The fundamental questions to be addressed by the Square Kilometre Array remain relevant today, despite the passage of time since the SKA Science book was published in 2004. The answer to the questions of Dark Energy, Cosmic Magnetism, Gravitation in Extreme Fields, and the Epoch of Reionisation, all require observational statistics on a very large scale. As a result, the SKA is being designed mainly as a large survey machine. Survey requirements place specific demands on the technical definition of the SKA, and the cost of implementation puts restrictions on the ultimate capability of the SKA. At the same time, we must not trade-off too much of the versatility of the SKA because, as has been seen many times in the past, it is the unexpected discoveries which turn out to be the most important contribution of an instrument.

This is the abstract from the presentation I made at the final SKADS conference “Wide Field Science and Technology for the SKA” in December 2009. You can read the published article, “The Questions that Drive the Specifications”