Quantum Geometry Imprints in the Black Hole Shadow
The shadow of a black hole is not just a dark silhouette. It is an imprint of the entire spacetime geometry, including the subtlest quantum effects.
A Vortex's Silent Patch Reveals Its Speed
In a water vortex swirling toward the drain, the flow speed near the center can exceed the speed of sound. Sound gets trapped: waves cannot escape back, forming a silent region — a sound shadow. Half a century ago, William Unruh realized that this is an exact copy of a black hole, but for sound instead of light.
Time Can Still Be Tricked
Some solutions to Einstein's equations allow closed timelike curves — loops that let you travel to the past. Two well-known designs, the Ori geometry and the Ahmed geometry, do without exotic matter, catching physicists' eyes.