William Andregg ushers me into the cluttered workshop of his startup Fathom Computing and gently lifts the lid from a bulky black box. Inside, green light glows faintly from a collection of lenses, brackets, and cables that resemble an exploded telescope. It’s a prototype computer that processes data using light, not electricity, and it’s learning to recognize handwritten digits. In other experiments the device learned to generate sentences in text.

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