Our perceptions are relative because there are no absolute concepts of time, space and motion. These concepts are relative. They exist in relation to us. If we wouldn’t possess an internal notion of time, space and motion, then we would perceive them differently. We conclude that a person is kind of a “black box” – a completely enclosed system. What gets into this box is what a person knows, feels and senses. The sum total of these sensations is what we call “our world”, “this world” or simply “the world”. Everything else that possibly exists outside of this box, but does not get into it, is unknown to the person. The person cannot even guess that there may be something else outside of his realm of perception.
Courtesy of http://www.youtube.com/watch?v=X1ohmSeQELw