There is only one empty set in existence, and all references to the empty set refer to the same thing. All physical reactions to the empty set are reactions to the same thing. This gives the empty set characteristics of a physical object.
Paul the Apostle (Wikipedia)Paul (also named Saul of Tarsus; c. 5 – c. 64/65 AD), commonly known as Paul the Apostle and Saint Paul, was a Christian apostle who spread the teachings of Jesus in the first-century world. Generally regarded as one of the most important figures of the Apostolic Age, he founded several Christian communities in Asia Minor and Europe from the mid-40s to the mid-50s AD.