Amount of substance Amount of substance Amount of substance is a standard-defined quantity that measures the size of an ensemble of particles, such as atoms, molecules, electrons, and other particles. It is sometimes referred to as chemical amount. The International System of Units (SI) defines the amount of substance to be proportional to the number of entities present. The SI unit for amount of substance is the mole. It has the unit symbol mol. The proportionality constant is the inverse of the Avogadro constant. The mole is defined as the amount of substance that contains an equal number of elementary entities as there
What Is Life? published in 1944. At that time DNA was not yet accepted as the carrier of hereditary information, which only was the case after the Hershey–Chase experiment of 1952. One of the most successful branches of physics at this time was statistical physics, and quantum mechanics, a theory which is also very statistical in its nature. Schrödinger himself is one of the founding fathers of quantum mechanics. Max Delbrück's thinking about the physical basis of life was an important influence on Schrödinger. However, long before the publication of "What is Life?", geneticist and 1946 Nobel-prize winner H. J. Muller had in