Terrell rotation or Terrell effect is the name of a mathematical and physical effect. Specifically, Terrell rotation is the visual distortion that a passing object would appear to undergo, according to the special theory of relativity if it were travelling a significant fraction of the speed of light. This behaviour was described independently by both James Terrell and Roger Penrose in pieces published in 1959, though the general phenomenon was noted already in 1924 by Austrian physicist Anton Lampa.
Due to an early dispute about priority and correct attribution, the effect is also sometimes referred to as the Penrose–Terrell effect, the Terrell–Penrose effect or the Lampa–Terrell–Penrose effect, but not the Lampa effect.
Terrell's and Penrose's papers pointed out that although special relativity appeared to describe an "observed contraction" in moving objects, these interpreted "observations" were not to be confused with the theory's literal predictions for the visible appearance of a moving object. Thanks to the differential timelag effects in signals reaching the observer from the object's different parts, a receding object would appear contracted, an approaching object would appear elongated (even under special relativity) and the geometry of a passing object would appear skewed, as if rotated.
For images of passing objects, the apparent contraction of distances between points on the object's transverse surface could then be interpreted as being due to an apparent change in viewing angle, and the image of the object could be interpreted as appearing instead to be rotated. A previously popular description of special relativity's predictions, in which an observer sees a passing object to be contracted (for instance, from a sphere to a flattened ellipsoid), was wrong.
Terrell's and Penrose's papers prompted a number of follow-up papers, mostly in the American Journal of Physics, exploring the consequences of this correction. These papers pointed out that some existing discussions of special relativity were flawed and "explained" effects that the theory did not actually predict – while these papers did not change the actual mathematical structure of special relativity in any way, they did correct a misconception regarding the theory's predictions.
References and further reading
- James Terrell (1959). "Invisibility of the Lorentz Contraction". Physical Review. 116 (4): 1041–1045. Bibcode:1959PhRv..116.1041T. doi:10.1103/PhysRev.116.1041.
- Roger Penrose (1959). "The Apparent Shape of a Relativistically Moving Sphere". Proceedings of the Cambridge Philosophical Society. 55 (01): 137–139. Bibcode:1959PCPS...55..137P. doi:10.1017/S0305004100033776.
- Anton Lampa (1924). "Wie erscheint nach der Relativitätstheorie ein bewegter Stab einem ruhenden Beobachter?" (PDF). Zeitschrift für Physik (in German). 27 (1): 138–148. Bibcode:1924ZPhy...27..138L. doi:10.1007/BF01328021.
- Mary L. Boas (1961). "Apparent shape of large objects at relativistic speeds". American Journal of Physics. 29 (5): 283–286. Bibcode:1961AmJPh..29..283B. doi:10.1119/1.1937751.
- Eric Sheldon (1988). "The twists and turns of the Terrell Effect". American Journal of Physics. 56 (3): 199–200. Bibcode:1988AmJPh..56..199S. doi:10.1119/1.15687.
- James Terrell (1989). "The Terrell Effect". American Journal of Physics. 57 (1): 9–10. Bibcode:1989AmJPh..57....9T. doi:10.1119/1.16131.
- Eric Sheldon (1989). "The Terrell Effect: Eppure si contorce!". American Journal of Physics. 57 (6): 487. Bibcode:1989AmJPh..57..487S. doi:10.1119/1.16144.
- John Robert Burke and Frank J. Strode (1991). "Classroom exercises with the Terrell effect". American Journal of Physics. 59 (10): 912–915. Bibcode:1991AmJPh..59..912B. doi:10.1119/1.16670.