During their long propagation, neutrinos undergo flavour conversions.
High-energy astrophysical neutrinos propagate unperturbed over a billion light years in vacuum and are potentially sensitive to small effects caused by new physics.
For instance, they are sensitive to the effects of quantum gravity, which are expected to be suppressed by inverse powers of the Planck energy in our low-energy scales.
Measuring the coupling of particles to such small effects is difficult via kinematic observables, but could be observable through flavour conversions.
Here, we report a recent result from the IceCube Neutrino Observatory, which uses astrophysical neutrino flavours to search for new space-time structure.
We found no evidence of anomalous flavour conversion in the IceCube astrophysical neutrino flavour data.
Our analysis yielded the most stringent constraint of any known technologies, down to 10$^{-42}$~GeV$^{-2}$ on dimension-six operators that parametrize the interactions of neutrinos with new fields in vacuum with Bayes factor corresponding to a ``strong'' rejection.