Reversibility: Irreversible
All systems with reversibility: irreversible
Systems (37)
Belousov-Zhabotinsky (BZ) reaction computer
f(x) = boolean logic / reaction-diffusion computation (via chemical wave collisions)
The BZ reaction is an oscillating chemical system that produces propagating excitation waves in a thin layer of reagent (typically ferroin or ruthenium catalyst in acidified bromate/malonate). Signals...
Biological brain
f(x) = general intelligence / perception, memory, reasoning, motor control
The human brain contains ~86 billion neurons connected by ~10¹⁵ synapses. Each neuron integrates thousands of synaptic inputs and fires a spike when its membrane potential crosses threshold — a leaky ...
Boson sampler
f(x) = sampling from the permanent of a unitary matrix (classically #P-hard)
Identical single photons enter an m-mode linear optical network (beam splitters and phase shifters implementing a unitary U). Detectors at the outputs sample from a distribution whose probabilities ar...
Coherent Ising machine (OPO network)
f(x) = Ising Hamiltonian ground state / combinatorial optimization (MAX-CUT, QUBO)
A network of degenerate optical parametric oscillator (DOPO) pulses circulating in a fiber ring cavity. Each pulse can oscillate in one of two phase states (0 or π), encoding a spin. Measurement-feedb...
Coupled oscillator network (Kuramoto / XY model)
f(x) = MAX-CUT / graph partitioning (approximate)
A network of identical oscillators — pendula, LC circuits, or CMOS ring oscillators — coupled to their neighbours by springs or resistive links. The Kuramoto model describes how each oscillator's phas...
DNA computer (Adleman 1994)
f(x) = Hamiltonian path via strand hybridization
Leonard Adleman's 1994 demonstration solved the directed Hamiltonian path problem using DNA strand hybridization. Cities encoded as DNA sequences, flight connections as complementary strands. Massivel...
DNA strand-displacement computer
f(x) = boolean logic / neural network inference (via hybridization cascades)
Single-stranded DNA molecules in solution compute via toehold-mediated strand displacement: a short single-stranded 'toehold' on a partially double-stranded gate complex allows an input strand to inva...
Differential analyzer
f(x) = solutions to systems of ODEs (via chained mechanical integration)
Built by Vannevar Bush and Harold Hazen at MIT in 1928–1931, the differential analyzer is a general-purpose analog ODE solver. The core component is a wheel-and-disk integrator: a disk rotates at rate...
Diffractive deep neural network (D²NN)
f(x) = neural network inference / image classification (at the speed of light)
A stack of passive, 3D-printed diffraction layers implements a trained neural network entirely in the optical domain. Each layer is a mask with pixel-wise phase or amplitude modulation, trained offlin...
DishBrain (in-vitro neural culture)
f(x) = closed-loop sensorimotor control / game-playing (via biological learning)
~800,000 human iPSC-derived or mouse cortical neurons are plated onto a high-density multi-electrode array (HD-MEA). The DishBrain system (Kagan et al., 2022, Neuron) embeds the culture in a simulated...
Domino computer
f(x) = boolean logic (AND, OR, NOT)
Standing dominoes propagate a falling signal. Fan-outs split signals, and careful geometry implements AND and OR gates. Signal is one-shot — must reset by standing dominoes again. Speed: ~1 domino per...
Galton board (bean machine)
f(x) = Gaussian / binomial distribution
Balls dropped through a triangular array of pegs deflect left or right at each level. The distribution of balls in the output bins converges to a Gaussian as N→∞. Each peg is an independent Bernoulli ...
Hanging chain (catenary)
f(x) = hyperbolic cosine / thrust line
A chain suspended from two fixed points and left to hang under gravity settles into a curve that exactly realizes the hyperbolic cosine. Gaudí used physical catenaries (inverted) to design the arches ...
Kelvin tide-predicting machine
f(x) = sum of sinusoids / tidal height (Fourier synthesis)
Designed by Lord Kelvin (William Thomson) in 1872–73, this special-purpose mechanical analog computer performs real-time Fourier synthesis. Each tidal harmonic constituent (M2, S2, N2 …) is represente...
LEGO mechanical computer
f(x) = arbitrary digital logic / sequential game state
A fully mechanical computer built from LEGO Technic with no electronics. Binary memory is stored as lever positions on a rotating drum (rod logic); a read/write head flips levers to write bits and sen...
MONIAC (Phillips hydraulic computer)
f(x) = Keynesian macroeconomic equilibrium (ODE system)
Built by Bill Phillips (1949). Water flows through tanks and pipes representing economic sectors — income, consumption, taxation, investment. Flow rates encode economic quantities. The system settles ...
Marble computer
f(x) = binary arithmetic / boolean logic
Gravity-fed marble runs with rocker/seesaw gates implement binary arithmetic and logic operations. One marble = 1 bit. The rocker flips state on each pass, implementing half-adders and logic gates. Th...
Mechanical fire-control computer
f(x) = ballistic trajectory / gun bearing and elevation (multivariate real-time ODE)
Electromechanical analog computers installed on WWII-era warships (e.g. the US Navy Mark 1) continuously computed the correct bearing and elevation for naval guns from up to 25 live inputs: target ran...
Mechanical gyroscope
f(x) = time-integral of angular velocity (orientation tracking)
A spinning rotor mounted in gimbals conserves angular momentum. Any external torque causes precession perpendicular to both the spin axis and the applied torque — rather than tilting directly. By read...
Memristive Hopfield network optimizer
f(x) = optimization via chaotic annealing / transient dynamics
Memristive circuits implementing Hopfield network topology where the intrinsic nonlinearity of memristors creates transient chaotic annealing processes. The chaotic dynamics enable escape from local m...
Memristor crossbar
f(x) = analog matrix-vector multiplication
Crossbar arrays of memristors (memory resistors) perform matrix-vector operations in analog. Voltages applied to rows, currents collected from columns. Resistance values encode matrix elements. Enable...
Neuromorphic chip (Intel Loihi / IBM TrueNorth)
f(x) = spiking neural network computation
Silicon chips that mimic neural computation using spiking neurons and synaptic connections. Intel Loihi and IBM TrueNorth implement event-driven, asynchronous processing with on-chip learning capabili...
Op-amp analog computer
f(x) = ODE integration via Kirchhoff's laws
Operational amplifiers configured as integrators, adders, and multipliers solve differential equations in real-time. Voltages represent variables, circuit topology encodes the equation structure. Clas...
Optical correlator (4f / VanderLugt filter)
f(x) = cross-correlation / matched filtering (pattern detection in O(1) optical time)
A 4f lens system consists of two lenses separated by twice their focal length with a holographic or spatial-light-modulator (SLM) filter at the shared Fourier plane. The first lens computes the Fourie...
Photonic integrated circuit (silicon photonics)
f(x) = matrix-vector multiplication / unitary linear transforms (for neural network inference)
Arrays of Mach-Zehnder interferometers (MZIs) and microring resonators on a silicon chip implement programmable unitary matrices in the optical domain. Light encodes values as amplitude or phase; pass...
Physarum polycephalum (slime mold)
f(x) = Steiner tree / shortest transport network (approximate)
The plasmodial slime mold extends filaments toward nutrient sources and progressively reinforces paths that carry more flow, pruning inefficient routes. Toshiyuki Nakagaki showed it reproduces the Tok...
Pneumatic logic (Coanda-effect fluidics)
f(x) = boolean logic (AND, OR, NOT, NOR) via wall-attachment bistability
A jet of air entering a Y-shaped channel naturally attaches to one wall (the Coandă effect) and locks into that state by low-pressure recirculation. A small control jet on the opposite side provides e...
Quantum and quantum-inspired annealers
f(x) = Ising model energy minimization / QUBO optimization
Quantum and quantum-inspired systems for solving combinatorial optimization problems through annealing processes. Includes true quantum annealers (D-Wave) using superconducting qubits and quantum-insp...
Repressilator (synthetic gene oscillator)
f(x) = limit-cycle oscillation / biological clock (via negative-feedback transcription loop)
Elowitz & Leibler (2000, Nature) constructed a synthetic oscillator in E. coli from three mutual repressor genes wired in a ring: LacI represses tetR; TetR represses cI; CI represses lacI. No gene pro...
Reservoir computer
f(x) = temporal pattern recognition / dynamical system computation
Fixed nonlinear dynamical system (reservoir) coupled to a trained linear readout layer. Input drives the reservoir dynamics, output layer learns to extract desired computations. Echo state networks an...
Simulated annealing (thermal)
f(x) = argmin of energy / cost landscape
A physical system coupled to a heat bath at slowly decreasing temperature explores its energy landscape. At high temperature it escapes local minima; as T→0 it settles into a global minimum — if cooli...
Soap film
f(x) = minimal surface (Plateau's problem)
A soap film spanning a closed wire boundary settles into the surface of minimum area — the solution to Plateau's problem. For two parallel rings it realizes a catenoid. Can approximate Steiner trees f...
Spaghetti sort
f(x) = total ordering of positive reals (sorting) in O(n) physical time
Cut n spaghetti strands to lengths proportional to the n values to be sorted. Gather them loosely in a fist and lower them vertically onto a flat table so all strands stand upright. Lower a flat hand ...
Thermodynamic computer
f(x) = sampling from Boltzmann distributions
Uses thermal noise in analog circuits to sample from Boltzmann distributions. Thermal fluctuations provide natural randomness that follows statistical mechanics principles. The Normal Computing SDE (S...
Thermodynamic computer (Normal Computing SPU)
f(x) = probabilistic sampling / linear algebra via thermal equilibration
Analog physics-based computers using thermodynamic principles for computation. Normal Computing's Stochastic Processing Unit (SPU) uses RLC circuits as unit cells with all-to-all coupling via switched...
Water (fluidic) computer
f(x) = binary addition / boolean logic (AND, XOR)
Water levels in vessels encode binary digits; a siphon and slow drain combine to implement AND and XOR in a single cup-and-tube unit. A filled cup is a 1, an empty cup a 0. When two cups feed one cont...
Watt centrifugal governor
f(x) = proportional speed regulation (continuous set-point tracking via negative feedback)
Two steel balls are mounted on hinged arms linked to a rotating vertical shaft driven by the engine. As engine speed increases, centrifugal force swings the balls outward and upward; through a collar ...