Light can propagate without any loss in open systems

https://phys.org/news/2024-01-team-robust-propagation.html

"energy gain and loss systematically distributed cancelling each other out, ensured by parity-time (PT) symmetry... tests on laser photonic chips mimic behavior of natural and synthetic materials arranged in periodic lattice structures... laser-inscribed photonic waveguide induced topological insulators convey lossless stream of electrons or light (retaining average amplitude) along their boundary, suppressing impact of topology's varying defects and scattering... robust electric, light and sound wave circuits"