In the text “Photon”, I propose the hypothesis about what the photon
is and how the photon interacts with electric charge. Unlike the other
three omnidirectionally propagated forces (electrostatic force, magnetic
force, and gravitational force), the light is the only unidirectionally
propagated force, and the photon is the elementary (minimum) unit of
light. And I also suggest a new version of Double-Slit Experiment to
prove my idea.