Vale Steven Weinberg, and wild wattles where they're not wanted

This week Chris remembers the life and work of American theoretical physicist Steven Weinberg who passed away recently. Famous among physicists but little known among the general public, he was widely regarded as the one of the greatest physicists of his time. Claire looks into another little known area of science, that of indigenous weeds. In a country the size of Australia, it's not unusual to find plants which are native to the continent, but causing havoc where they are not wanted.