One of the first instruments for directly observing single quantum events was the human eye. A device called the spinthariscope, consisting of a phosphor screen and a lens, allows a human eye to see flashes of light caused by individual charged elementary particles impacting on the phosphor screen. The now-obsolete cathode ray tubes worked by transforming the impact of high-speed electrons into bright flashes of light on a phosphor screen. Many of the early physics experiments on alpha-particle scattering (including Nobel Laureate Ernest Rutherford's experiment that first determined the structure of the atom) were carried out by human eyes working long hours counting light flashes on phosphor screens. These naked-eye detectors have long since been superceded in physics by ingenious electronic means of registering charged particles and photons, down-grading the unsophisticated spinthariscope to the status of a toy.
Recently however, physicist Nicolas Gisin and his colleagues at the University of Geneva have revived interest in the human eye as a detector of light. The modern field of quantum optics has allowed physicists to produce many varieties of "unnatural light", including "squeezed light", "sub- and super-Poissonian light", "Fock state light" as well as "coherent" and "entangled" light. So far all of this "lux contra natura" has only been observed by electronic photon detectors but Gisin et al are now considering for the first time to involve the human eye in these quantum measurements.
Gisin's proposal has inspired wild speculations on the Internet about the possibility of "quantum entangling human beings" by allowing a pair of people to simultaneously observe unnatural forms of light.
Similar speculations concerning the deep entanglement of human beings by exposing their retinas to unusual forms of light were posed earlier in this blog in the context of devices called Stellerator and Lunerator.
Like the motto of Star Trek, the very essence of science is to boldly go where no man has gone before. Most likely deep human entanglement by simple retinal exposure to unnatural forms of illumination will turn out to be a pipedream, but, in science, experiment will always trump speculation.
Gentlemen (and ladies) our scientists have created for your pleasure several astonishingly new forms of light.
Please enter our Geneva light lab, wait your turns, then simply open your eyes.