I’m extremely excited to see my new paper with Miguel Sabogal, Luis Escamilla, Davide Pedrotti, and Edvig Selimaj out today, making it yet another paper (almost) entirely produced within my group, of which Luis is by now de facto honorary member 😉! The usual argument against late-time solutions to the Hubble tension is essentially a normalization one, i.e. the fact that the “amplitude” of BAO data is H0*rd, so raising H0 necessarily requires lowering rd, calling for pre-recombination new physics. However, we recently realized that the shape of the expansion history, i.e. the dimensionless expansion rate E(z), is extremely tightly constrained by unanchored SNeIa, as well as uncalibrated BAO: we would therefore expect a “shape wall” to exist beyond the usual normalization wall, and our aim in this paper was to point this out while quantifying exactly how strong the shape wall is. In short, the analysis turned out to be a bit more complicated than we initially thought, but we were able to robustly show that a percent-level shape wall is present, potentially stronger than the BAO normalization wall: therefore, it is not just the BAO normalization which forbids late-time solutions to the Hubble tension, but also (and perhaps especially) the shape of the expansion history, something we hope our paper will help appreciate more. You can read our results in the preprint we just posted on arXiv: 2607.21244.