Open, flat, and closed universes

081104-1060413
http://www.flickr.com/photos/waiferx/3003896971/
Originally uploaded by Waifer X

Models representing a negative curvature "open" universe, a zero curvature "flat" universe, and a positive curvature "closed" universe. The closed universe is constructed by removing two triangles from a flat sheet, and taping the resulting cutout edges together. These triangles are then taped into slits cut into another flat sheet, producing the open universe. The black-and-white inverted version of the same photo is shown below.

081104-1060413-inverted
http://www.flickr.com/photos/waiferx/3004952710/
Originally uploaded by Waifer X