Fundamentals

  Gravity’s Tenacity

  For to him that has will more be given; and he will have abundance: and from him who has not, even what he has will be taken away.

  —Mark 4:25

  For to every one who has will more be given, and he will have abundance; but from him who has not, even what he has will be taken away.

  —Matthew 25:29

  These quotations describe what has come to be called the “Matthew effect,” although Mark’s gospel is almost certainly earlier. Loosely stated it means “the rich get richer while the poor get poorer.”

  The gravitational instability that is central to the emergence of complexity in the universe is a version of the Matthew effect. Dense regions in the universe exert more powerful attractions, and thus accumulate more matter, and thus become still denser. Regions that are less dense than average, conversely, will lose to the competition, and empty out further. In this way, the density contrast sharpens over time. Small contrasts evolve into larger ones. That is the gravitational instability.

  To get the most out of the big bang theory, we need to refine our assumption that the distribution of matter early on was completely uniform. Small deviations from uniformity will do, because they get amplified by gravitational instability.

  Happily, the cosmic microwave background, which gives us a picture of the universe 380,000 years after the big bang, is not quite uniform. Its intensity varies with angle, at the level of parts in ten thousand, reflecting density contrasts of similar size. The detection of such tiny nonuniformities was a triumph of experimental technique. John Mather and George Smoot shared the 2006 Nobel Prize for their pioneering work on this subject.

  These tiny seeds get amplified in time, by gravitational instability. According to calculations, they are just the right size to grow, in the available time, into density contrasts large enough to evolve into galaxies, stars, and the structures we presently observe in the universe.

  Why was matter in the early universe so nearly—but not quite—uniform? We don’t know for sure, but there’s a beautiful possibility I’d like to share with you. The theory of cosmic inflation, on the face of it, suggests a conceptual explanation for perfect uniformity, as we discussed earlier. But when we try to embody the theory within the framework of fundamental physics, using quantum fields, we discover that this isn’t quite right. Quantum fields have quantum-mechanical uncertainty built into them. Because of this they can’t generate perfect uniformity, though they can get close. It is possible, therefore, that a good physical implementation of inflation will convince us that the structure we observe in the universe was triggered by quantum uncertainty in the early universe.

  Matter’s Unfinished Business

  As we discussed in our fifth fundamental, nuclear burning in the Sun is the key to dynamic complexity on Earth. The Sun is, fortunately, still evolving. It has not reached equilibrium. Yet matter, according to the big bang theory, started in thermal equilibrium. How did the material of our Sun escape from it?

  We can trace the sequence of events. The cosmic fireball expanded and cooled. Thermal equilibrium requires frequent interactions, but the fireball was becoming less intense and increasingly sluggish. Eventually, thermal equilibrium started to break down.

  The cosmic microwave background and other potential lingering afterglows we discussed reflect breakdown of equilibrium. Here photons—or neutrinos, gravitons, and axions—came to interact very rarely.

  For the Sun and other stars, what’s important is that nuclear burning during the big bang did not run to its logical conclusion. In the expanding universe, many protons could not find each other and combine, until—much later—they got brought back together, in the Sun and other stars. The combustible mixture of nuclei that emerges from the big bang is another of its lingering afterglows.

  SENSITIVITY: THE BRANCHING OF REALITY

  Dice games, bowling, and many other recreations and sports would be dull—though possibly lucrative—if you could reliably connect input to output. You could master the motions required to roll a seven, or to bowl a strike, once and for all, and be done with it. But in practice this is impossible, because small differences in muscular motions, moisture on your hand, dirt on the rolling surfaces, or many other tiny effects can change your outcome. In short, the final result depends sensitively upon many factors that are essentially impossible to predict or control.

  Similarly, as gravitational instability plays out and matter clumps, the exact form this clumping ultimately takes in any particular place depends sensitively on the starting positions and velocities of many individual particles. Calculations reveal that gas clouds with only subtle differences to begin with can yield systems of stars and planets that differ drastically. Slight tweaks in the starting positions of a few particles can change the number of planets, or even the number of stars.

  Observations bear this out. Astronomers have long observed that stars often form binary systems. Recently the study of planets around stars other than our own Sun—exoplanets—has begun to flourish, and astronomers are observing wide variations in their sizes and in how they are distributed around their host stars.

  Very slight tweaks to the early history of the solar system can make the difference between an asteroid that impacts Earth and kills off the dinosaurs and one that misses.

  Thus, while a few ingredients, a few laws, and a strangely simple origin govern the broad framework and overarching flow of cosmic history, they are powerless to predict its rich local details. The world is like a tree that, following simple rules of growth, sprouts many branches, each different in detail, providing suitable homes for different birds and insects.

  It is no contradiction that the history of, say, Sweden is more complicated than the history of the universe. Indeed, our fundamentals predict it.

  THE FUTURE OF COSMIC COMPLEXITY

  Heat Death and Its Remedies

  The long-range future of the universe, on the face of it, looks bleak. Galaxies will keep receding from one another, stars will run out of nuclear fuel, the microwave background radiation will redshift into radio waves and peter out. Even before the emergence of big bang cosmology and the expanding universe, cosmologists worried about the “heat death” of the universe, as its approach to some sort of equilibrium seemed inevitable, after which nothing interesting would happen.

  The first thing to say about this is that it’s not an immediate worry. Our Sun has at least a couple of billion good years ahead of it, and stars continue to be born elsewhere in our galaxy, many of which (the M stars) will provide reliable heat for much longer than the Sun ever did.

  With that much lead time, we should not underestimate how resourceful engineers might respond creatively. Dyson spheres around artificially constructed stars, together with energy-conserving technologies, could support intelligent life well beyond the natural lifetime of stars.

  Especially good news here is that minds can run on very little energy—or maybe none. Quantum computers operate best in the cold and dark, where there’s nothing fouling up their delicate works. A sufficiently complicated time crystal* of this kind could run through an elaborate program over and over again, giving joy to the AIs it contains.

  Finally, we should remember that our scientific understanding of the universe is incomplete and evolving. The best thinking about every one of our fundamentals has changed drastically within just the past hundred years. Could we find ways to burn “dead” stars further, releasing the true bulk of their energy—the E = mc2 energy of the nuclei they contain—in a usable form?* Could we re-create something like the big bang itself, giving birth to a baby universe? Could we tap into “dark matter” as an energy source?* We don’t really know, and, of course, other pleasant surprises might arise. In the history of science and technology, a few billion years is a long time.

  Complexity Within Simplicity

  The universe (which others ca
ll the Library) is composed of an indefinite and perhaps infinite number of hexagonal galleries, with vast air shafts between, surrounded by very low railings.

  —Jorge Luis Borges

  Here, in sixteen words, I will supply a simple algorithm for producing the complete works of Shakespeare, at least one proof of Fermat’s Last Theorem, and the paper that will win the Nobel Prize for physics in 2025:

  Choose an ASCII character—a letter, number, space, or punctuation mark—at random.

  Record it.

  Repeat.

  The output will contain all those promised things, and (much) more.

  Borges’s “The Library of Babel” expresses similar thoughts more poetically. Our program will generate “The Library of Babel,” too.

  This outrageous thought experiment illustrates how a very simple—that is, easily described—structure can contain vast complexities within it.

  Our thought experiment might reflect reality. Quantum-mechanical wave functions contain vast amounts of information. The wave function for something as large as our universe could house the Library of Babel comfortably. Simple rules can generate capacious wave functions, just as our simple algorithm generates a capacious output.

  Putting these thoughts together, it becomes tempting to think that the wave function of the universe is generated by a simple rule, yet to be discovered. If so, then the universe we experience and are part of is the ultimate fulfillment of “complexity emerges.”

  8

  THERE’S PLENTY MORE TO SEE

  When I was a child, I spoke and thought and reasoned as a child. But when I grew up I put away childish things.

  Now we see things imperfectly, like puzzling reflections in a mirror, but then we will see everything with perfect clarity. All that I know now is partial and incomplete, but then I will know everything completely.

  —Saint Paul, 1 Corinthians

  Visionaries of many persuasions have long suspected that there’s much more to the world than our unaided senses reveal.

  Saint Paul, in the passage above, contrasts the world that children construct, which takes things at face value, with the vague intuitions of thoughtful adults that there’s more to be seen, and that we’re headed toward a hoped-for and dazzling truth.

  In Plato’s Allegory of the Cave, Socrates describes a strange prison to his friend Glaucon. The prisoners inhabit a dark cave, and the only sights they are allowed to see are puppet shows projected on a wall. The prisoners mistakenly believe that what they see is the fullness of reality. Glaucon remarks, “This is an unusual picture that you are presenting here, and these are unusual prisoners,” to which Socrates replies, “They are very much like us humans.”

  And William Blake, in a passage from The Marriage of Heaven and Hell, declared his faith that “if the doors of perception were cleansed, every thing would appear to man as it is: Infinite.”

  Science, in its account of the physical world, provides an inventory of what might possibly be observed. That inventory supports the visionaries. It reveals how impoverished natural human perception is, compared with the full content of physical reality. Science can help us to overcome our deficits. Much has been achieved, but much more can be done.

  OPENING THE DOORS OF OUR PERCEPTION

  Many animals inhabit a distinct sensory universe from humans. We share the physical world with them, but we experience it quite differently, not only at the level of intellect, but even at the level of raw perception.

  Dogs and many other mammals live in a parallel universe dominated by smells. Dogs’ noses are chemical laboratories, confronting incoming molecules with three hundred million receptors, compared to six million for humans. And a large portion—about 20 percent—of a dog’s brain processes the result, compared with less than 1 percent for humans.

  Bats navigate in the absence of light by sending out extremely high-pitched sounds—ultrasound—and analyzing the (ultra)sounds that bounce back. Human ears are deaf to ultrasound. They cannot be used for fine navigation, because the wavelength of humanly audible sound is too large. People have a poor sense of where the sounds they hear originate, in general.

  Spiders construct sensory nets of another kind. Their webs are not only traps, but signaling devices, whose vibrations indicate the presence and position of prey.

  Vision is our main portal to the external world, considering both how much information it gathers and how much of our brain—anywhere from 20 percent to 50 percent, depending on how you count*—is devoted to processing that information. Yet even here, our sampling of the external world is paltry relative to what’s out there. Human vision samples the state of the electromagnetic field. But it samples only the radiation that happens to impinge on our pupils. Further, it is sensitive only to radiation within a narrow range of wavelengths, from about 350 to 700 nanometers (that is, around half a millionth of a meter, or a few hundred-thousandths of an inch). This defines “visible light.” We don’t take in a proper spectrum, either, even within that range of wavelengths. Instead, we have three* different kinds of cone cells, broadly tuned to different wavelength ranges, involved in color vision, plus rod cells, also broadly tuned, that kick in for peripheral and night vision. Many snakes and other reptiles are sensitive to infrared. Bees are sensitive to ultraviolet, as are many birds. Birds also do a better spectral analysis of visible light. Their receptor cells contain oil droplets that selectively filter different wavelength ranges. Strangely enough, the order* of crustaceans known as mantis shrimps seem to be the best natural spectroscopists, by far. Depending on the species, mantis shrimps have between twelve and sixteen different kinds of receptors, compared with the human four. Their sensitivity extends well into the infrared and ultraviolet, and they are also sensitive to polarization (which humans are not).

  Our ancestors inhabited a distinct sensory universe, too. It is difficult to imagine a world without eyeglasses, mirrors, magnifying lenses (and their advanced forms—microscopes and telescopes), artificial lighting and flashlights, clocks and watches, smoke alarms, thermometers, barometers, and a host of other devices that enrich our perception in many directions. Yet that was the world in which humans lived over most of our history.

  Technology has already given us superpowers, and there is no end in sight. Receivers and generators of electromagnetic radiation both within and beyond the visible are becoming small and cheap, as are magnetic field sensors, generators and receivers of ultrasound, and devices that can perform chemical sampling of many kinds (“artificial noses”). The doors of perception are opening wider, as part of everyday life.

  HARD-EARNED REVELATIONS

  Other projects for expanding our perception call on extraordinary resources from many parts of science and technology. They are meant to address grand questions by consulting Nature in new ways. The new perceptions they yield will not for the foreseeable future be part of everyday life. But people have been inspired to work hard to answer them, simply because they are interesting.

  Here I will briefly describe two big projects that have expanded our perception of the world in recent years. They are examples of planned discovery, where we put sharply posed questions to Nature and expect to get answers. In each case, I’ll explain why we’re asking the question, what it makes us want to explore, and how we take on the exploration.

  These projects push the limits of what we know how to do,* in order to expand the horizon of knowledge. Thus, they give stress tests to our fundamental understanding.

  THE HIGGS PARTICLE

  Why We Look, and What We Look For

  Imagine a planet or moon encrusted with ice, beneath which a vast ocean lies—a planet like Saturn’s Europa. Imagine that within that ocean a brilliant species of fish evolves—a species so intelligent that they take up the physics of motion. Because the way that bodies move in water is complicated, their work produces many interesting observations an
d rules of thumb, but no coherent system. And so it goes, until one day a genius among fish, we’ll call her Fish Newton, has a startling new idea. Fish Newton proposes new, much simpler laws of motion—Newton’s laws. They are much simpler than the old rules, but they don’t describe the way that things actually move (in water, that is). Fish Newton proposes that you can reproduce the observed motions from the new, simpler laws if you assume that a medium fills space. Her hypothetical medium—the material we call water—affects the behavior of bodies. Fish Newton’s idea reconciles the complications of observed reality with a more fundamental, underlying simplicity.

  Ah Love! could thou and I with Fate conspire

  To grasp the sorry Scheme of Things entire,

  Would not we shatter it to bits—and then

  Remould it nearer to the Heart’s Desire!

  —Omar Khayyam (Fitzgerald translation)

  When the appearance of things is disappointing or discordant, we can, like Fish Newton, imagine a better world, and then try to build up ours within it. This was the strategy that led to the modern understanding of the weak force.

  The medium that complicates the weak force is called the Higgs condensate, after Peter Higgs, a Scottish physicist who made important contributions to its theory.* It was first introduced theoretically, as a way to get more beautiful equations, à la Fish Newton.

  Once we strip away the Higgs condensate, we can construct a theory of the weak force that looks a lot like our theories of the strong and electromagnetic forces. In the imaginary world, the weak force is mediated by gluon-like (and photon-like) particles—the W and Z bosons—that change and respond to two new kinds of charge. The new kinds of charge—let’s call them weak charge A and weak charge B—are similar to, but distinct from, the three color charges of quantum chromodynamics and the one electric charge of quantum electrodynamics. The weak force—and only the weak force—can transform a unit of type A charge into a unit of type B charge, or vice versa. Since particles are defined by properties, these transformations of weak charge change one kind of particle into another. This, in our deeper understanding, is the nature of the weak force’s transformative power.