Editing Superluminal motion (section)

===Some contrary evidence===
As early as 1983, at the "superluminal workshop" held at [[Jodrell Bank Observatory]], referring to the seven then-known superluminal jets,

<blockquote>Schilizzi ... presented maps of arc-second resolution [showing the large-scale outer jets] ... which ... have revealed outer double structure in all but one ([[3C 273]]) of the known superluminal sources. An embarrassment is that the average projected size [on the sky] of the outer structure is no smaller than that of the normal radio-source population.<ref>{{Cite journal|doi=10.1038/302753a0|title=Superluminal motions: Astronomers still puzzled|date=1983|last1=Porcas|first1=Richard|journal=Nature|volume=302|issue=5911|pages=753–754|bibcode = 1983Natur.302..753P |doi-access=free}}</ref></blockquote>

In other words, the jets are evidently not, on average, close to the Earth's line-of-sight. (Their apparent length would appear much shorter if they were.)

In 1993, Thomson et al. suggested that the (outer) jet of the quasar [[3C 273]] is nearly collinear to the Earth's line-of-sight. Superluminal motion of up to ~9.6''c'' has been observed along the (inner) jet of this quasar.<ref>{{Cite journal|doi=10.1038/365133a0|title=Internal structure and polarization of the optical jet of the quasar 3C273|date=1993|last1=Thomson|first1=R. C.|last2=MacKay|first2=C. D.|last3=Wright|first3=A. E.|journal=Nature|volume=365|issue=6442|pages=133|bibcode = 1993Natur.365..133T |s2cid=4314344}};</ref><ref>{{Cite journal|doi=10.1038/290365a0|title=Superluminal expansion of quasar 3C273|date=1981|last1=Pearson|first1=T. J.|last2=Unwin|first2=S. C.|last3=Cohen|first3=M. H.|last4=Linfield|first4=R. P.|last5=Readhead|first5=A. C. S.|last6=Seielstad|first6=G. A.|last7=Simon|first7=R. S.|last8=Walker|first8=R. C.|journal=Nature|volume=290|issue=5805|pages=365|bibcode = 1981Natur.290..365P |s2cid=26508893}};</ref><ref>{{Cite journal|doi=10.1038/354374a0|title=Large-scale superluminal motion in the quasar 3C273|date=1991|last1=Davis|first1=R. J.|last2=Unwin|first2=S. C.|last3=Muxlow|first3=T. W. B.|journal=Nature|volume=354|issue=6352|pages=374|bibcode = 1991Natur.354..374D |s2cid=4271003}}</ref>

Superluminal motion of up to 6''c'' has been observed in the inner parts of the jet of [[Messier 87|M87]]. To explain this in terms of the "narrow-angle" model, the jet must be no more than 19° from the Earth's line-of-sight.<ref name="nature891">{{Cite journal|doi=10.1038/44780|date=1999|last1=Biretta|first1=John A.|title=Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole|last2=Junor|first2=William|last3=Livio|first3=Mario|journal=Nature|volume=401|issue=6756|pages=891|bibcode = 1999Natur.401..891J |s2cid=205034376}} ; {{Cite journal|doi=10.1086/307499|title=Hubble Space TelescopeObservations of Superluminal Motion in the M87 Jet|date=1999|last1=Biretta|first1=J. A.|last2=Sparks|first2=W. B.|last3=MacChetto|first3=F.|journal=The Astrophysical Journal|volume=520|issue=2|pages=621|bibcode = 1999ApJ...520..621B |doi-access=free}}</ref> But evidence suggests that the jet is in fact at about 43° to the Earth's line-of-sight.<ref>{{Cite journal|doi=10.1086/175901|title=Detection of Proper Motions in the M87 Jet|date=1995|last1=Biretta|first1=J. A.|last2=Zhou|first2=F.|last3=Owen|first3=F. N.|journal=The Astrophysical Journal|volume=447|pages=582|bibcode = 1995ApJ...447..582B }}</ref> The same group of scientists later revised that finding and argue in favour of a superluminal bulk movement in which the jet is embedded.<ref>{{Cite journal|doi=10.1086/307499|title=Hubble Space TelescopeObservations of Superluminal Motion in the M87 Jet|date=1999|last1=Biretta|first1=J. A.|last2=Sparks|first2=W. B.|last3=MacChetto|first3=F.|journal=The Astrophysical Journal|volume=520|issue=2|pages=621|bibcode = 1999ApJ...520..621B |doi-access=free}}</ref>

Suggestions of turbulence and/or "wide cones" in the inner parts of the jets have been put forward to try to counter such problems, and there seems to be some evidence for this.<ref>{{cite journal|doi=10.1038/44780|date=1999|last1=Biretta|first1=John A.|title=Formation of the radio jet in M87 at 100 Schwarzschild radii from the central black hole|last2=Junor|first2=William|last3=Livio|first3=Mario|journal=Nature|volume=401|issue=6756|pages=891|bibcode = 1999Natur.401..891J |s2cid=205034376}}</ref>

====Signal velocity====
The model identifies a difference between the information carried by the wave at its signal velocity ''c'', and the information about the wave front's apparent rate of change of position. If a light pulse is envisaged in a wave guide (glass tube) moving across an observer's field of view, the pulse can only move at ''c'' through the guide. If that pulse is also directed towards the observer, he will receive that wave information, at ''c''.  If the wave guide is moved in the same direction as the pulse, the information on its position, passed to the observer as lateral emissions from the pulse, changes.  He may see the rate of change of position as apparently representing motion faster than ''c'' when calculated, like the edge of a shadow across a curved surface.  This is a different signal, containing different information, to the pulse and does not break the second postulate of special relativity. ''c'' is strictly maintained in all local fields.