The other day, I saw on social media that my 40th high-school reunion will happen next spring. I felt a pang. That sensation passed, and while it lasted, it offered some sweetness along with a sense of loss. I would not take a pill that prevented similar reactions in the future. Still, it was an interesting feeling that might tell me something about my personality or even about the nature of time and identity. Also, I suspect that my nostalgia reflected a mistake: a desire for something impossible (backward time-travel) or a failure to appreciate the living present sufficiently. Although […]