John B. Johnson

John Bertrand Johnson was born in Sweden in 1887 and emigrated to the United States, where he earned his doctorate and joined the research staff of Bell Telephone Laboratories. There, in 1927, he made the careful measurements that revealed an irreducible random voltage present across every resistor — a noise that could not be eliminated by improving the apparatus.

Johnson found that this noise grew with temperature and with resistance, but was independent of the resistor's material or the current through it, marking it as a fundamental thermal effect rather than an artefact. The phenomenon is now called Johnson noise, or Johnson–Nyquist noise in recognition of the theoretical explanation supplied by his colleague.

Beyond the discovery of thermal noise, Johnson worked on thermionic emission and on the development of improved cathode-ray and oscilloscope tubes, contributing to the instrumentation that made precise electronic measurement possible.

His discovery established a fundamental limit on the sensitivity of all electronic measurement and remains a daily concern for the designers of low-noise amplifiers and detectors. He died in 1970.