BEGIN:VCALENDAR
PRODID:-//eluceo/ical//2.0/EN
VERSION:2.0
CALSCALE:GREGORIAN
BEGIN:VEVENT
UID:6e9bb5af35ad7f05ac9d6b500b1ff618
DTSTAMP:20240412T183016Z
SUMMARY:Theory group seminar: Steffen Gielen – Unitarity and clock depend
ence in quantum cosmology
DESCRIPTION:Unitarity and clock dependence in quantum cosmology\nThe proble
m of time is often discussed as an obstacle in canonical quantisation of g
ravity: general covariance means there is no preferred time parameter with
respect to which evolution could be defined. We can instead characterise
dynamics in relational terms by defining one degree of freedom to play the
role of an internal clock for the other variables\; this leads to a “mu
ltiple choice problem”. I will review recent results obtained in a quant
um cosmological model with three dynamical degrees of freedom: a volume or
scale factor variable for the geometry\, a massless scalar matter field\,
and a perfect fluid. Each of these variables can be used as a clock for t
he other two. We obtain three different theories which\, if we require the
m to have unitary time evolution with respect to the given clock\, make ve
ry different statements about the fate of the Universe. Only one resolves
the classical singularity\, and only one leads to a quantum recollapse of
the Universe at large volume. Nonclassical behaviour arises whenever a cla
ssical solution terminates in finite time so that reflecting boundary cond
itions are needed to make the theory unitary.
URL:https://www.imperial.ac.uk/events/155699/theory-group-seminar-steffen-g
ielen/
DTSTART;TZID=Europe/London:20221206T131500
DTEND;TZID=Europe/London:20221206T150000
LOCATION:H503\, Huxley Building\, South Kensington Campus\, Imperial Colleg
e London\, London\, SW7 2AZ\, United Kingdom
END:VEVENT
BEGIN:VTIMEZONE
TZID:Europe/London
BEGIN:STANDARD
DTSTART:20221206T131500
TZNAME:GMT
TZOFFSETTO:+0000
TZOFFSETFROM:+0000
END:STANDARD
END:VTIMEZONE
END:VCALENDAR