Appearance of an expanding superluminal shell

Abstract

The appearance of a spherical shell expanding superluminally as seen by a stationary observer in an optically dense medium was studied in this paper. The stationary observer will not observe a constant, spherical shell immediately after expansion as expected from classical, nonrelativistic physics. The observer will not see any expansion until a minimum time has lapsed due to the delay caused by the travel time of light. When the radiation reaches the observer, the observer will not see the whole shell, but only a part of it. The different parts of the shell will be seen by the observer as time goes on. When all of the particles of the shell are visible, the observer will see an egg-shaped shell rather than the expected spherical shell.