Seminar
Abstract :
We critically examine the evidence
available of the early ideas on the
bending of light due to a gravitational
attraction, which led to the concept of
gravitational lenses, and attempt to
present an undistorted historical
perspective. Contrary to a widespread
but baseless claim, Newton was not the
precursor to the idea, and the first
Query in his Opticks is totally
unrelated to this phenomenon. We briefly
review the roles of Voltaire, Marat,
Cavendish, Soldner and Einstein in their
attempts to quantify the gravitational
deflection of light. The first, but
unpublished, calculations of the lensing
effect produced by this deflection are
found in Einstein's 1912 notebooks,
where he derived the lensing equation
and the formation of images in a
gravitational lens. The brief 1924 paper
by Chwolson which presents, without
calculations, the formation of double
images and rings by a gravitational lens
passed mostly unnoticed. The unjustly
forgotten and true pioneer of the
subject is F. Link, who not only
published the first detailed lensing
calculations in 1936, nine months prior
to Einstein's famous paper in Science,
but also extended the theory to include
the effects of finite-size sources and
lenses, binary sources, and limb
darkening that same year. Link correctly
predicted that the microlensing effect
would be easier to observe in crowded
fields or in galaxies, as observations
confirmed five decades later. The
calculations made by Link are far more
detailed than those by Tikhov and
Bogorodsky. We discuss briefly some
papers of the early 1960s which marked
the renaissance of this theoretical
subject prior to the first detection of
a gravitational lens in 1979. An
unpublished chapter of Petrou's 1981 PhD
thesis addressed the microlensing of
stars in the Magellanic clouds by dark
objects in the Galactic halo, a topic
which would be publicised by Paczynsky
five years later, and which led to the
first detections of microlenses within
the Milky Way in 1992.
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Bibliography
-
"The
conceptual origins
of gravitational
lensing"
David Valls-Gabaud,
in "Albert Einstein
Century
International
Conference", AIP
Conference
Proceedings, Volume
861, pp. 1163-1171
(2006).
http://arxiv.org/abs/1206.1165
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