It's been around for nearly 15 years. It's geared towards younger folks, folks with learning disabilities that might make it hard for them to read and people who are learning English as a second language.
Incidentally, for many readers of Wikipedia it may be not the language per se that is difficult to understand, so it would have been nice if there existed simpler versions of articles that otherwise may not be accessible to a lay person.
It is an intentionally simplified version of English. Although, in this case, the meaning of the article seems to have been affected by the simplification. The English version makes it clear that this is a theoretical concept, whereas the Simple English version makes it sound like something concrete/absolute.
Ironic but inevitable; the simplification appears to mostly be a matter of vocabulary. Reducing the vocabulary usually eliminates most technical jargon, and when the subject-matter is technical, the result is, well, a mess.
