Scientific American (July 10) -- Paul Kwiat asks his volunteers to sit inside a small, dark room and gaze with one eye at a dim red cross. On either side of the cross is an optical fiber, positioned to pipe a single photon of light at either the left or the right side of a volunteer’s eye. Even as he verifies the human eye’s ability to detect single photons, Kwiat, an experimental quantum physicist at Illinois, and his colleagues are setting their sights higher: to use human vision to probe the very foundations of quantum mechanics.