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CATEGORIES:Theoretical Physics Colloquium
SUMMARY:Quantum Universe - Neil Turok (Perimeter)
DTSTART;TZID=Europe/London:20170426T141500
DTEND;TZID=Europe/London:20170426T151500
UID:TALK71466AThttp://talks.cam.ac.uk
URL:http://talks.cam.ac.uk/talk/index/71466
DESCRIPTION:Observations reveal the cosmos to be astonishingly
simple\, and yet deeply puzzling\, on the largest
observable scales. Why is the mean spatial geome
try so close to flat? Why is the universe so unifo
rm and isotropic on large scales? Why is there a c
osmological constant and what fixes its value? How
did everything we see emerge from a singular poin
t in the past\, and how did time emerge? Why do th
e density fluctuations take such a simple form? Ma
ny lines of evidence point to the need for a quant
um theory of cosmology\, and Feynman’s path integr
al for quantum gravity provides a sensible startin
g point. One attractive idea is the ``no boundary”
hypothesis\, that the past consisted of a compact
four-geometry. I shall show how Picard-Lefschetz
theory allows one to make sense of the Lorentzian
(but not the Euclidean) path integral in this cont
ext\, revealing the ``no boundary" and ``tunneling
" proposals to be identical. One can then prove a
theorem to the effect that no smooth\, semi-classi
cal quantum beginning of spacetime of the kind env
isaged by Hartle and Hawking or Vilenkin is possib
le. I shall present a new proposal for the probabi
lity in quantum cosmology\, which ``explains”the b
ig bang singularity and offers new approaches to t
he above-mentioned puzzles.
LOCATION:MR2\, Centre for Mathematical Sciences
CONTACT:Shahar Hadar
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