Coming of Age in the Milky Way (58 page)

Science is inherently open-ended and exploratory, and makes mistakes every day. Indeed that will always be its fate, according to the bare-bones logic of Kurt Gödel’s second incompleteness theorem. Gödel’s theorem establishes that the full validity of any system, including a scientific one, cannot be demonstrated within that system itself. In other words, the comprehensibility of a theory cannot be established unless there is something outside the frame against which to test it—something beyond the boundary defined by a thermodynamics equation, or by the collapse of the quantum wave function, or by any other theory or law. And if there
is
such a wider reference frame, then the theory by definition does not explain everything. In short, there is not and never will be a complete and comprehensive scientific account of the universe that can be proved valid. The Creator must have been fond of uncertainty, for He (or She) has given it to us for keeps.

Which is, I would argue, a salutary finding and cause for good cheer. Hell would be a small universe that we could explore thoroughly and fully comprehend. Alexander the Great may have wept upon being told that there were infinite worlds (“And we have not conquered even one,” he sobbed) but the situation looks more sanguine to those inclined to untie rather than to cut nature’s gordian knot. No thinking man or woman ought really to want to know everything, for when knowledge and its analysis is complete, thinking stops.

René Magritte in 1926 painted a picture of a pipe and wrote beneath it on the canvas, in a careful schoolboy script, the words
“Ceci n’est pas une pipe”
—“This is not a pipe.”
³
His painting might suitably be made the emblem of scientific cosmology. The word “universe” is not the universe; neither are the equations of supersymmetry theory or the Hubble law or the Friedmann-Walker-Robinson metric
^*
Nor, more generally, is science very good at
explaining what anything, much less the entire universe, actually “is.” Science describes and predicts events, but it pays for this power in the coin of the
ding an sich
—the thing in itself.

Why, then, does science work? The answer is that nobody knows. It is a complete mystery—perhaps
the
complete mystery—why the human mind should be able to understand anything at all about the wider universe. As Einstein used to say, “The most incomprehensible thing about the universe is that it is comprehensible.”
⁴
Perhaps it is because our brains evolved through the workings of natural law that they somehow resonate with natural law. Nature exhibits a number of self-similarities—patterns of behavior that recur on different scales, making it possible to identify principles, such as the conservation laws, that apply universally—and these may provide the link between what goes on inside and outside the human skull. But the mystery, really, is not that we are at one with the universe, but that we are to some degree at odds with it, different from it,
and yet
can understand something about it. Why is this so?

In search of an answer, let us pause to slake our thirst one last time at symmetry’s bubbling spring. Symmetry, we recall, implies not only the existence of an invariance under a transformation, the basis of all natural law, but also a “due proportion” between the invariance at hand and some larger, more comprehensive frame of reference. In this relationship may be found parallels with the process of scientific thought. The mind with its inherent limitations makes a frame within which our ideas can cavort; even the most expansive theory is “framed” in a specific mathematical or verbal or visual vocabulary. We then test our ideas against a piece of the outer world, which, however, itself has a frame around it. This process will work so long as we never reach an unframed, limitless arena. Gödel’s theorem suggests that we never will—that a theory by its very nature requires for its verification the existence or contemplation of a larger reference frame. It is the boundary condition, then, that provides the essential distinction between mind and the universe: Thoughts and events are bounded, even if the totality is not.
^*

And where did the boundaries come from? Quite possibly from
the breaking of cosmic symmetries at the moment of genesis. We look out across a cosmic landscape riven by the fractal lines of broken symmetries, and draw from their patterns metaphors that aspire to be as creative, if not always quite as flawed, as the universe they purport to describe. (All metaphors are imperfect, said the poet Robert Frost, that is the beauty of them.)

It may be, then, that the universe is comprehensible because it is defective—that because it forsook the perfection of nonbeing for the welter of being, it is possible for us to exist, and to perceive the jumbled, blemished reality, and to test it against the ghostly specter of the primordial symmetry thought to have preceded it. We are, therefore we think. (Or, as the fabulist Jorge Luis Borges put it, “In spite of oneself, one thinks.”)
⁶

Science is a process, not an edifice, and sheds old concepts as it grows. “Theories,” said Ernst Mach, “are like withered leaves, which drop off after having enabled the organism of science to breathe for a time.”
⁷
The process depends upon error—as Popper notes, a theory is valuable only if it is capable of being disproved —as if to testify to the ubiquity and efficacy of cosmic imperfection. “Error can often be fertile,” remarked the historian A.J.P. Taylor, “but perfection is always sterile.”
⁸
Taken as a whole, the scientific endeavor is as open-ended as the expansion of the universe—which, I think, is what Bohr had in mind when on his deathbed he complained of the philosophers that they too often “have not that instinct that it is important to learn something, and that we must be prepared to learn.”
⁹
Every answer opens up new questions: Like Atalanta stooping to gather up the golden apples, we pause to marvel at each new discovery, only to realize that we have fallen behind in the race and must hurry on to the next turn in the path, where another golden apple awaits us.

Our explications of nature will always be inadequate, if only because it is the difference between the idea and the reality that makes the idea possible. Nature may be counted upon forever to retain the mysterious, magical quality that arises from the contrast between her innumerable splendors and the limitations of our metaphors. As Wheeler put it:

Science is young. Whether it will survive long enough to become old depends upon our sanity and courage and vigor, and, as one always must add in this nuclear age, upon whether we blow ourselves up first. “Nothing that is vast enters into the life of mortals without a curse,” as Sophocles said, and the knowledge of how the stars shine is very great, and its dark side is very dark indeed. Needless to say, science in itself will not deliver us from the dangers to which its knowledge has exposed us. “Scientific statements of facts and relations, indeed, cannot produce ethical directives,” wrote Einstein, though he allowed that “ethical directives can be made rational and coherent by logical thinking and empirical knowledge.”
¹¹

Viewed from so cold a perspective, we may esteem ourselves less but will know ourselves better, as creatures of darkness and light, in love with death as well as with life, as eager to destroy as to create. Our lives are suspended like our planet in a gimbals of duality, half sunlight and half shadow. If we plead with nature, it is in vain; she is wonderfully indifferent to our fate, and it is her custom to try everything and to be ruthless with incompetence. Ninety-nine percent of all the species that have lived on Earth have died away, and no stars will wink out in tribute if we in our folly soon join them.

Therefore, we say—speaking as living and (we think) thinking beings, as carriers of the fire—therefore, choose life.

           
T
he science of cosmology has made admirable progress during the past fifteen years. Some of its findings have been surprising, notably the discovery that the expansion of the universe evidently is accelerating, owing to the presence of a mysterious force called “dark energy” (about which more in a moment). Others have confirmed existing theories and built on them: Such results may make for fewer newspaper headlines, but one should keep in mind that observations that robustly confirm theories can be just as remarkable as those that contradict them. The upshot has been to increase the sum of human knowledge about the cosmos, and, no less important, to improve the quality of our cosmological questions.

The Hubble Space Telescope, launched in 1990, turned out to have a misshapen main mirror, but following its repair by a space shuttle team three years later, made observations that substantially clarified our vision of the cosmos. Astronomers using it to chart
Cepheid variable stars and other useful distance-measuring landmarks were able to refine their estimates of the cosmic expansion rate, with the result that the universe now appears to be slightly younger than had been thought—just under fourteen billion years old. High-resolution Hubble images of quasars confirmed that they are indeed located at the nuclei of galaxies and are almost certainly powered by black holes. Galaxies imaged by Hubble at vast distances showed evidence of cosmic evolution, with spirals evidently having once been more commonplace and many of them subsequently being stripped of interstellar gas by collisions with one another to turn them into bald-looking elliptical galaxies. The Hubble Deep Field, a patch of sky imaged in a very long exposure over ten full days of telescope time, revealed galaxies more than halfway across the observable universe and became a kind of scientific watering hole to which many other observers repaired to make comparison observations of their own.

Studies of the cosmic background radiation—now more often called the cosmic microwave background, or CMB, to distinguish it from primordial neutrinos, gravity waves, or other sorts of useful big-bang relics that may soon be detected—reaped major insights for cosmologists. The COBE (for Cosmic Background Explorer) satellite, launched on November 18, 1989, mapped the CMB and confirmed two important predictions of the big-bang theory. First, the background radiation does indeed exhibit a black-body spectrum, as theorists had predicted. Indeed the fit of data to prediction was so exact that, when scientists plotted the data over the predicted curve, you couldn’t tell which was which: It was like Robin Hood’s splitting an opponent’s arrow in an archery contest. Second, the CMB proved to be, as expected, homogeneous and anisotropic—that is, evenly distributed and the same in all directions—except for a small hot spot in one direction and a cool spot on the opposite side of the sky caused by Earth’s motion in its local intergalactic field. Within this global smoothness, however, the COBE data also revealed inhomogeneities—lumps in the primordial soup, out of which stars and galaxies were to grow.

These results sparked great interest in learning more about the CMB, which by then was being called a cosmological Rosetta Stone. The microwave background amounts, after all, to a flash photograph of the universe when it was under half a million years
old. The COBE satellite resembled a camera that could register its color (the black-body spectrum) and make out a few vague forms (the inhomogeneities) but was somewhat out of focus. Hence scores of experiments were conducted to study the CMB in other ways, at various wavelengths and differing angles of resolution. Warm air scatters CMB microwaves, so many of these observations were conducted from near the South Pole, where the air is cold and dry, and from balloons such as Boomerang, which flew over Antarctica at an altitude of 120,000 feet and detected evidence of sound waves moving through the primordial soup. Then, in 2001, NASA launched MAP, the Microwave Anisotropy Probe, a satellite equipped to scrutinize the CMB in unprecedented detail. Its findings, announced in 2003, confirmed that the geometry of the universe is close to being “flat”—that is, poised on the knife-edge separating closed and open models, as predicted by the inflationary hypothesis—and supported estimates, based on prior investigations, that the majority of cosmic matter/energy takes the form of a field, its nature as yet unknown, that was being called dark energy. The inhomogeneities in the background radiation mapped by MAP (or WMAP as it now was named, in honor of the Princeton cosmologist David Wilkinson, who died in September 2002) fit the theory that they originated as quantum flux events in the early universe. So it really does appear to be the case that subatomic phenomena authored the vast structures of galaxies and galaxy clusters that we see around us in the expanded universe today.