WordNet records no synonym and no antonym for field theory. It is the only member of its synset, which is common for technical, taxonomic and single-sense vocabulary — there is no other English word that means the same thing. The broader and narrower terms below are the useful relations in that case.
Counts are distinct word forms across every sense. A synonym that appears under three senses is counted once here and shown three times below, under each sense it belongs to.
(physics) a theory that explains a physical phenomenon in terms of a field and the manner in which it interacts with matter or with other fields
Synonyms, antonyms and the broader and narrower relations for field theory come from Princeton University’s WordNet. Full sources and licences.