“Nature isn't classical, dammit, and if you want to make a simulation of nature, you'd better make it quantum mechanical, and by golly it's a wonderful problem, because it doesn't look so easy.”Richard Feynman · Simulating Physics with Computers · 1982 · prelegerea «Simulating Physics with Computers» (1981), publicată în International Journal of Theoretical Physics, vol. 21, 1982
Nature computes quantum-mechanically, so only a quantum machine can simulate it faithfully.
Feynman starts from a simple observation. Simulating a physical system on a classical computer grows exponentially with the system's size, because quantum states cannot be represented efficiently with ordinary bits. So he proposes a computer that is itself quantum, one that processes amplitudes and interference rather than mere digits. Light is exactly such a system: photons propagate, interfere and combine according to quantum equations. An optical processor lets light perform the operation directly, through interference, instead of simulating it step by step in silicon. A neural network is, at its core, a chain of matrix multiplications, and an optical matrix performs that multiplication as the beam travels through it.
Why it matters Feynman's idea underlies today's photonic computing: if light is a quantum system, then neural networks can be carried and processed by photons rather than electrons, at near light speed and with far lower energy use than classical chips.