What is Life? was the title of a little pamphlet that ErwinSchrodinger, a theoretical physicist, published over 60 yearsago [1]. In my generation, every serious student of biologyand medicine read, and was deeply influenced by, What IsLife? James Watson claims that What is life? brought himto pursue and to answer this fundamental question.Schrodinger based his material on a seminal paper byNikolai Timofeeff-Ressovsky, Karl Zimmer, and MaxDelbruck published in 1935 in Berlin [2]. The three haddrawn conclusions from the observation that Drosophilaflies, when irradiated, exhibit an increased mutation ratethat is linearly related to the number of particles adminis-tered in terms of total radiation dose, rather than on theintensity. There exists an analogy to Einstein’s conclusionthat the photoelectric effect depends on the frequency of thelight source rather than on its intensity. The three authorsconcluded that genes had a definable, albeit unknown,chemical structure and a specific locus on the chromosome,and they calculated about how large a gene might be.Schrodinger wondered how many molecules it takes to makea living being, what these molecules might possess asproperties, and whether viruses are living, dead, or neither–nor. WhatprovokedSchrodingertoevenask these questions?We gain insight into his mind by revisiting the famousSchrodinger cat. Schrodinger wrestled in Berlin in the1920s with quantum mechanics, a discipline that necessar-ily deals with the duality of a material (if I may call light amaterial) that exists as both a wave and a particle. Thisnotion was termed “complimentarity” by those whosuffered with it. Werner Heisenberg, with close supportfrom Niels Bohr, had published his matrix mechanics,which showed that the position of a particle (say, anelectron) could never be determined with certainty even ifits impulse is known. On the other hand, when theelectron’s position is known, its impulse cannot bedetermined. Does biology also feature complimentarity?Schrodinger approached the quantum mechanics mysteryfrom the wave aspect. He derived an elucidating equationthat predicts about where electrons might be when theyorbit the atom. Schrodinger’s approach does not contradictthat of Heisenberg’s; as a matter of fact, the two notionssupport one another. Schrodinger brooded over quantummechanics. He attempted to reconcile the scurrilous worldof the quanta with the macroscopic tangible world byconstructing the cat paradox; a typical thought experiment(“Gedankenexperiment”) like Einstein’s studies. Imagine asingle atom of a radioactive element that has a half-life of60 min. The single atom, along with a Geiger counter, acrude mechanical hammer, a flask of cyanide gas, and aliving cat, are all housed within a box. The question is, after60 min, is the cat alive or dead? Here, we have a quantum-sized component discharging quanta, a device that cancount the quanta, and a machine that converts these quantainto a mechanical action that can kill the cat. Can wecalculate whether or not the cat is alive in 1 h? Well, everyschool child can tell us that the cat’s chances are 50–50.However, this estimate is imprecise (uncertain). The half-life was determined by observing billions of atoms. Ourprediction of a single atom’s behavior is uncertain. We canapply Schrodinger’s equation along with notation from PaulDirac and calculate how alive or dead the cat will be.However, the result is absurd: the cat is either dead or alive.These notions were the thought content that brought ErwinSchrodinger to biology.