We present a novel classification framework for severe global catastrophic risk scenarios. Extending beyond existing work that identifies individual risk scenarios, we propose analysing global catastrophic risks along three dimensions: the critical systems affected, global spread mechanisms, and prevention and mitigation failures. The classification highlights areas of convergence between risk scenarios, which supports prioritisation of particular research and of policy interventions. It also points to potential knowledge gaps regarding catastrophic risks, and provides an interdisciplinary structure for mapping and tracking the multitude of factors that could contribute to global catastrophic risks.

To mark the 250th anniversary of Thomas Young’s birth, Martin Rees, the UK’s Astronomer Royal, highlights the wide-ranging expertise and discoveries of the maverick British scientist.

Letter to the Editor

In the 1960s, novel and increasingly powerful observational techniques opened up the field of high-energy astrophysics. Cosmology started to become an empirical science, and there was a resurgence in the study of general relativity. Martin Rees became a graduate student at the University of Cambridge during that period and subsequently held postdoc positions in the United States. He was therefore fortunate to have a close-up perspective on some of these developments and to interact with many senior figures who were spearheading these advances. He himself became a phenomenologist, contributing his own ideas to several topics in these fields and working with many collaborators. This article offers an assessment of some key subsequent developments and personal perspectives from a diverse career spanning more than 50 years.

A response to the news story about NASA’s DART mission, which is testing for the first time whether an asteroid can be deflected.

The flames that engulfed Notre Dame Cathedral in April 2019 threatened one of the “peaks” of our Western heritage—and gave us cause to marvel at the ambition and vision that its construction entailed. Its builders knew of nothing beyond Europe; they thought there might be an apocalypse within a millennium. But despite these constricted horizons, in both time and space, despite the deprivation and harshness of their lives, despite their primitive technology and meager resources, they built this immense and glorious building—extending the frontiers of what was possible. Those who conceived the cathedral knew they wouldn’t live to see it finished. Their legacy still elevates our spirits, nearly a millennium later. Unlike our forebears, we know a great deal about our world—and indeed about what lies beyond. Many phenomena still make us fearful, but the advance of science spares us from irrational dread. We know that we are stewards of a precious “pale blue dot” in a vast cosmos—a planet with a future measured in billions of years—whose fate depends on humanity’s collective actions this century. But all too often our focus is short-term and parochial. Planning horizons span decades at most; they’re not matched to the global challenges that face us in the 21st century. There’s an explanation for this seeming paradox. Medieval people’s lives played out against a “backdrop” that changed slowly; they thought their children and grandchildren would lead similar lives and share their faith and culture. But, unlike our remote forebears, we expect the lives and priorities of new generations to be unpredictably different from ours. That’s why we, and our governments, react with torpor to the compelling concerns about the future: we retreat into inaction because we’re not confident enough of any scenario to commit to it. Humans are now so numerous and have such a heavy collective “footprint” that they have the ability to transform, or even ravage, the entire biosphere. The world’s growing and more demanding population puts the natural environment under strain; our collective actions

Letter to the Editor

The physical processes that determine the properties of our everyday world, and of the wider cosmos, are determined by some key numbers: the 'constants' of micro-physics and the parameters that describe the expanding universe in which we have emerged. We identify various steps in the emergence of stars, planets and life that are dependent on these fundamental numbers, and explore how these steps might have been changed, or completely prevented, if the numbers were different. We then outline some cosmological models where physical reality is vastly more extensive than the 'universe' that astronomers observe (perhaps even involving many 'big bangs'), which could perhaps encompass domains governed by different physics. Although the concept of a multiverse is still speculative, we argue that attempts to determine whether it exists constitute a genuinely scientific endeavor. If we indeed inhabit a multiverse, then we may have to accept that there can be no explanation other than anthropic reasoning for some features our world.

The Astronomer Royal, Martin Rees, spoke about the past and the future at the celebration of the bicentenary of the Royal Astronomical Society on 23 January 2020.

In January, the Royal Astronomical Society gathered in London to celebrate its bicentenary, welcomed by RAS president-elect Emma Bunce. On 23 January 2020, the Royal Astronomical Society gathered in London to celebrate its bicentenary, welcomed by RAS president-elect Emma Bunce