There is an old brainteaser about a monk who one day leaves his monastery at sunrise to hike up to a temple at the summit of a tall mountain. The mountain has just one path, quite narrow and winding, and he takes it slowly at times, as sections of it are rather steep, but he reaches the temple shortly before sunset. The next morning, he descends along the path, again beginning at sunrise, and reaches his monastery again at sunset. The question is: Is there a spot along the path that he will come to at exactly the same time on both days? The point is not to identify the spot, only to say whether there is one—or not.
This is not one of those riddles that depends on a trick, on camouflaged information, or on a novel interpretation of some word. There is no altar along the path that the monk prays at each day at noon, nothing you need to know about the speed of his ascent or descent, no other missing detail you’d have to guess at to solve the riddle. Nor is this like the riddle that tells you a butcher stands six feet tall and then asks what he weighs, to which the answer is “meat.” No, the situation in this puzzle is quite straightforward, and chances are you understood from just one reading everything you need to know to determine the answer.
Think about it for a while, because your success at solving this riddle, like many questions scientists have tried to answer through the ages, may depend on your capacity for patience and persistence. But even more to the point, as all good scientists know, it will depend on your ability to ask the question in the right way, to step back and see the problem from a slightly different angle of vision. Once you do that, the answer is easy. It’s finding that angle of vision that can be hard. That’s why Newton’s physics and Mendeleev’s periodic table and Einstein’s relativity required people of towering intellect and originality to create them—and yet they can be understood, when properly explained, by any college student majoring in physics and chemistry today. And that’s why what boggles the mind of one generation becomes common knowledge to those who follow, allowing scientists to scale ever greater heights.
To arrive at the solution to the monk puzzle, rather than replaying in your mind the picture of the monk climbing up the mountain one day and down the next day, let’s do a thought experiment and visualize the problem differently. Imagine that there are two monks—one who walks up and another who walks down, both departing at sunrise on the same day. Obviously, they will pass each other along the way. The point at which they pass is the spot that the monk of the riddle will come to at the same time on both days. So the answer to the riddle is “Yes.”
That the monk will reach a particular point along the path at the same time on both his ascent and his descent can seem like an unlikely coincidence. But once you free your mind to entertain the fantasy of two monks ascending and descending on the same day, you see that it’s not a coincidence—it’s an inevitability.
In a way, the advance of human understanding was made possible by a succession of such fantasies, each created by someone capable of looking at the world just a little bit differently. Galileo imagining objects falling in a theoretical world devoid of air resistance. Dalton imagining how elements might react to form compounds if they were made of unseeable atoms. Heisenberg imagining that the realm of the atom is governed by bizarre laws that are nothing like those we experience in everyday life. One end of the spectrum of fantastical thinking is labeled “crackpot,” and the other “visionary.” It is due to the earnest efforts of a long parade of thinkers whose ideas originate at various points in between that our understanding of the cosmos has progressed to where it is today.
If I achieved my goal, the preceding pages have imparted an appreciation of the roots of human thought about the physical world, the kinds of questions those who study it concern themselves with, the nature of theories and research, and the ways in which culture and belief systems affect human inquiry. That’s important for understanding many of the social, professional, and moral issues of our time. But much of this book has also been about the way scientists and other innovators think.
Twenty-five hundred years ago, Socrates likened a person going through life without thinking critically and systematically to an artisan such as a potter who practices his craft without following proper procedures. Making pottery may appear simple, but it isn’t. In Socrates’s time, it involved procuring clay from a pit south of Athens, placing the clay on a specially made wheel, spinning it at just the proper speed for the diameter of the part being made, and then sponging, scraping, brushing, glazing, drying, and firing twice in a kiln, each time at the right temperature and humidity. Departing from any of these procedures will result in pottery that is misshapen, cracked, discolored, or just plain ugly. Powerful thinking, Socrates pointed out, is also a craft, and it is one worth doing well. After all, we all know people who, applying it poorly, have created lives that are misshapen or otherwise sadly flawed.
Few of us study atoms or the nature of space and time, but we all form theories about the world we live in, and use those theories to guide us at work and at play, and as we decide how to invest, what’s healthy to eat, and even what makes us happy. Also, like scientists, in life we all have to innovate. That might mean figuring out what to make for dinner when you have little time or energy, improvising a presentation when your notes have gone missing and the computers are all down—or something as life-changing as knowing when to let go of the mental baggage of the past, and when to hold on to the traditions that sustain you.
Life itself, especially modern life, presents us with intellectual challenges analogous to those scientists face, even if we don’t think of ourselves as such. And so, of all the lessons that might have been gleaned from this adventure, perhaps the most important are those that have exposed the character of successful scientists, the flexible and unconventional thinking, the patient approach, the lack of allegiance to what others believe, the value of changing one’s perspective, and the faith that there are answers and that we can find them.
Where is our understanding of the universe today? The twentieth century saw huge advances on all fronts. Once physicists solved the riddle of the atom and invented quantum theory, these advances in turn made others possible, so that the pace of scientific discovery grew ever more frenzied.
Aided by new quantum technologies such as the electron microscope, the laser, and the computer, chemists came to understand the nature of the chemical bond, and the role of the shape of molecules in chemical reactions. Meanwhile, the technology to create and harness those reactions had also exploded. By the middle of the century, the world had been remade. No longer dependent on substances from nature, we learned how to create new artificial materials from scratch, and to alter old materials for new uses. Plastics, nylon, polyester, hardened steel, vulcanized rubber, refined petroleum, chemical fertilizers, disinfectants, antiseptics, chlorinated water—the list goes on and on, and as a result, food production grew, mortality plunged, and our life spans rocketed upward.
At the same time, biologists made great progress in detailing how the cell operates as a molecular machine, deciphering how genetic information is passed among generations, and describing the blueprint for our own species. Today we can analyze DNA fragments drawn from bodily fluids to identify mysterious infectious agents. We can splice sections of DNA into existing organisms to create new ones. We can place optical fibers into rats’ brains and control them as if they were robots. And we can sit before a computer and watch people’s brains form thoughts, or experience feelings. In some cases we can even read their thoughts.
But though we have come far, it is almost certainly wrong to believe that we are near any final answers. To think so is a mistake that has been made throughout history. In ancient times, the Babylonians felt sure that the earth was created from the corpse of the sea goddess Tiamat. Thousands of years later, after the Greeks made incredible advances in our understanding of nature, most were equally positive that all objects in the terrestrial world were made from some combination of earth, air, fire, and water. And after another two millennia had passed, the Newtonians believed that everything that has occurred or will occur, from the motion of atoms to the orbits of planets, could in principle be explained and predicted by employing Newton’s laws of motion. All these were fervently held convictions, and all were wrong.
At whatever time we live in, we humans tend to believe that we ourselves stand at the apex of knowledge—that although the beliefs of those before us were flawed, our own answers are correct, and will never be superseded as theirs were. Scientists—even great ones—are no less prone to this kind of hubris than anyone else. Witness Stephen Hawking’s pronouncement in the 1980s that physicists would have their “theory of everything” by the end of the century.
Are we today, as Hawking suggested decades ago, on the verge of having answered all our fundamental questions about nature? Or are we in a situation like that at the turn of the nineteenth century, in which the theories we think are true will soon be replaced by something completely different?
There are more than a few clouds on the horizon of science that would indicate that we may be in the latter scenario. Biologists still don’t know how and when life first originated on earth, or how likely it would be to originate on other earthlike planets. They don’t know the selective advantages that drove the evolutionary development of sexual reproduction. Perhaps most important of all, they don’t know how the brain produces the experiences of the mind.
Chemistry, too, has great unanswered questions, from the mystery of how water molecules form hydrogen bonds with their neighbors to create the magical properties of that vital liquid, to how long chains of amino acids fold to form the precise spaghetti-like proteins that are vital for life. It is in physics, though, that the most potentially explosive issues lie. In physics, the open questions have the potential to make us revise everything we think we now know about the most fundamental aspects of nature.
For example, although we have built a very successful “standard model” of forces and matter that unites electromagnetism and the two nuclear forces, almost nobody believes that model is acceptable as the final word. One major drawback is that the model excludes gravity. Another is that it has many adjustable parameters—“fudge factors”—which are fixed on the basis of experimental measurement but cannot be accounted for by any overarching theory. And progress on string theory/M-theory, which once seemed to hold the promise of meeting both of those challenges, seems stalled, calling into question the high hopes that many physicists had for it.
At the same time, we now suspect that the universe we can see with even the most powerful of our instruments is but a tiny fraction of what is out there, as if most of creation is a ghostlike netherworld destined to remain, at least for a while, a mystery. More precisely stated, the ordinary matter and light energy we detect with our senses and in our laboratories seem to make up just 5 percent of the matter and energy in the universe, while an unseen, never detected type of matter called “dark matter” and an unseen, never detected form of energy called “dark energy” are thought to make up the rest.
Physicists postulate the existence of dark matter because the matter we can see in the heavens seems to be pulled on by gravity of unknown origin. Dark energy is equally mysterious. The popularity of the idea stems from a 1998 discovery that the universe is expanding at an ever accelerating rate. That phenomenon could be explained by Einstein’s theory of gravity—general relativity—which allows for the possibility that the universe is infused throughout with an exotic form of energy that exerts an “antigravity” effect. But the origin and nature of that “dark energy” has yet to be discovered.
Will dark matter and dark energy prove to be explanations that fit into our existing theories—the standard model and Einstein’s relativity? Or, like Planck’s constant, will they eventually lead us to a completely different view of the universe? Will string theory prove true, or, if not, will we ever discover a unified theory of all the forces in nature, and one that is free of “fudge factors”? No one knows. Of all the reasons I wish I could live forever, living to know the answers to these questions is near the top of my list. I guess that’s what makes me a scientist.