universe vs mental object

universe and mental object both are nouns.

Word	Noun	Adjective	Verb	Adverb
universe	Yes	No	No	No
mental object	Yes	No	No	No

As nouns, mental object is a hypernym of universe; that is, mental object is a word with a broader meaning than universe:

universe: everything stated or assumed in a given discussion
mental object: the sum or range of what has been perceived, discovered, or learned

Other hypernyms of universe include cognitive content, content.

universe (noun)	mental object (noun)
everything stated or assumed in a given discussion	the sum or range of what has been perceived, discovered, or learned
(statistics) the entire aggregation of items from which samples can be drawn
everything that exists anywhere