Superluminal expansion

The longstanding idea of superluminal motion has become subject to renewed interest, due to a number of recent discoveries and observations, as described in a survey by Recami [27]. Thus the squared mass of muon-neutrinos is found to be negative. There are further observations that can be interpreted as superluminal expansions inside quasars, in some galaxies and in galactic objects. Also, so called X-shaped waves have been observed [69] to propagate at a... 

A number of orthodox models (some of which quite complex ) have been proposed in order to explain such apparent superluminal expansions (a brief... 

At present, the majority of astrophysicists are in favor of the standard interpretations. In fact, one is unable to give a definite answer to the question if astrophysical superluminal expansions are superluminal, indeed [1]. 

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