Dark Matter, Dark Energy and the Accelerating Universe

Gil Holder

It now appears that roughly 95% of the universe is composed of material which we don't understand. This unknown material seems to have (at least) two components: dark matter, which leads to gravitational attractions much greater than expected around some objects, and dark energy, which has recently been discovered to be causing the expansion of the universe to accelerate. Ongoing experiments are characterising the properties of dark matter and dark energy to ever greater precision, and theoretical ideas abound for what they could be, but understanding this mysterious 95% is one of the biggest challenges in particle astrophysics today.