A vacuum is defined as a space devoid of matter.

Atomism, a ancient Greek school of philosophy which flourished about 400 B.C., held that a vacuum was an essential part of nature in which atoms--the discreet, indestructible units of matter--could interact and thereby create the universe. The Greek philosopher Aristotle, however, decreed that a vacuum could not exist. He correctly believed that the atmosphere had weight, and as air became less dense it would be possible to move faster through the atmosphere. Yet the next step of his reasoning went somewhat astray. In a complete vacuum, he reasoned, infinite speed would be possible because motion would encounter no resistance. Since he did not accept the possibility of infinite speed, he decided that a vacuum was equally impossible.

Aristotle's views endured as the familiar dictum "nature abhors a vacuum," and was used to explain the action of such inventions...