Then he told me, very tenderly, that it can be dangerous to believe things just because you want them to be true. You can get tricked if you don’t question yourself and others, especially people in a position of authority. He told me that anything that’s truly real can stand up to scrutiny.

As far as I can remember, this is the first time I began to understand the permanence of death. As I veered into a kind of mini existential crisis, my parents comforted me without deviating from their scientific worldview.

“You are alive right this second. That is an amazing thing,” they told me. When you consider the nearly infinite number of forks in the road that lead to any single person being born, they said, you must be grateful that you’re you at this very second. Think of the enormous number of potential alternate universes where, for example, your great-great-grandparents never meet and you never come to be. Moreover, you have the pleasure of living on a planet where you have evolved to breathe the air, drink the water, and love the warmth of the closest star. You’re connected to the generations through DNA — and, even farther back, to the universe, because every cell in your body was cooked in the hearts of stars. We are star stuff, my dad famously said, and he made me feel that way.