light

Although in physics light is well-understood as electromagnetic energy of a very specific wavelength (between 390 and 740 nanometers: a nanometer is 10^–9 metre), the fact that this is just the energy that illuminates the world for us is evidently contingent upon the nature of our senses, and upon the adaptations they have made to the environment. Light can thus come to inherit the problems of secondary qualities (see primary/secondary qualities ), and just as the fact that trees are green can seem due to our design as much as to non-human nature, so the fact that it is light or dark may seem disturbingly anthropocentric or subjective. Descartes put the problem by asking ‘could nature not also have established some sign, which would make us have the sensation of light, even if the sign contained nothing in itself which is similar to this sensation?’ (Le Monde ). Light has been associated with the original primal creative principle in many religious and philosophical traditions, including Zoroastrianism and Neoplatonism.