The Baryon Acoustic Oscillation scale in Cosmology, model-independently

Astronomy Unit Seminars
Prof. Alan Heavens (Imperial College)
Richard Nelson
March 6th, 2015 at 14:30
GO Jones Room 610

By making precise measurements of the geometry of the Universe we can learn some remarkable things, such as whether it is curved or not, what the nature of Dark Energy is, whether we live in extra dimensions, and whether there are new species of fundamental particles that have not yet been discovered on Earth. We use a key observable quantity - the Baryon Acoustic Oscillation (BAO) scale, which is the distance sound waves travelled in the early Universe. These sound waves leave their imprint in the clustering of galaxies today, and this ‘sound horizon’ acts as a cosmic ruler that can be used to measure the Universe, and yield information on both the physics driving the acceleration of the Universe now, and also on possible new physics in the first million years after the Big Bang. Normally, the BAO length is a derived quantity, assuming a cosmological model, but in this talk I show how it has be measured from low-redshift clustering and supernova data, in an almost model-independent way. It is 104 +/- 2 Mpc/h, a measurement that any theory has to account for, and which would survive even if the favoured Lambda Cold Dark Matter model does not. The measurement assumes very little - not even General Relativity - just symmetry of the Universe and a smooth expansion history.