Research papers

• Dynamics of spatially inhomogeneous cosmological models

  1. Asymptotic silence of generic cosmological singularities (with Lars Andersson, Woei Chet Lim and Claes Uggla)
     Phys. Rev. Lett. 94 (2005), 051101 (1-4). [See also: Phys. Rev. Focus 15 (2005), story 8.]
     Preprint arXiv:gr-qc/0402051v2.
  2. Gowdy phenomenology in scale-invariant variables (with Lars Andersson and Claes Uggla)
     Class. Quantum Grav. 21 (2004), S29-S57.
     Contribution to the Vincent Moncrief Festschrift.
     Preprint arXiv:gr-qc/0310127v1.
  3. Asymptotic isotropization in inhomogeneous cosmology (with Woei Chet Lim, Claes Uggla and John Wainwright)
     Phys. Rev. D 69 (2004), 103507 (1-22).
     Preprint arXiv:gr-qc/0306118v1.
  4. The past attractor in inhomogeneous cosmology (with Claes Uggla, John Wainwright and George F R Ellis)
     Phys. Rev. D 68 (2003), 103502 (1-22).
     Preprint arXiv:gr-qc/0304002v1.
  5. Dynamical systems approach to G2 cosmology (with Claes Uggla and John Wainwright)
     Class. Quantum Grav. 19 (2002), 51-82.
     Preprint arXiv:gr-qc/0107041v2.
  6. Propagation of jump discontinuities in relativistic cosmology (with George F R Ellis and Bernd G Schmidt)
     Phys. Rev. D 62 (2000), 104023 (1-17).
     Preprint arXiv:gr-qc/0007003v2.
  7. Causal propagation of geometrical fields in relativistic cosmology (with George F R Ellis)
     Phys. Rev. D 59 (1999), 024013 (1-22).
     Preprint arXiv:gr-qc/9810058v1.
  8. Integrability of irrotational silent cosmological models (with Claes Uggla, William M Lesame, George F R Ellis and Roy Maartens)
     Class. Quantum Grav. 14 (1997), 1151-1162.
     Preprint arXiv:gr-qc/9611002v2.
  9. General relativistic 1+3 orthonormal frame approach (with Claes Uggla)
     Class. Quantum Grav. 14 (1997), 2673-2695.
     Preprint arXiv:gr-qc/9603026v1.
  10. The covariant approach to LRS perfect fluid spacetime geometries (with George F R Ellis)
      Class. Quantum Grav. 13 (1996), 1099-1127.
      Preprint arXiv:gr-qc/9510044v1.

• Quasi-Newtonian cosmologies and peculiar motions

  1. Geometrical order-of-magnitude estimates for spatial curvature in realistic models of the Universe (with Thomas Buchert and George F R Ellis)
     Gen. Rel. Grav. 41 (2009), 2017-2030. Dedicated to the memory of Jürgen Ehlers (1929-2008).
     Preprint arXiv:0906.0134v1 [gr-qc].
  2. General relativistic analysis of peculiar velocities (with George F R Ellis and Roy Maartens)
     Class. Quantum Grav. 18 (2001), 5115-5123.
     Preprint arXiv:gr-qc/0105083v2.
  3. Quasi-Newtonian dust cosmologies (with George F R Ellis)
     Class. Quantum Grav. 15 (1998), 3545-3573.
     Preprint arXiv:gr-qc/9805087v2.

• Other work

  1. Partially locally rotationally symmetric perfect fluid cosmologies (with Nazeem Mustapha, George F R Ellis and Mattias Marklund)
     Class. Quantum Grav. 17 (2000), 3135-3156.
     Preprint arXiv:gr-qc/9912107v2.
  2. Deviation of geodesics in FLRW spacetime geometries (with George F R Ellis)
     Contribution to the Engelbert Schücking Festschrift.
     Preprint arXiv:gr-qc/9709060v1.
  3. Kinematics and dynamics of f(R) theories of gravity (with Steve Rippl, Reza Tavakol and David Taylor)
     Gen. Rel. Grav. 28 (1996), 193-205.
     Preprint arXiv:gr-qc/9511010v1.
  4. Quantum cosmology and higher-order Lagrangean theories of gravity (with Jim Lidsey and Reza Tavakol)
     Class. Quantum Grav. 11 (1994), 2483-2497.
     Preprint arXiv:gr-qc/9404044v1.
  5. Evolution of the density parameter in inflationary cosmology in the presence of shear and bulk viscosity (with Reza Tavakol)
     Phys. Rev. D 49 (1994), 6460-6466.
  6. Jacobi metric for the Bartnik/McKinnon SU(2)-EYM field
     Gen. Rel. Grav. 25 (1993), 1295-1303.

Cargèse Lectures 1998

• 2008 upgrade (fully hyperlinked):
  Transcript of George Ellis' Cargèse Lectures 1998: Cosmological Models (87 pages, *.pdf) (891 kB).
  Also Preprint arXiv:gr-qc/9812046v5.

Ph.D. thesis

• Extensions and applications of 1+3 decomposition methods in general relativistic cosmological modelling
  Astronomy Unit, Queen Mary and Westfield College, University of London, 1996. (187 pages, *.pdf) (1.3 MB).

Presentations

• Kosmisches Höchstgeschwindigkeitsrennen? (Cosmic high speed race?) (30 pages, *.ppt; in German) (11.1 MB).
• Poetry-driven cosmology (Reza@60) (26 pages, *.ppt) (4.0 MB).
• Zustandsraumbeschreibung kosmologischer Dynamik (State space formulation of cosmological dynamics) (24 pages, *.pdf; in German) (11.2 MB).

Lecture notes

• MAS207: Electromagnetism (93 pages, *.pdf) (507 kB).
• MAS209: Fluid dynamics (with David Burgess) (139 pages, *.pdf) (721 kB).

Useful equation systems and notes

• Lemaître-Tolman-Bondi silent dust cosmologies (7 pages, *.pdf) (170 kB).
• Distance measurements in FLRW cosmology (7 pages, *.pdf) (170 kB).
• Vacuum Abelian G2 cosmologies: orthonormal frame equations (10 pages, *.pdf) (140 kB).
• Hubble-normalised orthonomal frame equations for perfect fluid cosmologies in component form (8 pages, *.pdf) (77 kB).
• Symmetric hyperbolic evolution systems: 2-D illustrative example (3 pages, *.pdf) (63 kB).
• (1+3)-orthonormal frame approach to perfect fluid spacetime geometries: the equations (11 pages, *.pdf) (160 kB).
• (1+3)-covariant methods in general relativistic cosmology (7 pages, *.pdf) (122 kB).

London Relativity Seminars

• London Relativity Seminars at Queen Mary, Wednesdays at 16.15h.

Classic research papers

• Classic (or otherwise useful) research papers in Relativistic Cosmology and General Relativity.
  (A very subjective selection!!!)

Research interests

[in German]

The most successful framework to date for the quantitative description of gravitational interactions is the general theory of relativity proposed by Einstein in 1915. My main research interest is in understanding the dynamical properties of Einstein's relativistic gravitational field equations in the context of spatially inhomogeneous cosmology. The central issue of the long-term research programme I am involved in is to analyse systematically the intrinsic, hierarchical, structure of the dynamical state space constituted by all cosmological solutions to Einstein's field equations, for a given matter model. Using well-defined mathematical tools from differential geometry and the theory of dynamical systems to formulate a scale-invariant state space approach to relativistic cosmology, our investigations are targeted towards a clear understanding of generic physical properties of spatially inhomogeneous cosmological models with different kinds of matter sources. The physics of spacetime geometries of this kind provides the explanatory basis for current mainstream research topics such as (i) the past, present, and future evolutionary history of the observable part of the Universe, (ii) a hypothetical phase of accelerated expansion in the early (and possibly present) Universe driven by a scalar field, (iii) gravitational lensing of electromagnetic waves by galaxies and clusters of galaxies, (iv) the dynamical formation of matter structures on cosmological distance scales, (v) the dark matter and "dark energy" problems, (vi) the generation and propagation of gravitational radiation in the early Universe and its interaction with intervening matter, or (vii) the nature of the cosmological initial singularity and cosmological boundary conditions.

A very important issue in studying the dynamical state space of relativitic cosmology is the question of which cosmological models can fit observations and which cannot. In particular, one would like to know what is the largest class of models that can look almost spatially homogeneous and isotropic at some stage of their evolutionary history. The standard model of cosmology assumes that on scales of the order of the present-day Hubble distance the physical conditions of the observable part of the Universe are indeed of this kind. However, evidence from systematic high-precision observational programmes is mounting which indicates that spatially inhomogeneous gravitational physics may be of relevance on these distance scales instead. It is thus of considerable interest to expand current research efforts into the study of alternative cosmological models which exhibit a much higher degree of complexity of gravitational physics. A special status in this context has been assumed by Buchert's scheme of spatial averaging over inhomogeneities in matter distributions and the resultant influences on the dynamics of cosmological gravitational fields. Here, I am particularly interested in the possibility of this scheme to account for apparent accelerated expansion of the observable part of the Universe as well as the consequences for the propagation of light. First successes of our efforts are gradually setting in. Recently, the scale-invariant state space approach, which regularises Einstein's field equations in the singular regime, led to significant progress in understanding the dynamics of cosmological spacetime geometries near generic initial singularities, including the formation of structure on small spatial scales.

Besides taking a qualitative analytic approach in pursuing the research targets outlined above, I am strongly interested in applying numerical approximation methods in relativistic cosmology. Symmetric hyperbolic reductions of Einstein's field equations appear ideally suited for extensive numerical experiments. Scale-invariant equation systems with well-posed initial value problems promise major benefits for numerical modelling.

Further research interests include the question of a physically meaningful description of the entropy intrinsic to (cosmological) gravitational fields. Central issues here are to test the consequences of the Weyl curvature hypothesis on the nature of the initial singularity for dynamical structure formation scenarios, and to what extent the strong constraints imposed by the Weyl curvature hypothesis on the initial conditions of relativistic cosmology can be motivated by the early Universe framework provided by loop quantum gravitation. An understanding of these issues will in turn be an important step in understanding the physics of the observable part of the Universe.