““So when nobody's watching, is the rainbow there? No, it is not. Your eyes are needed to complete the geometry. The triad of Sun, water droplets, and observer are all required for a rainbow. When no one is present, we can picture the situation as an infinity of potential rainbows, each slightly offset from the others with various color emphases (since bigger droplets produce more vivid rainbows but rob them of blue). Moreover, only when neurons in the retina and brain are stimulated by light's invisible magnetic and electrical pulses do they conjure the subjective experience of spectral colors. For both reasons, we are as necessary for rainbows as the Sun and the rain.””
