Light.
A word so simple it can hardly be simpler.
A phenomenon so common it couldn't be more common.
Yet it's a strand that runs through human scientific history, a mystery that remains elusive even into the 22nd century.
Speaking of light, later generations often first think of wave-particle duality.
Then comes Ultraman Tiga, followed by terms like interference and diffraction of light.
Actually.
Humankind's contemplation about the nature of light started to show hints even before the Common Era.
For example, in ancient East.
People believed the Sun was an embodiment of Divine Spirit, for instance, Xi He, Sun Lord, East Lord, and the Golden Crow shot down by Hou Yi, among others.
And in ancient West, the prevailing idea initially was Empedocles' view.
He believed the world was composed of four elements: water, fire, air, and earth, and human eyes were ignited by the goddess Aphrodite, with light also belonging to fire.
