Light consists of photons. When those photos get reflected (or emitted) from that object and reach our eye, we see the object. Technically, the photons reach the human eye and then a signal is passed to human brain to process the information. Since 1940, researchers have asked, how many photons are needed for a human eye to perceive a signal and send the message to brain for processing?
As per the research paper published by Nature Communications, human eyes have the capability to sense even a single photon. Alipasha Vaziri, a physicist at the Rockefeller University in New York City led an interesting experiment to make this observation. Three volunteers spent 40 minutes in absolute darkness. The volunteers were asked to push the button of an optical system that randomly fires a single photon. The volunteers don’t know when the optical system will fire a photon. The volunteers have to say, on which occasion they observed a photon and what was their confidence level on the scale of 1 to 3. From this experiment, it was revealed that, participants were able to guess the presence of photon with higher confidence.
The experiment performed by Alipasha Vaziri is crude and doesn’t provide 100% evidence to conclusively state that humans can sense single photons. Nonetheless, this experiment raises lot of important questions, which the researchers can seek answers. Photons exhibit both particle and wave nature and it would be very interesting to know, how it affect human biology.
Following articles by Nature are good read on this subject: