We are not able to see a light ray passing directly in front of our eyes because light rays are typically invisible to us unless they interact with something that scatters or reflects the light.
The process of vision involves light entering our eyes and interacting with the structures within them. When light enters the eye, it passes through the cornea, which is the transparent outer covering of the eye, and then through the pupil, which is the opening in the center of the iris. The iris controls the size of the pupil, regulating the amount of light that enters the eye.
Once the light passes through the pupil, it reaches the lens, which focuses the light onto the retina at the back of the eye. The retina contains specialized cells called photoreceptors, specifically rods and cones, which are responsible for detecting light.
The photoreceptors in the retina convert the incoming light into electrical signals. These signals are then transmitted through the optic nerve to the brain, where they are processed and interpreted as visual information.
However, the process described above occurs when light enters the eye and interacts with the structures within it. Light rays passing directly in front of our eyes without interacting with any structures would not produce a visual sensation because there is no stimulus for the photoreceptors to detect and convert into electrical signals.
So, while we may be aware of light sources or objects in our field of view, we do not directly perceive individual light rays passing in front of our eyes unless they interact with objects or surfaces and are scattered or reflected back into our eyes.