Item from remembrance-of-earths-past by
A small, paper-thin slip — the size of a credit card, white as a business card — which when activated collapses three-dimensional space into two dimensions over a runaway radius. The Dark Forest weapon that flattened the Solar System.
The dual-vector foil is the trilogy's apocalypse, delivered without effort. Singer — or whoever sent it — fired it like a man flicking a thumbtack. It collapses 3D into 2D and there is no defense; the only escape is curvature propulsion, and even that has to clear thirty AU before the foil's range outpaces escape velocity. The Solar System dies under one. Cheng Xin watches Pluto flatten from Halo's bridge.
A flat strip of perfectly smooth, perfectly white material, no thicker than ordinary paper, rectangular, slightly translucent. Indistinguishable from a piece of stationery until activated, after which it becomes a slowly expanding event-horizon-like field that collapses everything inside it from 3D to 2D. The collapse is visible to outside observers as a Van-Gogh-like Starry Night swirl of flattened matter.