# What is Life?

 Original cover to Erwin Schrodinger's famous 1994 Dublin lecture What is Life?, the book that inspired James Watson to discover DNA (1953) and that initiated the famous life feeds on negative entropy supposition. [3]
In famous publications, What is Life? - the Physicist's approach to the Subject: with an Epilogue on Determinism and Free Will, is a classic 1944 booklet by Austrian physicist Erwin Schrödinger, in which the puzzling aphorism that “life feeds on negative entropy” was presented to the lay public.

The book originated from a course of public lectures in February of the year prior at Trinity College, Dublin, in which Schrödinger attempted to explain, in lay terms, to explain how the events in space and time take place with the spatial boundary of a living organism or, in short, to give a definition of life according to physics and chemistry.

In thermodynamics, Schrödinger’s What is Life?, referring particularly to chapter six “Order, Disorder and Entropy”, in which a crude description on life and negative entropy was presented, is by far one of the the most-cited thermodynamics publications; a phenomenon do in large part to its small size (approximately 90-pages), its quaint lay-person style of writing, and to Schrödinger’s celebrity status for having won the 1933 Nobel Prize in physics for is work in quantum mechanics.

Order, Disorder and Life

The famous chapter six, of What is Life?, entitled "Order, Disorder and Entropy", is a rich source of famous quotations and a typical launching point or basis of logic in writings on life and thermodynamics. In this chapter, Schrodinger gives his famous derivation of "order". To begin with, he gives the following expression for entropy:

$\text{entropy} = k \log D \,$

where D is a quantitative measure of the atomistic disorder of the body in question; with the addendum that to give an exact explanation of D in non-technical terms is well-nigh impossible. On this, skipping a few paragraphs of discussion, he jumps to the conclusion that since the logarithm of 1/D is minus the log of D, we can thus write:

$- (\text{entropy}) = k \log \frac{1}{D} \,$

where, as he famously states, "the awkward expression 'negative entropy' can be replaced by the better one: entropy, taken with a negative sign, is itself a measure of order.

The following paragraph is a frequently quoted section of the chapter: [2]

“What then is that precious something that contained in our food which keeps us from death? That is easily answered. Every process, event, happening – call it what you will; in a word, everything that is going on in Nature means an increase of the entropy of the part of the world where it is going on. Thus a living organism continually increases its entropy – or, as you may say, produces positive entropy – and thus tends to approach the dangerous state of maximum entropy, which is death. It can only keep aloof from it, i.e. alive, by continually drawing from its environment negative entropy – which is something very positive as we shall immediately see. What an organism feeds upon is negative entropy. Or, to put it less paradoxically, the essential thing in metabolism is that the organism succeeds in freeing itself from all the entropy it cannot help produce while alive.”

The bolded line in this paragraph, in particular, is possibly the most quoted line in thermodynamics; aside from, of course, Clausius’ even more riddled statement that the "entropy of the universe tends to a maximum".

Note to Chapter 6
In the follow-up to this chapter, Schrodinger received a lot of flak from fellow physicists about various over simplifications and difficulties in his presentation; after which time he appended a two-page Note to Chapter 6 in which he explained that if he had been catering his talk to physicists that:

“[I should have] let the discussion turn on free energy instead [but that] this high technical term seemed linguistically too near to energy for making the average reader alive to the contrast between the two things … the concept [free energy] is a rather intricate one, whose relation to Boltzmann’s order-disorder principle is less easy to trace than for entropy and ‘entropy taken with a negative sign’, which by the way is not my invention.”

Other
American physicist Jack Hokikian states that Schrodinger coined the term “negative entropy”. [2] This, however, may not be the case, as the term or a variant of it seems to have been used prior to this.

References
1. (a) Schrödinger, Erwin. (1944). What is Life? (ch. 6 “Order, Disorder, and Entropy”, pgs. 67-75). Cambridge: Cambridge University Press.