Posted on 2019-05-10.

Being afraid of quantification is tantamount to disenfranchising yourself, giving up on one of the most potent prospects for understanding and changing the world.

My only previous exposure to Sagan was via his fiction, the novel and movie Contact. Now I have some sense of why he was such a beloved science communicator. Billions & Billions begins with a discussion of big numbers, using multiple approaches to help the reader get a sense both of what those numbers really mean and how, via exponential processes, seemingly small-scale activity can result in effects at drastically larger scales. This is an important foundation for the discussions of climate change that follow.

Sagan tells the story of the rise and fall of chlorofluorocarbons to illustrate both that human activity can have disastrous consequences for the environment, and that successful coordinated international action to curtail such harmful activity does have real historical precedent. I wasn’t too familiar with that history, so this was fascinating.

Unexpectedly, I also learned a lot about the history of abortion. The book includes a thoughtful essay Sagan co-wrote with his wife Ann Druyan, which makes an effort to present both sides’ arguments honestly and give them serious consideration. They argue that “[b]oth pro-choicers and pro-lifers (at least some of them) are pushed toward absolutist positions by parallel fears of the slippery slope,” but that the scientific realities, and the need to take seriously both women’s rights to control their bodies and the rights of young humans, call for a more nuanced view. One surprising claim to me was that the Catholic Church found abortion acceptable until the late 1800s, though some quick googling suggests the history was more complex than that.

Sagan also writes movingly about arms races. For those of us who did not live through the Cold War, it’s easy to forget about nuclear weapons; we learn about nuclear war in history books, as a threat that never came to pass. But the warheads are still around and they could still decimate our civilization in the space of minutes.

The book includes an inspiring essay that Sagan published in both the US and the Soviet Union called “The Common Enemy.” A trope in fiction is for two warring sides to come together when they realize they are being threatened by an even more menacing force. As Sagan points out, our own tendencies to destroy ourselves - by pursuing short-term gains that are ultimately disastrous for our environment, or by preparing ever-more-destructive weapons that ensure all our conflicts are increasingly catastrophic - should represent just such an enemy. The question is whether we’ll be able to unify against it before it wipes us out.

Sagan died before the publication of Billions & Billions; it concludes with reflections by himself and by Ann on his two-year struggle with illness. It’s poignant, and leaves one with the sense that they had a truly special relationship.