How well designed is the human visual system? Biophysics researchers from the Research Institute of Molecular Pathology in Austria and Rockefeller University recently demonstrated that people can see just a single photon of light. This led them to ask how evolution could have crafted a visual system sophisticated enough to overcome the overwhelming problem of discerning single photons from the sea of electromagnetic, molecular, and electrochemical “noise” inside a human head.
Research from the 1940s suggested human vision might have the ability to detect single photons, but the tests available back then couldn’t send just a single photon toward an observer’s eye. A new setup uses a crystal to split a high-intensity photon into two low-intensity photons. The process directs one low-intensity photon to the subject’s eye and the other low-intensity photon to a camera as a crosscheck.
The team performed over 30,000 trials. They wrote in the journal Nature Communications, “To our knowledge, these experiments provide the first evidence for the direct perception of a single photon by humans.”1
The designs of the man-made research camera and the human-visual system deserve comparison. The experiment’s camera engineers are smart, educated people, and they specified the right materials and the right shapes and sizes for all the camera’s components. They arranged them at the optimum angles and assembled them in the right order to manufacture the single-photon-detecting camera. What might they say about the assertion that chance evolutionary processes, not a person, engineered the entire human visual system?
Alipasha Vaziri is the senior author of the report and head of the Laboratory of Neurotechnology and Biophysics at Rockefeller University. He told Rockefeller news,
If you imagine this, it is remarkable: a photon, the smallest physical entity with quantum properties of which light consists, is interacting with a biological system consisting of billions of cells, all in a warm and wet environment. The response that the photon generates survives all the way to the level of our awareness despite the ubiquitous background noise. Any man-made detector would need to be cooled and isolated from noise to behave the same way.2
Indeed, his team had to cool the detector they used, an EMCCD camera, to -80C to get it within the sensitivity range of single photons. Low temperatures reduce the number of random detection events, called noise, which occur even when no photons enter the system. The team also had to optimize their camera by adjusting at least six other parameters, listed in Supplementary Table 2.
These two detectors offer a crisp analogy. If human camera construction and optimization requires sub-freezing and dry conditions to detect single photons, then only a super-human design could overcome the much more challenging noise problem that a wet and warm living environment adds to the human visual system.