Saturday, July 29, 2006

Hume and Darwin

A week or so ago I noticed a conjunction between the conjectures of David Hume and Charles Darwin (rudimentary sketch of a childish god, 7/20/06). Both men believed that God is not present in the world, guiding every thought and deed, determining every cause and its effect. Rather, they believed in a first-cause God, one that set in motion the process that is for us the unfolding universe and its contents. In putting forth their conclusions, both are very cautious about making inferences from weak evidence, and Hume in particular draws attention to the poverty of hard data available in his time. Considering what few facts we do have, he says it doesn't make sense for us to believe that some form of active intelligence ("reason") is the motive force in the universe. First, the facts don't point strongly to intelligent design: "[It is no] less intelligible, or less conformable to experience to say, that the world arose by vegetation from a seed shed by another world, than to say that it arose from a divine reason or contrivance." Next, taking this a step further, he says our experience suggests that natural processes of reproduction in plants and animals ("vegetation" and "generation") came before reason and instinct: "Judging by our limited and imperfect experience, generation has some privileges above reason: For we see every day the latter arise from the former, never the former from the latter." He is saying that experience leads us to conclude that our intelligence in a product of natural processes.

Putting the thought in Darwin's terms, it's possible to believe that Hume is saying our ability to reason is a product of evolution.

Hume, always cautious, says that the processes that underly "vegetation" and "generation" are not known and -- he reminds us -- for all we know there are many such principles -- governing rules, laws of nature -- about which we know nothing. But it's clear he's talking about orderly systems, symetries. Of the systems of "vegetation" and "generation" he say, "A tree bestows order and organization on that tree which springs from it, without knowing the order: an animal, in the same manner, on its offspring: a bird, on its nest." Hume does not have a theory that explains how the process of generation might produce reason, but from the evidence available to him he says he says there is a process -- of order and organization -- that makes this possible.

As I say both men argue that the unfolding of the universe is not predetermined, but accidental. There is no omnipresent God who directs all that occurs in the world and the universe. But I believe they also both recognize that the accidental -- contingent -- unfolding of all things is not without pattern. Experience -- especially the work of physicists -- shows us symetries everywhere we look (DNA molecules, atoms, snowflakes). As Michio Kaku says: "[For all we know,] all the beauty and symmetry we see around us, including sea shells, ice crystals, galaxies, molecules, even sub-atomic particles, are nothing but the pieces of the original symmetry that broke at the instant of the big bang."

Darwin and Hume had different purposes. Darwin's was to describe the natural process by which plants and animals evolve and Hume's was to show the weakness in the argument for intelligent design. Darwin was much more a scientist than a philosopher, Hume much more a philosopher than a scientist. Still, as I said at the outset, there's a conjuction in their thinking.

Hume appears to be a precusor of Darwin. He didn't use the term evolution or describe anything that resembled natural selection, but he said evidence pointed to a system of orderly unfolding which is self-directed, not guided by an intelligence: "To say that all this order in animals and vegetables proceeds ultimately from design is begging the question; nor can that great point be ascertained otherwise than by proving a priori, both that order is, from its nature, inseparably attached to thought, and that it can never, of itself, or from original unknown principles, belong to matter."

After I wrote last week's post on Darwin and Hume, I looked for sources that explained the relationship between the two -- working as they were more than a century apart. There doesn't seem to be much. The book Darwin's Dangerous Idea Evolution and the Meanins of Life, by Daniel C. Dennett, describes Hume in contrast to Darwin rather than a precursor. An article by William B. Huntley in the Journal of the History of Ideas for 1972 (which is available behind the JSTOR paywall) does see Hume as a precursor, but uses other writings of Hume, not the Dialogues Concerning Natural Religion from which I've been quoting. He says that Darwin was influenced by reading Hume and by reading other authors who were themselved influenced by Hume. One extract: "The contributions of Hume to the world in which Darwin was to thrive were then several fold. The little section on animals was to Darwin, it would seem, more suggestive than definitive. The section on miracles probably may be seen as a general evaluation of a world view rather than a direct influence upon Darwin, but an important world view that helped those around Darwin appreciate the theory offered. The sections on theory of knowledge and necessary connection stated by Hume form certain methodological presuppositions that were important, indeed, in Darwin's century." {Source: William B. Huntley, "David Hume and Charles Darwin," Journal of the History of Ideas, 1972, Vol. 33, pp. 457-470.}


1. Here's the full quotation from Michio Kaku:
Physicists think a theory is beautiful if it can explain the largest amount of physical data with the simplest mathematical structures. Consider a snowflake. It is beautiful and symmetrical because it remains the same when we rotate it by 60 degrees. But more important, this symmetry is also extremely practical. If we are only given a piece of the snowflake, we can reconstruct the entire crystal by repeating a piece of it six times. Our equations must also be symmetrical: they must remain the same whenever we reshuffle space and time or sub-atomic particles among themselves.

But why does nature use symmetry to express its deepest secrets? No one knows. This is one of the greatest mysteries of all time. I suspect that this is because we are slowly reconstructing the original symmetries that existed at the instant of the big bang, uncovering bits and pieces of new symmetries along the way. If this picture is correct, all the beauty and symmetry we see around us, including sea shells, ice crystals, galaxies, molecules, even sub-atomic particles, are nothing but the pieces of the original symmetry that broke at the instant of the big bang.
2. It's worth your time to read all of Kaku's essay. Another teaser:
In the 1600s, Isaac Newton banished centuries of mysticism and black magic with the idea of "forces", reducing the universe to precise, mechanical forces acting on all bodies. Think of each force in the universe as a tiny arrow. The greater the force, the longer the arrow. For the first time, Newton could predict mathematically and precisely the motion of the planets, comets and rocks by adding up the lengths of the arrows acting on each object.

Then, in the 1800s, Michael Faraday introduced the next great concept, magnetic and electric "fields" that can permeate space. To Faraday, at every point in space, one could introduce a collection of numbers, called the field, which describe the electric, magnetic, and even nuclear forces.

“What if we are wrong, if our life's work contains a fatal flaw? I face this every day”

I use fields every day of my life. I daydream of fields. Just as a carpenter uses wood to create beautiful furniture, I use Faraday's fields to describe the forces of the universe. When string theory first emerged, it was a jumble of loose formulae and chaotic rules of thumb that filled sheaves of paper. I remembered the work of Faraday and decided to rewrite all those equations in the language of field theory: to write an equation 2 centimetres long that summarised string theory.

With my colleague Keiji Kikkawa, we wrote down the field theory of strings. Previously, most physicists believed that strings could split and re-form in many complex ways, making the theory hopelessly complicated and a field theory impossible to write.

My eureka moment came when I was teaching a class. For the benefit of the students, I began to draw the field lines and equipotential lines that emanate from an electron like a spider's web. Each equipotential line is a circle surrounding a charge. These circles get larger and larger, until they collide and merge with other circular equipotential lines encircling other charges - rather like throwing two stones in a pond and the waves from each eventually merging into a larger wave.

Suddenly it dawned on me that those equipotential lines/circular waves corresponded to closed strings colliding with other closed strings. Excited by this insight, I proved that these lines traced out precisely the geometry of colliding strings, making a field theory possible. It was astounding that a first-year class was tracing out the most complex interactions of strings in 10 dimensions. Our resulting string field equation is so short that it has even appeared on T-shirts.
3. Here's the close of the dialogue in which Hume expresses his thoughts tending toward evolution. It's excellent Humean wit.
The Brahmins assert, that the world arose from an infinite spider, who spun this whole complicated mass from his bowels, and annihilates afterwards the whole or any part of it, by absorbing it again, and resolving it into his own essence. Here is a species of cosmogony, which appears to us ridiculous; because a spider is a little contemptible animal, whose operations we are never likely to take for a model of the whole universe. But still here is a new species of analogy, even in our globe. And were there a planet wholly inhabited by spiders (which is very possible), this inference would there appear as natural and irrefragable as that which in our planet ascribes the origin of all things to design and intelligence, as explained by Cleanthes. Why an orderly system may not be spun from the belly as well as from the brain, it will be difficult for him to give a satisfactory reason.
4. You might remember that last week's post on this subject had as its starting point a paraphrase of Hume by Borges.

Here's the Borges text (in translation): "The world - David Hume writes - is perhaps the rudimentary sketch of a childish god, who left it half done, ashamed by his deficient work; it is created by a subordinate god, at whom the superior gods laugh; it is the confused production of a decrepit and retiring divinity, who has already died ('Dialogues Concerning Natural Religion', V. 1779)."

Contrast this elaboration of the theme by Hume: "And what surprise must we entertain, when we find him [i.e. God] a stupid mechanic, who imitated others, and copied an art, which, through a long succession of ages, after multiplied trials, mistakes, corrections, deliberations, and controversies, had been gradually improving? Many worlds might have been botched and bungled, throughout an eternity, ere this system was struck out: Much labour lost: Many fruitless trials made: And a slow, but continued improvement carried on during infinite ages of world-making."

This sounds a lot like a popularization of Darwin: evolution as progress, but I beleive it's not what either really thought. I believe the process they both described did not have this bias toward "improvement," but is rather ethically neutral.

6. Dennett does not credit Hume as a Darwin precursor because he believes that Hume himself did not believe the arguments he put in the mouth of his protagonist, Philo, in the Dialogues. I believe otherwise but cheerfully concede that you can't really pin Hume down on this point.

1 comment:

Gregory said...

Erasmus Darwin has a direct reference to Hume's Dialogues in Zoonomia, which Darwin had read as early as his days in Edinburgh:

> “The late Mr. David Hume, in his posthumous works [Dialogues], places the powers of generation much above those of our boasted reason; and adds, that reason can only make a machine, as a clock or a ship, but the power of generation makes the maker of the machine; and probably from having observed, that the greatest [401] part of the earth has been formed out of organic recrements; as the immense beds of limestone, chalk, marble, from the shells of fish; and the extensive provinces of clay, sandstone, ironstone, coals, from decomposed vegetables; all which have been first produced by generation, or by the secretions or organic life; he concludes that the world itself might have been generated, rather than created; that is, it might have been gradually produced from very small beginnings, increasing by the activity of its inherent principles, rather than by a sudden evolution of the whole by Almighty fiat. What a magnificent idea of the infinite power of THE GREAT ARCHITECT! THE CAUSE OF CAUSES! PARENT OF PARENTS! ENS ENTIUM!” E.Darwin - Zoonomia.