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SUMMARY:Characteristic relativity in cosmology: the geometry of the Univer
 se from data\, and gravitational waves in de Sitter spacetime - Nigel Bish
 op (Rhodes University)
DTSTART:20160513T120000Z
DTEND:20160513T130000Z
UID:TALK65463@talks.cam.ac.uk
CONTACT:43345
DESCRIPTION:In the characteristic formalism of numerical relativity\, coor
 dinates\nare based on null cones generated by radial null geodesics. This\
 nformalism is appropriate to cosmology\, since nearly all data comes\nfrom
  observations on our past null cone. It is in principle possible\nto measu
 re the initial data required in order to calculate an\nevolution into the 
 interior of the past null cone\, and codes have been\nimplemented to perfo
 rm the evolution. In the case of spherical\nsymmetry\, it is now possible 
 to apply this process using actual\nobservations leading to constraints on
  the geometry of the Universe.\n\nOn linearization\, the formalism may be 
 used to investigate\ncosmological effects\, such as the accelerated expans
 ion\, on the\npropagation of gravitational waves. It is found that the eff
 ect of\nusing a de Sitter rather than a Minkowski background for gravitati
 onal\nwaves in the LIGO frequency band\, is negligible. However\, a somewh
 at\ncounter-intuitive result is found for the gravitational wave energy:\n
 energy conservation does not normally apply to inertial observers\, but\nc
 an be formulated for a class of accelerated observers\, i.e. with\nworldli
 nes that are timelike but not geodesic.
LOCATION:Pavilion B Potter Room (B1.19)
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