“What we observe is not nature itself, but nature exposed to our method of questioning.” -Werner Heisenberg
Empty space, according to quantum mechanics, isn’t exactly empty. Take away all the matter, radiation and anything else you can have populating your space, and you’ll still have some amount of energy in there: the zero-point energy of the Universe. One consequence of quantum electrodynamics is that this sea of virtual particles is always present, and a strong magnetic field can lead to some really bizarre behavior.
Known as vacuum birefringence, it was theorized by Werner Heisenberg and Hans Euler more than 80 years ago, as these electron/positron pairs get yanked along the magnetic field lines. In theory, this should polarize the light from photons passing through fields that are strong enough, but we’ve never been able to observe it. Until now. Thanks to the VLT and light from a neutron star, the prediction is confirmed for the very first time.