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SUMMARY:Quantum Universe - Neil Turok (Perimeter)
DTSTART:20170426T131500Z
DTEND:20170426T141500Z
UID:TALK71466@talks.cam.ac.uk
CONTACT:Shahar Hadar
DESCRIPTION:Observations reveal the cosmos to be astonishingly simple\, an
 d yet deeply puzzling\, on the largest observable scales.  Why is the mean
  spatial geometry so close to flat? Why is the universe so uniform and iso
 tropic on large scales? Why is there a cosmological constant and what fixe
 s its value? How did everything we see emerge from a singular point in the
  past\, and how did time emerge? Why do the density fluctuations take such
  a simple form? Many lines of evidence point to the need for a quantum the
 ory of cosmology\, and Feynman’s path integral for quantum gravity provi
 des a sensible starting 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 Lorentzia
 n (but not the Euclidean) path integral in this context\, revealing the ``
 no boundary" and ``tunneling" proposals to be identical. One can then prov
 e a theorem to the effect that no smooth\, semi-classical quantum beginnin
 g of spacetime of the kind envisaged by Hartle and Hawking or Vilenkin is 
 possible. I shall present a new proposal for the probability in quantum co
 smology\, which ``explains”the big bang singularity and offers new appro
 aches to the above-mentioned puzzles.
LOCATION:MR2\, Centre for Mathematical Sciences
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