If, for some reason, you managed to make an egg stand on its end during the recent equinox, experimental physicists could do with your help. An exquisitely sensitive experiment that can only be performed during equinoxes could test some of the theories that offer an alternative to dark matter.

Stars on the outskirts of galaxies are moving much faster than can be explained by the gravity of visible matter. To account for the extra gravity, astronomers have proposed the existence of dark matter. In the 1980s, Mordechai Milgrom, then at Princeton University, suggested that the observations could also be explained …