Sometimes, the magnetic fields are relatively weak, like the ones that thread their way through the spiral arms of galaxies. Sometimes, they're medium-strength, like Earth's.

Floating in water, 12 tiny magnetic droplets spin in unison under the influence of a rotating magnetic field. Credit: Thomas P. Russell “We almost couldn’t believe it,” Russell says.

Two German physicists have reimagined how to create powerful and uniform magnetic fields using compact permanent magnets. By overcoming the limitations of the well-known Halbach array, which works ...