31 July 2013

Primary Source: Erwin Schrödinger's "What is life?" and the Public Understanding of Science in 1951

While working in the National Archives (London), I stumbled upon another gem from the Festival of Britain, 1951. This one is a script by Erwin Schrödinger focused on the living organism. Schrödinger had published in 1944 his What is life? which was among the more important works of popular science published in the twentieth-century. Interestingly, here Schrödinger only toys around the edges of the mind and brain problem, mentioning perception and sensation only tangentially. His interest here seems to be with the way life introduces order to the universe. You may therefore be able to apprehend in this reductive contemplation Schrödinger's larger resolution of the hard problem of mind.

Quote begins.

Suggestions for demonstrating some ideas on living organisms.

Show a simple pendulum clock (driven by a spring), in motion, so that the working mechanism of the cogs can be seen.

This ingenious mechanism owes the regularity of its movements, which are predictable with great accuracy to the fact that it is composed of nearly rigid parts, arranged to a plan, and to the constant action of gravity on the pendulum. Very nearly the same can be said about the system of the Sun and the planets with their moons. So regular is this motion, that Thales of Milet in the 6th century B.C. could predict an eclipse of the Sun from simple rules of thumb that he had learnt from the Babylonians; and modern astronomers could from their observations date this event, which founded Thales' frame, as having taken place on the 28th of May, 585 B.C.

Show the motion of the planets somehow. A stereoscopic trick-film would do, showing the motion of Mercury, Venus, Earth (with Moon), and Mars, in 60 secs., say about 600 pictures covering one year (e.g. one revolution of the Earth), then jumping back to the beginning.

But such simple mechanisms are exceptions. Most of the "laws of nature" (more properly called: observed regularities) that we discover in our environment and use for industrial or more objectionable purposes, are of an entirely different kind - they come about haphazardly, or by chance. But how can chance-events obey, let alone produce law?

Table giving the annual means of temperature of London for 200 odd years, and indicating how an approximate value of Pie = 3.14159 is computed from them.

A table can show the annual means of temperature in London between 17 and 19. The slight and entirely accidental deviations from the general mean are nonetheless controlled by Gauss' law, which enables us to compute from them the approximate value of the ratio between the circumference of a circle and its diameter (called Pie in mathematical jargon).

Physical laws, based on chance, own their rigour to the enormous number of single (atomic) events contributing to the phenomenon in question, this number being out of the order of a few hundreds, but rather of billions (10^24) and more (p. 2).

A typical example is "vapour pressure". Any liquid, for example water, emits at a given termperature vapour of a definite density or pressure which increases rapidly with temperature. The apparent "equilibrium" between the liquid and the vapour consists actually of a continual exchange of molecules between the two states; the number of molecules that evaporate spontaneously from the liquid is balanced by those that return to it from the vapour.

Here one might show a picture of the random motion of molecules in a gas. If the lower half of the picture is shadowed it may represent the liquid from which molecules emerge continuously, while others return to it. 

Show a second picture, which the molecules are more crowded and move more rapidly, corresponding to a higher temperature. Technical remark: A quite good picture of a gas can be obtained as follows. Dispose on a horizontal glass-pane a simple wooden frame of quadrangle or rectangular shape, place steel balls (say ball bearings) on the glass, the frame preventing them from rolling off, and arrange some mechanism to shake the frame continually in a rapid and irregular way. A second plate, covering the frame and fixed to it will prevent the balls from occasionally jumping out. The motion of the balls, caused by the shaking frame, is very much like our idea of gas molecules. If the whole thing is given a slope, the average density of the balls will be smaller in the upper parts, but will increase their automatically, as the shakings are intensified. Numerous experiments with a gas can be illustrated in this manner. It would probably be best to withdraw the apparatus itself from the eyes of the spectator, and show only a shadow picture.

(page 3) A single event of a molecule hitting the surface and being caught, or of a molecule escaping from the surface, is a chance event, that might also turn out differently. Yet the statistical result, owing to the great number, is sufficiently certain to let steam engines work with a precision that rivals with a pendulum clock of the planetary system.

Show a little steam engine functioning or a trick-film thereof.

An organism grows from a fertilised egg or seed - that is from a single cell - by subsequent cell-divisions, into the fully developed pattern of the species.

Show three or four tables with picture-series of the successive stages of some animals and plants, for instance, of the chicken, of some reptile, of man, of mais, of some flowers or tree; of of whatever is easily accessible.

Every single cell divisions that go - billions of them - to build up this process of organic development is a marvel of well-ordered regular events.

Show a cell division, either in a series of pictures, or, better, in a motion picture.

The same holds for all the infinitely manifold physiological processes going on in every organism during its life-time, constituting its 'life', which relies entirely on their regular and, as it were, well-planned interplay.

Illustrations for this could be: - blood circulation, contraction of a muscle, a cross-section of the eye with the nerves leading to the brain, a breathing lung, circulation of the sap in a living plant, opening of a budding leaf, etc., etc...

The remarkable thing is the absolute constancy with which any of these patterns are repeated in all the individuals of the same species - both the patterns of their development from the egg or seed, and the patterns of their functioning during life-time. They follow the patterns of the parents, and all this must be the pre-determined by the structure of the one, single, egg-cell!

Show egg-cells of various plants and animals, with chromosomes visible, such as for instance, man, a reptile, a bird, a flower, a tree, mais, a sea-urchin - whatever can be found in a text-book. It would be as well to add a sketch of the full-grown organism in every case to contrast the similarity of the egg-cells to the wider difference between, say, an elephant and a rose-tree.

In outward appearance these egg cells are remarkably alike for widely different organisms.

The whole plan of the future development and physiological functioning must be laid down in the structure of this one, single cell (which by the way, in its outward appearance resembles very much any other body-cell). We have good reason to believe that the 'plan' is contained mainly, if not exclusively, in the dark bodies visible in all these cells, the bodies called chromosomes. The complicated, sort of striated, structure of these chromosomes can be directly seen in the salivary gland cells of the little fruit-fly drosophila (for some reason these cells are naturally gigantic).

Show a picture of the salivary gland cells of drosophila. 

Vastly extended experiments on heredity and 'mutations' (not to be described here in detail) have even led to the localization of certain features of this fruit-fly within the single dark bodies (chromosomes).

Show chromosome charts for drosophila and the mais-plant - or any others available.

(page 4) Features located in the same chromosome are usually transferred together (they are 'linked'). So-called colour-blindness (better to be termed Dichromatism) in man is 'sex-linked'; that is to say it is localized in the same chromosome that determines the sex. That is why this peculiar kind of colour-vision, quite frequent in men, is extremely rare in women. (The daughters of a dichromatic fatherare always 'carriers' and transfer this - by the way quite harmless - peculiarity to approximately half of their sons).

Show an ordinary spectrum from red over green to violet, and, under it, the spectrum as it appears to the colour-blind, viz: a band shaded off fromintense yellow (at the 'red' end) over grey (under blue-green) to intense dark blue (under violet).

How is the whole pattern of an organism of a given species - how are even minute peculiarities of the individual parents laid down in those minute specks of matter (the chromosomes) of a single cell, the fertilized egg? Does the 'mechanism' by which the process of 'development according to pattern' is enacted, follow more the paradigm of a pendulum clock or a planetary system, or more the kind of 'statistical type of law' illustrated by the laws of vapour pressure. Needless to say, it is infinitely more complicated than either. What are the chromosomes?

They are neither gaseous nor fluid; they are tiny infinitely complicated solid bodies - though they might just well be called - enormously big, infinitely complicated, organic molecules. They are aggregates of hundreds of thousands, nay millions of atoms, bound together by the same kind of forces that produce the rigid structures of solids and crystals. To give an idea of the relationship we could show a model of a simple crystal.

Give a model of, e.g. CACO3, any crystal built out of 3 or 4 different kinds of atoms; more than one 'cell' must be shown, at least 3 or 4 in every direction.

In this model the red balls might mean Calcium atoms, the black balls....., the white balls......, etc.. One would see that here the same pattern is repeated again and again, actually many thousand times, to enable one to form an idea of even a tiny grain of a crystal of CaCO3. Now one should imagine a somewhat similar structure, just as rigid, but without the mosaic of varying structure. This picture is certainly not correct, but somewhat near the true structure of a chromosome.

How do we know? Because in no other way could such a vast amount of specific determination of the future pattern of the organism be pre-determined in such tiny specks of matter, codified in a form that resists disturbances (page 5) from outside and carries the pattern of that specific organism in continual repetition, with only small and gradual changes from generation to generation through hundreds of thousands of centuries.

The point is that, to all appearances, each region or part or district of the huge chromosome molecule plays an individual role in directing the sequence of marvelously well-determined events that takes place from the moment of the fertilization of the egg, until the phase, thus inaugurated, ends by so-called death - an individual role, one one of statistical contribution, as that of molecules in inorganic processes. In this respect (and also by being solid structures) the chromosomes and their several parts are more analogous to a driving gear and its cog-wheels than to the molecules of inorganic matter.

Prepared by Professor E. Schrodinger
Dublin Institute for Advanced Studies
25 April 1950

quote ends.
From NA Work 25/23: Specialist Scripts: Biology, parts 1,2, and 3.

No comments:

Post a Comment