More than two decades ago, the renowned astronomer Carl Sagan wrote that “We live in a society exquisitely dependent on science and technology, in which hardly anyone knows anything about science and technology. This is a clear prescription for disaster.” Unfortunately, Sagan’s warning remains as true today as ever: American culture is deeply infused with an anti-intellectual distrust of scientific knowledge, a failure to understand the nature of peer-review, and an unwavering predilection for conspiracy theories and pseudoscience.

In some cases, scientific illiteracy is nothing more than an occasion for chuckling, such as when the rapper B.o.B insisted that Earth is flat rather than an “oblate spheroid,” prompting a “mic drop” response from the famed astrophysicist Neil DeGrasse Tyson. But in many other cases, the consequences of ignorance about reality are very real. The most salient instance of this concerns the slow-motion catastrophe of climate change. According to a recent paper published in Nature, the policies we implement in the next few decades will determine the habitability of our planet for the next 10,000 years. The stakes really are high today — higher than ever before — and the fact that many public leaders fail to understand the urgency and causes of climate change, not to mention the difference between ions and eons, as Sarah Palin demonstrates in a tweet from 2009, is reason for genuine anxiety about the future of humanity.

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Aside from the existential importance of understanding science, there’s also a purely aesthetic issue. The scientific worldview offers, I would argue, a far richer and more elegant picture of the cosmos than any ancient myth or grand narrative conjured up by the human imagination during the Iron Age. As Charles Darwin would put it, there is grandeur in this view of the universe. And he’s right. Consider a few nuggets of mind-boggling truths, courtesy of science’s ongoing investigation into the arcana of reality: the cosmos has no center and no boundaries. The fastest moving organism travels more than half the speed of sound — and it’s a plant. You very likely have some DNA from an ancient Neanderthal in your cells. Earth rotated faster when the dinosaurs were alive, meaning that the days used to be shorter. The universe is, in other words, an endless playground for curious minds.

Sean Carroll is one of the few scientists today who excels at conveying complex ideas in simple — but not simplistic — terms to the public. A cosmologist at the California Institute of Technology (Caltech), his work focuses on dark matter and general relativity. You may have seen him discussing these topics on The Colbert Report or in Through the Wormhole, a documentary series hosted by Morgan Freeman. Dr. Carroll is also a vocal atheist who’s debated Christian apologists such as Dinesh D’Souza and William Lane Craig. His new book, The Big Picture, explores a wide range of fascinating topics, from the submicroscopic components of the universe to whether human existence can have meaning without God — and everything in-between. It’s a tour de force that offers a comprehensive snapshot of the human situation in our infinitely strange universe, and it does this with highly accessible language and engaging storytelling.

Curious about some of The Big Picture’s central themes, as well as the impetus for writing it, I contacted Dr. Carroll through email.

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What inspired you to write this book? What kinds of topics does The Big Picture cover? Given the finite resources of time and memory, is it possible for any single individual today to truly acquire a “big-picture” understanding of the human condition?

We tend to talk about the world in a myriad of ways – a microscopic world of elementary particles, a biological world of organisms and evolution, a social world of morality and meaning. But it’s all the same underlying world. That’s the underlying theme of The Big Picture. My goal was to use science and philosophy to weave together a story of how all the different strands fit together.

In particular, the story of the world that has been assembled by modern science can seem utterly different from the world of our everyday. Physics talks about particles and forces and wave functions, using an intimidating language of mathematics and jargon, while our immediate surroundings are populated by familiar things like people and cars and tables. I wanted to show, or at least hint at, the world with which we are all familiar can emerge out of the very different-sounding world of modern science. That involves a journey through cosmology, epistemology, ontology, physics, complexity, biology, neuroscience, and ethics. It’s a fun ride!

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Of course I’m not an expert in all of the fields I talk about in the book – nobody is. But the different disciplines need to keep up a continual conversation, if we’re to fit the big picture together. And individuals can certainly grasp the basic ideas behind the most important topics, no question.

You call your philosophical approach to the world “poetic naturalism.” This is a lovely term that, to my knowledge, you coined. What exactly does it mean? What is “naturalism,” and in what sense is your version of it “poetic”?

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Naturalism is the simple idea that there is only one world, the natural world; there isn’t a separate spiritual or theistic realm of existence. In practice, naturalists are also usually willing to accept that the natural world obeys rigid patterns, the “laws of nature,” and that we can discover what it’s like through the process of scientific investigation. Naturalists are atheists – they don’t believe in God – but the label is a positive claim about what one does believe in, rather than what one rejects.

Naturalists don’t all agree with each other. On the one end of the spectrum you have the most hard-core variety, who claim that only the most deep-down fundamental description of nature can be said to describe something “real.” They might say that consciousness, or morality, or free will, are all just illusions. On the other end of the spectrum you have naturalists who believe in only the natural world, but are willing to ascribe objective reality to various extra properties it might have – moral judgments, for example, or inner states of conscious experience.

Poetic naturalism sits in between. There is only one world, but we have many ways of talking about that world. And if a particular way of talking gives us a useful handle on what the world is and how it behaves, it’s completely appropriate to consider the concepts it evokes as “real.” Air is really made of atoms, but its temperature and pressure are real, even though the individual atoms don’t have temperatures or pressures. Human consciousness and free will are real, even though they’re not present in the individual particles or cells of which we are made.

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When it comes to meaning and morality, there are multiple allowed ways of talking, and the correctness of one or the other can’t be settled by doing experiments. That’s where naturalism becomes its most poetic – when we use our creative powers to attach judgment and significance to what goes on all around us.

You also talk about “planets of belief,” a metaphor that one could have guessed came from a cosmologist! What do you mean by this term, and what makes a planet of belief “stable”?

Ever since René Descartes and his famous Cogito, Ergo Sum, people have sought out an absolutely firm and unshakable foundation for their beliefs. An honest poetic naturalist admits that such a foundation just doesn’t exist. We could, however unlikely it may seem, be brains living in vats, or be misled by a mischievous demon.

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What happens, instead, is that we assemble together a variety of different beliefs about the world. To the extent that these beliefs are compatible with each other, we can think of them as mutually reinforcing, as if they exert a gravitational field that pulls together a “planet of belief.” A stable planet is one where the different pieces truly are compatible – we’re not just fooling ourselves about the consistency of different parts of our belief systems. If they’re not stable, beliefs that we simultaneously hold can come into conflict, forcing us to reject one of them (or just live with the burden of cognitive dissonance). Alternatively, new information can cause us to change our beliefs, as if a giant asteroid barrels into a planet and causes disruption.

As we get older, we tend to grow quite fond of the planets of belief we have constructed for ourselves. We build elaborate defense mechanisms to ward off attacks from competing ideas or new data. The system makes us comfortable, but resistant to change, no matter how much change might be called for.

One thing you emphasize in The Big Picture is the importance of being comfortable with “uncertainty” and “incomplete knowledge.” Unlike religion, which sees beliefs as the points of departure, science sees them as the destinations of an ongoing journey for truth. Why exactly is it so crucial to be flexible in our belief systems? What if flexibility is too uncomfortable for people?

I talk a lot in The Big Picture about Bayesian reasoning. To some set of competing ideas, we assign a “prior” credence (roughly, the probability we think each one might be true), then update those credences as we gather new information. It’s crucial that our credence in a given idea never go all the way to precisely 0 or 1, because that means that no new information could possibly change our mind about it. That’s no way to go through life.

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The universe is big and complicated and subtle, and we human beings are small and short-lived and not always as rational as we like to think we are. We are the product of millions of years of evolution, optimized for survival in a challenging world, not necessarily for puzzling out the ultimate laws of reality. We need to recognize that we are subject to biases, that we have incomplete information, and that we can always be surprised.

This kind of flexibility can be psychologically challenging, but it shouldn’t be debilitating. Just because we never reach perfect certainty doesn’t imply that we can’t go through life believing certain things with very high confidence. It’s an important skill to be able to navigate between dogmatic certainty and enervating skepticism.

You’re a self-described atheist, but you don’t appear to be “militant” like some other New Atheist leaders. For example, you write, “The universe is much bigger than you or me, and the quest to figure it out unites people with a spectrum of substantive beliefs. It’s us against the mysteries of the universe; if we care about understanding, we’re on the same side” (italics added). Could you elaborate on your approach to disbelief?

As I write in the book, I don’t want to think of someone as my enemy just because we disagree about some issue of science or philosophy. As a working scientist, I disagree with my professional colleagues all the time, and we still manage to be friendly to each other. Disagreement about theism or naturalism should work the same way.

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I’m not someone who is so eager to paper over disagreement that I would end up claiming that one’s stance toward God or the universe doesn’t matter. These things do matter – not only directly for how we think about the world, but also for how we construe meaning and purpose in our lives, and ultimately for how we choose to live together. I strongly feel that the methods of science and empirical investigation can be brought to bear on all interesting questions about the fundamental nature of the universe, including whether or not God exists, and the evidence is pretty incontrovertible that he doesn’t. If I meet someone who disagrees, I am happy to engage them in dialogue and work to understand each other better.

Some people argue that every effect has a cause. If the universe is an effect — which one could certainly argue that it is — then what caused it? Why does it exist? Was there just a large empty space waiting to be filled, and then the universe popped into existence?

It’s not true that every effect has a cause! That’s just a convenient way of talking about certain features of the macroscopic world of our everyday experience, one that is not applicable to how nature works at a deeper level.

When you want to tackle questions about the fundamental nature of reality, it’s necessary to leave behind concepts of “cause and effect” and replace them with “the laws of physics.” Those laws take the form of patterns relating different parts of the universe to each other, not relationships of causality.

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So a better question is: what does our best understanding of the laws of physics tell us about the origin of the universe, and why it might exist at all? The answer is “not much.” This is a case where we have to be humble. The universe might have had a beginning, or it might have existed forever, we just don’t know. There’s certainly no reason to think that there was something that “caused” it; the universe can just be.

I’ve often thought of science as a special kind of story-telling in “assertion mode.” And the story it tells — involving quivering atoms, swirling galaxies, and evolving organisms — is without a doubt the “greatest story ever told.” But what’s missing from the story is a transcendent source of meaning for our lives. Without such a source — usually said to be God — how can our lives have true meaning? If the ultimate fate of the universe is a state of infinite entropy, then what makes life valuable and worth living?

The trick here is “true” meaning. My life has meaning without any supernatural guidance, no matter what anyone else might say about it. The meanings that we finite human beings attribute to our lives are the only kinds of true meanings, because those are the only kinds of meanings there are.

In my view, the fact that life is temporary is precisely what does give it value. Why should we care about a century-long existence if it was followed by an infinitely-long span of additional existence? We are fragile, ephemeral, finite creatures, bringing meaning to the world around us through our understanding and our care. Our lives have meaning exactly because they are all we have, and therefore are infinitely precious to us.

What’s the number one message or idea that you’d like readers of The Big Picture to take away from the book?

I need to cheat and pick two messages. First, we live in a natural world, obeying unbreakable laws. Second, that’s okay. It’s not a reason for existential despair. There’s plenty of room for us to create meaning and mattering, if we can muster the imagination and courage to do so.