noun which may take the genitive case particle 'no', adverb
in accordance with theory; as theorized
Used when something happens exactly as predicted by a theory, model, or logical expectation. Often appears in contexts where a result matches a theoretical prediction, sometimes with a nuance of surprise or confirmation.
実験結果は理論通りだった。
The experimental results were in accordance with theory.
理論通りに進めば、問題はないはずだ。
If we proceed as theorized, there should be no problem.
理論的 is an adjective meaning 'theoretical', while 理論通り is an adverb/no-adjective meaning 'in accordance with theory' or 'as theorized'.
Compound of 理論 (theory) + 通り (in accordance with).