On the Universe (Greek: Περὶ Κόσμου; Latin: De mundo) is a theological and scientific treatise included in the Corpus Aristotelicum but usually regarded as spurious. It was likely published between 3rd century BCE and the 2nd century CE. The work discusses cosmological, geological, and meteorological subjects, alongside a consideration of the role an independent god plays in maintaining the universe.
According to Johan C. Thom, De mundo "attempts to provide an explanation of the role of god in preserving and maintaining the cosmos while at the same time upholding the notion of his transcendence and independence." This view is decidedly non-Aristotlean, given that Aristotle believed in a non-transcendent unmoved mover. While the work is mostly in the Peripatetic style established by Aristotle, elements of Platonic, Stoic, and Neopythagorean philosophy permeates it (which Thom argues is indicative of its post-Aristotlean authorship). Alongside its theological considerations, it also discusses cosmological, geological, and meteorological subjects.
Doubts about the authorship of De Mundo were already expressed in antiquity: when Proclus mentioned the work in one of his commentaries he added "if the book De Mundo is by him". In the Middle Ages, it was widely believed that De Mundo was a genuine product of Aristotle. The notable exception was the 12th-century philosopher Maimonides who rejected it outright. Doubts were expressed again in the 15th and 16th centuries, and it became common to reject the work in the 17th century. General agreement to deny Aristotle's authorship was reached in the 19th century, with only a few voices dissenting since then.
The main reasons to reject the work are:
Attempts have sometimes been made to identify the author of the work. In the 19th century, when the Stoic philosopher Posidonius was thought to be in the background of many treatises on natural philosophy, it was common to regard the book as based on his writings, and the work itself was sometimes ascribed to him. As late as 1905 Wilhelm Capelle (Neue Jahrbücher, 1905), traced most of the doctrines to Posidonius. Another name occasionally proposed as author but now rejected was Nicolaus of Damascus. Today the general position is simply to assume it was written by an anonymous eclectic philosopher,  and as such the author is referred to now as Pseudo-Aristotle. The writer "knew a great deal about philosophy, yet cherished Aristotelian philosophy above all others", but there are "no grounds even to speculate" who the author was.