This omission mocked the universality of natural law. How could atoms and photons on one side of the universe behave exactly like atoms and photons on the other side, if they had never communicated with one another? To visualize the problem, imagine a marching band gathered on a greensward, ready to start playing as soon as the drummer standing at the center delivers a downbeat. At the moment that time begins, the band members march rapidly away from the drummer in all directions, at nearly the speed of sound. The result will be chaos. Only a few musicians will hear the downbeat; most will go hurrying away, unable to hear it, and so will not know when to start playing or what to play. In cosmological terms, the speed of sound is replaced by the speed of light, the fastest velocity at which information can be exchanged. The standard model required that the particles of the early universe depart before they could get their marching orders: Without hearing the drumbeat, then, how did the first quarks “know” how to be quarks, and all the photons learn the rules that govern photons? Had such been the true tale of genesis, nearly every cluster of galaxies would be made of different stuff and would obey different laws. Instead, the observable universe is a lawful unity. How so?
At first blush, inflation would seem only to make matters worse, since it postulates an even speedier cosmic expansion rate. But actually it resolves the dilemma, by permitting the material of the very early universe to remain together, in causal contact, for a relatively long period before inflation began. The band members now have time to listen for the downbeat before leaving; then they board the inflationary express, which goes so fast that they soon catch up with the linear expansion rate. Now they all have their marching orders when they go, and all, consequently, can play the same tune. Inflation thus explained why the cosmic background radiation is isotropic, and why the quarks and electrons of the earth are identical to those of the Coma cluster of galaxies.*
All of which was cheering to Ed Tryon and his little cadre of vacuum genesis enthusiasts. The inflationary hypothesis made vacuum genesis appear more plausible, by admitting the possibility that the universe could have started as a relatively modest, cold particle, with the heat of the big bang coming later, in the blast of fire released by latent vacuum energy when the inflationary epoch ended. And inflation painted the vacuum in new and more vibrant colors. Once one entertained the idea that all the matter and energy in the universe erupted from a vacuum at a brief but finite interval after the beginning of time, it no longer seemed quite so preposterous to imagine that the whole affair might have begun as a vacuum.
Guth, for his part, became an aficionado of the vacuum, regarding it less as emptiness than as a cornucopia. He calculated that only a small amount of vacuum flux might, if sufficiently concentrated, have been enough to set off inflation. If, then, our universe began as a quantum flux—a sort of bubble—in a primordial vacuum, other universes might reasonably be imagined to have formed from other bubbles. Moreover, Guth conjectured, creation need not necessarily be relegated solely to the past, but might happen again: If a vacuum instability in our universe were to blister in such a way as to form another universe, we would never know it. From our perspective, the only trace of the new creation event would be a pinpoint of infinite spatial curvature. As it happens, there appear to be such places here and there, in the infinitely curved regions of space surrounding black holes. Conceivably, every time a giant star goes supernova and its remnant collapses to form a black hole it might give birth to a new universe, on another side of spacetime.
If so, Guth speculated, the artificial creation of a black hole through application of an advanced technology could create another universe. Nor would such a custom-made black hole have to be terribly massive. “You might even be able to start a new universe using energy equivalent to just a few pounds of matter,” Guth suggested, in a 1987 interview. “Provided you could find some way to compress it to a density of about 1075 grams per cubic centimeter, and provided you could trigger the thing, inflation would do the rest.” And if we could do it, so, perhaps, could someone else have done it long ago. “For all we know,” said Guth, who had a gift for the laconic statement of radical ideas, “our own universe may have started in someone’s basement.”9
If only to get our feet back on the ground, let it be noted that there were problems with both the inflationary universe and vacuum genesis. Inflation smoothed out the early universe, all right, but did so with such a vengeance that theorists had trouble coaxing enough lumpiness out of the equations to allow for the formation of galaxies and of the superclusters (and, evidently, meta-superclusters) in which they are gathered. Vacuum genesis suffered from a lingering suspicion that, if anything, it was just not crazy enough. The quantum vacuum is a characteristic of the universe we live in—virtual particles today boil in the space between real particles —but who was to say that the same was true of the “vacuum” that allegedly preceded the beginning of the expansion of the universe? That vacuum, after all, ought to have been very different from the one we encounter in the present-day universe: Presumably its relativistic curvature was infinite and its matter content zero, and neither is true of cosmic space today.
Some theorists proposed, instead, a set of even stranger but at least equally promising hypotheses. Together, these ideas went by the name of “quantum genesis.” Their approach involved taking the random nature of quantum flux to heart and enshrining it as the ruling law of the extremely early universe. Here a pioneer was Stephen Hawking, holder of Newton’s old chair as Lucasian Professor of Mathematics at Cambridge University. Described by colleagues as “the nearest thing we have to a living Einstein,” Hawking carried on a productive career in physics despite suffering from ALS, a disease that attacks the central nervous system. He worked from a wheelchair, writing and communicating by means of a computer controlled by a toggle that he manipulated with one finger. He expressed impatience less with his affliction than with people who worshiped him as a hero, pitied him as a sick man, or otherwise treated him as if he were any different from any other genius. In his postdoctoral days Hawking and his colleague Roger Penrose demonstrated that general relativity implies that the universe began in a “singularity,” a state of infinitely curved space in which the laws of relativity break down; this proved, as Hawking put it, that “relativity predicts its own downfall.”10
But quantum theory might function where relativity did not, and in later years Hawking began to explore the prospect of understanding the origin of the universe in terms of quantum probabilities. His tools included “imaginary time”—a kind of time measured in terms of imaginary numbers—and Richard Feynman’s “sum over histories” method of doing quantum mechanics.
Imaginary numbers make no sense when handled by customary mathematical rules. An example is the square root of —1, which will produce an “error” message if demanded of an electronic calculator. They work quite well, however, according to their own rules; imaginary numbers have been employed to excellent effect, for instance, in hydrodynamics. Feynman’s “sum over histories” strategy consists of calculating all the possible past trajectories of a particle, and arriving, via quantum probabilities, at the most likely path by which the particle reached its observed state. Hawking, working with the American cosmologist James Hartle at the University of California at Santa Barbara, applied this method to the universe as a whole. Speaking via an interpreter, in a vaulted hardwood hall at Padua where Galileo used to lecture, Hawking announced that he had been able to derive the quantum wave function of the universe as a whole. “The universe today is accurately described by classical general relativity,” he said.
However, classical relativity predicts that there will be a singularity in the past, and near that singularity, the curvature [of space] will be very high, classical relativity will break down, and quantum effects will have to be taken into account. In order to understand the initial conditions of the universe, we have to turn to quantum mechanics, and the quantum state of the universe will determine the initial condit
ions for the classical universe. So today I want to make a proposal for the quantum state of the universe.11
What emerged was a tale of cosmic evolution possessed of a strangely alien beauty. All world lines diverge from the singularity of genesis, Hawking noted, like longitude lines proceeding from the north pole on a globe of the earth. As we travel along our world line we see the other lines moving away from us, as would an explorer sailing south along a given longitude; this is the expansion of the universe. Billions of years hence the expansion will halt and the universe will collapse, eventually to meld into another fireball at the end of time. There is, however, no meaning to the question of when time began, or when it will end: “If the suggestion that spacetime is finite but unbounded is correct,” said Hawking on another occasion, “the big bang is rather like the North Pole of the earth. To ask what happens before the big bang is a bit like asking what happens on the surface of the earth one mile north of the North Pole. It’s a meaningless question.”12
Imaginary time in Hawking’s view was the once and future time, and time as we know it but the broken-symmetry shadow of that original time. When a hand calculator cries “error” upon being asked the value of the square root of —1, it is telling us, in its way, that it belongs to this universe, and knows not how to inquire into the universe as it was prior to the moment of genesis. And that is the state of all science, until we have the tools in hand to explore the very different regime that pertained when time began.
Another quantum approach to genesis, championed by John Wheeler, emphasized the quantization of space itself. Just as matter and energy are made of quanta, went this line of reasoning, so space itself ought to be quantized at its foundations. Wheeler liked to compare quantum space to the sea: Viewed from orbit, the surface of the ocean looks smooth, but if we set out in a rowboat on the surface, “we see foam and froth and breaking waves. And that foam and froth is how we picture the structure of space down at the very smallest scales.”13
In the present-day universe, the foamy structure of space manifests itself in the constant blooming forth of virtual particles. In the extremely early universe—meaning prior to the Planck time—space would have been a very rough sea indeed, and its storm-tossed quantum flux might have dominated all particle interactions. How, here, do we find our bearings?
Wheeler—an elder statesman who learned his science from Einstein and Bohr and in turn educated a whole generation of physicists—thought the answer lay in spacetime geometry: “What else is there out of which to build a particle except geometry itself?”14 he asked. Wheeler compared the quantum flux of the early universe to a complicated sailor’s knot of a kind that looks impossibly tangled, yet will fall apart if one can find the end of the rope and give it a tug in the right way. The knot in his simile is the hyperdimensional geometry of the original universe, the untangled rope the universe we inhabit today. Penrose had said, “I do not believe that a real understanding of the nature of elementary partides can ever be achieved without a simultaneous deeper understanding of the nature of spacetime itself.”15 For Wheeler, this was true of the universe as a whole:
“Space is a continuum.” So bygone decades supposed from the start when they asked, “Why does space have three dimensions?” We, today, ask instead, “How does the world manage to give the impression it has three dimensions?” How can there be any such thing as a spacetime continuum except in books? How else can we look at “space” and “dimensionality” except as approximate words for an underpinning, a substrate, a “pre-geometry,” that has no such property as dimension?16
To answer such questions, Wheeler argued, science would somehow have to bootstrap itself into a new realm, a world of “law without law,” in which, as taught by the quantum indeterminacy principle, the answer depends upon the question asked. Wheeler recalled being the subject in a game of twenty questions. He left the room for a period during which the answer was to be decided upon by the other players, then returned and started asking questions. The answers were progressively slower in coming, until Wheeler finally guessed, “Cloud,” and was told, to general amusement, that he was right. When his friends stopped laughing they explained that they had been playing a trick on Wheeler: There had originally been no right answer; his friends had agreed to formulate their answers so that each would be consistent with the answers given to his previous questions. “What is the symbolism of the story?” asked Wheeler.
The world, we once believed, exists “out there” independent of any act of observation. The electron in the atom we once considered to have at each moment a definite position and a definite momentum. I, entering, thought the room contained a definite word. In actuality the word was developed step by step through the questions I raised, as the information about the electron is brought into being by experiment that the observer chooses to make; that is, by the kind of registering equipment that he puts into place. Had I asked different questions or the same questions in a different order I would have ended up with a different word as the experimenter would have ended up with a different story for the doings of the electron. … In the game no word is a word until that word is promoted to reality by the choice of questions asked and answers given. In the real world of quantum physics, no elementary phenomenon is a phenomenon until it is a recorded phenomenon.17
We are left, then, with an image of genesis as a soundless and insubstantial castle, where our eyes cast innovative, Homeric beams and the only voices are our own. Having ushered ourselves in and having reverently and diligently done our scientific homework, we ask, as best we can frame the question, how creation came to be. The answer comes back, resounding through vaulted chambers where mind and cosmos meet. It is an echo.
*“Initial” conditions in cosmology are seldom absolutely initial, since nobody yet knows how to calculate the state of matter and space-time prior to the Planck time, which culminated at about 10−43 second ABT. One instead designates as “initial” some point subsequent to the Planck epoch. For most purposes this is regarded as quite initial enough.
*The sphere can be in many dimensions; that is another question, addressed by the supersymmetry theories, which did not as yet prescribe a timetable describing when the young universe allegedly collapsed its ten or so dimensions into three of space and one of time.
*Inflation theory indicates that the universe is many billions of times greater in volume than had been estimated in the old big bang model. The observable universe, however, is thought to constitute but a fraction of the universe as a whole: Its limits are determined less by space than by time, in that we can see only those events the light from which has had time to reach Earth. If, for instance, the first stars began to shine thirteen billion years ago, then no observer will see stars any farther than thirteen billion light-years away, regardless of how large the universe as a whole may be.
19
MIND AND MATTER
Life, like a dome of many-colored glass, Stains the white radiance of Eternity.
—Shelley
A sad spectacle. If they be inhabited, what a scope for misery and folly. If they not be inhabited, what a waste of space.
—Thomas Carlyle
The scientific developments we have been discussing in this book have worked, however inadvertently, to implicate and involve our species in the wider universe. Astronomy, in shattering the crystalline spheres that had been said to seal off the earth from the aethereal realms above the moon, placed us in the universe. Quantum physics cracked the metaphorical pane of glass that had been assumed to separate the detached observer from the observed world; we are, we found, unavoidably entangled in that which we study. Astrophysics, in determining that matter is the same everywhere and that it everywhere obeys the same rules, laid bare a cosmic unity that extends from nuclear fusion in stars to the chemistry of life. Darwinian evolution, in indicating that all species of earthly life are related and that all arose from ordinary matter, made it clear that there is no wall dividing us from our fellow creature
s on Earth, or from the planet that gave us all life—that we are such stuff as worlds are made of.
The conviction that we are in some sense at one with the universe had of course been promulgated many times before, in other spheres of thought. Yahweh fashioned Adam out of dust; Heraclitus the Greek wrote that “all things are one;” Lao-tzu in China depicted man and nature alike as ruled by a single principle (“I call it the Tao”); and a belief in the unity of humankind with the cosmos was widespread among preliterate peoples, as evidenced by the Suquamish Indian chief Seattle, who declared on his deathbed that “all things are connected, like the blood which unites one family. It is all like one family, I tell you.” But there is something striking about the fact that the same general view has arisen from sciences that pride themselves on their clearheaded pursuit of objective, empirical fact. From the chromosome charts and fossil records that chart the interrelatedness of all living things on Earth to the similarity of the cosmic chemical abundance to that of terrestrial biota, we find indications that we really are a part of the universe at large.
This scientific verification of our involvement in the workings of the cosmos has of course many implications. One of them—the subject of this chapter—is that, if intelligent life has evolved on this planet, it may have also done so elsewhere.* Darwin’s theory of evolution, though it does not explain away the ancient conundrum of why there is such a thing as life, does make it clear that life may arise from ordinary matter and evolve into an “intelligent” form, at least on an Earthlike planet orbiting a sunlike star. As there are plenty of sunlike stars (over ten billion of them in the Milky Way galaxy alone), and, presumably, more than a few Earthlike planets, we can speculate that we are not the only species ever to have studied the universe and wondered about our role in it.
Coming of Age in the Milky Way Page 38
