The universe is not what it used to be, nor what it appears to be.
What's it all about? People reflecting upon the wide world around them, the varied and often bewildering experience of life, and the prospect of death, are driven to ask that question. We seek answers from many sources: ancient texts and continuing traditions, the love and wisdom of other people, the creative products of music and art. Each of these sources has something to offer.
Logically, however, the first step in the search for answers should be to understand what "it" is. Our world has some important and surprising things to say for itself. That's what this book is about. I want to enrich your understanding of just what "it" is that you and I find ourselves within.
To begin, we build our world-models from strange raw materials: signal-processing tools "designed" by evolution to filter a universe swarming with information into a very few streams of incoming data.
Data streams? Their more familiar names are vision, hearing, smell, and so forth. From a modern point of view, vision is what samples the electromagnetic radiation that passes through a tiny hole in our eyes, picking up only a narrow rainbow of colors inside a much broader spectrum. Our hearing monitors air pressure at our eardrums, and smell provides a quirky chemical analysis of the air impinging on our nasal membranes. Other sensory systems give some rough information about the overall acceleration of our body (kinesthetic sense), temperatures and pressures over its surface (touch), a handful of crude measures of the chemical composition of matter on our tongue (taste), and a few other odds and ends.
Those sensory systems allowed our ancestors -- just as they allow us -- to construct a rich, dynamic model of the world, enabling them to respond effectively. The most important components of that world-model are more-or-less stable objects (such as other people, animals, plants, rocks, . . . the Sun, stars, clouds, . . .) some of them moving around, some dangerous, some good to eat, and others -- a select and especially interesting few -- desirable mates.
Devices to enhance our senses reveal a richer world. When Antonie van Leeuwehoek looked at the living world through the first good microscopes in the 1670s, he saw totally unsuspected, hidden orders of being. In short order he discovered bacteria, spermatozoa, and the banded structure of muscle fibers. Today we trace the origin of many diseases (and of many benefits) to bacteria. The basis of heredity (well, half of it) is found within the tiny spermatozoa. And our ability to move is anchored in those bands. Likewise, when Galileo Galilei first turned a telescope to the sky in the 1610s, new riches appeared: he found spots on the Sun, mountains on the Moon, moons around Jupiter, and multitudes of stars in the Milky Way.
But the ultimate sense-enhancing device is a thinking mind. Thinking minds allow us to realize that the world contains much more, and is in many ways a different thing, than meets the eye. Many key facts about the world don't jump out to our senses. The parade of seasons, in lock-step with the yearly cycle of sunrise and sunset, the nightly rotation of stars across the sky, the more intricate but still predictable motions of the Moon and planets, and their connection with eclipses -- these patterns do not leap to the eye, ear, or nose. But thinking minds can discern them. And having noticed those regularities, thinking minds soon discover that they are more regular than the rules of thumb that guide our everyday plans and expectations. The more profound, hidden regularities lend themselves to counting and to geometry: in short, to mathematical precision.
Other hidden regularities emerged from the practice of technology -- and, remarkably, of art. The design of stringed musical instruments is a beautiful and historically important example. Around 600 BCE, Pythagoras observed that the tones of a lyre sound most harmonious when the ratio of string lengths forms a simple wholenumber fraction. Inspired by such hints, Pythagoras and his followers made a remarkable intuitive leap. They foresaw the possibility of a different kind of world-model, less dependent on the accident of our senses but more in tune with Nature's hidden harmonies, and ultimately more faithful to reality. That is the meaning of the Pythagorean Brotherhood's credo: "All things are number."
The scientific revolution of the seventeenth century began to validate those dreams of ancient Greece. That revolution led to Isaac Newton's mathematical laws of motion and of gravity. Newton's laws permitted precise calculation of the motion of planets and comets, and provided powerful tools for describing the motion of matter in general.
Yet the Newtonian laws operate in a world-model that is very different from everyday intuition. Because Newtonian space is infinite and homogeneous, Earth and its surface are not special places. The directions "up," "down," and "sideways" are fundamentally similar. Nor is rest privileged over uniform motion. None of these concepts matches everyday experience. They troubled Newton's contemporaries, and even Newton himself. (He was unhappy with the relativity of motion, even though it is a logical consequence of his equations, and to escape it he postulated the existence of "absolute" space, with respect to which true rest and motion are defined.)
Another big advance came in the nineteenth century, with James Clerk Maxwell's equations for electricity and magnetism. The new equations captured a wider range of phenomena, including both previously known and newly predicted kinds of light (what we now call ultraviolet radiation and radio waves, for example), in a precise mathematical world-model. Again, however, the big advance required a readjustment and vast expansion of our perception of reality. Where Newton described the motion of particles influenced by gravity, Maxwell's equations filled space with the play of "fields" or "ethers." According to Maxwell, what our senses perceive as empty space is actually the home of invisible electric and magnetic fields, which exert forces on the matter we observe. Although they begin as mathematical devices, the fields leap out of the equations to take on a life of their own. Changing electric fields produce magnetic fields, and changing magnetic fields produce electric fields. Thus these fields can animate one another in turn, giving birth to self-reproducing disturbances that travel at the speed of light. Ever since Maxwell, we understand that these disturbances are what light is.
These discoveries of Newton, Maxwell, and many other brilliant people greatly expanded human imagination. But it's only in twentieth and twenty-first century physics that the dreams of Pythagoras truly approach fruition. As our description of fundamental processes becomes more complete we see more, and we see differently. The deep structure of the world is quite different from its surface structure. The senses we are born with are not attuned to our most complete and accurate world-models. I invite you to expand your view of reality.
When I was growing up, I loved the idea that great powers and secret meanings lurk behind the appearance of things.1 I was entranced by magic shows and wanted to become a magician. But my first magic kit was a profound disappointment. The secret of the magic, I learned, was not genuine power, just trickery.
Later, I was fascinated by religion: specifically, the Roman Catholic faith in which I grew up. Here I was informed that there are secret meanings behind the appearance of things, great powers that can be swayed by prayer and ritual. But as I learned more about science, some of the concepts and explanations in the ancient sacred texts came to seem clearly wrong; and as I learned more about history and historiography (the recording of history), some of the stories in those texts came to seem very doubtful.
What I found most disillusioning, however, was not that the sacred texts contained errors, but that they suffered by comparison. Compared to what I was learning in science, they offered few truly surprising and powerful insights. Where was there a vision to compete with the concepts of infinite space, of vast expanses of time, of distant stars that rival and surpass our Sun? Of hidden forces and new, invisible forms of "light"? Or of tremendous energies that humans could, by understanding natural processes, learn to liberate and control? I came to think that if God exists, He (or She, or They, or It ) did a much more impressive job revealing Himself in the world than in the old books -- and that the power of faith and prayer is elusive and unreliable compared to the everyday miracles of medicine and technology.
"Ah," I hear the traditional believer object, "but scientific study of the natural world does not reveal its meaning." To which I reply: Give it a chance. Science reveals some very surprising things about what the world is. Should you expect to understand what it means, before you know what it is?
In Galileo's time, professors of philosophy and theology -- the subjects were inseparable -- produced grand discourses on the nature of reality, the structure of the universe, and the way the world works, all based on sophisticated metaphysical arguments. Meanwhile, Galileo measured how fast balls roll down inclined planes. How mundane! But the learned discourses, while grand, were vague. Galileo's investigations were clear and precise. The old metaphysics never progressed, while Galileo's work bore abundant, and at length spectacular, fruit. Galileo too cared about the big questions, but he realized that getting genuine answers requires patience and humility before the facts.
That lesson remains valid and relevant today. The best way to address the big ultimate questions is likely to be through dialogue with Nature. We must pose pointed sub-questions that give Nature a chance to respond with meaningful answers, in particular with answers that might surprise us.
This approach does not come naturally. In the life we evolved for, important decisions had to be made quickly using the information at hand. People had to spear their prey before they became the prey. They could not pause to study the laws of motion; the aerodynamics of spears, and how to compute a trajectory. And big surprises were definitely not welcome. We evolved to be good at learning and using rules of thumb, not at searching for ultimate causes and making fine distinctions. Still less did we evolve to spin out the long chains of calculation that connect fundamental laws to observable consequences. Computers are much better at it!
To benefit fully from our dialogue with Nature, we must agree to use Her language. The modes of thought that helped us to survive and reproduce on the African savannah of 200000 BCE will not suffice. I invite you to expand the way you think.
In this book we'll explore some of the grandest questions imaginable: questions about the ultimate structure of physical reality, the nature of space, the contents of the Universe, and the future of human inquiry. Inspired by Galileo, however, I will address these questions as they arise in the course of a natural dialogue with Nature, about a specific topic.
The topic that will be our doorway into much bigger questions is mass. To understand mass deeply, we'll move past Newton, Maxwell, and Einstein, calling on many of the newest and strangest ideas of physics. And we'll find that understanding mass allows us to address very fundamental issues about unification and gravity that are at the forefront of current research.
Why is mass so central? Let me tell you a story.
Once upon a time there was something called matter that was substantial, weighty, and permanent. And something else, quite different, called light. People sensed them in separate data streams; touching one, seeing the other. Matter and light served -- and still do serve -- as powerful metaphors for other contrasting aspects of reality: flesh and spirit, being and becoming, earthy and celestial.
When matter appeared from nowhere, it was a sure sign of the miraculous, as when Jesus served the multitude from six loaves of bread.
The scientific soul of matter, its irreducible essence, was mass. Mass defined matter's resistance to motion, its inertia. Mass was unchangeable, "conserved." It could be transferred from one body to another but could never be gained or lost. For Newton, mass defined quantity of matter. In Newton's physics, mass provided the link between force and motion, and it provided the source of gravity. For Lavoisier, the persistence of mass, its accurate conservation, provided the foundation of chemistry, and offered a fruitful guide to discovery. If mass seems to disappear, look for it in new forms--voila, oxygen!
Light had no mass. Light moved from source to receptor incredibly fast, without being pushed. Light could be created (emitted) or destroyed (absorbed) very easily. Light exerted no gravitational pull. And it found no place in the periodic table, which codified the building blocks of matter.
For many centuries before modern science, and for the first two and a half centuries of modern science, the division of reality into matter and light seemed self-evident. Matter had mass, light had no mass; and mass was conserved. As long as the separation between the massive and the massless persisted, a unified description of the physical world could not be achieved.
In the first part of the twentieth century, the upheavals of relativity and (especially) quantum theory shattered the foundations beneath classical physics. Existing theories of matter and light were reduced to rubble. That process of creative destruction made it possible to construct, over the second part of the twentieth century, a new and deeper theory of matter/light that removed the ancient separation. The new theory sees a world based on a multiplicity of space-filling ethers, a totality I call the Grid. The new world-model is extremely strange, but also extremely successful and accurate.
The new world-model gives us a fundamentally new understanding of the origin of the mass of ordinary matter. How new? Our mass emerges, as we'll discuss, from a recipe involving relativity, quantum field theory, and chromodynamics -- the specific laws governing the behavior of quarks and gluons. You cannot understand the origin of mass without profound use of all these concepts. But they all emerged only in the twentieth century, and only (special) relativity is really a mature subject. Quantum field theory and chromodynamics remain active areas of research, with many open questions.
High on their success, and having learned much from it, physicists enter the twenty-first century with ideas for further syntheses. Today, ideas that go far toward achieving a unified description of the superficially different forces of nature, and toward achieving a unified account of the superficially different ethers we use today, are ready for testing. We have some subtle, tantalizing hints that those ideas are on the right track. The next few years will be their time of trial, as the great accelerator LHC (Large Hadron Collider) begins to operate.
listen: there's a hell of a good universe next door; let's go.
-- e e cummings
1. I still do! (back).