維格納的友人

維格納的友人（英語：Wigner's friend）是一個理論量子物理學的思想實驗，最初由匈牙利裔美國物理學家尤金·維格納於1961年提出^[1]，並由戴維·多伊奇於1985年進一步發展^[2]。該情境涉及對量子測量的間接觀測：觀測者 $W$ 觀測另一位觀測者 $F$ 對物理系統執行量子測量。隨後兩位觀測者依據量子理論法則，共同對測量後物理系統的狀態作出陳述。在哥本哈根詮釋中，兩位觀察者得出的陳述相互矛盾。這反映出該詮釋中兩條法則的表面不相容性：封閉系統狀態的確定性與連續時間演化，以及系統狀態在測量時發生的非確定性、不連續性坍縮。因此，維格納的友人問題直接關聯到量子力學中的測量問題及其著名的薛丁格貓悖論。

維格納的友人的實驗已衍生出多種推廣與延伸版本。其中兩種涉及多重友人的實驗情境，已透過實驗室實證實現——實驗中以光子替代友人角色進行模擬^[3]^[4]^[5]。然而，將光子作為觀察者的做法遭到了特拉維夫大學量子物理學家列夫·瓦伊德曼（英语：Lev Vaidman）的批評，他認為此舉「荒謬至極；觀察者必須是巨觀的」。紐約大學物理哲學家提姆·莫德林（英语：Tim Maudlin）則指出：「沒有人會認為光子是觀察者。」^[6]

參考資料

^ Wigner, Eugene P. Remarks on the Mind-Body Question. Good, I. J. (编). The Scientist Speculates: An Anthology of Partly-Baked Ideas. London: Heinemann. 1961. OCLC 476959404. Reprinted in Wigner, Eugene P. Remarks on the Mind-Body Question. Mehra, Jagdish (编). Philosophical Reflections and Syntheses. The Collected Works of Eugene Paul Wigner B/6. Berlin, Heidelberg: Springer. 1995: 247–260 [2022-03-13]. ISBN 978-3-540-63372-3. OCLC 924167486. doi:10.1007/978-3-642-78374-6_20 （英语）.
^ Deutsch, D. Quantum theory as a universal physical theory. International Journal of Theoretical Physics. 1985, 24 (1): 1–41. Bibcode:1985IJTP...24....1D. S2CID 17530632. doi:10.1007/BF00670071.
^ Proietti, Massimiliano; Pickston, Alexander; Graffitti, Francesco; Barrow, Peter; Kundys, Dmytro; Branciard, Cyril; Ringbauer, Martin; Fedrizzi, Alessandro. Experimental test of local observer independence. Science Advances. 2019-09-20, 5 (9). Bibcode:2019SciA....5.9832P. ISSN 2375-2548. PMC 6754223 . PMID 31555731. arXiv:1902.05080 . doi:10.1126/sciadv.aaw9832 （英语）. 已忽略未知参数|article-number= (帮助)
^ Musser, George. Quantum paradox points to shaky foundations of reality. Science. 17 August 2020 [17 August 2020].
^ Bong, Kok-Wei; et al. A strong no-go theorem on the Wigner's friend paradox. Nature Physics. 17 August 2020, 27 (12): 1199–1205. Bibcode:2020NatPh..16.1199B. arXiv:1907.05607 . doi:10.1038/s41567-020-0990-x .
^ Merali, Zeeya. This Twist on Schrödinger's Cat Paradox Has Major Implications for Quantum Theory. Scientific American. 17 August 2020 [17 August 2020].

[:0-1] Wigner, Eugene P. Remarks on the Mind-Body Question. Good, I. J. (编). The Scientist Speculates: An Anthology of Partly-Baked Ideas. London: Heinemann. 1961. OCLC 476959404. Reprinted in Wigner, Eugene P. Remarks on the Mind-Body Question. Mehra, Jagdish (编). Philosophical Reflections and Syntheses. The Collected Works of Eugene Paul Wigner B/6. Berlin, Heidelberg: Springer. 1995: 247–260 [2022-03-13]. ISBN 978-3-540-63372-3. OCLC 924167486. doi:10.1007/978-3-642-78374-6_20 （英语）.

[deutsch1985-2] Deutsch, D. Quantum theory as a universal physical theory. International Journal of Theoretical Physics. 1985, 24 (1): 1–41. Bibcode:1985IJTP...24....1D. S2CID 17530632. doi:10.1007/BF00670071.

[3] Proietti, Massimiliano; Pickston, Alexander; Graffitti, Francesco; Barrow, Peter; Kundys, Dmytro; Branciard, Cyril; Ringbauer, Martin; Fedrizzi, Alessandro. Experimental test of local observer independence. Science Advances. 2019-09-20, 5 (9). Bibcode:2019SciA....5.9832P. ISSN 2375-2548. PMC 6754223 . PMID 31555731. arXiv:1902.05080 . doi:10.1126/sciadv.aaw9832 （英语）. 已忽略未知参数|article-number= (帮助)

[SM-20200817-4] Musser, George. Quantum paradox points to shaky foundations of reality. Science. 17 August 2020 [17 August 2020].

[NAT-20200817-5] Bong, Kok-Wei; et al. A strong no-go theorem on the Wigner's friend paradox. Nature Physics. 17 August 2020, 27 (12): 1199–1205. Bibcode:2020NatPh..16.1199B. arXiv:1907.05607 . doi:10.1038/s41567-020-0990-x .

[SA-20200817-6] Merali, Zeeya. This Twist on Schrödinger's Cat Paradox Has Major Implications for Quantum Theory. Scientific American. 17 August 2020 [17 August 2020].

[1]

[2]

[3]

[4]

[5]

[6]