The general theory of relativity describes light rays as null geodesics in a curved spacetime. In the general case, then, the looks of an object are also influenced by gravitational light deflection in addition to the effects described above.
The effects of light deflection can be directly seen in astronomical observations: Galaxies or clusters of galaxies act as gravitational lenses so that quasars or galaxies lying behind the lenses appear distorted or in multiple images. Especially dramatic, although not directly observable, is light deflection near compact objects like neutron stars and black holes. In this case and also in more exotic scenes like wormholes or the warp drive, computer simulations can convey the phenomena in a descriptive way.
Simulations of this kind can also be performed as spacetime ray tracing with the sole difference that the light rays are not straight lines but instead geodesics of a given metric.
The visualizations, special or general relativistic, are best when seen as films. Therefore, we would like to end by pointing out some websites with films on them to those readers that have hung on till now.
An online version of this article with films of the most important examples integrated into the text and with further simulations of special and general relativity can be found under
http://www.tempolimit-lichtgeschwindigkeit.de/ and its English version http://www.spacetimetravel.org/
More special and general relativistic simulations:
Such films can convey better than words and pictures the peculiar structure of our spacetime. We wish our readers as much fun watching them as we had producing them.
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