Physics of the Living State

Book excerpt: Fluctuations are usually regarded as unwanted phenomena which mask signals that we need. Various techniques have been developed to suppress fluctuations or noise. In dealing with electronic devices we are always confronted with noise, which is classified as thermal noise, shot noise, generation-recombinant noise and 1/f noise. The first three noises are known well, the fourth is not so well known. 1/f noise has been a mystery for a long time since it was first observed by Johnson in 1925 in the low frequency part of the noise spectrum of an electrical current passing a vacuum tube.