Order Disorder and Entropy

A REMARKABLE GENERAL CONCLUSION FROM THE MODEL

The miniature code of the molecular picture of the gene should be in one-to-one correspondence with a highly complicated and specified plan of development.

It should contain the means of putting it into operation.

How are we going to turn ‘conceivability’ into true understanding?

Delbriick’s molecular model has no hint as to how the hereditary substance works.

I do not expect that any detailed information on this question is likely to come from physics in the near future.

The advance is proceeding and will, I am sure, continue to do so, from biochemistry under the guidance of physiology and genetics.

No detailed information about the functioning of the genetical mechanism can emerge from a description of its structure so general as has been given above.

That is obvious. But, strangely enough, there is just one general conclusion to be obtained from it, and that, I confess, was my only motive for writing this book.

From Delbriick’s general picture of the hereditary substance it emerges that living matter, while not eluding the ’laws of physics’ as established up to date, is likely to involve ‘other laws of physics’ hitherto unknown, which, however, once they have been revealed, will form just as integral a part of this science as the former.

ORDER BASED ON ORDER

This is a rather subtle line of thought, open to misconception in more than one respect. All the remaining pages are concerned with making it clear. A preliminary insight, rough but not altogether erroneous, may be found in the following considerations:

It has been explained in chapter I that the laws of physics, as we know them, are statistical laws. I They have a lot to do with the natural tendency of things to go over into disorder.

But, to reconcile the high durability of the hereditary substance with its minute size, we had to evade the tendency to disorder by ‘inventing the molecule’, in fact, an unusually large molecule which has to be a masterpiece of highly differentiated order, safeguarded by the conjuring rod of quantum theory.

The laws of chance are not invalidated by this ‘invention’, but their outcome is modified. The physicist is familiar with the fact that the classical laws of physics are modified by quantum theory, especially at low temperature.

There are many instances of this. Life seems to be one of them, a particularly striking one. Life seems to be orderly and lawful behaviour of matter, not based exclusively on its tendency to go over from order to disorder, but based partly on existing order that is kept up.

To the physicist - but only to him - I could hope to make my view clearer by saying: The living organism seems to be a macroscopic system which in part of its behaviour approaches ITo state this in complete generality about ’the laws of physics’ is perhaps challengeable. The point will be discussed in chapter 7.

to that purely mechanical (as contrasted with thermodynami- cal) conduct to which all systems tend, as the temperature approaches the absolute zero and the molecular disorder is removed.

The non-physicist finds it hard to believe that really the ordinary laws of physics, which he regards as the prototype of inviolable precision, should be based on the statistical tendency of matter to go over into disorder.

I have given examples in chapter I. The general principle involved is the famous Second Law of Thermodynamics (entropy principle) and its equally famous statistical foundation.

On pp. 69-74 I will try to sketch the bearing of the entropy principle on the large-scale behaviour of a living organism - forgetting at the moment all that is known about chromosomes, inheritance, and so on.

LIVING MATTER EVADES THE DECAY TO EQUILIBRIUM

What is the characteristic feature of life? When is a piece of matter said to be alive?

When it goes on ‘doing something’, moving, exchanging material with its environment, and so forth, and that for a much longer period than we would expect an inanimate piece of matter to ‘keep going’ under similar circumstances.

When a system that is not alive is isolated or placed in a uniform environment, all motion usually comes to a standstill very soon as a result of various kinds of friction; differences of electric or chemical poten tial are equalized, substances which tend to form a chemical compound do so, temperature becomes uniform by heat conduction.

After that the whole system fades away into a dead, inert lump of matter.

A permanent state is reached, in which no observable events occur.

The physicist calls this the state of thermodynamical equilibrium, or of ’ maximum entropy’. Practically, a state of this kind is usually reached very rapidly.

Theoretically, it is very often not yet an absolute equilibrium, not yet the true maximum of entropy. But then the final approach to equilibrium is very slow.

It could take anything between hours, years, centuries, … To give an example - one in which the approach is still fairly rapid: if a glass filled with pure water and a second one filled with sugared water are placed together in a hermetically closed case at constant temperature, it appears at first that nothing happens, and the impression of complete equilibrium is created.

But after a day or so it is noticed that the pure water, owing to its higher vapour pressure, slowly evaporates and condenses on the solution. The latter overflows. Only after the pure water has totally evaporated has the sugar reached its aim of being equally distributed among all the liquid water available.

These ultimate slow approaches to equilibrium could never be mistaken for life, and we may disregard them here. I have referred to them in order to clear myself of a charge of Inaccuracy.