Cosmology

Background

Cosmological applications of Classical General Relativity were initiated by Einstein himself (in Germany), by de Sitter (in the Netherlands), Friedmann (in Russia), and Lemaitre (in Belgium). Many of the modern cosmological models on exhibit classic features obtained by these early researchers.

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Cosmology at Victoria University of Wellington

Cosmological research carried out by this group focuses on two main ideas:

• Cosmography is good: A good part of cosmology is purely kinematic in character, and independent of the Einstein equations. These segments of cosmology can be treated in a purely descriptive manner, and you do not need a dynamical analysis until you try to explain the observations. For instance, many cosmologists have forgotten that the Hubble law is purely kinematic, and that it can be derived based on symmetry principles without using the Einstein equations.
• Only after the Hubble parameter and deceleration parameter have been measured by direct observation can we begin to ask direct observational questions about the density and pressure of the cosmological fluid. If you wish to extract even a linearized equation of state from the observational data one will need to measure the jerk parameter, the next term after the deceleration parameter.

The alternative is to decide on an "a priori" equation of state based on your favourite toy model, and then try to get away with using only the Hubble parameter and deceleration parameter. In contrast, if you do not pre-choose the preferred equation of state you have no choice but to attempt to measure the jerk (and then the snap, crackle, and pop) of the cosmological expansion.

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References on Cosmology

For details see:

• Matt Visser, Jerk, snap, and the cosmological equation of state. Class. Quant. Grav. 21 (2004) 2603 arXiv: gr-qc/0309109.
• Céline Cattoën, Matt Visser, Necessary and sufficient conditions for Big Bangs, Bounces, Crunches, Rips, Sudden singularities, extremality events, and more.... Class. Quantum Grav. 22 (2005) arXiv: gr-qc/0508045
• Céline Cattoën, Matt Visser, The Hubble series: Convergence properties and redshift variables. Accepted for publication in Class. Quantum Grav. arXiv: gr-qc/0710.1887
• Céline Cattoën, Matt Visser, Cosmography: Extracting the Hubble series from the supernova data. arXiv: gr-qc/0703122

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