New Year Lecture "Exploring the Dark Sector of the Universe"

Dark matter and dark energy play a dominant role in the dynamics of our universe on large scales. Despite their making up 95% of the energy content of the universe, little else is known about these two distinct phenomena apart from their long-range gravitational interactions.

Dark matter provides an attractive force that is relevant on galactic scales and above. The standard explanation is that it is composed of cold, weakly interacting particles that do not emit light, hence we cannot see them. A number of experiments have attempted to detect dark matter particles in the lab, but so far have been unsuccessful.

Dark energy provides a significant repulsive force on galaxy cluster scales and above, and is responsible for driving the accelerated expansion of the universe. The simplest explanation for this phenomenon is a cosmological constant and/or quantum mechanical vacuum energy, but both ideas predict a much larger effect than we see in the universe today.

In this talk I will give a brief overview of the above two topics, and will then discuss the possibility that our theory of gravity could be incomplete. This general approach, termed modified gravity, is an active area of research today, and could play an important role in the explanation of dark matter and dark energy.