隱變量理論（英語：hidden variable theory）又稱隱變數理論，是由物理學家質疑量子力學完備性而提出的替代理論。歷史上隨著量子力學的發展，而提出了海森堡不確定原理等限制，一別於古典物理，諸如位置與動量等無法同時精準測出其值；此外關於粒子位置等特性由機率密度描述所取代。一些物理學家例如愛因斯坦，認為量子力學並未完整地描述物理系統的狀態，亦即質疑量子力學是不完備的。因此量子力學的背後應該隱藏了一個尚未發現的理論，可以完整解釋物理系統所有可觀測量的演化行為，而避免掉任何不確定性或隨機性。
歷史上愛因斯坦是隱變量理論的主要倡導者，出於對標準量子力學詮釋的機率性解釋的不滿。[1]他曾說：「我相信上帝不擲骰子。」[2]
1935年，愛因斯坦與波多爾斯基、羅森共同提出的EPR悖論（以姓氏字首為縮寫）試圖對哥本哈根詮釋做出挑戰，論文中指出「實在性元素」（即隱變量）應該加入量子力學中，俾使在量子纏結現象中不會出現鬼魅般的超距作用。在提出後，這樣的爭辯仍停留在物理哲學的範疇，直到約翰·貝爾提出貝爾定理方得區分兩者差異。透過實驗證實：一定類型的局域隱變量理論與實驗結果不相符，包括EPR佯謬中提出的詮釋版本。非局域（廣域）的隱變量理論最知名者為德布羅意-玻姆理論。
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