Conclusion: The Spirit of Eddington

To put the conclusion crudely—the stuff of the world is mind-stuff.

Arthur Eddington (The Nature of the Physical World)

THE THINKING UNIVERSE

The idea that our view of the world is invented and not discovered has a long history in philosophy. To most physicists, however, it is anathema. When Eddington in the 1930s and 1940s championed the view that science is subjective, his peers roundly lambasted him. Only a few other British scientists, who eschewed physics for metaphysics, such as A. Whitehead and E. A. Milne, took a similar stance. But recently a number of scholars have reexamined Eddington’s legacy and marveled at his intellectual fortitude.

Eddington was a remarkable figure in science. In the 1920s he was one of the half-dozen people in the world who properly understood Einstein’s theory of general relativity. This was a time when the competing schema of quantum theory was advancing rapidly. Appreciating both theories, Eddington tried to reconcile these starkly different worldviews. Into the mix he inserted potent Quaker beliefs that remained a vital part of his being until his premature death. Although his papers were posthumously examined and clarified by



The National Academies | 500 Fifth St. N.W. | Washington, D.C. 20001
Copyright © National Academy of Sciences. All rights reserved.
Terms of Use and Privacy Statement



Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter. Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.

Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos Conclusion: The Spirit of Eddington To put the conclusion crudely—the stuff of the world is mind-stuff. Arthur Eddington (The Nature of the Physical World) THE THINKING UNIVERSE The idea that our view of the world is invented and not discovered has a long history in philosophy. To most physicists, however, it is anathema. When Eddington in the 1930s and 1940s championed the view that science is subjective, his peers roundly lambasted him. Only a few other British scientists, who eschewed physics for metaphysics, such as A. Whitehead and E. A. Milne, took a similar stance. But recently a number of scholars have reexamined Eddington’s legacy and marveled at his intellectual fortitude. Eddington was a remarkable figure in science. In the 1920s he was one of the half-dozen people in the world who properly understood Einstein’s theory of general relativity. This was a time when the competing schema of quantum theory was advancing rapidly. Appreciating both theories, Eddington tried to reconcile these starkly different worldviews. Into the mix he inserted potent Quaker beliefs that remained a vital part of his being until his premature death. Although his papers were posthumously examined and clarified by

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos physicists, it is only now that philosophers have also come to recognize his innovative way of thinking. Often emphasizing that he was not a solipsist, Eddington clearly stated that he believed in the existence of an external world. Nevertheless, he was convinced that our way of viewing it is limited by our biology. This conviction led him to the conclusion that science is, at least partly, subjective. His most memorable defense of this unpopular view was an analogy involving the meshsize of a fishnet. Eddington imagined an ichthyologist investigating ocean life. He casts a net, with gaps two inches wide, into the water. When he retrieves his catch, he finds it full of fish, each more than two inches long. This leads him to generalize that no sea creature is smaller than two inches. By analogy, we retrieve from the sea of knowledge only what the mesh of our methodology allows. Other (smaller) things pass through. As Eddington pointed out, scientists are often boxed in by the boundaries of physical observation. They tend to discount what they can’t directly perceive. Eddington emphasized this view when, continuing the tale of the ichthyologist, he related how difficult it can be to challenge improper scientific assumptions: An onlooker may object that the first generalization is wrong. “There are plenty of sea creatures under two inches long, only your net is not adapted to catch them.” The ichthyologist dismisses this objection contemptuously. “Anything uncatchable by my net is ipso facto outside the scope of ichthyological knowledge and is not part of the kingdom of fishes…. In short, what my net can’t catch isn’t fish.” Or—to translate the analogy—“If you are not simply guessing, you are claiming a knowledge of the physical universe discovered in some other way than by the methods of physical science, and admittedly unverifiable by such methods. You are a metaphysician. Bah! In Eddington’s day, labels for various physical phenomena were starting to break down. As the Copenhagen interpretation of

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos quantum mechanics emphasized, all particles have wavelike properties, and all forms of radiation have corpuscular features. In some contexts, momentum is a property determined by an object’s mass and velocity. In others it has to do with an entity’s wavelength. Whether to use one or the other depends on what type of measurement an observer is making. Bohr called this union of opposites “complementarity.” Others might call it Zen Buddhism. The phraseology of quantum physics bears striking resemblance to the parables known as Zen koans. If a particle crosses a detector but no one bothers to measure its velocity, does it have a definite speed? It doesn’t; quantum theory informs us. Rather, its speed is a mixture of possibilities. How would the particle react if placed in a magnetic field? Once again, we don’t know until the actual measurement is taken. The instant the magnet was switched on, the wave function representing the particle would “collapse” into one of a range of possibilities—like a jostled house of cards falling to either the left or the right. Like quantum physics, relativity also involves embracing seemingly contradictory views. For example, under certain circumstances mass is considered a feature of a solid object. In other cases it represents a pool of energy. Once again, an observer’s interaction with a body (particularly his or her relative speed) decides how much of its mass comprises its traditional bulk and how much stems from its dynamics. Eddington was one of the first to recognize the morphing definitions of modern science. Early on he emphasized the observer’s role in any measurement. He cautioned that scientific inquiry often tells us more about ourselves than about an “objective” external universe. As he once summarized contemporary scientific inquiry: We have found a strange footprint on the shores of the unknown. We have devised profound theories, one after another, to account for its origin. At last, we have succeeded in reconstructing the creature that made the footprint. And lo! It is our own.

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos THE DYNAMIC TRIO Uniting quantum physics and general relativity, which is one of the foremost goals of modern theoretical physics, offers a true test of embracing Eddington’s call for flexibility. In some sense such a unification would involve reconciling three completely different universes. First, there is the mundane world of our immediate experiences. In this realm, time flows ever forward. Objects move, over time, along discernable paths from one position to another. For all intents and purposes, Newtonian physics works well to describe this realm. Second, there is the Einsteinian domain, where space and time are inseparable twins. With space-time a unitary four-dimensional block, motion has a much different character. Everything, in some sense, happens at once. Like Billy Pilgrim’s frozen timeline, the past, present, and future are one and the same. Finally, there is the nebulous dominion of quantum mechanics. Its dynamics operate within a realm called Hilbert space, which, strangely enough, possesses an infinite number of dimensions. Particles don’t move in this space directly. Rather, their interactions are represented through the comings and goings of wave functions. Thus, Hilbert space represents a shadow venue—not the stage for the actual drama. Despite profound differences, these various kingdoms are closely entwined. As Einstein showed, along with his assistants Leopold Infeld and Banesh Hoffmann, general relativity can be used to derive the ordinary movements of particles, thus cementing the connection between Einstein’s eternal cosmic script and the moving pen of familiar classical mechanics. Classical mechanics is also connected to the quantum world, through the apparatus of quantum measurement. A mathematical procedure can be used to extract information from wave functions about positions, momenta, or other physical observables—though emphatically, following Heisenberg, not all of these quantities at

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos once. Rather, if some of these properties are ascertained closely, others are known only approximately. Thus, the mundane world is a hazy, incomplete image of the mechanisms of Hilbert space. Among this trio of physical realms, the connection between general relativity and quantum mechanics is undoubtedly the most tenuous. Physicists have been trying to solidify this link since the 1920s. The first attempt—Klein’s innovative contribution to Kaluza-Klein theory—was a creative way of framing the inexactitudes of quantum physics in terms of projections from a more complete five-dimensional world. Klein’s colleagues in Copenhagen admonished him, however, that he had not reckoned with the infinity of Hilbert space dimensions, only the dimensions of space-time (with one more added). Gradually, Klein and others came to realize that a full description of quantum physics needed more breathing space than standard general relativity, even extended to five dimensions, would permit. A MATTER OF SEMANTICS Modern physical theories have come to include both external dimensions (space, time, and any added directions) and internal dimensions that cannot be directly perceived. Such internal dimensions explain particle properties as symmetries of abstract manifolds. For example, protons can be transformed into neutrons through rotations in so-called isotopic spin space. Supersymmetry represents a similar means of rotating bosons into fermions (and vice versa) along an abstract direction. Most recently, M-theory has utilized this principle, within an 11-dimensional framework, to forge “dualities” (transformative connections) between strings and membranes of various types. It may appear that the difference between abstract internal dimensions and physical external dimensions is purely semantic, especially in scenarios where some of the latter dimensions cannot

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos be fully observed. Indeed, if we interpret nature through an Eddingtonian perspective, that is precisely the point. Through the power of language and reasoning, we divide the world into various categories, deeming some qualities actual and others intangible. Take, for example, gravitation. What could feel more substantial than the pounding of rain on your head during a sudden storm or the wrenching of your body during a steep roller-coaster plunge? Thus, following the Newtonian tradition, we tend to think of gravity as a force. Even after Einstein informed us that gravity is just a curving of space-time—resulting from the patching together of various local coordinate systems—it’s hard to shake the old view. A doctor would well understand a patient who complained that sudden jolts made him nauseous and might suggest a brand of motion sickness medicine. If, on the other hand, he whined that rapid coordinate system transformations made him sick, the physician might look at him askance and prescribe a very different kind of medication! Imagine a being with no capacity for feeling physical forces, for seeing light, for hearing sound, and so on. Suppose this sensory deprivation were balanced, though, with a keen capability of perceiving geometric changes in the fabric of the universe. Not only could this being discern ripples in ordinary space-time, she could also fathom the nuances of higher dimensions. She could even sense transformations of wave functions in internal dimensions. What could she tell us about the cosmos? If there were some way of communicating with such a being, we would learn that geometry is real and that mass, force, time, and so forth are all illusions. Our attempts to describe perceptions such as heaviness, loudness, darkness—in short, everything familiar—would likely be met by sheer disbelief. Even the chronicles of our lives, laid out over time, would have absolutely no meaning to such a timeless creature. In Eddington’s parlance, our worlds would be as different as our minds.

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos As mortals with mental and sensory limitations, we cannot know everything about the cosmos. The mathematician Kurt Gödel made this point when he demonstrated that no logical system is complete. His findings clashed sharply with attempts by Hilbert to systematize the mathematical and physical universes. Perhaps this is for the best. As the famed Argentine writer Jorge Luis Borges described in such short stories as “The Aleph” and “The Zahir,” a person to whom every facet of reality was suddenly revealed could well go mad. Maybe it is fortunate, then, that our knowledge of the universe arrives by dribs and drabs. Photon by photon, we slowly drink in one particular type of cosmic energy, leaving us ample time to savor (and interpret) this brew. Through gravitational detectors, we soon hope to savor a different type of broth. As connoisseurs of such stellar ferment, we pride ourselves in our growing appreciation of what we sip. Yet we also realize that much lies in the bottom of the barrel, inaccessible to our tasting, and that all this could have quite an alien flavor. TRUTH AND MATHEMATICS Eddington wrestled with the question of how best to interpret the limited information about the universe revealed to us through science. This issue remained of paramount importance to him throughout his life. If the bulk of the cosmos is composed of dark matter, dark energy, and perhaps even inaccessible extra dimensions, how can we best extend our current understanding to plumb at least part of these hidden depths? For example, what physical labels should we assign to these higher dimensions? Is there a unique mapping between observational data and physical actuality, or could the truth be a hydra of countless faces? As Eddington emphasized, there are as many ways to describe our world as there are intelligent observers. Each cognizant being interacts with reality uniquely. There needs, however, to be an

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos interaction. In contrast to Kant, Eddington was doubtful that pure reasoning could lead to new scientific knowledge. Eddington’s personal means of understanding, especially in his later years, centered on the mathematical subjects of number theory and tensor calculus. He was obsessed with finding simple numerical patterns that would encompass physical truths. His preference for mathematical methods stemmed, no doubt, from his own exceptional skills in that field. However, he made it clear in his writings that he was open to different approaches (including the religious one involving the Friends’ Meeting House, which he attended regularly). He chose mathematics because it seemed to him to be the most effective means of description. This view, while disputable, is nevertheless pragmatic. It is indeed this view that underlies much of modern work in the physics of fields and particles. The present emphasis on descriptions of the world in terms of higher-dimensional geometry is analogous to the extension of ordinary two-dimensional chess to the three-dimensional variety now available; both represent a trend to increased sophistication. But as in the case of 3D chess, physics in higher dimensions needs to invent new rules of play. The nature of such rules will likely spark debate for quite some time. Reduction of the mechanical concepts of physics to the more intuitive ones of philosophy is an ongoing process. Eddington, in recognizing this, left a major legacy for both fields. ALL THE MYRIAD WAYS It is strange to think that the truths we discover about our universe may not be true for all possible universes. Thus, even if a modern Eddington stumbled on mathematical relationships that precisely define the space we see, there is no guarantee that all possible realms would have the same relationships. Maybe other universes exist with three types of electrical charge, dozens of fundamental forces, and

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos thousands of stable chemical elements. Perhaps, somewhere in the labyrinth of possibilities, there are places where time runs backward and black holes light up the skies. In the many-worlds interpretation of quantum mechanics, proposed by Hugh Everett and championed by Bryce DeWitt, each time a subatomic process has several possible results, the universe bifurcates. Each copy is identical save for one distinction—the particular quantum process in question has a different outcome. For example, in one version a certain electron might jump from one atomic level to another, triggering the release of a photon, while in all others no such transition occurs. After bifurcation each parallel realm carries on as if nothing had happened. No trace exists of the alternatives, save in the minds of speculative thinkers. Many modern cosmological models similarly embrace the notion of parallel universes: alternative realities that coexist side by side with our own. Chaotic inflation, the self-reproducing universe, and kindred descriptions of the cosmos conceive of a gardenlike multiverse sprouting various types of plants—some gentle, some quite prickly. Because the cosmic horizon’s high picket fence would hide such exotic growth from our view, testing such scenarios would be challenging. The limits of luminous communication are daunting indeed. Imagine what fantastic possibilities would await, however, if we could somehow jump this fence and explore other patches. In Larry Niven’s classic short story, “All the Myriad Ways,” a future corporation—called Crosstime—develops the means for contact between alternative realities, offering people access to all the worlds that could have been. Each possibility, no matter how strange, has its own romping ground wherein its events could be played out. As Niven describes this jumble: There were timelines branching and branching, a megauniverse of universes, millions more every minute…. The universe split every

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos time someone made a decision…. Every choice made by every man, woman and child on Earth was reversed in the universe next door…. At least one innovative young thinker, MIT physicist Max Tegmark, believes that parallel-universe models are “empirically testable, predictable and falsifiable.” Originally from Stockholm, Tegmark arrived at his present position by way of Princeton, where he had the opportunity to collaborate with John Wheeler. Like Wheeler he enjoys pondering the most far-flung interpretations of physics, while simultaneously conducting more mainstream research. Tegmark refers to the former as “crazy stuff.” At a Princeton conference held in 2002 in honor of Wheeler’s 90th birthday, various physicists and other experts seemed engaged in a contest to paint the most all-encompassing portraits of the cosmos. In terms of far-reaching schemes, Tegmark arguably outdid his colleagues, however, by framing their proposals and others in terms of an intricate multitiered labyrinth of parallel realms. He asserted that the infinite expanse of space made it certain that there exist multiple copies of every person, place, and thing in the cosmos. These replicas cannot be observed because they lie well beyond the Hubble radius. “Is there another copy of you reading this,” asked Tegmark in an article summarizing his talk, “deciding to put it aside without finishing this sentence while you are reading on? A person living on this planet called Earth, with misty mountains, fertile fields and sprawling cities, in a solar system with eight other planets. The life of this person has been identical to yours in every respect—until now, that is when your decision to read on signals that your two lives are diverging.” Tegmark classified parallel universes into four distinct categories. Level One, he suggested, included parts of space that lie forever outside the range of telescopes. They would be “parallel” in the sense that they’d contain many duplicates and near duplicates, arising

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos through the vagaries of chance. This is a spatial version of Nietzsche’s old idea of “eternal return”: given a finite number of atomic configurations and an unlimited amount of time, random actions would eventually produce clones. Somewhere, perhaps, a duplicate of Nietzsche is writing a paper pointing out that infinite space could serve just as well as infinite time in reproducing all structures again and again. And maybe in another remote corner of reality a third Nietzsche is preparing to sue the second for plagiarism. As strange as other Level One realms would seem, at least they’d have the same natural laws as ours. In Level Two regions, on the other hand, the fundamental constants, properties of elementary particles, and so forth could well be very different. The second tier in Tegmark’s scheme comprises the set of all “bubble universes” produced during chaotic inflation. Because each bubble would begin its life as a simple quantum fluctuation with few of its attributes set, it could develop in multifarious ways. Successful bubbles would grow infinitely large, potentially evolving into viable universes. Others would fizzle out, faltering before they had a chance to generate structures. They’d vanish back into the primordial nothingness. Blessed with ample time, the bubbles that did happen to grow would pass through numerous stages of symmetry breaking. During each transition, unified fields would break down into various interactions, and simple particles would give birth to complex menageries with assorted masses and properties. Depending on special models of development, some of these steps could coincide with certain dimensions curling up. Alternatively, all of the dimensions could remain of equal magnitude. The timing and order of these phases would be specific to each bubble, resulting in diverse possibilities for the strengths of different forces and the masses and types of different particles. So, for instance, in some bubbles the charges of the proton and electron would be very different, precluding the formation of neutral atoms. Naturally, such conditions would hinder the growth of stable structures.

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos As each universe matured, it would generate regions of strong gravity. These would serve as spawning grounds to produce new fluctuations. These fluctuations, in turn, could evolve into new bubble universes—generating more and more generations. One might wonder how a multiverse could accommodate so many bubble universes, each of unlimited size. Fortunately, infinity’s hotel always has room for new guests. A variation of this bubble geneology is Perimeter Institute physicist Lee Smolin’s notion of cosmic survival of the fittest. Smolin has constructed a clever biological analogy between the replication of universes and the reproduction of living organisms. Black holes, he has asserted, would offer ideal wombs for the gestation of baby universes. Therefore, universes with more black holes could produce more offspring and tend to dominate over competing cosmologies. Each time a baby universe emerged, its fundamental constants would be different—the equivalent of genetic mutation. Some of the changes would auger well for nucleosynthesis, producing massive stars that would eventually collapse into black holes. Other alterations would turn out to be duds—allowing few or no stars to reach maturity. Naturally, these would have far fewer black holes—and less opportunity to breed. Their “genetic” lines would thus tend to die out over time. Now here’s the clincher—because universes favorable to the production of many black holes would be well suited for nucleo-synthesis, they would also produce many vibrant stars like the Sun, well suited for habitable planets. Hence, these universes would also tend to have the conditions favorable to support life. The process of natural selection would thereby explain the emergence of living beings, justifying why conditions in the cosmos are so supportive. In addition to eternal inflation scenarios and Smolin’s evolutionary idea, Tegnark also grouped brane-world models into Level Two. However, he pointed out that other branes would gravitationally interact with ours, rendering them more symbiotic than separate. Therefore, their status as truly parallel would not be quite as solid.

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos Next in Tegmark’s scheme comes Level Three, his designation for Everett’s many-worlds interpretation. This level has an altogether different character than the first two, since it is quantum mechanical— not cosmological—in origin. If this model were correct, reality would bifurcate each time an experimenter made a subatomic measurement. Therefore, unlike the other possibilities for alternative worlds, the production of parallel realities would transpire right here and now. Finally, Level Four, the most abstract grouping of all. It includes the set of all conceivable mathematical structures. A mathematical structure is an axiomatic system in which certain suppositions imply a variety of theorems. Euclidean and non-Euclidean geometries represent examples of these. We can show that there is an unlimited range of possible mathematical rules that would produce a neverending assortment of relationships. For instance, in some realities there would be five Platonic solids (regular polyhedra such as cubes), in others there would be 10, and in yet others there would be an infinite number. Why should varying mathematical relationships make a difference to the material universe? Just as flat universes and curved universes, because of their differing geometries, have distinct physical properties, any novel axiomatic system engenders a new physics. Hence, unlimited types of mathematical structure would correspond to a plethora of divergent realities. Tegmark called this state of affairs “mathematical democracy.” Though highly speculative, Tegmark’s talk was one of the many highlights of a truly thought-provoking conference. Other talks included DeWitt describing the many-worlds hypothesis, Randall discussing warped dimensions, Smolin delving into quantum gravity, Linde speaking about inflation, and so forth. All the while, a gratified Wheeler sat at the front of the hall, sampling the philosophical fruit of the many gardens of inquiry he had nurtured. By sheer coincidence, shortly after the Wheeler commemoration, Tegmark and one of us (Halpern) found ourselves members of the “jury” at a production of Michael Frayn’s acclaimed play

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos “Copenhagen.” The play is about the changing relationship of Bohr and Heisenberg before and during the Second World War, when they found themselves working for opposite sides. (Heisenberg was involved in the Nazi nuclear fission program—but the court of history has not rendered a verdict on whether he helped or hindered it.) One of the themes of the drama is that quantum uncertainty allows for simultaneous alternative realities—such as Bohr and Heisenberg being friends (because of their long-standing collaboration) and foes (because of the war) at the same time. At least in some productions a few members of the audience are seated in a “jury box” on stage—presumably to render a verdict on Heisenberg’s intentions. Thus, we found ourselves on the same panel, watching and judging the show. Tegmark appeared to enjoy seeing these alternative realities play out—like parallel realms in the multiverse of history. Indeed, confined to our small enclave of space, we are all jurors, rendering a verdict on the unfolding cosmic drama. Like any jury, our varied prejudices and perspectives affect the outcome of our conclusions. Each of us decides what seems to be “crazy stuff” and what appears to be mainstream. No measurement we make is wholly independent of our human experiences. Because we filter all information through our perceptions, in some sense we generate our own parallel universes—each a different facet of a multifarious prism. Hence, as Eddington pointed out, even if there is a true reality, it could well be lost in the mirror maze of subjectivity. TRIUMPH AND ITS AFTERMATH From the lowly vantage point of Earth, our instruments and intuitions have propelled us billions of light-years into the void and eons back in time. Questions unanswered for millennia have finally found credible answers. The ancient philosopher’s quest for the age of the

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos heavens has in some way been resolved, with the knowledge that 13.7 billion years have passed since the primordial fireball let loose its power. Like exacting surveyors, we have scoped out the shape of visible space. In a wry twist on the legacy of Columbus, we can finally proclaim that the universe is flat—at least in three dimensions and possibly in five dimensions. Cosmology has ample reason to glow in triumph. In the particle realm, scientists similarly have much cause for celebration. Two of the four forces of nature are united as the electroweak theory, a highly successful physical model with astonishing predictive powers. As for the strong interaction, quantum chromodynamics remains widely accepted. It is more difficult to work with than the other models but nevertheless seems to serve well. With regard to gravity, true, there’s no quantum theory as of yet. But at least it is well described by Einstein’s remarkable theory. So far, all known measurements of general relativity appear to verify its validity. Optimism abounds in the superstring community that a “theory of everything” will soon be forthcoming. Many times in the history of knowledge, various thinkers have proclaimed the imminent end of science. Practically all there is to know, they’ve asserted at such moments, has already been discovered. For example, in the late 19th century, physicists considered Newtonian physics a perfect description of mechanics and Maxwell’s equations a complete model of electromagnetism and light. Though these theories harbored mutual contradictions, many scientists believed that the existence of aether could help explain these. Physics seemed virtually complete. Only a few “minor mysteries,” such as the reason for discrete spectral lines and the origins of radioactivity (discovered in 1895), appeared to remain. Nevertheless, it was those very conundrums that opened up the floodgates, ushering in waves of new scientific activity. Today cosmology has arrived at a concordance model—one that meshes well with all known data. Probes of distant supernovas,

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos gravitational lensing measurements, and readings of the cosmic microwave background have pinned down cosmological parameters to an unprecedented level. Yet what is so striking about the new results is that science once again faces gaps and contradictions. So much of the substance and power of the cosmos simply cannot be explained. Addressing these hidden materials and forces could well spark a revolution in physics as far-reaching as that of the early 20th century. As we have seen, theorists have been off to a good start. From models with changing mass to those with variable speed of light, and from various recipes for inflation to assorted prescriptions for higher-dimension dynamics, there seems no end to clever ideas for resolving the deepest mysteries of the cosmos. One common theme is that the simplest form of general relativity could require some type of modification—be it by simply restoring the cosmological constant, adding additional fields, or extending it through extra dimensions. Some of these novel schemes, however, explain what we can or cannot observe by positing vast new sectors of reality—parallel universes, of various sorts. This can be a tricky business. By positing new territories that could never be explored, we render a theory essentially nontestable. The best new models have clear predictions that allow for careful matching with experiment data. “Observation,” as Eddington once wrote, “is the supreme Court of Appeal.” One of the greatest mysteries arises when we turn to the cosmic future. Current scenarios suggest that the universe will expand forever. Some researchers have attempted to map out the far future of the universe, painting a bleak picture of the slow demise of all vibrant entities—from stars to life. Like the grim reaper, entropy will eventually cloak the cosmos in absolute darkness. Even more terrifying is the possibility of a “big rip”—the tearing apart of the fabric of the universe: the ultimate doomsday. If scenarios for cosmic demise remind us of Western apocalyptic notions, the alternative is reminiscent of Eastern views of endless

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos renewal. In oscillatory scenarios, such as the cyclic model, the universe will eventually be reenergized. Heeding Eddington’s words, it will be interesting to see what evidence accrues for each of these possibilities. THE FUTURE OF COSMOLOGY Luckily, researchers are planning a number of exciting new experiments that will help sort the theoretical wheat from the chaff. Due in part to unfortunate budget cuts in American experimental programs, the center of activity for fundamental science has largely shifted to Europe. Therefore a number of the planned experiments will take place under the auspices of CERN and the ESA. CERN’s flagship project, the Large Hadron Collider (LHC), will be the most powerful particle accelerator in the world. Scheduled to begin operations in 2007, it will have the capability of smashing together beams of protons at energies of 14 TeV (approximately two-millionths of a Joule). Although a fraction of a Joule (much smaller than a nutritional calorie) may not seem like much, that is significantly higher than the capacity of its closest contender, the Tevatron at Fermilab. Moreover, these energies are concentrated in an incredibly tiny region of space. Experiments designed for the LHC include searches for supersymmetric companion particles, a hunt for the Higgs boson (an essential missing ingredient of modern field theories, believed to have an ultrahigh mass), and tests to discern if gravitons vanish from certain collisions (and presumably escape into a higher dimension). Given that modern cosmology has many ties to particle physics, these experiments would help distinguish various models of the universe. For example, if experimenters find that certain byproducts of a collision are missing, suggesting that the gravitons produced in the crash have escaped into another dimension, this result would offer a boost for scenarios based on large extra dimensions.

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos The long-awaited year of LHC’s inauguration coincides with the launching of a major space probe, the Planck satellite. Sponsored by the ESA, it represents the next step beyond WMAP for precise measurements of minute anisotropies in the cosmic microwave background. Its intended final orbit, approximately 1 million miles away, offers an ideal situation for taking sensitive temperature readings far from the influences of the Earth, Moon, and Sun. The Planck satellite’s great precision will enable it to discern tiny changes in the fine-structure constant—one part in a thousand over the age of the universe. This accuracy will substantially improve on the bounds set by WMAP and other instruments. Pinning down whether or not alpha varies has wide-ranging implications, given that many higher-dimensional theores predict a small change over time. Thus, it will be riveting to see on what side the Planck data come down—variation or not. Another important gauge of whether or not the natural constants are changing involves another satellite, Gaia. Originally an acronym for the Global Astrometric Interferometer for Astrophysics but later modified, Gaia is scheduled for launch by the ESA in 2011. This probe will be the most precise astronomical mapping device in history, pinpointing the exact distances and movements of billions of stars. Two scientific instruments placed on board will serve to collect and analyze light from large sectors of the sky. A Russian Soyuz rocket will help propel Gaia into the same orbital region occupied by Planck, granting it a similarly clear view. Performing such detailed measurements will place Gaia in the ideal position to measure changes in the gravitational constant. The motions of interacting celestial bodies, such as binary star systems, strongly depend on the form of the law of gravity. If the constant driving that relationship has altered in any way over time, Gaia would have the capability of recording such discrepancies. Less than a century ago, Hubble revealed the cosmos to be a vibrant structure, full of explosive energy. For the first time in history,

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos humankind realized that from the smallest meteors to the largest galaxies the heavens were in a constant state of flux. Newton’s hallowed jewel, the delicate latticework of fixed stars, seemed to fracture like shattered glass. General relativity stood as the perfect means of modeling a dynamic universe, yet its author was reluctant at first to step away from stability. Gradually he and others came to accept an evolving cosmos. Through thinkers such as Eddington, Lemaitre, and Gamow, the world came to appreciate the significance of this radical new perspective. Today we face another revolution in cosmology. Astonishing new findings challenge explanation. Unlike the discoveries of the 1920s, no widely accepted theory accounts for all the recent results. Contending theories, such as those with a changing gravitational constant, variable light speed, quintessence, colliding membranes, extra dimensions, and so forth, call for fundamental alterations in our conception of the universe. We cannot yet tell which (if any) of these will direct researchers along the path of truth. If any of these theories pass the test of experiment, it will undoubtedly launch physics into an astonishing new era. Given our species’ insatiable curiosity, we surely will not rest until the great cosmic conundrums are resolved. Until then, as the saying goes, there is joy in the journey.

OCR for page 215
Brave New Universe: Illuminating the Darkest Secrets of the Cosmos This page intially left blank