Talk:Terrell rotation

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Linked animation[edit]

The linked animation seems to be in error. It claims that Terrell rotation cancels out Lorentz contraction so that it looks the same length. This is incorrect. If the object is moving towards you, the effect of Terrel rotation is stronger, and the object appears elongated overall. If it's moving away from you, both effects cause contraction, so it will be even more contracted. — DanielLC 05:19, 9 July 2012 (UTC)[reply]

Either they've replaced the animation, or you're mis-interpreting it. What is (currently) displayed is a cube viewed strictly at the point of passing by for each increment in velocity. Perhaps you missed the velocity-counter. This is not an animation of the cube in continuous passage by us (the observer). It shows how a fixed lateral view of the cube changes for different relativistic velocities.

Watch only the front face of the cube. Although there may be an optical illusion for some people suggesting there is a difference in the lateral widths of the two cubes, the measure and the appearance do, in fact, show the same contraction value for both the classical relativistic contraction, and the P-T contraction/rotation counterpart view. You can confirm this by measuring off the GIF-final width of that front cube-face wih a pencil-end and your finger and comparing it to the other cube, when the animation end-point comes around again. JohndanR (talk) 02:53, 17 July 2019 (UTC)[reply]

priority[edit]

The Terrell effect was found by the austrian physicist Anton Lampa (1868-1938) in 1924: Z. physik T27, 1924, p138-148. — Preceding unsigned comment added by Claudeh5 (talk • contribs) 16:26, 27 March 2013 (UTC)[reply]

Added, thanks. 130.225.98.201 (talk) 13:43, 3 July 2013 (UTC)[reply]

Two popular misconceptions[edit]

There are two common misconceptions regarding the Terrell "rotation":

it's a pure rotation
the Lorentz-Fitzgerald contraction is "invisible": it's not detectable by a single detector, in which the past light-cone of the detector intersects with the history of a relativistic object. Instead, the detector sees a purely rotated object, with no contraction.

According to the references listed below, both of these assertions are false.

The geometrical appearance of large objects moving at relativistic speeds, G.D. Scott, M. R. Viner (University of Toronto), Am. J. Phys. 33, 534-536 (1965), https://doi.org/10.1119/1.1971890, Bibcode: 1965AmJPh..33..534S

"The calculated geometrical appearance of objects moving at relativistic speeds and subtending large angles at the observer is illustrated by diagrams of a plane grid and perspective views of a group of boxes. In addition to the distortion of scales in the direction of motion, planes perpendicular to the motion appear as hyperboloids. Contrary to an impression which might be taken from some papers on the subject, the Lorentz contraction is visible under suitable conditions, in particular for observations approximately at right angles to the motion."

also:

"... the explanation of the appearance in terms of a rotation is quite inadequate."

Geometrical Appearances at Relativistic Speeds, G. D. Scott, H. J. van Driel, University of Toronto, Am. J. Phys. vol 38 No. 8 August 1970, https://doi.org/10.1119/1.1976550

"Geometrical appearances at relativistic speeds (β=0.5,0.9,and 0.995) are illustrated for the following examples: (i) the celestial sphere with a number of constellations, (ii) the surface features of a sphere passing close to an observer, and (iii) a train of rectangular boxes. The figures make clear the nature of the distortions which occur in appearances, indicate the limited significance of the so-called 'apparent rotation', and show the conditions under which the Lorentz contraction can be seen or photographed. Though a sphere remains essentially circular in outline, the apparent cross section may be grossly distorted and under some conditions the outside surface of the sphere appears concave."

On the Apparent Visual Forms of Relativistically Moving Objects, P. M. Mathews, M. Lakshmanan (University of Madras), Nuovo Cimento B, Vol. , 12B, Ser. 11, p. 168 - 181, 11-November-1972, https://link.springer.com/article/10.1007/BF02895571, http://dx.doi.org/10.1007/BF02895571, Bibcode: 1972NCimB..12..168M

"The question of the apparent visual shape of an object moving at relativistic speeds, as perceived by a single observer, is analysed afresh. It is shown by qualitative arguments that the apparent shape is related to the shape at rest through a combination of nonuniform shear and extension/contraction parallel to the direction of motion, which does not reduce to a rotation even in the case of distant objects subtending a small angle at the observer. The two-dimensional projection (as in a photograph) of this distorted shape may coincide with that of the object (suitably rotated) at rest; but we emphasize that it would be grossly misleading to conclude from this, as is generally done in the literature, that distant relativistically moving objects appear as if simply rotated. The 'train paradox' is discussed in illustration of this point. Analytical formulae relating the apparent visual shape to the shape at rest are given. Also the striking fact that the apparent speed of the object as seen by visual observation may well exceed the speed of light is brought out. Finally it is pointed out that the phenomenon is closely analogous to the relativistic Doppler effect."

They correct Terrell, saying it's not a pure rotation, but nonuniform shear + extension/contraction, even in the case of small solid angle.

The twists and turns of the Terrell effect, Eric Sheldon (University of Lowell), American Journal of Physics 56, 199 (1988), https://doi.org/10.1119/1.15687 full text, (letter to the editor)

He corrects 'rotation' to 'shear', 'a skew twist'. He points to Weisskopf's error about pure rotation, and subsequent corrections by Scott-van Driel and Mathews-Lakshmanan.

The Terrell Effect: Eppure si muove!, Eric Sheldon (University of Lowell), American Journal of Physics 57, 6 p487 (1989), https://aapt.scitation.org/doi/abs/10.1119/1.16144 full text, letter

Johanley (talk) 11:15, 16 June 2020 (UTC)[reply]

Rename article?[edit]

If the phenomenon was both discovered and published, respectively, by Penrose before Terrell, then why have we named the article "Terrell rotation"? (To me, that's a bit absurd.) Wouldn't it be more suitable to call it "Penrose–Terrell rotation"? Or if we decide that we only want to call it by a short name, call it "Penrose rotation" instead of "Terrell rotation"? —Kri (talk) 20:48, 9 April 2023 (UTC)[reply]