Editing Shadow (section)

== Propagation speed ==
{{see also|Lighthouse paradox}}
[[File: Steam phase eruption of Castle Geyser with crepuscular rays and shadow.jpg|thumb|[[Steam]] phase [[eruption]] of [[Castle Geyser]] in [[Yellowstone National Park]] casts a shadow on its own steam. [[Crepuscular rays]] are also visible.]]
The farther the distance from the object blocking the light to the surface of projection, the larger the silhouette (they are considered [[Proportionality (mathematics)|proportional]]). Also, if the object is moving, the shadow cast by the object will project an image with dimensions (length) expanding proportionally faster than the object's own rate of movement. The increase of size and movement is also true if the distance between the object of interference and the light source are closer. 
Eventually, this speed may exceed the speed of light.;<ref>Nemiroff et. al (2016) https://iopscience.iop.org/article/10.1088/0031-9120/51/4/043005/meta</ref> however, this does not violate special relativity as shadows do not carry any information or momentum.{{Cn|date=March 2025}}

Although the edge of a shadow appears to "move" along a wall, in actuality the increase of a shadow's length is part of a new projection that propagates at the speed of light from the object of interference. Since there is no actual communication between points in a shadow (except for reflection or interference of light, at the speed of light), a shadow that projects over a surface of large distances (light years) [[Special relativity#Causality and prohibition of motion faster than light|cannot convey information]] between those distances with the shadow's edge.<ref>Philip Gibbs (1997) [http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html#3 Is Faster-Than-Light Travel or Communication Possible?] {{webarchive|url=https://web.archive.org/web/20100310205556/http://math.ucr.edu/home/baez/physics/Relativity/SpeedOfLight/FTL.html |date=10 March 2010 }} math.ucr.edu</ref>