What does it mean for us that the world’s population has reached 7 billion? Is it sustainable? Will there be enough food, energy, land space, or even enough oxygen, for not just the 7 billion we have now, but the 9 billion we are estimated to have by 2015? What can we do about it? The Festival of Social Sciences event ‘The World at 7 Billion’ is certainly not shying away from brave questions.