The Hidden Meanings of Noise
Scientific breakthroughs often depend on discovering the meaning of seemingly random fluctuations.
In his essay “On Noise,” the 19th-century German philosopher Arthur Schopenhauer wrote that “the most eminent intellects have always been strongly averse to any kind of disturbance, interruption and distraction, and above everything to that violent interruption which is caused by noise.” He was referring to audible sounds, in particular the “infernal cracking of whips… which paralyzes the brain.”
Scientists have a wider concept of noise, using the word to describe any kind of fluctuation that has an element of randomness. Noise contrasts with signal, which is valuable because it conveys sought-after information. Separating interesting signals from obscuring noise is a big part of the art of experimental science and statistics.
Sometimes, however, the noise is the signal. Two of Einstein’s three great discoveries in his “miracle year” of 1905 involved learning from noise. Very recently, creative work with noise has once again powered a series of breakthrough discoveries in basic physics.
Einstein traced the jitter of pollen grains, when immersed in fluids and observed under a microscope, to their random encounters with individual fluid molecules. This explanation enabled him to make a convincing case for the existence of molecules and to determine their masses. In his work on black body radiation, Einstein built on the work of Max Planck to show that graininess in the radiation’s flow means that light comes in lumps, or quanta. Today, we call the quanta of light photons.
In everyday life, we usually think of an electric current as a smooth flow. In fact, the flow involves lumps of charge—electrons, usually—leading to an irreducible graininess in the current, known as shot noise. Shot noise becomes particularly noticeable for weak currents, and its strength can be used to measure an electron’s charge. In 1995, scientists used shot noise to show that in certain states of matter the granules of charge carry only a fraction of the charge of an electron, verifying a startling prediction of Robert Laughlin and opening up a thriving new field of “subelectronics.”
Last month, the cover of Science announced that physicists had detected a new third kingdom of sub-electronic particle called anyons, which join the long-established bosons and fermions. Theorists have been looking forward to anyons for many years. (I named them in 1982.)
The crucial observations here concern a more sophisticated version of shot noise, which involves not merely fluctuations in a single current but correlations between fluctuations in two of them. The new research opens up new worlds of possibilities, including the construction of more effective quantum computers.
Fluctuating currents and correlations among them might seem like pretty esoteric subjects, but they’re a big part of the way we think, under the hood. Information in our brains is largely encoded in firing patterns of neurons, which are essentially spiky electric currents. Correlations among fluctuations in the currents flowing through different neurons are the information-bearing patterns that embody perception and thought.
Of course, noise can be noisome. The jumbled activation of injured nerves is involved in the pain of wounds or inflammation. Epilepsy is a mind-storm of noise, and as Schopenhauer wrote, “a great intellect has no more power than an ordinary one as soon as it is interrupted, disturbed, distracted or diverted.” But when noise is mined and harnessed, it can be a valuable resource.
Originally appeared on May 28, 2020 on The Wall Street Journal website as ‘The Hidden Meanings of Noise’
Frank Wilczek is the Herman Feshbach Professor of Physics at MIT, winner of the 2004 Nobel Prize in Physics, and author of the books Fundamentals: Ten Keys to Reality (2021), A Beautiful Question: Finding Nature’s Deep Design (2015), and The Lightness of Being: Mass, Ether, and the Unification of Forces (2009).
