earth on foot 10
The population of Mainz, Germany, is approximately 223,000 as of 2023. It is the largest city in the state of Rhineland-Palatinate.
As of 2025, Berlin has an estimated population of approximately 3.58 million people, making it the largest city in Germany and the most populous city in the European Union. The city has seen steady population growth in recent years.
I’m sitting on a bench beside a hilltop path in Mainz, Germany. The area, Historische Balanitiseiche, translated as “historic balanced oak”, is called a “garden” by Google Maps. Intermittently, someone walks or rides by, mostly with their dogs. An airplane from Frankfurt Airport groans overhead. The cool, overcast afternoon resonates with crickets’ late July susurrations.
Yesterday we took the train back from Berlin, a five-hour ride. David gave a talk on entropy, and we visited family who live in the Kreuzberg region.
An enclave for artists, Kreuzberg, which was once surrounded on three sides by the Berlin Wall, now boasts intense levels of street art. Pretty much everywhere you turn. Coffee houses, flea markets, galleries, and good pizza, too. Super fun.
Entropy
Buildings in Berlin seem both fixed in time, half in rubble, and, in my brief visit to Mitte—the city center—also bright and new. It seems a city chill in its embrace of change. But, of course, my take is but one tiny atom’s, one particle awash in the cosmic landscape, motivated to share her view with you.
As I reflect, strolling back-and-forth in front of my bench, I observe a woman pushing a white-haired person wearing a knit vest. The pair chat enthusiastically as they make their way up the hill. Meanwhile, another guy walks his bike up a steep incline, then gets onto it and pedals away, his bright blue Wolt insulated box retreating quickly around the bend. He’s probably delivering somebody’s lunch.
I say “Guten Tag” to the wheelchair couple as they pass me, and we all nod at each other and smile, though with some seriousness. We are all in the middle of something else.
The temperature has dropped and the breeze presently gives me goosebumps. Still, I stay a while, remembering running along the canals and parks in Berlin, of which there are many, including the curious Tempelhofer Feld, since 2008 a decommissioned airport in the middle of the city. On Saturday the terminal building was beautiful and strange, inching towards ruin while outside of it carnival tents swayed; an asphalt tract attracted rollerbladers and fast-moving cyclists who chatted loudly. We watched as security told a woman from afar to leash her dog, all of us walking on some part of former runways.
Entropy*, David’s topic, makes sense for a city like Berlin. It makes sense, too, that artists think about it, and ask a physicist to come explain what it means.
Turning and turning in the widening gyre
The falcon cannot hear the falconer;
Things fall apart; the centre cannot hold;
Mere anarchy is loosed upon the world,
The blood-dimmed tide is loosed, and everywhere
The ceremony of innocence is drowned;
The best lack all conviction, while the worst
Are full of passionate intensity.
—William Butler Yeats, 1919
The poem is more fierce than the mood I’m reaching to describe. Berlin, for me, is a city with a multiplicity of states existing simultaneously, each with its own trajectory, differing velocities, thermal equilibriums… True everywhere, I suppose, but somehow Berlin really encapsulates a feeling of tragic simultaneity—like someone who has seen it all, lives to tell the tale, still hopes.
Mainz, by comparison, even with its construction, busy bike lanes, and delicious Ethiopian food, feels like everyone’s gone on holiday. It’s quiet here, and that feels nice. Yesterday I enjoyed a long run after the train ride, rejuvenated as I crossed the languorous Rhine and back, enjoying lush green spaces on either side. I lucked out and hit the 1.5-hour window of no rain when all was fresh and new.
Time to prepare for the flight in three days as we return stateside!
click below to watch a short film I made with david’s explanation of *entropy
The weaving together of physics, observation and Yeats—thank you!