Question

What difference we cannot see of people with our naked eye?
For ex — we can see the physical attributes such as hair colour, weight, likes, etc.

Answer 1

The human eye can only see visible light, but light comes in many other "colors"—radio, infrared, ultraviolet, X-ray, and gamma-ray—that are invisible to the naked eye. On one end of the spectrum there is infrared light, which, while too red for humans to see, is all around us and even emitted from our bodies.