An experiment to test the limits of human vision has provided the strongest evidence yet that our eyes can sense flashes of light as feeble as three photons.

The study, which involves firing photons into the eyes of people sitting in a dark room, could ultimately show whether people can sense single photons, according to Rebecca Holmes, a physicist from the University of Illinois at Urbana-Champaign. She presented her team's results at a meeting of the American Physical Society on 10 June in Columbus, Ohio. Holmes also hopes to test whether the human eye can register quantum effects, such as a photon being in two places at the same time.

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