Yu-Xiao Liu

A black hole's shadow is a dark spot against the bright light bent by strong gravity. Usually, this spot is an almost perfect circle with a smooth edge. But if a black hole is not quite what Einstein's theory predicts, a sharp kink, like a corner on a crumpled piece of paper, can appear at the shadow's edge.

Light usually behaves like a pedestrian on a two-way street: the path from a streetlamp to a camera matches the reverse path. But near a rotating black hole with broken spatial symmetry, this street becomes one-way. Swap the light source and observer, and the hole's shadow changes shape: from an oval resembling a rugby ball, it turns into a teardrop.

Gravitational wave detectors work like sensitive microphones, picking up the trembling of space from distant cosmic catastrophes. When two black holes merge into one, the newborn object rings like a bell, and that ringing is a unique 'voice' of gravity.

Throw a stone into a pond — ripples spread out, changing the scale of the wave. The new theory works much the same way: it gives each particle its own "scale ripple," and it's this curvature of an invisible space that turns out to be the source of mass.

Quantum field theory is the language physicists use to describe elementary particles and their interactions. The authors of the work decided to slightly "tweak" this language: they introduced deformations, that is, small changes to the rules of the game.