When there are light sources and objects, shadows can be sure there.On the contrary, I assume that you found the shadow. There is an object blocking the light by all means there. The shadow is proof for "There is the object there".If the shadow has disappeared... you should think that the object had disappeared. It is the only reality.
Graduate Work 2010, Tokyo University of the Arts, Graduate School of Film and New Media, Department of Animation
(Source: Geidai Animation)