Exactness: Exact
All systems with exactness: exact
Systems (12)
Billiard-ball computer
f(x) = reversible boolean logic (Fredkin gate)
Proposed by Fredkin & Toffoli (1982). Balls travel on paths representing wires; presence/absence of a ball encodes a bit. Collisions at path intersections implement logic gates. Logically and thermody...
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...
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...
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...
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 ...
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...
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...
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 gate computer (superconducting qubits)
f(x) = unitary transformations / quantum algorithms
Superconducting qubits manipulated by microwave pulses to perform unitary operations. Quantum gates like Hadamard, CNOT, and phase gates enable quantum algorithms such as Shor's factoring and Grover's...
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 ...
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...