LIGO uses 4-kilometre laser arms to detect gravitational waves at hundreds of hertz. Pulsar timing arrays use millisecond pulsars scattered across the Milky Way — arms measured in light-years — to detect gravitational waves at nanohertz frequencies, ten orders of magnitude lower. In June 2023, five independent pulsar timing arrays simultaneously announced the detection of a stochastic gravitational wave background. The Milky Way itself was the detector.

A unit for lower secondary physics classes (grades 8–10) on detecting exoplanets with analogy experiments. Published in Unterricht Physik in 2023, it starts where students’ misconceptions are — with the (wrong) assumption that you can just look at exoplanets through a telescope — and works forward from there.

Three years after writing about why classroom video works, Charlotte Kramer, Kai Kaspar, and I wrote a manual on how to actually do it. The gap between knowing that video-based learning is effective and being able to produce usable footage turns out to be substantial. The manual is open access. Here is what is in it and why some of it surprised me to write.

Messiaen’s seven modes of limited transposition cannot be fully transposed through all twelve keys — not by convention, but because of group theory. The modes are pitch-class sets whose stabiliser subgroups in ℤ₁₂ are non-trivial. The orbit–stabiliser theorem gives the exact count of distinct transpositions for each mode, and the subgroup lattice of ℤ₁₂ maps directly onto the hierarchy of the seven modes.

“Aus der Nähe betrachtet ist keiner normal.” The slogan of a Sozialpsychiatrisches Zentrum sounds compassionate. It is, under scrutiny, a gift to everyone who has ever said “but everyone gets depressed sometimes.” It attacks a concept psychiatry abandoned decades ago, dilutes the clinical categories people with severe conditions need to be taken seriously, and — most ironically — argues against the relevance of its own institution. A Karneval roast, with citations.

Alongside physics and astronomy, two other things have occupied an unreasonable share of my attention since adolescence: mathematics and music. Lateralus by Tool — released 2001, still in rotation — is the piece that most conspicuously occupies the intersection. The song is structurally built around the Fibonacci sequence, from the syllable counts in Maynard Keenan’s vocals to the time signature pattern that concatenates to F(16). This post works through the mathematics in some detail and asks why it works musically.

The EHT images of M87* and Sgr A* are remarkable not because they surprised us, but because they confirmed a century-old prediction at microarcsecond precision. The more interesting question: what would a wormhole look like? Completely different — and we have never seen that.

In spring 2020, the astro-lab at the University of Cologne shut down like everything else. The question was whether you could replicate a hands-on student lab using smartphones and household materials — and send it home. This is the story of how we tried, what we published in CAPjournal, and what happened when schools reopened.

In June 2022 I presented on educast.nrw at the Tag der Lehre at HfMT Köln. This is the longer argument behind that talk: why universities should not outsource their video infrastructure to commercial platforms, and what a better alternative looks like in practice.

Stellar evolution is now in the NRW physics curriculum, but there are almost no direct experiments you can do with it. Two responses: some DIY smartphone experiments for stellar formation, and a board game called “Staub und Sterne” (Dust and Stars) that lets students play through the stellar lifecycle. Both grew from the astro-lab project at the University of Cologne.