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SUMMARY:The Effect of Gravitational Lensing on Cosmological Parameter Esti
 mation - Nick Kaiser (ENS\, Paris)
DTSTART:20181015T120000Z
DTEND:20181015T130000Z
UID:TALK109453@talks.cam.ac.uk
CONTACT:Tobias Baldauf
DESCRIPTION:A long standing question in cosmology is whether gravitational
  lensing by structure biases the apparent distance or the mean flux densit
 y of sources. Interest in this has been rekindled by recent calculations i
 n 2nd order relativistic perturbation theory which suggest significant imp
 lications for cosmological parameter estimation from both supernovae and t
 he microwave background.  In this talk I shall first review the somewhat c
 onfusing history of the subject\, going back to the early '60s and includi
 ng both Weinberg's 1976 argument that there should be no effect on grounds
  of flux conservation and the general relativistic "focusing theorem" of t
 he '80s that seems to contradict this and which foreshadows the more recen
 t results.  I then describe recent work with John Peacock where we have sh
 own how these conflicts are resolved. Regarding Weinberg we show that ther
 e is a loophole in his argument\, and lensing does in fact bias the appare
 nt distance\, but it is a very small effect. We show that the apparent int
 rinsic tendency for\nstructure to cause focusing of light rays that emerge
 s from the focusing theorem is a statistical rather than a physical effect
 s. 
LOCATION:CMS\, Pav. B\, CTC Common Room (B1.19) [Potter Room]
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