Two water droplets tremble in sync — because they're connected by a straw. So it is with entangled particles: their unity may be held together by a microscopic wormhole. Juan Maldacena and Leonard Susskind called this conjecture ER=EPR: Einstein-Rosen bridges (ER) equal the Einstein-Podolsky-Rosen paradox (EPR).
If such a wormhole exists, a charged particle could lose part of its electric field into the tunnel. For the simplest atom — hydrogen — this would result in a frequency shift of the famous 21 cm line, its 'radio voice'. Spectral analysis could detect a change of billionths of a percent. But more importantly: an impassable wormhole would lock away some charge inside, making the atom slightly charged.
Yet hydrogen is exceptionally neutral. Measurements give zero down to 10⁻²¹ of the electron charge — like looking for a single grain of sand on all the beaches of Earth.
Precision experiments within ordinary physics are valuable because they can test the boldest hypotheses about the geometry of the universe.
The 21 cm radio line is the voice of the universe's most abundant element. Using it, astronomers map invisible hydrogen and hunt for dark matter.
In 'Interstellar', wormholes are colossal portals between stars; this new work brings those bridges to the subatomic level, inside the hydrogen atom.