People can sense single photons

Posted on Mar 9, 2022      186

A photon is an amazing elementary particle, a quantum of electromagnetic radiation. It has no mass and can only exist moving at the speed of light. Simply put, a photon is light. Everything we see around us is the merit of countless photons, which, reflecting off objects, reach the retina of our eye, where there are about 126,000,000 light-sensitive stick cells to “receive” them. The brain then transforms the information it receives into a three-dimensional image.

Scientists have long been interested in the question of what the minimum number of photons must hit the retina for a person to feel them, or even for a moment saw a small flash of light. Back in the late second half of the 20th century, researchers have conducted many experiments, which concluded that a person sees a tiny flash of light, or at least feel photons, if the retina hits at least five elementary particles. But now scientists are ready to declare: nature has given man such a sensitive mechanism for perceiving electromagnetic radiation that we can react even to 1 photon!

The study, published in the scientific journal Nature, claims that the people who took part in the experiment feel the photon hitting the retina not as a flash, but as a kind of “feeling on the verge of imagination”.

Three volunteers sat in a dark room for 40 minutes and then, without turning on the lights, sat in front of a special optical device with a single button. By pressing the button, they heard two beeps with an interval of one second. At random, simultaneously with one of the sound signals, the system emitted one photon toward the sitting person’s eye.

Subjects were asked to answer when they thought the photon hit their retinas and how sure they were on a scale of 1 to 3. most times people answered incorrectly, which was predictable since in 90% of attempts a single photon does not reach those very stick cells, being reflected or absorbed by other parts of the eye. In the remaining cases, however, subjects responded correctly with a much higher probability than if they were just trying to guess the result. Interestingly, when the participants in the experiments were correct, their confidence was at the 3-point level.

There were over 2,400 cycles of the experiment involving photons and several times as many cycles without the participation of the elementary particle. Scientists who conducted the experiment, believe that such a sample gives them the right to declare the validity of the experiment and the recognition that the person can feel the impact on the retina of just one photon.