“I love seeing all the people in the park,” my sister told me on the phone the other night. “I can tell who is together because they are walking in little clumps!” I love that idea: little satellites orbiting the park—usually with a dog—keeping a safe distance from the other orbiting clumps nearby. My sister is in a clump consisting of herself, her husband, their two children, a dog and a cat. (I’m not sure if the cat considers himself part of the clump or not. Possibly not.) The kids are doing their homework in record time, sports are discontinued but music ...