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SUMMARY:Singularities\, Fluids\, and the BKL Conjecture - Elliot Marshall 
 (postdoc at FORTH in Crete\, Greece)
DTSTART:20260220T130000Z
DTEND:20260220T140000Z
UID:TALK244666@talks.cam.ac.uk
CONTACT:Lorenzo Gavassino
DESCRIPTION:The Penrose-Hawking singularity theorems guarantee that a wide
  class of cosmological models are past geodesically incomplete\, indicatin
 g that these spacetimes contain ‘big bang’ singularities. However\, th
 ese theorems do not provide any information about the nature of the singul
 arity. A longstanding problem in mathematical cosmology\, therefore\, has 
 been to understand the dynamical behaviour of solutions to the Einstein eq
 uations near the big bang. In the seminal work of Belinskiǐ\, Khalatnikov
 \, and Lifschitz (BKL)\, it was conjectured that the initial singularity i
 s generically spacelike\, local\, and oscillatory. Roughly speaking\, this
  means that solutions to the Einstein equations are well-approximated by a
  chaotic system of ODEs near the big bang. Rigorous results in this settin
 g have thus far been limited to spatially homogeneous spacetimes\, althoug
 h there is an extensive body of numerical work for vacuum spacetimes which
  supports the BKL picture. However\, there has been comparatively little r
 esearch (numerical or otherwise) into the dynamics of inhomogeneous cosmol
 ogies containing non-stiff matter near the big bang. In this talk\, I wil
 l give an overview of the BKL conjecture and discuss recent numerical work
  for inhomogeneous cosmologies containing a non-stiff perfect fluid. In pa
 rticular\, I will show that the fluid velocity in these models develops ch
 aotic oscillatory behaviour\, known as tilt transitions. 
LOCATION:Potter Room / Zoom :  https://cam-ac-uk.zoom.us/j/85131795570
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