What's the Worst that Could Happen? Existential Risk and Extreme Politics, by AndrewLeigh (<scp>MIT</scp> Press, Cambridge, MA, 2021), 234 pages + iv front matter

Plato and his mentor Socrates were famously ambivalent about democracy. They were suspicious of the passions of the crowd and preferred to be ruled by the learned who were skilled in governance. But what if there were a learned person who had also won over the crowd, would that please them? If so, then Andrew Leigh would be their man. A Harvard PhD and former professor of economics at the Australian National University, Leigh was elected to the Australian House of Representatives in 2010 and is currently an assistant minister in the Labor government. This is his 11th book, churned out during the COVID period. He has since written a 12th, and the baker's dozen is sure to follow. What's the Worst That Could Happen? is a deeply researched book looking at the mathematical likelihood of various calamities coming to pass. It says a great deal in a modest 167 substantive pages. In his opening chapter, Leigh takes note of the many apocalyptic movies that have challenged us in the past few decades; he recalls the doomsday clock hovering at mere minutes to midnight; and he pays tribute to his key intellectual source, Toby Ord's The Precipice: Existential Risk and the Future of Humanity (2020, Hachette Books). But I wonder if there is an unnamed influence lurking. Leigh was entering teenagehood when the Midnight Oil lead singer Peter Garrett turned his talents to politics and cast nuclear disarmament onto the national political stage. Surely, young Andrew was paying attention. Nuclear war is one of the existential risks Leigh examines, and the figures bear out his analysis. Even though the number of warheads has been reduced from 70,000 to 14,000, that figure is surely sufficient to do the job of creating nuclear winter, allowing the ants, cockroaches and rats to fight it out for dominion over the planet. Putting our faith in the rationality of governments seems like a risky proposition given that the totalitarian regime of the Democratic People's Republic of Korea is among them. And even if governments act rationally, the chances are far from negligible that a terrorist group will get its hands on a nuke and be a catalyst for full-scale war. H. G. Wells's War of the Worlds was written in the late nineteenth century and concluded with the indomitable aliens being defeated by the Earth's humble germs. In the twenty-first century we have come to accept that it is not only the aliens that can succumb. Thus far, our bugs have been either highly contagious or highly deadly, but not both. There is a Darwinian logic to that. A deadly parasite that spreads exponentially would itself die out in the process. But what about bugs grown in labs? Labs can leak, by misadventure or otherwise. One figure Leigh quotes is that there is a 1 per cent chance per decade that a lab will leak its lethal product. Leigh deals with two further physical risks. One is climate change, the risk of which is so well known that it requires little further elaboration. But perhaps a rumination is in order. Florida is a climate-denying state, consistently voting Republican. It is almost in the realm of the biblical that the various plagues of climate catastrophes are being visited upon its shores. A robot may not injure a human being or, through inaction, allow a human being to come to harm. A robot must obey orders given it by human beings except where such orders would conflict with the First Law. A robot must protect its own existence as long as such protection does not conflict with the First or Second Law. A mere 60 words, but it seems impossible for the computer scientists to program it into their AI systems. The fear is that HAL, from Stanley Kubrick's movie 2001: A Space Odyssey, will yet have the last word. Leigh summarises the risks numerically and using normal probability mathematics comes to the figure of a one in six chance of one of these existential risks occurring. We are unwittingly playing Russian roulette. Leigh also puts forward in each case the processes to mitigate the risks. These have previously been stated, and many of the avoidance and mitigation strategies are policy positions that have already been adopted or proposed. It is nevertheless comforting to have the risks balanced with actions available to humanity to counter them. Thus far, we have heard from Leigh the academic, but the balance of the book is a cris du coeur from Leigh the politician. He deals with the threat of populism and demonstrates an admirable facility for sharp and succinct analysis – the causes of populism are jobs, snobs, race, pace and luck. I will let the book's readers unpack these words, each supported by statistics and examples. The populist threat is not unrelated to the physical existential risks because in their blind jingoism, the populists reject international cooperation, which is a necessary condition to avert each of the elaborated risks. And in their prevarication with evidence-based decision making, the populists are likely to choose a disastrous short-term action rather than a felicitous policy for the long term and for the benefit of future generations. A corollary of the populist risk is the threat to democracy, and that is the subject of Leigh's penultimate chapter. It is a subject on which I have also written (Rich, 2017), and it also defaults to the problem of democracy in its leading nation, the USA. With the 2024 presidential election campaign in full swing as this review is written, the issues Leigh raises are magnified with every morning headline. Leigh advocates many of the institutional design solutions that I also put forward flowing from our common familiarity with Australian politics. But I have come to realise that although propitious institutional design may be a necessary requirement, it is far from sufficient. I was encouraged that Leigh also writes about civic education as a requirement for maintaining democracy. Ultimately, a nation needs a culture of democracy if it is to sustain a democratic political system. We need to listen to others, maintain civility in our public discourse, learn to evaluate evidence dispassionately, deliberate on difficult problems and accept the inevitable setbacks that democracy will produce. Learning these skills begins in school. Leigh's final chapter is a mix of philosophical considerations and examples of the criticality of effective leadership. That is where this review began. I believe Leigh passes the Platonic test. Hopefully, he will also continue to benefit from the wisdom of the crowd.