Broca's Brain: The Romance of Science

billion galaxies, each containing more than a hundred billion stars-speaks to us of the inconsequentiality of human events in the cosmic context. We see a universe simultaneously very beautiful and very violent. We see a universe that does not exclude a traditional Western or Eastern god, but that does not require one either.

My deeply held belief is that if a god of anything like the traditional sort exists, our curiosity and intelligence are provided by such a god. We would be unappreciative of those gifts (as well as unable to take such a course of action) if we suppressed our passion to explore the universe and ourselves. On the other hand, if such a traditional god does not exist, our curiosity and our intelligence are the essential tools for managing our survival. In either case, the enterprise of knowledge is consistent with both science and religion, and is essential for the welfare of the human species.

CHAPTER 24

GOTT AND THE TURTLES

Now entertain conjecture of a time

When creeping murmur and the poring dark

Fills the wide vessel of the universe.

WILLIAM SHAKESPEARE,

Henry V, Act IV, Prologue

IN THE EARLIEST myths and legends of our species, there is a common and understandable view of the cosmos: it is anthropocentric. There were gods, to be sure. But the gods had feelings and weaknesses and were very human. Their behavior was seen as capricious. They could be propitiated by sacrifice and prayer. They intervened regularly in human affairs. Various factions of gods supported opposing sides in human warfare. The Odyssey expresses a generally held view that it is wise to be kind to strangers: they may be gods in disguise. Gods mate with humans, and the offspring are generally indistinguishable, at least in appearance, from people. The gods live on mountains or in the sky, or in some subterranean or submarine realm-at any rate, far off. It was difficult unambiguously to come upon a god, and so it was hard to check a story told about the gods. Sometimes their actions were controlled by more powerful beings yet, as the Fates controlled the Olympian gods. The nature of the universe as a whole, its origin and fate, were not considered well understood. In the Vedic myths, doubt is raised not only about whether the gods created the world but even about whether the gods know who did create it. Hesiod in his “Cosmogony” says that the universe was created from (or maybe by) Chaos-perhaps only a metaphor for the difficulty of the problem.

Some ancient Asian cosmological views are close to the idea of an infinite regression of causes, as exemplified in the following apocryphal story: A Western traveler encountering an Oriental philosopher asks him to describe the nature of the world:

“It is a great ball resting on the flat back of the world turtle.”

“Ah yes, but what does the world turtle stand on?”

“On the back of a still larger turtle.”

“Yes, but what does he stand on?”

“A very perceptive question. But it’s no use, mister; it’s turtles all the way down.”

We now know that we live on a tiny dust mote in an immense and humbling universe. The gods, if they exist, no longer intervene daily in human affairs. We do not live in an anthropocentric universe. And the nature, origin and fate of the cosmos seem to be mysteries far more profound than they were perceived to be by our remote ancestors.

But the situation is once again changing. Cosmology, the study of the universe as a whole, is becoming an experimental science. Information obtained by optical and radio telescopes on the ground, by ultraviolet and X-ray telescopes in Earth orbit, by the measurement of nuclear reactions in laboratories, and by determinations of the abundance of chemical elements in meteorites, is shrinking the arena of permissible cosmological hypotheses; and it is not too much to expect that we will soon have firm observational answers to questions once considered the exclusive preserve of philosophical and theological speculation.

This observational revolution began from an unlikely source. In the second decade of this century there was-as there still is-in Flagstaff, Arizona, an astronomical facility called the Lowell Observatory, established by none other than Percival Lowell, for whom the search for life on other planets was a consuming passion. It was he who popularized and promoted the idea that Mars was crisscrossed with canals, which he believed to be the artifacts of a race of beings enamoured of hydraulic engineering. We now know that the canals do not exist at all. They apparently were the product of wishful thinking and the limitations of observing through the Earth’s murky atmosphere.

Among his other interests, Lowell was concerned with the spiral nebulae-exquisite pinwheel-shaped luminous objects in the sky, which we now know to be distant collections of hundreds of billions of individual stars, like the Milky Way Galaxy of which our Sun is a part. But at that time there was no way to determine the distance to these nebulae, and Lowell was interested in an alternative hypothesis-that the spiral nebulae were not enormous, distant, multistellar entities, but rather smaller, closer objects which were the early stages of the condensation of an individual star out of the interstellar gas and dust. As such gas clouds contract under their self-gravitation, the conservation of angular momentum requires that they speed up to rapid rotation and shrink to a thin disc. Rapid rotation can be detected astronomically by spectroscopy, letting light from a distant object pass consecutively through a telescope, a narrow slit and a glass prism or other device which spreads white light out into a rainbow of colors. The spectrum of starlight contains bright and dark lines here and there in the rainbow, images of the slit of the spectrometer. An example is the bright yellow lines emitted by sodium, apparent as we throw a small piece of sodium into a flame. Material made of many different chemical elements will show many different spectral lines. The displacement of these spectral lines from their usual wavelengths when the light source is at rest gives us information on the velocity of the source toward and away from us-a phenomenon called the Doppler effect and familiar to us, in the physics of sound, as the increase or decrease in the pitch of an automobile horn as the car rapidly approaches or recedes.

Lowell is thought to have asked a young assistant, V. M. Slipher, to check the larger spiral nebulae to determine whether one side showed spectral lines shifted toward the red and the other toward the blue, from which it would be possible to deduce the speed of rotation of the nebula. Slipher investigated the spectra of the nearby spiral nebulae but found to his amazement that almost all of them showed a red shift, with virtually no sign of blue shifts anywhere in them. He had found not rotation, but recession. It was as if all the spiral nebulae were retreating from us.

A much more extensive set of observations was obtained in the 1920s at the Mount Wilson Observatory by Edwin Hubbell and Milton Humason. Hubbell and Humason developed a method of determining the distance to the spiral nebulae; it became apparent that they were not condensing gas clouds relatively nearby in the Milky Way Galaxy, but themselves great galaxies millions or more light-years away. To their amazement, they also found that the more distant the galaxy, the faster it was receding from us. Since it is unlikely that there is anything special about our position in the cosmos, this is best understood in terms of a general expansion of the universe; all galaxies recede from all others so that an astronomer on any galaxy would observe all other galaxies apparently retreating.

If we extrapolate such a mutual recession back into the past, we find that there was a time-perhaps 15 billion or 20 billion years ago-when all of the galaxies must have been “touching”; that is, confined to an extremely small volume of space. Matter in its present form could not survive such astonishing compressions. The very earliest stages of that expanding universe must have been dominated by radiation rather than matter. It is now