How cosmic voids bend the cosmic microwave background—and what that tells us

Cosmic voids—vast empty regions between galaxy clusters—bend light from the cosmic microwave background as it travels to us, creating a detectable lensing signature. Using realistic mock catalogs, researchers quantified how different measurement choices affect this signal and forecast what Roman, Planck, and next-generation CMB surveys can achieve. The void-lensing signal is robust to mock construction details, and combined surveys could measure it at 31-sigma significance—far stronger than current galaxy clustering constraints.