Magnetic fields are an often-overlooked but ever-present component of the universe's structure. The looped tangles on the Sun, Earth's north–south axis, the spiral pattern weaving through the plane of the Milky Way — all share a common origin. Where that origin lies has long been debated.

The standard cosmological picture is that the strong fields seen on galactic scales did not arise on their own. The galactic dynamo amplifies a faint seed field by factors of millions through the motions of interstellar gas; but the dynamo must have something — however weak — to amplify. The seeds most likely came from quantum fluctuations frozen in during the universe's earliest moments, perhaps during cosmic inflation or during electroweak phase transitions in the first fractions of a second.

Direct observation is hard: primordial fields are extremely faint and are probed through their subtle imprint on the polarization of the cosmic microwave background. Missions like Planck and the upcoming CMB-S4 have placed upper limits but not yet a definitive detection. Even so, the magnetic texture of every galaxy we now observe is best understood as the amplified echo of a faint signal from the universe's earliest instants.