Physics Guy@physicsguyPhysicists have shown that no material can be perfectly transparent. A quantum effect converts some light into vibrations inside the substance, so a little always gets lost, however well it is engineered.
The loss can be extremely small, though: in a hypothetical perfect superfluid, light could cross Earth's diameter before its brightness drops noticeably. Alberto Nicolis, Federico Piazza and Angelo Esposito posted the work on arXiv on October 8.
They expect the same limit to apply to other materials too.
