There’s a quote floating around the internet attributed to Thomas Merton: “if the you of five years ago would not consider the you of today a heretic, you are not growing spiritually.” I have not been able to find the quote in any of his writings, so that attribution is dubious, but I do find that I agree with the message. And certainly the me of five years ago—struggling to keep my head above water in the first semester of a brand new tenure-track job, agnostic (when I thought about it, which wasn’t often), and generally indifferent to the idea of religious community—that person would have been stunned, absolutely floored, if someone had said, “in five years you’ll be giving a sermon to the congregation where you attend church every Sunday.” But there I was.

The first time I went to the Unitarian Universalist church, it was on the recommendation of my friend Paul, who divides his time between the U.S. and Costa Rica. I had just returned to this country after a few years of living down there, and I was struck by how hard it is to get to know people here. In Heredia, within a few months of arriving, I knew my neighbors. I knew the people who ran the fruit stand, the corner grocery store, the pizza shop. A quick trip for dinner ingredients was also a chance to check in: cómo están sus primos? Ya se mejoró Doña Lela? Here in New York, after two years in the same house, I knew hardly anyone.

“People don’t talk to each other,” I complained. “How can I meet people if they never talk?”

“You should go to a Unitarian church,” he said. “They talk.”

“A church?”

“You should go and see.”

And that was how I found myself sitting in the very back row, somewhat petrified, listening to Rev. Dr. Michael Tino. He has a doctorate in molecular biology as well as his M.Div. As I would later find out, he also has a loving husband and an adorable baby daughter. I think I was there four weeks before anybody actually said “god” from the pulpit. Instead, the services were more about how to be a good person, how to enjoy the blessings of everyday life. And people do talk, in the coffee hour after the service. And they listen. The friends I’ve met through the UU fellowship are considerate, deep-thinking, irreverent, funny, and generous.

After about six months of attending services (and playing the piano when the regular accompanist was out of town), I decided to become a member. I had a moment of trepidation telling my mother about it, given my atheist upbringing.

“Oh, Unitarians!” she said. “They have the best pot lucks. And they sponsor all those social justice events. I’d probably go if the nearest UU church wasn’t so far away.”

The church has been a surprising source of solace and inspiration for me. I say surprising because it surprises me, but I imagine that it doesn’t come as a surprise at all for people who grew up in churches where they felt welcome.

The UU faith is often misrepresented as “go ahead and believe anything you want!” It’s true that the church is full of people who believe different things—atheists, agnostics, and people from a whole host of other faiths—but there are some core principles that unite us. The “Unitarian” part of the name comes from the belief that Jesus was human like the rest of us, not the son of God, though he did bring a great prophetic message to the world. The “Universalist” part comes from the belief that we are all “saved:” there is divine grace in each of us that we are all capable of reaching. Beyond that, rather than shared dogma, the faith community is united around shared principles that we commit to upholding in our daily lives. I was amazed how well these principles corresponded to the humanist values that have guided me for my whole life.

Years ago, I argued with my friend Emily, who was in divinity school at the time, about whether it was possible to be spiritual without being religious. She held that it was not possible, and I—who considered myself entirely “spiritual without being religious”—objected pretty strongly. I felt wonder at the miraculous nature of life and the universe, I felt thankful for this gift of existence. I didn’t feel the need, at the time, to share these feelings with a community. At the time, I associated organized religion with dogma, and I hadn’t ever found a body of dogma that fully conformed to my understanding of the world. After all this time, I am reconsidering my position on the issue. I still think it’s possible to be spiritual without being religious, but I find it vastly more rewarding to be part of a spiritual community. Being “spiritual but not religious” in the space of my own head, I was like a musician who practices behind closed doors and never shares the music with the world. As part of a faith community, I’m playing as part of an orchestra, sometimes as a soloist and sometimes blending into the background, but now part of a soundscape quite beyond anything that I could have made alone. No one is more astounded than I by this turn of events.

Here is the text of the sermon from this morning:

I have to say that it’s strange to me to be standing in a pulpit, speaking to a congregation. I’m not a minister; I’m a professor of environmental science at a public university. Organized religion, such as it is, played essentially no role in my life until very recently; I was raised atheist, and in my upbringing there was something of a sense that we educated people, scientists, were above all that. Usually when I give a lecture to a large group of people, I’m teaching an undergraduate course. It’s a role that I’m comfortable with. But I’m here before you today to share some ideas outside of that factual envelope that I generally inhabit. I have to admit, as a scientist, I’m a little uncomfortable talking about my faith. But I hope that there will be value in it.

The scientist and philosopher Stephen Jay Gould speaks of science and religion as “non-overlapping magisteria,” these separate realms of inquiry. Science deals with the objective, the measurable and factual; religion deals with the subjective and miraculous. In my view, it’s a nice, neat approximation—and, like most nice, neat approximations, it leaves out most of the interesting stuff.

The truth, in my view, is that science and religion need one other. Science is important because it’s the best method we’ve found yet for giving us a reality-based view of the world we live in. In the past four hundred years or so, science has given us enormous power. We can understand and respond to the causes of disease, allowing us to live longer and healthier lives than our ancestors ever dreamed of. We can produce food using a fraction of the time it once required, allowing many of us to dedicate our lives to interests beyond the day-to-day necessity of feeding ourselves. We’re surrounded by conveniences and luxuries we take for granted. We can literally travel around the world with a speed and ease that would have astounded my great-great grandparents on their voyage across the Atlantic escaping the potato famine. We understand so much about our world and its creatures and the complex, interrelated web of interactions that binds our biosphere together. We know something about our galaxy and our breathtakingly enormous universe. All these things, and many others, we understand thanks to the process of science.

But here’s the thing—not many people, these days, actually understand how science works. I see headlines all the time that grossly misrepresent it. “Scientists prove that Wikipedia is not scientifically accurate!” (Tell that to my freshmen!) “Scientists prove that 80s pop music is boring!” (Yeah, that’s a real headline.) The thing is, you can’t actually prove anything with science.

Here’s how the scientific method actually works. The only assumptions are that the universe behaves according to certain fixed laws—the speed of light, Planck’s constant, gravitation—and that human reason and senses, aided by instrumentation like telescopes, are sufficient to make sense of these natural laws.

You observe something happening in the universe—think of Charles Darwin observing the beaks of finches, or Marie Curie observing that atoms release enormous amounts of energy as they fall apart. Based on these observations, you develop a hypothesis, which is a falsifiable statement. That is, there has to be some way to definitively figure out whether it is true or false.

And then you do everything you can to show that that hypothesis is false. You test it in every way that you can imagine, and then you imagine some more tests. You can’t prove anything with science; you can only disprove and disprove and disprove until whatever’s left, this little kernel of information that you can’t refute no matter how you test it, becomes our working understanding of the world.  

In the Origin of Species, after presenting the theory of evolution by natural selection, Charles Darwin wrote a challenge to future generations of scientists. “If it could be demonstrated [he wrote] that any complex organ existed, which could not possibly have been formed by numerous, successive, slight modifications, my theory would absolutely break down. But I can find no such case.” Today, 156 years after Darwin’s book was published, we still haven’t been able to find one, which is why evolution forms a cornerstone of the science of biology.

Science is fundamentally about uncertainty. And so is religion. The difference lies in the relationship with uncertainty. Science asks us to probe the uncertainty, to try to reduce it, to treat it as a challenge to be overcome. Religion, especially a questioning faith such as ours, asks us instead to sit with uncertainty.  We recognize its presence in our lives, even perhaps honor it. Where have we come from? Where are we going? Why are we here? Religion asks us to treat these mysteries as holy. Religion asks us, like the trees in Mary Oliver’s poem [“When I Am Among the Trees,” read earlier in the service], “to go easy, to be filled with light, and to shine.”

The statement “god exists” is not really a hypothesis, because it’s not really testable. What would constitute conclusive proof of god’s existence or non-existence? You get almost as many answers as you have human beings.

On the other hand, a statement like, “increasing carbon dioxide levels are causing the Earth’s atmosphere to heat up” is a hypothesis. There are many ways to test it: you can examine the heat-holding properties of different gases in the laboratory. You can examine the atmospheres of other planets and their resulting temperatures. You can drill down into ancient glaciers and use bubbles of atmosphere caught in the ice to examine how the carbon dioxide concentration has changed over time, and use other indicators to see how temperature has changed. You can build computer models of how the Earth stores and transfers heat, and you can change the parameters of the models to test different scenarios. With all these tools, scientists are trying to disprove the hypothesis that CO2 emissions are heating up the planet. And so far we haven’t been able to.

Science itself often proceeds by numerous, slight, successive modifications. We find that CO2 is increasing in the atmosphere, that it’s heating the planet, that human activity is responsible, and that the consequences—for human health, biodiversity, and the future of the world as we know it—are, frankly, terrifying. Science can tell us what is, and it gives us good tools to predict what might be. But science can’t tell us what should be. That is the realm of ethics, philosophy, and yes, religion.

Mahatma Gandhi said, “if you want something really important to be done you must not merely satisfy the reason, you must move the heart also.”

Science satisfies the reason, but that other all-important part, moving the heart, is central to human decision-making. For billions of people around the world, religious communities are a big part of what moves our hearts. And I don’t mean to conflate morality and religion—as I said, I was raised atheist, and I was a moral person long before I joined a church. But I think there’s a great power in the messages that religious communities transmit. Right now, faith communities are taking a stand on climate change. In June, the Pope released an encyclical that lays out the moral case for confronting climate change. In August, Muslim clerics from 20 countries came together to call for climate action.

As Unitarian Universalists, we are called to respect the worth and dignity of every human life, and the interdependent web of life that supports us all. In past moments of humanitarian crisis, UUs have rescued refugees from war and stood up for the rights of the oppressed. In our current crisis, we can be leaders again.

Climate change is the defining challenge of this generation. The climate scientist Curt Stager makes a strong analogy for human control over the Earth’s climate systems. He says it’s as though we’ve just woken up to find ourselves hurtling down the highway in a giant truck going the wrong way with our hands on the wheel. And what do we do? Do we accept the responsibility and bring it safely to a stop? Or do we give up and steer into the ditch?

To confront this unprecedented threat to our world, we need to build the biggest coalition possible. And the good news is, that coalition is already coming together. Last fall in New York, many of us joined the People’s Climate March. I walked with other scientists, but I stopped at one point to watch the march stream past. Nearly half a million people had converged. I saw representatives of unions, preschools, Southern Baptist congregations, investment banks, Amnesty International. I saw people of all races, all ages, all genders; everyone committed to building a brighter future for us all.

Back to my central thesis, that science and religion need one another. Science can show us what the world is and what it might be. Science shows us an almost incomprehensibly vast universe in which our planet is a tiny speck, but it also shows us that we are quite literally children of that universe. The calcium and phosphorus in our bones were forged in the hearts of giant, perished stars. Our scientific quest for understanding calls us to explain our world. Our faith calls us to love that world and all it contains: the pain, the beauty, the uncertainty. And our faith calls us to action. May it be so.