1 The Fundamental Nature of Reality In the old Road Runner cartoons, Wile E. Coyote would frequently find himself running off the edge of a cliff. But he wouldn''t, as our experience with gravity might lead us to expect, start falling to the ground below, at least not right away. Instead, he would hover motionless, in puzzlement; it was only when he realized there was no longer any ground beneath him that he would suddenly crash downward. We are all Wile E. Coyote. Since human beings began thinking about things, we have contemplated our place in the universe, the reason why we are all here. Many possible answers have been put forward, and partisans of one view or another have occasionally disagreed with each other.

But for a long time, there has been a shared view that there is some meaning, out there somewhere, waiting to be discovered and acknowledged. There is a point to all this; things happen for a reason. This conviction has served as the ground beneath our feet, as the foundation on which we''ve constructed all the principles by which we live our lives. Gradually, our confidence in this view has begun to erode. As we understand the world better, the idea that it has a transcendent purpose seems increasingly untenable. The old picture has been replaced by a wondrous new one-one that is breathtaking and exhilarating in many ways, challenging and vexing in others. It is a view in which the world stubbornly refuses to give us any direct answers about the bigger questions of purpose and meaning. The problem is that we haven''t quite admitted to ourselves that this transition has taken place, nor fully accepted its far-reaching implications.

The issues are well-known. Over the course of the last two centuries, Darwin has upended our view of life, Nietzsche''s madman bemoaned the death of God, existentialists have searched for authenticity in the face of absurdity, and modern atheists have been granted a seat at society''s table. And yet, many continue on as if nothing has changed; others revel in the new order, but placidly believe that adjusting our perspective is just a matter of replacing a few old homilies with a few new ones. The truth is that the ground has disappeared beneath us, and we are just beginning to work up the courage to look down. Fortunately, not everything in the air immediately plummets to its death. Wile E. Coyote would have been fine if he had been equipped with one of those ACME-brand jet packs, so that he could fly around under his own volition. It''s time to get to work building our conceptual jet packs.

What is the fundamental nature of reality? Philosophers call this the question of ontology-the study of the basic structure of the world, the ingredients and relationships of which the universe is ultimately composed. It can be contrasted with epistemology, which is how we obtain knowledge about the world. Ontology is the branch of philosophy concerned with the nature of reality; we also talk about "an" ontology, referring to a specific idea about what that nature actually is. The number of approaches to ontology alive in the world today is somewhat overwhelming. There is the basic question of whether reality exists at all. A realist says, "Of course it does"; but there are also idealists, who think that capital-M Mind is all that truly exists, and the so-called real world is just a series of thoughts inside that Mind. Among realists, we have monists, who think that the world is a single thing, and dualists, who believe in two distinct realms (such as "matter" and "spirit"). Even people who agree that there is only one type of thing might disagree about whether there are fundamentally different kinds of properties (such as mental properties and physical properties) that those things can have.

And even people who agree that there is only one kind of thing, and that the world is purely physical, might diverge when it comes to asking which aspects of that world are "real" versus "illusory." (Are colors real? Is consciousness? Is morality?) Whether or not you believe in God-whether you are a theist or an atheist-is part of your ontology, but far from the whole story. "Religion" is a completely different kind of thing. It is associated with certain beliefs, often including belief in God, although the definition of "God" can differ substantially within religion''s broad scope. Religion can also be a cultural force, a set of institutions, a way of life, a historical legacy, a collection of practices and principles. It''s much more, and much messier, than a checklist of doctrines. A counterpart to religion would be humanism, a collection of beliefs and practices that is as varied and malleable as religion is. The broader ontology typically associated with atheism is naturalism-there is only one world, the natural world, exhibiting patterns we call the "laws of nature," and which is discoverable by the methods of science and empirical investigation.

There is no separate realm of the supernatural, spiritual, or divine; nor is there any cosmic teleology or transcendent purpose inherent in the nature of the universe or in human life. "Life" and "consciousness" do not denote essences distinct from matter; they are ways of talking about phenomena that emerge from the interplay of extraordinarily complex systems. Purpose and meaning in life arise through fundamentally human acts of creation, rather than being derived from anything outside ourselves. Naturalism is a philosophy of unity and patterns, describing all of reality as a seamless web. Naturalism has a long and distinguished pedigree. We find traces of it in Buddhism, in the atomists of ancient Greece and Rome, and in Confucianism. Hundreds of years after the death of Confucius, a Chinese thinker named Wang Chong was a vocal naturalist, campaigning against the belief in ghosts and spirits that had become popular in his day. But it is really only in the last few centuries that the evidence in favor of naturalism has become hard to resist.

[ All of these isms can feel a bit overwhelming. Fortunately we don''t need to be rigorous or comprehensive about listing the possibilities. But we do need to think hard about ontology. It''s at the heart of our Wile E. Coyote problem. The last five hundred or so years of human intellectual progress have completely upended how we think about the world at a fundamental level. Our everyday experience suggests that there are large numbers of truly different kinds of stuff out there. People, spiders, rocks, oceans, tables, fire, air, stars-these all seem dramatically different from one another, deserving of independent entries in our list of basic ingredients of reality.

Our "folk ontology" is pluralistic, full of myriad distinct categories. And that''s not even counting notions that seem more abstract but are arguably equally "real," from numbers to our goals and dreams to our principles of right and wrong. As our knowledge grows, we have moved by fits and starts in the direction of a simpler, more unified ontology. It''s an ancient impulse. In the sixth century BCE, the Greek philosopher Thales of Miletus suggested that water is a primary principle from which all else is derived, while across the world, Hindu philosophers put forward Brahman as the single ultimate reality. The development of science has accelerated and codified the trend. Galileo observed that Jupiter has moons, implying that it is a gravitating body just like the Earth. Isaac Newton showed that the force of gravity is universal, underlying both the motion of the planets and the way that apples fall from trees.

John Dalton demonstrated how different chemical compounds could be thought of as combinations of basic building blocks called atoms. Charles Darwin established the unity of life from common ancestors. James Clerk Maxwell and other physicists brought together such disparate phenomena as lightning, radiation, and magnets under the single rubric of "electromagnetism." Close analysis of starlight revealed that stars are made of the same kinds of atoms as we find here on Earth, with Cecilia Payne-Gaposchkin eventually proving that they are mostly hydrogen and helium. Albert Einstein unified space and time, joining together matter and energy along the way. Particle physics has taught us that every atom in the periodic table of the elements is an arrangement of just three basic particles: protons, neutrons, and electrons. Every object you have ever seen or bumped into in your life is made of just those three particles. We''re left with a very different view of reality from where we started.

At a fundamental level, there aren''t separate "living things" and "nonliving things," "things here on Earth" and "things up in the sky," "matter" and "spirit." There is just the basic stuff of reality, appearing to us in many different forms. How far will this process of unification and simplification go? It''s impossible to say for sure. But we have a reasonable guess, based on our progress thus far: it will go all the way. We will ultimately understand the world as a single, unified reality, not caused or sustained or influenced by anything outside itself. That''s a big deal. [ Naturalism presents a hugely grandiose claim, and we have every right to be skeptical. When we look into the eyes of another person, it doesn''t seem like what we''re seeing is simply a collection of atoms, some sort of immensely complicated chemical reaction.

We often feel connected to the universe in some way that transcends the merely physical, whether it''s a sense of awe when we contemplate the sea or sky, a trancelike reverie during meditation or prayer, or the feeling of love when we''re close to someone we care abou.