# Physically-grounded computing

February 21, 2015 — April 30, 2024

Theories of computation grounded in what is physically realisable versus waht is logically possible

TODO: relation to algorithmic statistics, thermodynamics of life.

@GershenfeldPhysics2000:

The Physics of Information Technology explores the familiar devices that we use to collect, transform, transmit, and interact with electronic information. Many such devices operate surprisingly close to very many fundamental physical limits. Understanding how such devices work, and how they can (and cannot) be improved, requires deep insight into the character of physical law as well as engineering practice. The book starts with an introduction to units, forces, and the probabilistic foundations of noise and signalling, then progresses through the electromagnetics of wired and wireless communications, and the quantum mechanics of electronic, optical, and magnetic materials, to discussions of mechanisms for computation, storage, sensing, and display. This self-contained volume will help both physical scientists and computer scientists see beyond the conventional division between hardware and software to understand the implications of physical theory for information manipulation.

Same author, possibly more compact: @GershenfeldAligning2011, @GershenfeldSignal1996.

## 1 Thermodynamics

Baez on The Mathematical Origin of Irreversibility

Could it be that thermal phenomena, forgetful information processing and adaptive evolution are governed by the same stochastic mechanism?

The answer is — yes! The key to this rather profound connection resides in a universal property of Markov processes discovered recently in the context of non-equilibrium statistical mechanics, and known as the ‘fluctuation theorem’. Typically stated in terms of ‘dissipated work’ or ‘entropy production’, this result can be seen as an extension of the Second Law of Thermodynamics to small systems, where thermal fluctuations cannot be neglected. But it is actually much more than this: it is the mathematical underpinning of irreversibility itself, be it thermodynamical, evolutionary, or else. To make this point clear, let me start by giving a general formulation of the fluctuation theorem that makes no reference to physics concepts such as ‘heat’ or ‘work’.

## 2 Incoming

- Dan Roberts, Black Holes and the Intelligence Explosion