Cosmologists have done lots of excellent work over the past few decades creating more and more precise instruments and telescopes that study the large-scale structure of the universe. Many questions have been answered but many more questions have arisen. To explain galaxy rotation curves we gained dark matter. To explain observations of supernovae and the cosmic microwave background we have introduced dark energy. I’m sat in the “Dark matter, dark energy and cosmological parameters” session at NAM as are a few of the other NAM Bloggers.

The first talk is by Carlos Frenk of Durham University. He has done lots of work on the Millennium Simulation - a huge computer simulation of a large fraction of the universe which attempted to work out how matter and dark matter would form structures over the lifetime of the Universe. Most people will have heard of dark matter but may not be aware that there are different types of dark matter that have been proposed. These now fall into three categories; cold, warm and hot dark matter. The temperature label indicates the amount of energy carried by the potential candidate particles.

One of the ‘hot’ dark matter candidates is neutrinos. However, theorists have calculated that neutrinos cannot be a significant part of the dark matter content of the universe as that would leave the universe with only large scale structure - on the scale of galaxy super-clusters - and we don’t see that in real life. Using data from the 2dFGRS and WMAP, cosmologists see that lambda-CDM (cold dark matter) seems to be the best solution on large scales. But is lambda-CDM also consistent with the data on small scales? To answer that question we need to work out some statistics about the small-scale dark matter and that is where simulations such as the Millennium Simulation and observations come in. The Millenium Simulation has some great images and movies some of which are available on the web.