The opposite of "is the up" can be expressed in various ways, depending on the context. If we consider the phrase as a colloquial expression meaning success or improvement, its antonyms could be terms such as failure, decline, or setback. In a spatial or directional sense, the opposite of "is the up" could be "is the down," "is the bottom," or "is the lower." To negate the verb "is," one could use antonyms like "is not," "isn't," "doesn't exist," or "is absent." Depending on the intention behind the phrase, there could be many different words with opposite meanings, making it essential to consider the context in which it is used.