In his lithographs Relativity(1953) and Balcony (1945), M.C. Escher interrogates the spectator about gravity by representing paradoxical three-dimensional images in a two-dimensional medium.

      In Relativity, 16 bulb-headed, identical humanoid figures in an architectural structure seem proceeding ordinary life. Three disparate gravity sources coexisting in the same picture produce the paradox. There are four stairways, and each stairway is subject to different gravity sources. Newton’s law of gravity does not govern this depiction. Instead, the artist explores the possibility that Albert Einstein suggested in General Relativity. As the homo erectus walks upright, his tailbone points toward the gravity source. Five figures, one at the very bottom climbing up the stairs, one walking after another one on the left stairway, one climbing down on the right stairs, and one leaning and looking down from the top right corner, share the same gravity source. Five other figures, one walking down on the right stairway carrying a bottle on top of a tray in the lower right quadrant, one sitting and reading in the upper left quadrant, two sitting and eating on the terrace in the lower right corner, and one walking up a horizontally depicted stairway at the top of the picture, are supported by the same gravity source. Six more figures, one descending the same stairway, two holding arms in an archway at the top left corner, one standing up and resting his hands on the parapet, one climbing up from the basement in the center of the picture, and one carrying a basin walking down on the lower left stairway, are beholden to their own source of gravity.  

In Balcony, Escher distorts his perspective with a gravitational singularity. He depicts an apartment complex next to a river embankment. The image exaggerates the center of the building, and magnifies a fifth floor balcony, as if a powerful magnet placed just before the spectator were to thrust it outwards. Yet the distorted image remains captured in a two-dimensional lithograph.

      In these two works, Escher successfully realizes his conception of impossible spaces by embedding vivid three-dimensional images in the flat surface of a gray scale print.   

 *The official M. C. Escher website: http://www.mcescher.com/
** The picture source of Relativity: http://en.wikipedia.org/wiki/Image:Escher%27s_Relativity.jpg
***The picture source of Balcony: http://www.globalgallery.com/enlarge/015-20758/