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SUMMARY:The classical equations of motion of quantised gauge theories - To
 m Melia (IPMU)
DTSTART:20230803T150000Z
DTEND:20230803T160000Z
UID:TALK200473@talks.cam.ac.uk
CONTACT:Benjamin Christopher Allanach
DESCRIPTION:The Einstein and Maxwell equations are the jewels in the crown
  of classical physics. But classical physics is only an approximation to n
 ature\, arising as a limit of the underlying quantum mechanical descriptio
 n. And in the case of both general relativity and electromagnetism\, owing
  to their gauge theory nature\, the full set of classical equations of mot
 ion are not guaranteed to follow from the quantum theory. The time-time an
 d time-space components of the Einstein equations in GR and Gauss’ law i
 n EM are enforced ‘by hand' in the quantisation procedure—a choice so 
 as to make the classical-like states behave as per our classical belief. \
 n \nBut what if our universe was actually described by another classical-l
 ike state? For GR\, the resulting modification of the Einstein equations c
 an be packaged as the inclusion of an auxiliary energy-momentum tensor des
 cribing a ’shadow’ matter that adds no additional degrees of freedom t
 o the theory. The homogenous and isotropic background piece of this auxili
 ary matter contributes to expansion of the universe identical to cold dark
  matter\, and the inhomogeneous components source curvature perturbations 
 that grow linearly at linear order.
LOCATION:Potter Room\, B1.34\, DAMTP
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