article
Long geodesics on convex surfaces
published
yes
Arseniy
Akopyan
author 430D2C90-F248-11E8-B48F-1D18A9856A870000-0002-2548-617X
Anton
Petrunin
author
HeEd
department
The goal of this article is to introduce the reader to the theory of intrinsic geometry of convex surfaces. We illustrate the power of the tools by proving a theorem on convex surfaces containing an arbitrarily long closed simple geodesic. Let us remind ourselves that a curve in a surface is called geodesic if every sufficiently short arc of the curve is length minimizing; if, in addition, it has no self-intersections, we call it simple geodesic. A tetrahedron with equal opposite edges is called isosceles. The axiomatic method of Alexandrov geometry allows us to work with the metrics of convex surfaces directly, without approximating it first by a smooth or polyhedral metric. Such approximations destroy the closed geodesics on the surface; therefore it is difficult (if at all possible) to apply approximations in the proof of our theorem. On the other hand, a proof in the smooth or polyhedral case usually admits a translation into Alexandrov’s language; such translation makes the result more general. In fact, our proof resembles a translation of the proof given by Protasov. Note that the main theorem implies in particular that a smooth convex surface does not have arbitrarily long simple closed geodesics. However we do not know a proof of this corollary that is essentially simpler than the one presented below.
Springer2018
eng
Mathematical Intelligencer
1702.0517210.1007/s00283-018-9795-5
40326 - 31
A. Akopyan, A. Petrunin, Mathematical Intelligencer 40 (2018) 26–31.
Akopyan, A., & Petrunin, A. (2018). Long geodesics on convex surfaces. <i>Mathematical Intelligencer</i>. Springer. <a href="https://doi.org/10.1007/s00283-018-9795-5">https://doi.org/10.1007/s00283-018-9795-5</a>
Akopyan, Arseniy, and Anton Petrunin. “Long Geodesics on Convex Surfaces.” <i>Mathematical Intelligencer</i>, vol. 40, no. 3, Springer, 2018, pp. 26–31, doi:<a href="https://doi.org/10.1007/s00283-018-9795-5">10.1007/s00283-018-9795-5</a>.
Akopyan A, Petrunin A. Long geodesics on convex surfaces. <i>Mathematical Intelligencer</i>. 2018;40(3):26-31. doi:<a href="https://doi.org/10.1007/s00283-018-9795-5">10.1007/s00283-018-9795-5</a>
Akopyan A, Petrunin A. 2018. Long geodesics on convex surfaces. Mathematical Intelligencer. 40(3), 26–31.
Akopyan, Arseniy, and Anton Petrunin. “Long Geodesics on Convex Surfaces.” <i>Mathematical Intelligencer</i>. Springer, 2018. <a href="https://doi.org/10.1007/s00283-018-9795-5">https://doi.org/10.1007/s00283-018-9795-5</a>.
A. Akopyan and A. Petrunin, “Long geodesics on convex surfaces,” <i>Mathematical Intelligencer</i>, vol. 40, no. 3. Springer, pp. 26–31, 2018.
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