Large-scale structure
Large-scale structure in the 2dF Galaxy Redshift Survey.
Understanding how large-scale structure in the Universe formed is an important goal of cosmology. On very large scales (more than 100 Mpc) the Universe is homogeneous (the same everywhere) and isotropic (the same in all directions). However, on smaller scales, the Universe contains a wealth of structure: planets and stars, galaxies, clusters of galaxies, etc. The largest objects in the Universe are large, filamentary structures seen in galaxy surveys, such as the 2dF Galaxy Redshift Survey (pictured right) and in cosmological simulations (see below). In our current picture of the Universe, these large-scale structures began as tiny seed fluctuations in the very early Universe, which were amplified by gravitational collapse.
A powerful tool for studying the development of structure is the power spectrum - the amplitude of density fluctuations as a function of scale. This can be measured with large galaxy surveys, but relating the galaxy power spectrum to the spectrum of initial fluctuations is difficult for several reasons. The main one is that once the amplitude of density fluctuations on some scale approaches the mean density of the Universe, the fluctuations becomes non-linear and numerical techniques are needed to follow their growth.
Large-scale structure in an N-body simulation.
We are using N-body simulations to investigate the flow of information in the non-linear power spectrum. Our aim is to find out if information (about the initial spectrum of fluctuations) is preserved through non-linear evolution. If it is then this means that - at least in theory - we should be able to reconstruct the spectrum of primordial fluctuations from the present-day galaxy distribution.
You can download a short animation (MPEG-4, 401kB) of structure forming in an N-body simulation. The animation is of the same simulation shown to the left. Different shades of blue are used to show different densities of dark matter (the brightest areas are the most dense). The legend in the top-right corner is the size of the Universe, relative to the present day.