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Cambridge University Science Magazine
It is a question which many of us were asked at school, and “MRS NERG” was often given as the answer. It is the question of What is Life? Many biologists have tackled this question over the years but quantum physicist Erwin Schrödinger (of eponymous equation and cat fame) approached it in a way unlike any other had before. His book, What is life? was written based on a series of lectures he delivered in 1943. It inspired Watson and Crick in their research, which famously culminated in the discovery of DNA’s double helical structure, and paved the way for humanity’s understanding of the essence of life. But what were the “naïve physicist’s ideas about organisms” which contributed to one of the most ground-breaking discoveries in science? Here I explore some of his key ideas which contributed to a growing intellectual conversation on the nature of DNA in the 1940s.

Aperiodic crystals – a not-so-periodic 3D table?

Nearly a decade before DNA’s double helical structure was identified, Schrödinger believed that chromosomes were “aperiodic solid[s]”, with genes made up of atoms arranged “without the dull device of repetition”. This novel theory was later proven to be correct; 4 bases are indeed arranged in a specific sequence – without repetition – within DNA to form a crystal of sorts. His concept is further developed when he explains that “this well-ordered association of atoms” is the “only conceivable material structure that offers a variety of possible arrangements”. These suggestions clearly highlight his belief in the importance of a genetic code that “contain[s] an elaborate code-script involving all the future development of the organism”. At a time when genes were a “hypothetical material structure” underlying a particular hereditary feature, these progressions gave a real insight into the potential make-up of life itself.

Quantum theory of biology – DNA ‘physicsified’

Unlike the interdisciplinary nature of science today, this “poor theoretical physicist” divulging into the mystical world of biology back in the 1940s was somewhat of a rarity (although it was becoming less so) and yet it resulted in a barrage of radical biophysical thoughts. An example of this is Schrödinger’s observation that, since mutations are not “small, continuous variations” as Darwin suggested, but are actually discontinuous with “no intermediate forms”, mutations could be caused by “quantum jumps in the gene molecule”. Hence his “quantum theory of biology”. This discussion on the nature of mutations also focuses on the importance of rare mutations; if they were too frequent within an individual, “the injurious ones [mutations] would…predominate over the advantageous ones”. A simple thought that led him to a fascinating conclusion. Whilst we do not think of mutations as quantum leaps today, Schrödinger was clearly forging a path of bold, interdisciplinary thinking.

New laws of physics – pass me the smelling salts!

After describing some interesting X-rays experiments, Schrödinger predicts that genes only consist of about 1000 atoms - not ‘atoms’ in the traditional sense, but in the sense of code elements (base pairs). These genes not only have a “durability or permanence that borders on the miraculous” but also the ability to mutate into other stable states. Earlier in the book, he explains that only through an “enormously large number of atoms” (far higher than the 1000 atoms in a gene) can statistical laws have meaning, and orderliness be achieved. An example of this is the extreme order found in a ‘permanent gene’ since a significant alteration of a gene’s structure would usually prevent viable offspring existing. Otherwise, the “unceasing heat motion of the atoms” would disrupt the essential order of DNA’s atomic structure, demonstrated by Schrödinger through clear explanations on the phenomena of paramagnetism and diffusion! In summary, to reconcile the order evident in DNA with the far too few number of atoms involved, Schrödinger believes that living matter is “likely to involve ‘other laws of physics’ hitherto unknown”. As of yet, we haven’t found any “other laws of physics” but he has provided us with an exciting prospect nonetheless, and added fuel to a growing intellectual pursuit in the mid twentieth century.

Negative entropy – what (anti)CHAOS!

If Schrödinger’s ponderings haven’t surprised you so far, perhaps you will be taken aback by his introduction of the term “negative entropy” to the field of thermodynamics. Entropy is the disorder/chaos of a system and is “not a hazy concept or idea, but a measurable physical quantity”. Life is inherently a chaotic system: metabolism releases energy necessary for survival and life “continually increas[es] its entropy”, obeying the second law of thermodynamics, which states that the total entropy of an isolated system always increases. This increase continues until death, the “state of maximum entropy” and the system decays into thermodynamic equilibrium. So how does an organism stay alive and delay its decay? Schrödinger suggests that life can only prevail by continually feeding on “negative entropy”, a “measure of order” gained from its food, compensating for the entropy it produces when living. Therefore, he believes life exists because organisms ‘suck the order from the environment’ to make up for the chaos occurring in their bodies.

Should I take the plunge and read What is Life? by Schrödinger?

Aside from the titillating thoughts of Schrödinger, the real joy of this book is his beautiful style of writing. He turns writing about simple genetic inheritance into a well-crafted and intimate experience with the author. For example, he vividly describes the independent assortment of chromosomes during meiosis by explaining that “even if it were known that my paternal chromosome No.5 came from my grandfather Josef Schrödinger, the No.7 still stands an equal chance of being either also from him, or from his wife Marie, née Bogner”. Equally personal is Schrödinger’s description of the “harmful effect of close-breeding”, analysing the genetics of incest in the context of his hypothetical descendants. If you are still unspurred to read What is Life? then I don’t blame you, for it is tricky to get your head around. Schrödinger and his scandalous ménage à trois however – that’s a tad easier to read!

Lush life?

Yes – life is lush and still quite a marvel over 75 years on from Schrödinger’s speculative work. Humanity’s development in biochemistry and molecular biology since then has been astounding: the progression from Schrödinger’s “aperiodic crystal” to today’s understanding of DNA has occurred within the lifetime of Golden Hollywood legend Olivia de Havilland! Despite this, we still have a lot to discover about life’s workings and I am confident that Schrödinger would have been amazed by what we’ve come to understand so far.

A link to a free copy of What is Life? by Schrödinger may be found here.

Savanna Leboff is a third year undergraduate in Natural Sciences at Clare College