Mirror paradox

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Mirror effect

The mirror paradox is a paradox that is described by this question: "Why does the mirror image swap right and left, but not above and below?"

In principle, the mirror does not swap right and left, but rather the direction along the spatial axis of its surface normals , i.e. front and rear. The exchange of front and rear, however, corresponds to the exchange of right and left with respect to a rotation about the vertical axis by 180 °. If you were to turn around the horizontal axis to the mirror by 90 ° or if you turn an object around the horizontal axis to the mirror, the result is an exchange of top and bottom. To put it more generally: The mirror reverses the direction of rotation . Since a rotation around the horizontal axis appears intuitively nonsensical, the viewer assumes that the image is rotated around the vertical axis.

The following thought experiment shows that the question is not of a physical but of a psychological nature: Imagine a water world between two vertical plates that are very close together. It is home to high-backed, flat-body fish that all look in the same direction from birth and can never turn around. Otherwise they can move freely. To see each other face to face, one of the two fish would have to turn upside down. “Standing upside down” would be the usual social interaction. If these fish look in the mirror, they see a fish with the belly side down in a very unusual way. The right pectoral fin would also remain on the right from the observer. These fish would say that the mirror "swaps up and down". But in this setting, too, the mirror primarily swaps “front and back”, because normally the fish only sees the rear fin side of its fellow fish, seeing the front in the mirror is already an interpretation of an act of communication.

The paradox lies “in our identification with the image, the person in the mirror.” The mirror only swaps left and right because the vertical axis of rotation is the primary parameter of the socio-psychological models of our physical reality through gravity .

In fact, mirrors don't “interchange” at all, they just reflect . The philosopher and epistemological theorist Umberto Eco called this the “pragmatics of the mirror” and states that “the mirror does not interpret the objects”, but “we speak wrongly about the mirror”, so the paradox is actually of a linguistic nature.

The latter statement can be determined from the fact that a horizontally lying mirror - for example a reflective floor or a smooth surface of water - naturally "swaps top and bottom", but this is not interpreted as a possible "normal" perception, but always recognized as an obvious reflection. The question, “why the mirror swap right and left”, implicitly presupposes the perpendicular mirror in order to construct a supposed paradox.

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Individual evidence

  1. a b Weblink Stöcher, SteyrerBrains.at: Summary: One question, 3 answers .
  2. Formulated as the 3rd mirror law: Lutz Schön: A look in the mirror - from perception to physics. From: Physik in der Schule 32 (1994), 1., pp. 2–5. Publication 2 in: Humboldt University of Berlin: Optics in middle and high school. Physics didactics. Berlin, April 2003, there 2.1.3 Has the mirror swapped left and right? , P. 30 ( entire collection, pdf , didaktik.physik.hu-berlin.de; there p. 40).
  3. Konstantin Hondros: Mirror and Man. An analysis of advertising images. Master's thesis, University of Vienna, 2013, Chapter 2 Der Spiegel , p. 14 ( whole work, pdf ; othes.univie.ac.at).
  4. Umberto Eco : sugli specchi e altri saggi: Il Segno, La rappresentazione, L'illusione, L'immagine. Bompiani, Milan 1985. Dt. Übers. About mirrors and other phenomena. Verlag Hanser, Munich 1988, ISBN 3-446-14681-4 , there p. 34 and p. 29-31; Quoted from the paperback edition, dtv 1990, ISBN 3-423-11319-7 , p. 34 and p. 29–31.
  5. This opens up the possibility of different kinds of puzzles , see Fig. 6: Shadow or mirror image or both? In: H. Joachim Schlichting: Elementary physical model concepts for light phenomena. In: Gisela Lück, Hilde Köster (Hrsg.): Physics and chemistry in the subject. Heilbronn / Braunschweig 2006, pp. 57-74; S. 3 column 2 of the article ( article, pdf , uni-muenster.de).