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Outside In is a 22-minute-long educational short film about sphere eversion, the mathematical process of turning a sphere inside out using topological transformations. It was produced by the Geometry Center at the University of Minnesota and was published by A K Peters in 1994, along with a 48-page companion workbook, Making Waves.

Background
Outside In was produced by a team at the Geometry Center using a interactive geometry program they developed called Geomview, in addition to a custom C++ program. The team was led by Silvio Levy, Delle Maxwell, and Tamara Munzner, the first of whom also wrote the accompanying guidebook Making Waves.

Synopsis
Outside In has two characters, named Xanthippe and Yorick, narrating over a geometric animation. Yorick introduces the topic of the film, which is sphere eversion, and Xanthippe states the rules of the topological surface: it can be stretched and have self-intersections, but creases and punctures are not allowed (else the material gets destroyed). Yorick attempts this, but destroys the sphere each time; Xanthippe demonstrates it being done through a complex process and introduces a two-dimensional circle for a simpler analogy. They show that the circle cannot be turned inside out due to the invariant of turning numbers, using "smiles" and "frowns" to visualize the concept on curves. They then extend this to three-dimensional surfaces, with the sum of "domes" and "bowls" (vertical local extrema) minus the number of saddle points, as a saddle point can cancel out with either a dome and a bowl. Finally, to prove that the two spheres (one everted) can be transformed into each other, Xanthippe once again goes into two dimensions, first proving the Whitney–Graustein theorem (that any two curves with the same turning number can be transformed into each other). She introduces Thurston's corrugations: on a two-dimensional curve, adding "waves" such that smaller segments of the curve can be moved into their desired position without creasing and then aligned. Then, she demonstrates the motion of one vertical strip of a sphere undergoing eversion: as the two end caps of the sphere are pushed through each other, the strip forms a loop that then straightens out when the caps turn in opposite directions. This is shown with more strips and with corrugations as well, and views of horizontal sections are provided as well. At the very end, the entire process is shown once again, going step by step.

Reception
In the Handbook of Computational Geometry, mathematicians Jörg-Rüdiger Sack and Jorge Urrutia stated that together with other Geometry Center films Not Knot and The Shape of Space, they "show that a great deal of effort went into their production" and that they "achieve the difficult task of explaining problems in topology to novices. http://www.geom.uiuc.edu/docs/outreach/oi//awards.html