In Central Park, there’s a whole vibrant society of those of us with dogs, especially during the off-leash hours before 9 a.m. and after 9 p.m., when I let Regan lead the way and the people I get to know are appendages of the dogs she decides to wrestle with. They’re not chosen by some social-media algorithm, sorted by income level, screened by political affiliation.

Which is to say that these communions are gloriously out of step with the times. Over the past decade, I’ve watched more and more Americans retreat with greater and greater efficiency into increasingly homogeneous enclaves. I’ve marveled over our fine-grained tiers of affluence and our microclimates of privilege, which are reflected in and reinforced by the neighborhoods that we settle in, the vacation spots that we flock to, the exercise fads that we embrace, the schools that we send our children to.

And technology both speeds us to people who think precisely as we do and filters out anyone who might challenge us. We can click, scroll, sweep, share, like and favorite our way into a meticulously tailored and reliably validating tribe. There’s no real surprise, no true spontaneity, no actual serendipity.