.

I've discussed the book and the code I wrote based on it with Norm Margolus, one of the authors, and he mentioned that he really likes rules that are based on simulating physics, and also thinks reversible cellular automata rules are extremely important (and energy efficient in a big way, in how they relate to physics and thermodynamics).

The book has interesting sections about physical simulations like spin glasses (Ising Spin model of the magnetic state of atoms of solid matter), and reversible billiard ball simulations (like deterministic reversible "smoke and mirrors" with clouds of moving particles bouncing off of pinball bumpers and each other).

Spin Glass:

https://en.wikipedia.org/wiki/Spin_glass

>In condensed matter physics, a spin glass is a magnetic state characterized by randomness, besides cooperative behavior in freezing of spins at a temperature called 'freezing temperature' Tf. Magnetic spins are, roughly speaking, the orientation of the north and south magnetic poles in three-dimensional space. In ferromagnetic solids, component atoms' magnetic spins all align in the same direction. Spin glass when contrasted with a ferromagnet is defined as "disordered" magnetic state in which spins are aligned randomly or not with a regular pattern and the couplings too are random.

Billiard Ball Computer:

https://en.wikipedia.org/wiki/Billiard-ball_computer

>A billiard-ball computer, a type of conservative logic circuit, is an idealized model of a reversible mechanical computer based on Newtonian dynamics, proposed in 1982 by Edward Fredkin and Tommaso Toffoli. Instead of using electronic signals like a conventional computer, it relies on the motion of spherical billiard balls in a friction-free environment made of buffers against which the balls bounce perfectly. It was devised to investigate the relation between computation and reversible processes in physics.

https://en.wikipedia.org/wiki/Reversible_cellular_automaton

>A reversible cellular automaton is a cellular automaton in which every configuration has a unique predecessor. That is, it is a regular grid of cells, each containing a state drawn from a finite set of states, with a rule for updating all cells simultaneously based on the states of their neighbors, such that the previous state of any cell before an update can be determined uniquely from the updated states of all the cells. The time-reversed dynamics of a reversible cellular automaton can always be described by another cellular automaton rule, possibly on a much larger neighborhood.

>[...] Reversible cellular automata form a natural model of reversible computing, a technology that could lead to ultra-low-power computing devices. Quantum cellular automata, one way of performing computations using the principles of quantum mechanics, are often required to be reversible. Additionally, many problems in physical modeling, such as the motion of particles in an ideal gas or the Ising model of alignment of magnetic charges, are naturally reversible and can be simulated by reversible cellular automata.

Also I've frequently written on HN about Dave Ackley's great work on Robust-First Computing and the Moveable Feast Machine, which I think is brilliant, and quite important in the extremely long term (which is coming sooner than we think).

https://news.ycombinator.com/item?id=22304110

https://news.ycombinator.com/item?id=22300376

https://news.ycombinator.com/item?id=22303313