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Title: Conserved quantities in cosmology // A practical use for redshift drift
Speaker: Phillip Helbig
Time: Thursday 27 October 2022, 1400 to 1500
Location: 80101Å
Abstract:
1. Lake (PRL, 94, 201102, 2005) pointed out that a certain combination (dubbed alpha) of the density parameter Omega and the cosmological constant lambda is a constant of motion for evolutionary trajectories in the lambda-Omega plane and used mapping between alpha and the lambda-Omega plane to demonstrate the lack of a flatness problem for spatially closed cosmological models with a positive cosmological constant which will expand forever. In such models, the conserved quantity corresponds to the product of Lambda and the square of the mass (of dust in the cosmological sense) of the universe. Here, I don't dwell on the flatness problem but rather investigate other quantities which correspond to alpha and other constants of motion in the lambda-Omega plane.
2. Although already implicit in 1920s cosmology, redshift drift (the change in the cosmological redshift of an object between epochs of observation) was discussed by Sandage in 1962 but remained a curiosity until a few years ago, when technology made it possible to measure it on a timescale of at most a few decades. It is usually seen as a consistency check for standard cosmology, but can also rule out most models with alternative explanations for cosmological redshift; however, both of those uses will simply confirm what most people already accept, namely that the Universe is well described by an FRW model. I discuss a case in which redshift drift can provide us with useful information which we cannot otherwise obtain on a reasonable timescale.