This article is missing information about many basic details, including the equation associated with the theorem or even a sketch of its proof. Please expand the article to include this information. Further details may exist on the talk page.(January 2020)
Gauss's Theorema Egregium (Latin for "Remarkable Theorem") is a major result of differential geometry, proved by Carl Friedrich Gauss in 1827, that concerns the curvature of surfaces. The theorem says that Gaussian curvature can be determined entirely by measuring angles, distances and their rates on a surface, without reference to the particular manner in which the surface is embedded in the ambient 3-dimensional Euclidean space. In other words, the Gaussian curvature of a surface does not change if one bends the surface without stretching it. Thus the Gaussian curvature is an intrinsicinvariant of a surface.
A consequence of the Theorema Egregium is that the Earth cannot be displayed on a map without distortion. The Mercator projection, shown here, preserves angles but fails to preserve area.
Gauss presented the theorem in this manner (translated from Latin):
Thus the formula of the preceding article leads itself to the remarkable Theorem. If a curved surface is developed upon any other surface whatever, the measure of curvature in each point remains unchanged.
The theorem is "remarkable" because the starting definition of Gaussian curvature makes direct use of position of the surface in space. So it is quite surprising that the result does not depend on its embedding in spite of all bending and twisting deformations undergone.
In modern mathematical terminology, the theorem may be stated as follows:
Animation showing the deformation of a helicoid into a catenoid. The deformation is accomplished by bending without stretching. During the process, the Gaussian curvature of the surface at each point remains constant.
A sphere of radius R has constant Gaussian curvature which is equal to 1/R2. At the same time, a plane has zero Gaussian curvature. As a corollary of Theorema Egregium, a piece of paper cannot be bent onto a sphere without crumpling. Conversely, the surface of a sphere cannot be unfolded onto a flat plane without distorting the distances. If one were to step on an empty egg shell, its edges have to split in expansion before being flattened. Mathematically, a sphere and a plane are not isometric, even locally. This fact is significant for cartography: it implies that no planar (flat) map of Earth can be perfect, even for a portion of the Earth's surface. Thus every cartographic projection necessarily distorts at least some distances.[1]
The catenoid and the helicoid are two very different-looking surfaces. Nevertheless, each of them can be continuously bent into the other: they are locally isometric. It follows from Theorema Egregium that under this bending the Gaussian curvature at any two corresponding points of the catenoid and helicoid is always the same. Thus isometry is simply bending and twisting of a surface without internal crumpling or tearing, in other words without extra tension, compression, or shear.
An application of the theorem is seen when a flat object is somewhat folded or bent along a line, creating rigidity in the perpendicular direction. This is of practical use in construction, as well as in a common pizza-eating strategy: A flat slice of pizza can be seen as a surface with constant Gaussian curvature 0. Gently bending a slice must then roughly maintain this curvature (assuming the bend is roughly a local isometry). If one bends a slice horizontally along a radius, non-zero principal curvatures are created along the bend, dictating that the other principal curvature at these points must be zero. This creates rigidity in the direction perpendicular to the fold, an attribute desirable for eating pizza, as it holds its shape long enough to be consumed without a mess. This same principle is used for strengthening in corrugated materials, most familiarly corrugated fiberboard and corrugated galvanised iron,[2] and in some forms of potato chips.
O'Neill, Barrett (1966). Elementary Differential Geometry. New York: Academic Press. pp. 271–275.
Stoker, J. J. (1969). "The Partial Differential Equations of Surface Theory". Differential Geometry. New York: Wiley. pp. 133–150. ISBN0-471-82825-4.
External links
Theorema Egregium on Mathworld
December 31, 2022
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This article has multiple issues Please help improve it or discuss these issues on the talk page Learn how and when to remove these template messages This article needs additional citations for verification Please help improve this article by adding citations to reliable sources Unsourced material may be challenged and removed Find sources Theorema Egregium news newspapers books scholar JSTOR December 2019 Learn how and when to remove this template message This article is missing information about many basic details including the equation associated with the theorem or even a sketch of its proof Please expand the article to include this information Further details may exist on the talk page January 2020 Learn how and when to remove this template message Gauss s Theorema Egregium Latin for Remarkable Theorem is a major result of differential geometry proved by Carl Friedrich Gauss in 1827 that concerns the curvature of surfaces The theorem says that Gaussian curvature can be determined entirely by measuring angles distances and their rates on a surface without reference to the particular manner in which the surface is embedded in the ambient 3 dimensional Euclidean space In other words the Gaussian curvature of a surface does not change if one bends the surface without stretching it Thus the Gaussian curvature is an intrinsic invariant of a surface A consequence of the Theorema Egregium is that the Earth cannot be displayed on a map without distortion The Mercator projection shown here preserves angles but fails to preserve area Gauss presented the theorem in this manner translated from Latin Thus the formula of the preceding article leads itself to the remarkable Theorem If a curved surface is developed upon any other surface whatever the measure of curvature in each point remains unchanged The theorem is remarkable because the starting definition of Gaussian curvature makes direct use of position of the surface in space So it is quite surprising that the result does not depend on its embedding in spite of all bending and twisting deformations undergone In modern mathematical terminology the theorem may be stated as follows The Gaussian curvature of a surface is invariant under local isometry Contents 1 Elementary applications 2 See also 3 Notes 4 References 5 External linksElementary applications Edit Animation showing the deformation of a helicoid into a catenoid The deformation is accomplished by bending without stretching During the process the Gaussian curvature of the surface at each point remains constant A sphere of radius R has constant Gaussian curvature which is equal to 1 R2 At the same time a plane has zero Gaussian curvature As a corollary of Theorema Egregium a piece of paper cannot be bent onto a sphere without crumpling Conversely the surface of a sphere cannot be unfolded onto a flat plane without distorting the distances If one were to step on an empty egg shell its edges have to split in expansion before being flattened Mathematically a sphere and a plane are not isometric even locally This fact is significant for cartography it implies that no planar flat map of Earth can be perfect even for a portion of the Earth s surface Thus every cartographic projection necessarily distorts at least some distances 1 The catenoid and the helicoid are two very different looking surfaces Nevertheless each of them can be continuously bent into the other they are locally isometric It follows from Theorema Egregium that under this bending the Gaussian curvature at any two corresponding points of the catenoid and helicoid is always the same Thus isometry is simply bending and twisting of a surface without internal crumpling or tearing in other words without extra tension compression or shear An application of the theorem is seen when a flat object is somewhat folded or bent along a line creating rigidity in the perpendicular direction This is of practical use in construction as well as in a common pizza eating strategy A flat slice of pizza can be seen as a surface with constant Gaussian curvature 0 Gently bending a slice must then roughly maintain this curvature assuming the bend is roughly a local isometry If one bends a slice horizontally along a radius non zero principal curvatures are created along the bend dictating that the other principal curvature at these points must be zero This creates rigidity in the direction perpendicular to the fold an attribute desirable for eating pizza as it holds its shape long enough to be consumed without a mess This same principle is used for strengthening in corrugated materials most familiarly corrugated fiberboard and corrugated galvanised iron 2 and in some forms of potato chips See also EditSecond fundamental form Gaussian curvature Differential geometry of surfaces Carl Friedrich Gauss Theorema EgregiumNotes Edit Geodetical applications were one of the primary motivations for Gauss s investigations of the curved surfaces wired comReferences EditGauss C F 2005 Pesic Peter ed General Investigations of Curved Surfaces Paperback ed Dover Publications ISBN 0 486 44645 X O Neill Barrett 1966 Elementary Differential Geometry New York Academic Press pp 271 275 Stoker J J 1969 The Partial Differential Equations of Surface Theory Differential Geometry New York Wiley pp 133 150 ISBN 0 471 82825 4 External links EditTheorema Egregium on Mathworld Retrieved from https en wikipedia org w index php title Theorema Egregium amp oldid 1117335154, wikipedia, wiki, book, books, library,
