The Big Picture: On the Origins of Life, Meaning, and the Universe Itself

by Sean Carroll

A person is a diminutive, ephemeral thing, standing smaller in comparison with the universe than a single atom stands in comparison with the Earth. Can any one individual existence really matter?

Everybody dies. Life is not a substance, like water or rock; it’s a process, like fire or a wave crashing on the shore. It’s a process that begins, lasts for a while, and ultimately ends. Long or short, our moments are brief against the expanse of eternity.

Life is a process, not a substance, and it is necessarily temporary. We are not the reason for the existence of the universe, but our ability for self-awareness and reflection makes us special within it.

Poetic naturalism strikes a middle ground, accepting that values are human constructs, but denying that they are therefore illusory or meaningless. All of us have cares and desires, whether given to us by evolution, our upbringing, or our environment. The task before us is to reconcile those cares and desires within ourselves, and amongst one another. The meaning we find in life is not transcendent, but it’s no less meaningful for that.

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.

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.

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.

Ship of Theseus that raises some of the same issues. Theseus, the legendary founder of Athens,

The strategy I’m advocating here can be called poetic naturalism. The poet Muriel Rukeyser once wrote, “The universe is made of stories, not of atoms.” The world is what exists and what happens, but we gain enormous insight by talking about it—telling its story—in different ways. Naturalism comes down to three things: There is only one world, the natural world. The world evolves according to unbroken patterns, the laws of nature. The only reliable way of learning about the world is by observing it. Essentially, naturalism is the idea that the world revealed to us by scientific investigation is the one true world. The poetic aspect comes to the fore when we start talking about that world. It can also be summarized in three points: There are many ways of talking about the world. All good ways of talking must be consistent with one another and with the world. Our purposes in the moment determine the best way of talking.

Poetic naturalism is a philosophy of freedom and responsibility. The raw materials of life are given to us by the natural world, and we must work to understand them and accept the consequences. The move from description to prescription, from saying what happens to passing judgment on what should happen, is a creative one, a fundamentally human act. The world is just the world, unfolding according to the patterns of nature, free of any judgmental attributes. The world exists; beauty and goodness are things that we bring to it.

The experiment we know Galileo actually performed was an easier one to construct and control: he rolled balls of different masses down inclined planes. He was able to show that the balls accelerated in a uniform fashion, by an amount that depended on the angle of the plane but not on the masses of the balls. He then suggested that if we could trust this result all the way to planes that were inclined absolutely perpendicular to the floor, that would be exactly like dropping objects straight down, without a plane there at all. Therefore, he concluded, all masses would fall in a uniform way under the force of gravity, if it weren’t for the influence of air resistance.

It was a small step forward, but one that opened up a new vista on how to think about the nature of motion. Rather than talking about causes, the focus shifted to quantities and properties of matter itself.

This brings us remarkably close to the modern idea of inertia—the concept that bodies will move uniformly unless acted upon.

Pierre-Simon Laplace, a French physicist and mathematician born a century after Newton, thought differently. Scholars debate over his true religious views, which seem to have vacillated between deism (God created the world, but did not subsequently intervene in its operation) and outright atheism. Laplace is the one who, when asked by Emperor Napoleón why God didn’t appear in his book on celestial mechanics, purportedly replied, “I had no need of that hypothesis.” Whatever his ultimate beliefs, it seems that Laplace held steadfastly against the idea of a Creator who would ever directly interfere in the motions of the world.

Ernst Haeckel would dub this viewpoint dysteleology, though the term is so ungainly that it never really caught on.

In modern parlance, Laplace was pointing out that the universe is something like a computer. You enter an input (the state of the universe right now), it does a calculation (the laws of physics) and gives you an output (the state of the universe one moment later). Similar ideas had previously been suggested by Gottfried Wilhelm Leibniz and Roger Boscovich, and were prefigured over two millennia earlier by Ajivika, a heterodox school of ancient Indian philosophy. Since computers hadn’t been invented yet, Laplace imagined a “vast intellect” that knew the positions and velocities of all the particles in the universe, and understood all the forces they were subject to, and had sufficient computational power to apply Newton’s laws of motion. In that case, as he put it, “for such an intellect nothing would be uncertain, and the future just like the past would be present before its eyes.” His contemporaries immediately judged “vast intellect” to be too boring, and renamed it Laplace’s Demon.

the future

conservation of information implies that each moment contains precisely the right amount of information to determine every other moment.

The real issue with classical mechanics is that it’s not how the world works. These days we know better: quantum mechanics, which came along in the early twentieth century, is an entirely different ontology. There are no “positions” and “velocities” in quantum mechanics; there is only “the quantum state,” also known as “the wave function,” which we can use to calculate the outcomes of experiments that observe the system.

There are several competing approaches as to how to best understand the measurement problem in quantum mechanics. Some involve true randomness, while others (such as my favorite, the Everett or Many-Worlds formulation) retain complete determinism. We’ll talk about the alternatives in chapter 21. All of the popular versions of quantum mechanics, however, maintain the underlying philosophy of Laplace’s analysis, even if they do away with perfect predictability: what matters, in predicting what will happen next, is the current state of the universe. Not a goal in the future, nor any memory of where the system has been. As far as our best current physics is concerned, each moment in the progression of time follows from the previous moment according to clear, impersonal, quantitative rules.

The physical notion of determinism is different from destiny or fate in a subtle but crucial way: because Laplace’s Demon doesn’t actually exist, the future may be determined by the present, but literally nobody knows what it will be. When we think of destiny, we think of something like the Three Fates of Greek mythology or the Weird Sisters of Shakespeare’s Macbeth, wizened oracles who will use riddles to indicate our future path, which we will try to escape from and fail. The real universe is nothing like that. It’s more like an annoying child who likes to approach people and say, “I know what’s going to happen to you next!” Then, when you ask what will happen, the child says, “I can’t tell you.” And after it happens, they say, “See? I knew that was going to happen!” That’s the universe for you.

Looking for causes and reasons is a deeply ingrained human impulse. We are pattern-recognizing creatures, quick to see faces in craters on Mars or connections between the location of Venus in the sky and the state of our love life. Not only do we seek order and causation, but we favor fairness as well. In the 1960s, psychologist Melvin Lerner proposed the “Just World Fallacy” after noticing people’s tendency to blame victims of misfortune when something went wrong. To test his idea, he and his collaborator Carolyn Simmons conducted experiments in which subjects were shown other people apparently suffering the effects of electrical shocks. Afterward, many of the subjects—who knew nothing about the people supposedly being shocked—passed harsh judgments against them, berating their character. The more violent the shocks appeared to be, the harder the subjects were on the victims.

If the world consists of certain things and behaves in certain ways, we think, there must be a reason why it is so. This mistake has a name: the Principle of Sufficient Reason. The term was coined by German philosopher and mathematician Gottfried Leibniz, but the essential idea had been anticipated by many earlier thinkers, most notably by Baruch Spinoza in the seventeenth century. One way of stating it would be: Principle of Sufficient Reason: For any true fact, there is a reason why it is so, and why something else is not so instead.

Our standards for promoting a commonsensical observation to a “metaphysical principle” should be very high indeed. As Scottish philosopher David Hume—who, if anyone, deserves to be called the father of poetic naturalism, perhaps with his Roman predecessor Lucretius as the grandfather—pointed out, the Principle of Sufficient Reason doesn’t seem to rise to that level. Hume noted that conceiving of effects without causes might seem unusual, but it does not lead to any inherent contradiction or logical impossibility.

don’t know whether the Big Bang was the actual beginning of time, but it was a moment in time beyond which we can’t see any further into the past, so it’s the beginning of our observable part of the cosmos.

An obvious place where it’s tempting to look for reasons why is the question of why various features of the universe take the form that they do. Why was the entropy low near the Big Bang? Why are there three dimensions of space? Why is the proton almost 2,000 times heavier than the electron? Why does the universe exist at all? These are very different questions from “Why is there an accordion in my bathtub?” We’re no longer asking about occurrences, so “Because of the laws of physics and the prior configuration of the universe” isn’t a good answer. Now we’re trying to figure out why the fundamental fabric of reality is one way rather than some other way. The secret here is to accept that such questions may or may not have answers. We have every right to ask them, but we have no right at all to demand an answer that will satisfy us. We have to be open to the possibility that they are brute facts, and that’s just how things are.

But the universe, and the laws of physics, aren’t embedded in any bigger context, as far as we know. They might be—we should be open-minded about the possibility of something outside our physical universe, whether it’s a nonphysical reality or something more mundane, like an ensemble of universes that make up a multiverse. In that context we could start asking questions about what kinds of universes are “natural” or easy to create, and possibly discover an explanation for the particular features we observe. Alternatively, we could discover reasons why the laws of physics themselves necessitate that something we thought was arbitrary (like the masses of the proton and the electron) can actually be derived from a deeper principle. Then, in a different way, we would be able to pat ourselves on the back for having explained something.

It wasn’t until Giordano Bruno, a sixteenth-century Italian philosopher and mystic, that anyone suggested that the sun was just one star among many, and the Earth one of many planets that orbited stars. Bruno was burned at the stake for heresy in Rome in 1600, his tongue pierced by an iron spike and his jaw wired shut. His cosmological speculations were probably not the part of his heresy that the Church found most objectionable, but they didn’t help any.

Now the basics have been well established. The Milky Way we see stretching across the dark night sky is a galaxy—a collection of stars orbiting under their mutual gravitational attraction. It’s hard to count precisely how many, but there are over 100 billion stars in the Milky Way. It’s not alone; scattered throughout observable space we find at least 100 billion galaxies, typically with sizes roughly comparable to that of our own. (By coincidence, the number 100 billion is also a very rough count of the number of neurons in a human brain.) Recent studies of relatively nearby stars suggest that most of them have planets of some sort, and perhaps one in six stars has an “Earth-like” planet orbiting around it.

In the 1920s, Edwin Hubble discovered that our universe is indeed expanding. Given that discovery, we can use our theoretical understanding to extrapolate backward in time. According to general relativity, if we keep running the movie of the early universe backward, we come to a singularity at which the density and expansion rate approach infinity.

That scenario, developed by Belgian priest Georges Lemaître under the name “the Primeval Atom” but eventually dubbed “the Big Bang model,” predicts that the early universe was not only denser but also hotter. So hot and dense that it would have been glowing like the interior of a star, and all of that radiation should still suffuse space today, ready for detection in our telescopes. That’s just what happened in the fateful spring of 1964, when astronomers Arno Penzias and Robert Wilson at Bell Laboratories detected the cosmic microwave background radiation, leftover light from the early universe that has cooled off as space expanded. Today it is just a bit less than 3 degrees above absolute zero; it’s a cold universe out there.

The Big Bang itself, as predicted by general relativity, is a moment in time, not a location in space. It would not be an explosion of matter into an empty, preexisting void; it would be the beginning of the entire universe, with matter smoothly distributed all throughout space, all at once. It would be the moment prior to which there were no moments: no space, no time. It’s also, most likely, not real. The Big Bang is a prediction of general relativity, but singularities where the density is infinitely big are exactly where we expect general relativity to break down—they are outside the theory’s domain of applicability. At the very least, quantum mechanics should become crucially important under such conditions, and general relativity is a purely classical theory. So the Big Bang doesn’t actually mark the beginning of our universe; it marks the end of our theoretical understanding. We have a very good idea, on the basis of observational data, what happened soon after the Bang. The microwave background radiation tells us to a very high degree of precision what things were like a few hundred thousand years afterward, and the abundance of light elements tells us what the universe was doing when it was a nuclear fusion reactor, just a few minutes afterward. But the Bang itself is a mystery. We shouldn’t think of it as “the singularity at the beginning of time”; it’s a label for a moment in time that we currently don’t understand.

Normally we’d expect the expansion of the universe to slow down as the gravitational forces between the galaxies worked to pull them together. The observed acceleration must be due to something other than matter as we know it. There is a very obvious, robust candidate for what the culprit might be: vacuum energy, which Einstein invented and called the cosmological constant. Vacuum energy is a kind of energy that is inherent in space itself, remaining at a constant density (amount of energy per cubic centimeter) even as space expands. Due to the interplay of energy and spacetime in general relativity, vacuum energy never runs out or fades away; it can keep pushing forever. We don’t know for sure whether it will keep pushing forever, of course; we can only extrapolate our theoretical understanding into the future. But it’s possible, and in some sense would be simplest, for the accelerated expansion to simply continue without end.

Ultimately, as Stephen Hawking taught us, even those black holes will evaporate. After about 1 googol (10100) years, all of the black holes in our observable universe will have evaporated into a thin mist of particles, which will grow more and more dilute as space continues to expand. The end result of this, our most likely scenario for the future of our universe, is nothing but cold, empty space, which will last literally forever.