And thirdly, there is the so-called many worlds or, better, many universes idea. And this is what I had in mind when I was talking about history at the beginning. Namely, that if at every microinstant of time the universe splits into alternate universes in which things go differently, and that if there is at the same moment an enormously, tremendously large, perhaps infinitely large array of other universes with other laws of nature and other constants, then our existence is not really that remarkable. There are all those other universes in which there isn't any life. We just, by accident, happen to be in the one that has life. It's a little bit like a winning hand at bridge. The chance of, let's say, being dealt twelve spades is an absurdly low probability. But it is as likely as getting any other hand, and therefore, eventually, if you play long enough, some universe has to have our laws of nature.
Well, I believe that we are seeing a still largely unexplored area of physics being projected upon by the same sorts of human hopes and fears that have characterized the entire history of the Copernican debate.
I wanted to say just two final things. One is, if the very strong version of the anthropic principle is true, that is, that God-we might as well call a spade a spade-created the universe so that humans would eventually come about, then we have to ask the question, what happens if humans destroy themselves? That would make the whole exercise sort of pointless. So if only we could believe the strong version, we would have to conclude either (a) that an omnipotent and omniscient God did not create the universe, that is, that He was an inexpert cosmic engineer, or (b) that human beings will not self-destruct. Either alternative, it seems to me, is a matter of some interest, would be worth knowing. But there is a dangerous fatalism lurking here in the second branch of that fork in this road.
Well, I would like to conclude, then, by just a few lines of poetry, this one from Rupert Brooke, called "Heaven."
FISH (fly-replete, in depth of June, Dawdling away their wat'ry noon) Ponder deep wisdom, dark or clear, Each secret fishy hope or fear.
Fish say, they have their Stream and Pond; But is there anything Beyond? This life cannot be All, they swear, For how unpleasant, if it were!
One may not doubt that, somehow, Good Shall come of Water and of Mud; And, sure, the reverent eye must see A Purpose in Liquidity.
We darkly know, by Faith we cry, The future is not Wholly Dry. Mud unto mud!-Death eddies near- Not here the appointed End, not here!
But somewhere, beyond Space and Time, Is wetter water, slimier slime! And there (they trust) there swimmeth One, Who swam ere rivers were begun,
Immense, of fishy form and mind, Squamous, omnipotent, and kind; And under that Almighty Fin, The littlest fish may enter in.
Three
Once upon a time, the best minds of the human species believed that the planets were attached to crystal spheres, which explained their motion both daily and over longer periods of time. We now know this is not true in several •ways, one of which is that the Copernican theory explains the observed motion to higher precision and with a more modest investment of assumptions. But we also know this is not true, because we have sent spacecraft to the outer solar system with acoustic micro-meteorite detectors-and there was no sound of tinkling crystal as the spacecraft passed the orbits of Mars or Jupiter or Saturn. We have direct evidence that there are no crystal spheres. Now, Copernicus did not have such evidence, of course, but nevertheless his more indirect approach has been thoroughly validated. Now, when they were believed to exist, how was it that these spheres moved? Did they move on their own? They did not. Both in classic and in medieval times, it was prominently speculated that gods or angels propelled them, gave them a twirl every now and then.
The Newtonian gravitational superstructure replaced angels with GMm/r2, which is a little more abstract. And in the course of that transformation, the gods and angels were relegated to more remote times and more distant causality skeins. The history of science in the last five centuries has done that repeatedly, a lot of walking away from divine microintervention in earthly affairs. It used to be that the flowering of every plant was due to direct intervention by the Deity. Now we understand something about plant hormones and phototropism, and virtually no one imagines that God directly commands the individual flowers to bloom.
So as science advances, there seems to be less and less for God to do. It's a big universe, of course, so He, She, or It could be profitably employed in many places. But what has clearly been happening is that evolving before our eyes has been a God of the Gaps; that is, whatever it is we cannot explain lately is attributed to God. And then after a while, we explain it, and so that's no longer God's realm. The theologians give that one up, and it walks over onto the science side of the duty roster.
We've seen this happen repeatedly. And so what has happened is that God is moving-if there is a real God of the Western sort, I am, of course, speaking only metaphorically- God has been evolving toward what the French call un roi faineant-a do-nothing king-who gets the universe going, establishes the laws of nature, and then retires or goes somewhere else. This is not far at all from the Aristotelian view of the unmoved prime mover, except that Aristotle had several dozen unmoved prime movers, and he felt that this was an argument for polytheism, something that is often overlooked today.
Well, I want to describe one of the most major gaps that is in the course of being filled in. (We cannot surely say it is fully filled in yet.) And that has to do with the origin of life.
There was, and in some places still is, a very intense controversy about the evolution of life, about the scandalous suggestion that humans are closely related to the other animals and especially to nonhuman primates, that we had an ancestor who would be, if we met it on the street, indistinguishable from a monkey or an ape. A great deal of the attention has been devoted to the evolutionary process, where, as I tried to indicate earlier, the key impediment to its being intuitively obvious is time. The period of time available for the origin and evolution of life is so much vaster than an individual human lifetime that processes that proceed at paces too small to see during an individual lifetime might nevertheless be dominant over 4,000 million years.
One way to think about this, by the way, is the following: Suppose your father or mother-let's say father for the sake of definiteness-walked into this room at the ordinary human pace of walking. And suppose just behind him was his father. And just behind him was his father. How long would we have to wait before the ancestor who enters the now-open door is a creature who normally walked on all fours? The answer is a week. The parade of ancestors moving at the ordinary pace of walking would take only a week before you got to a quadruped. And our quadruped ancestors are, after all, only a few tens of millions of years ago, and that's 1 percent of geological time. So there are many different ways of calibrating this immense vista of time that was necessary to evolve the complexity and beauty of the natural world, and this is one.
Now, the evidence for evolution is ubiquitous, and I will not spend a great deal of time on it here. But just to remind everyone. The centerpiece is, of course, the fossil record. Here we find a correlation of geological strata otherwise identifiable and datable by radioactive dating and other methods-with fossils, the remains, the hard parts-of organisms largely now extinct.