Seeing the Natural World With a Physicist’s Lens

Yet for all these apparent flaws, the basic building blocks of humaneyesight turn out to be practically perfect. Scientists have learned that the fundamental units of vision, the photoreceptor cells that carpet the retinal tissue of the eye and respond to light, are not just good or great or phabulous at their job. They are not merely exceptionally impressive by the standards of biology, with whatever slop and wiggle room the animate category implies. Photoreceptors operate at the outermost boundary allowed by the laws of physics, which means they are as good as they can be, period. Each one is designed to detect and respond to single photons of light — the smallest possible packages in which light comes wrapped.

“Light is quantized, and you can’t count half a photon,” said William Bialek, a professor of physics and integrative genomics at Princeton University. “This is as far as it goes.”

So while it can take a few minutes to adjust to the dark after being fooled by a flood of artificial light, our eyes can indeed seize the prize, and spot a dim salting of lone photons glittering on the horizon.

Photoreceptors exemplify the principle of optimization, an idea, gaining ever wider traction among researchers, that certain key features of the natural world have been honed by evolution to the highest possible peaks of performance, the legal limits of what Newton, Maxwell, Pauli, Planck et Albert will allow.