Cate Blanchett is not a lady for turning. Yesterday, the Oscar-winning actress and mother of three joined her co-chairs of the 2020 Summit and declared that she feels "glad to be part of the big team".

If she had listened to the Prime Minister it would have been otherwise: three days ago, Kevin Rudd suggested she might instead like to put her feet up, having just given birth to her third son, Ignatius.

"I said to her, 'you've just had a bub, you know, take it easy, you don't need to be at this thing'," Mr Rudd said yesterday.

"But she was absolutely determined to come."

Blanchett was true to her word, posing yesterday for photographs in Parliament House's foyer with the other co-chairs who will steer discussions at the summit.

But about 50 of the "best and brightest" have declined the Prime Minister's invitation to take part in the historic summit which starts this morning at Parliament House.

Some notable no-shows are media mogul James Packer, Enough Rope host Andrew Denton, environmental guru Professor Tim Flannery and film director John Polson.

But there are some prominent additions including Chief of the Defence Force Air Chief Marshall Angus Houston, ex-Reserve Bank governor Bernie Fraser and indigenous leader Lowitja O'Donoghue.

Senior public servants and parliamentarians will also take up seats around the tables.

In all, about 1000 people will take part in the two-day summit.

The participants will discuss the long-term challenges facing the country in 10 areas including productivity, the economy, environment, health, the arts, governance, strengthening communities and the future for indigenous people, rural towns and the entire country in a rapidly changing world.

"I don't have the view that people who sit in Canberra as politicians, or the public servants who advise them, have a monopoly on wisdom," Mr Rudd said.