Erwin Schrödinger, a Nobel laureate in physics, posed one of the most profound questions of the 20th century in his influential 1944 book, What Is Life?. His work was a deliberate attempt to bridge the conceptual gap between the physical laws governing inanimate matter and the complex, self-sustaining nature of living organisms. Schrödinger approached the problem of life as a theoretical physicist seeking to understand how events within a cell could be accounted for by the known laws of physics and chemistry. His analysis provided a revolutionary theoretical framework, suggesting that the order of life was merely an expression of physical laws operating under unique biological conditions. The book captivated a generation of scientists, shifting the focus of biological inquiry and directly inspiring figures like James Watson and Francis Crick in their later discovery of the structure of DNA.
The Challenge to Classical Physics
Schrödinger recognized that classical physics, particularly statistical mechanics, was inadequate for explaining the unique properties of the gene. Classical laws rely on the idea of “order from disorder,” where macroscopic regularity, such as gas pressure, emerges only from the random movements of countless individual atoms. This statistical approach suggested that the hereditary substance would need to be enormous to maintain stability and resist thermal agitation at body temperature.
The reality observed by geneticists, however, was that hereditary structures must be microscopic, yet they retain their complex configuration with incredible permanence over generations. In a small system governed by classical thermodynamics, the constant chaotic bombardment of heat energy would quickly lead to structural decay and randomness. Life presented a paradox: it operated at high biological temperatures where random forces were strong, yet it maintained a highly specific, stable structure. This stability, which allows traits to be passed down with near-perfect fidelity, contradicted the “order from disorder” principle governing non-living systems. Schrödinger concluded that life must therefore rely on a different physical mechanism to maintain its structure.
The Genetic Blueprint: The Aperiodic Crystal
To account for the stability and information capacity of the gene, Schrödinger proposed that the hereditary substance must take the form of an “aperiodic crystal.” A typical crystal, such as a salt crystal, is a periodic structure, meaning its atomic arrangement consists of a simple, endlessly repeating pattern. While highly stable, this repetitive nature makes a periodic crystal information-poor, like a plain wallpaper pattern.
Schrödinger reasoned that the genetic material must hold a vast, complex amount of information—a detailed “code-script”—to determine the entire development and function of an organism. This required a structure that was solid and stable like a crystal, but aperiodic, meaning its atomic sequence did not simply repeat. This aperiodic nature allows for the sequential variation needed to encode an immense number of instructions within a relatively small molecular structure. This concept was a powerful catalyst for the search that eventually identified the deoxyribonucleic acid (DNA) molecule, which is precisely a long, complex, and non-repeating macromolecule.
Fighting Decay: Order from Negative Entropy
Schrödinger tackled the question of how a living organism can maintain its highly organized state without violating the Second Law of Thermodynamics, which states that the total entropy (disorder) of an isolated system must always increase. Living systems are characterized by their remarkable ability to resist this universal tendency toward decay and equilibrium. They continuously build and maintain complex, low-entropy internal structures.
Schrödinger’s solution was to recognize that an organism is an open system that continuously interacts with its environment. To keep its internal entropy low and avoid decay, the organism must continually draw in “Negative Entropy,” a term he used to describe the order and energy extracted from its surroundings. The most common source of this order is highly organized matter, such as food or the energy from sunlight.
The process of metabolism is fundamentally an entropy-export machine. By consuming organized matter, an organism generates internal disorder, but it immediately exports a greater amount of disorder—in the form of heat, waste products, and less organized molecules—back into the environment. The overall effect is that the total entropy of the organism plus its immediate surroundings increases, upholding the Second Law of Thermodynamics.
Stability and Mutation: Quantum Mechanics in Heredity
To provide the necessary stability for the aperiodic crystal, Schrödinger invoked the laws of quantum mechanics. He argued that the atoms within the gene are held together by strong, specific chemical bonds whose stability is governed by quantum theory. This quantum-mechanical stability ensures that the genetic structure is robust and can resist the randomizing forces of thermal motion at biological temperatures, allowing the “code-script” to remain largely unchanged across generations.
The electrons in the atoms of the gene exist in discrete, stable energy states, which prevents the molecule from constantly fluctuating into new configurations. This stability explains the remarkable fidelity of heredity, allowing traits to be passed down accurately.
However, the same quantum principles that ensure stability also provide the physical mechanism for change: mutation. Schrödinger proposed that a mutation is a rare, discrete event, akin to a “quantum jump” at the molecular level. This translates to a spontaneous, sudden rearrangement of atoms within the molecule, fundamentally altering the genetic code and providing the physical basis for evolutionary change. The quantum view thus elegantly explained both the enduring stability of heredity and the necessary mechanism for biological evolution.