Davies - The Fifth Miracle: The Search for the Origin and Meaning of Life

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ALSO BY PAUL DAVIES

The Physics of Time Asymmetry

Space and Time in the Modern Universe

The Runaway Universe

The Forces of Nature

Other Worlds

The Search for Gravity Waves

The Edge of Infinity

The Accidental Universe

Quantum Fields in Curved Space (with N. D. Birrell)

God and the New Physics

Superforce

Quantum Mechanics

The Ghost in the Atom (with J. R. Brown)

The Cosmic Blueprint

Fireball

Superstrings: A Theory of Everything? (with J. R. Brown)

The New Physics (editor)

The Matter Myth (with J. Gribbin)

The Mind of God: The Scientific Basis for a Rational World

The Last Three Minutes

Are We Alone? The Philosophical Basis of the Search for Extraterrestrial Life

About Time: Einsteins Unfinished Revolution

The Big Questions (with Phillip Adams)

More Big Questions (with Phillip Adams)

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Designed by Ruth Lee

The Library of Congress has cataloged the hardcover edition as follows:

Davies, P. C. W.

The fifth miracle : the search for the origin and meaning of life / Paul Davies.

p. cm.

Includes bibliographical references and index.

1. LifeOrigin. 2. Life. I. Title.

QH325.D345 1999

576.8'3dc21

98-33421

CIP

ISBN 0-684-83799-4

0-684-86309-X (Pbk)

ISBN 978-1-4391-2682-0 (eBook)

In memory of Keith Runcorn

I N A UGUST 1996, the world was electrified by news that an ancient meteorite may contain evidence for life on Mars. President Clinton himself conveyed the story to the public and a startled scientific community. The momentous implications of the discovery, if such it was, were expressed in appropriate superlatives. This memorable event marked one of the few occasions when a scientific result had a direct impact on the public. Yet the plaudits and the banter glossed over the true significance of the findings.

For several years, scientists have been dramatically rethinking their ideas about the origin of life. The textbooks say that life began in some tepid pool on the Earths surface, billions of years ago. Increasingly, however, the evidence points to a very different scenario. It now appears that the first terrestrial organisms lived deep underground, entombed within geothermally heated rocks in pressure-cooker conditions. Only later did they migrate to the surface. Astonishingly, descendants of these primordial microbes are still there, kilometers beneath our feet.

Until a few years ago, nobody suspected that life could exist in such a harsh environment, but once it was accepted that organisms can flourish beneath the Earths surface, an even more exotic possibility presented itself. Perhaps microbes also lurk in the rocks beneath the surface of Mars? The discovery of a Martian rock containing possible fossilized bacteria was a major boost to this theory. But that was not all. Scientists were quick to spot a fascinating consequence. It could be that life actually began on Mars and then traveled to Earth in a meteorite.

The feverish excitement surrounding the Martian meteorite concealed deep divisions among the experts over the interpretation of the evidence. If confirmed, it could mean either that life has started twice in the solar system, or, alternatively, that it has spread from one planet to another. Exciting though it would be to discover that organisms can leap from planet to planet, the ultimate origin of life would still be left as an unresolved enigma if the latter explanation were correct.

How, precisely, did life begin? What physical and chemical processes can transform nonliving matter into a living organism? This much tougher problem remains one of the great scientific challenges of our age. It is currently being tackled by an army of chemists, biologists, astronomers, physicists, and mathematicians. On the basis of their research, many of them fervently conclude that the laws of nature are, to put it bluntly, rigged in favor of life. They expect that life will form wherever conditions permitnot just on Mars, but throughout the universe; and, more provocatively, in a test tube. If they are right, it will mean that life is part of the natural order of things, and that we are not alone.

Belief that life is written into the laws of nature carries a faint echo of a bygone religious age, of a universe designed for habitation by living creatures. Many scientists are scornful of such notions, insisting that the origin of life was a freak accident of chemistry, unique to Earth, and that the subsequent emergence of complex organisms, including conscious beings, is likewise purely the chance outcome of a gigantic cosmic lottery. At stake in this debate is the very place of mankind in the cosmoswho we are and where we fit into the grand scheme.

Astronomers think that the universe began in a big bang between ten and twenty billion years ago. Its explosive birth was accompanied by a flash of intense heat. During the first split second, the basic physical forces and fundamental particles of matter emerged. By the time that one second had elapsed, the essential materials of the cosmos had already formed. Space was everywhere filled with a soup of subatomic particlesprotons, neutrons, and electronsbathed in radiation at a temperature of ten billion degrees.

By present standards the universe at that epoch was astonishingly featureless. The cosmic material was spread through space with almost perfect uniformity. The temperature was the same everywhere. Matter, stripped down to its basic constituents by the fierce heat, was in a state of extraordinary simplicity. A hypothetical observer would have had no inkling from this unpromising state that the universe was primed with awesome potentialities. No clue would betray that, several billion years on, trillions of blazing stars would organize themselves into billions of spiral galaxies, that planets and crystals, clouds and oceans, mountains and glaciers would arise, that trees and bacteria and elephants and fish would inhabit one of these planets, and that this world would ring to the sound of human laughter. None of these things could be foretold.

As the universe expanded from its uniform primeval state, it cooled. And with lower temperatures came more possibilities. Matter was able to aggregate into vast amorphous structuresthe seeds of todays galaxies. Atoms began to form, paving the way for chemistry and the formation of solid physical objects.

Many wonderful phenomena have emerged in the universe since that time: monstrous black holes weighing as much as a billion suns that eat stars and spew forth jets of gas; neutron stars spinning a thousand times a second, their material crushed to a billion tons per cubic centimeter; subatomic particles so elusive that they could penetrate light-years of solid lead; ghostly gravitational waves whose fleeting passage leaves no discernible imprint at all. Yet, amazing though these things may be, the phenomenon of life is more remarkable than all of them put together. It didnt bring about any sudden and dramatic alterations on the cosmic scene. In fact, if life on Earth is anything to go by, the changes it has wrought have been extremely gradual. Nevertheless, once life was initiated, the universe would never be the same. Slowly but surely it has transformed Planet Earth. And by offering a route to consciousness, intelligence, and technology, it has the potential to change the universe.