Article on Why Is It Empty
The phrase why is it empty comes from the physics concept of "empty space", which refers to the amount of space that exists between particles. It is an important part of the electromagnetic theory of light and also applies to sound waves and other physical phenomena. In modern physics, the empty space is sometimes considered to be the background of the universe and may be viewed as an invisible "ether" or "field".
In mathematics, empty means lacking contents which could or should be present. The word is most often used in the context of set theory. In standard axiomatic set theory, the empty set is implied by the axioms of separation and infinity. It is a closed set, being the complement of any open set, and it is compact (i.e., every finite set is a clopen set).
Outside of the context of set theory, the word empty can be used in many ways, with varying meanings. For example, the expression "half empty" is a figure of speech that suggests one is indifferent to whether something is full or empty. The expression is most commonly associated with glassware, but it can also be used to describe a feeling of depression or the inability to move on from an event. The term is often accompanied by the word "why" and may be used as an informal question or statement. It can also be a rhetorical question or an accusation.