The Decisive End of All
Scientific Contribution to »Zusammenstoß«
The end of the world is a story as old as mankind. The Käte Hamburger Centre for Apocalyptic and Post-Apocalyptic Studies (CAPAS) at Heidelberg University uses the prism of the apocalypse to examine the effects of end-time scenarios on society, individuals and the environment. The underlying question is which world will end, and thus from which perspective the world's end is viewed. The end of the world or the entire universe in a cosmic catastrophe represents in such scenarios the decisive end of humanity, and possibly of all things. For centuries, mankind has been preoccupied with this possibility, with celestial phenomena playing a major role in the most diverse cultural circles. For example, the appearance of Halley's Comet in the 15th century was part of the omens of the Mexica (a people within the Nahua culture in present-day Mexico), which described colonialism and thus the destruction of the pre-colonial world. However, in the natural sciences and aerospace engineering, collision scenarios are calculated and solutions are sought for defence against collisions with asteroids or comets. For decades, the question and story of a cosmic end have also provided narrative material for the film industry. The question of how and whether humanity could prevent such an event or ensure its existence by resettling another planet is always a central theme.
As early as 1951, this was a central plot line in the classic film »When Worlds Collide«. In summer 2023, the film was part of the public film and talk series Apocalyptic Cinema, which takes place every semester and is part of CAPAS’ science communication activities.
The film was scientifically commented on by CAPAS fellow Richard J. Wilman. In Heidelberg, the astrophysicist explored apocalyptic cosmic threats and a post-apocalyptic future for humanity in space.
Existential Space Risks – a scientific commentary on »When Worlds Collide«
The 1951 sci-fi classic »When Worlds Collide« was an early adaptation for the big screen of a theme revisited by Hollywood many times over the ensuing decades: the impending destruction of the Earth by a rogue celestial object and the societal response to the threat. In the movie, produced by George Pal and based on a 1933 novel of the same title by E. Balmer and P. Wylie, the storyline begins with the realisation that the Earth is on a collision course with a newly-discovered star Bellus, with the impact due within a year. An astronomer presents the case to the United Nations and argues in vain for the construction of a space »lifeboat« to ferry a select group of humanity to safety on Bellus’ accompanying planet Zyra. In response to the failure to mount a unified international response, the mantle is taken up by private industrialists who finance the hurried construction of a spacecraft. Much of the film is devoted to the fraught selection of its passengers amid scenes of rising human drama and panic as the destruction unfolds and doomsday approaches. The film ends with the craft landing safely on Zyra and the passengers and crew disembarking onto the habitable terrain of a bright new world. The sequel book, »After Worlds Collide«, never made it to screen.
Over 70 years on, there is much for the critic to feast on in terms of the science and the special effects. But seen as a product of its time – 10 years before the first human spaceflight and almost 50 years before the discovery of the first exoplanets – these can be forgiven. The legacy of the film lies in its depiction of the multi-faceted and all-too-real human drama which plays out alongside the unfolding natural disaster; human psychology and society’s capacity to respond in a coherent way to an existential threat have arguably changed little, for all the strides in our scientific understanding and technological prowess.
In terms of the science, the most obvious shortcoming of the film lies in the sheer improbability of the Earth colliding with another star. In our neighbourhood of the Milky Way Galaxy, the distances between stars are so vast that even close stellar encounters, let alone actual collisions, are fantastically rare, even on cosmic timescales. For example, an approach between the Sun and another star within 100 times the Earth-Sun distance – the proximity required to disrupt planetary orbits— is expected roughly every 100 billion years. This is several times the age of the Universe, so it is highly unlikely to happen over the next 1 billion years whilst Earth remains habitable; more distant but more frequent stellar approaches could slightly change Earth’s orbit and climate. The Milky Way contains a few hundred billion stars, a significant fraction of which likely host habitable rocky planets (a matter on which the film was prescient for the case of Bellus and Zyra), some in denser environments such as star clusters or the Galactic Centre. Therefore, in the Galaxy as a whole, destructive stellar encounters – possibly involving life-bearing planets – may be quite common.
Turning to other cosmic hazards, life on Earth has undergone several mass extinctions, such as the one that killed off the dinosaurs 66 million years ago with the impact of a 10 km asteroid or comet. Sterilizing radiation from stars exploding as supernovae or gamma-ray bursts may have caused some of the others. Zooming in from geological to human timescales, in the coming centuries or even in our own lifetimes we could face more modest but still serious threats, e.g. the need to avert the impact of a small asteroid with a large city; or a strong solar flare which destroys critical infrastructure. Or perhaps we will discover intelligent life elsewhere in space. In any event, such threats continue to provide rich material for dramatic entertainment and study of the human response to an impending apocalypse, even as we grapple with more urgent ‘home grown’ threats such as nuclear war or climate change.
Richard J. Wilman is Associate Professor in Physics at Durham University, UK, and was a fellow of the Centre for Apocalyptic & Post-Apocalyptic Studies, Heidelberg University, in 2023.