I head out for a walk with the dog as I listen to one of Sam Harris’s latest editions of the Waking Up podcast in which he discusses the nature of time with physicist Frank Wilczek. We like to think of time as this little moving slice of now that’s passing through the past into the future, but it’s really not like that at all. Time in a sense is the measure of change, and basically clocks things that change predictably and regularly against which we mark the seeming passing of time. In that sense, then, everything that changes is a clock, Wilczek points out.

Everything is a clock. I stopped in mid-stride to think about that. It’s so profound and yet so simple at the same time, an observation that’s been staring us in the face all our lives but eluding us at the same time. Simple, elegant.

As I continue my walk, I pass a man standing in his garage talking on the phone. I raise my hand in greeting. It’s a Southern thing — we wave at everyone — but he doesn’t wave back. “Perhaps he didn’t see me,” I think. Then, noticing some of the flags hanging in his garage indicating a political persuasion diametrically opposed to mine, a little thought experiment begins in my head. “What if we could read each other’s minds? We’d know where the other stands on so many issues that we otherwise keep to ourselves. We’d really, truly know one another. Would we be less likely to wave at each other?” And that’s a terrifying thought.

About this time, I grow tired of the podcast and switch to a playlist I’ve created called “Nostalgia” — songs to induce just that. The first song up: “Private Universe” by Crowded House. What a strangely perfect song. It’s not at all about the private universe I’ve been contemplating, but what a coincidence. Private universes — the physicists’ idea of a multiverse is a reality, because we all live in our own private universe. It sounds lonely, but it’s much more comfortable for us to live in these little walled-off universes because they afford some privacy that a non-private, evening-walk-thought-experiment mind-reading universe would render impossible. Even if that means we never truly know one another, it’s better in our private universes. We’re passing our experiences and memories, emotions and impulses through our own filters as we share them with others who then pass them through their interpretive filters. There are so many layers separating us that it’s a miracle we can claim to know anyone at all.

But there’s a hint of tragedy in this, because even with those with whom we’d be most willing to share such a non-private universe, it’s impossible. I will never truly know my children because of all the things they don’t, won’t, or can’t share with me, and they will never really know me. In a sense, we live with strangers, each and every one of us. The only thing we truly have in common is the fate that awaits us all — when the clock that is our body wears down and stops recording time for us as conscious individuals and begins to be a measure of unconscious decay.

It’s about this time that the next song comes on: Billy Joel’s “Lullabye (Goodnight My Angel).” This song has always made me think of Natalia, a student I taught in Poland who died before her senior year in the summer of 1999. “That’s almost 22 years ago now,” I think. “Had she not died, she’d now be old enough to have children older than she was when she died.” The song winds down:

Someday we’ll all be gone
But lullabies go on and on
They never die
That’s how you
And I will be

How did I never notice that nod to mortality at the end of the song? And how is it that a talk about physics can end with such nostalgia? I feel like I should have an answer, but I also feel like none is needed. I’ve done what I set out to do: record some thoughts I had one February evening as I walk our silly dog, and that’s really all this is for. Billy Joel writes his songs that will never die; I write a blog a decade after they ceased being hip.