OPTICAL VARIABILITY
It well known that the optical variability of quasars and the arguments which
follow from the size limits set by the variability, pose a serious difficulty
for the cosmological interpretation (Weekes, 1969).
Very small sizes lead to a paradoxical situation in models for very high luminosities
(Hoyle et al, 1966).
Several ingenious, though rather top-heavy, models have been suggested to get
around this difficulty. To quote
G.Burbidge :
'In spite of impressions to the contrary, nobody has published a well worked
out model in which they can account for the continuum source properties and
avoid the paradox if the QSO is at a cosmological distance.'
Next Section: Redshift - Apparent Magnitude Diagram