Detecting any evolution of dimensionless in the ratios of physical quantities, such as the fine structure constant, would prove that the Weak Equivalence Principle is violated and lead to a paradigm shift in physics. High resolution spectroscopy of quasar absorption systems can be used to test cosmological variations in time and/or in space. A sample of 300 measurements using data from 8m class optical telescopes provides hints that such variations are indeed present in a form of a spatial dipole across the sky, although systematic effects could dominate. Two recent developments, one in instrumentation and the other in analysis methods, promise to produce a new sample of measurements free from all known systematic effects to test the tentative dipole.
Comment: Contribution to the 2023 Gravitation session of the 57th Rencontres de Moriond