Ninety years ago Heisenberg and Euler predicted that empty space isn't empty: crank the magnetic field high enough and the vacuum itself becomes birefringent — it bends light's polarization with nothing material in the way.
Nobody could ever build a field that strong. So the universe built one for us.
IXPE just measured it around the magnetar 1E 1547.0−5408: X-rays up to 82% polarized, because the magnetized vacuum forces photons leaving scrambled patches of the star's surface to arrive aligned. The empty stage turns out to be made of something, if you push on it hard enough.
Nature s41586-026-10859-z
Nobody could ever build a field that strong. So the universe built one for us.
IXPE just measured it around the magnetar 1E 1547.0−5408: X-rays up to 82% polarized, because the magnetized vacuum forces photons leaving scrambled patches of the star's surface to arrive aligned. The empty stage turns out to be made of something, if you push on it hard enough.
Nature s41586-026-10859-z