Book summary “Worlds without end”: summary

Introduction

You live in a time when cutting-edge cosmology increasingly replaces our singular universe with infinite multiverses. Yet you might wonder how modern science arrived at this dizzying vision of countless worlds. Mary-Jane Rubenstein argues that the contemporary scientific multiverse is not a purely secular breakthrough. Instead, it directly inherits centuries of theological and philosophical wrestling with the concept of divine infinity.

You will trace this fascinating historical arc from ancient Greek philosophy through medieval scholasticism to modern quantum mechanics. The book explores how humanity repeatedly expanded its cosmic horizons, and why we keep inventing worlds beyond our own.

• How did ancient thinkers imagine plural worlds before the invention of the telescope?
• What role did medieval theology play in breaking open the Aristotelian cosmos?
• How do modern inflation and string theory revive ancient debates about infinity?

1. Plato Aristotle and the Singular Cosmos

Classical antiquity established a finite, bounded, and singular universe governed by external divine ordering and natural motion rather than internal chaos.

Plato's Timaeus and Cosmogony

You find that Plato's Timaeus describes the birth of the cosmos not as an internal emergence from chaos, but as an external ordering performed by a divine craftsman. The demiourgos finds the universe in disorderly motion and shapes it into a visible image of the eternal Form of the perfect living creature at 30a, 31b.

The Aristotelian Cosmos

Aristotle establishes the singularity of the universe through his theory of natural motion rather than divine benevolence. In De caelo, Aristotle argues that because elements like earth and fire move naturally toward the center or periphery, admitting multiple worlds would result in contradictory natural motions. This proves there can only be one center, one periphery, and one world at 276b21-22, alongside the rule at 271b26 that a body moving in a circle must be finite.

Peter Apian's 1524 Cosmographia illustrates the Ptolemaic universe where concentric spheres consolidate Aristotle's geocentric model.

2. Ancient Openings of Multiplicity

Early Atomists, Stoics, and Christian theologians fiercely debated the spatial and temporal multiplicity of worlds long before the modern scientific revolution.

Atomist Configurations

Leucippus and Democritus originated the theory of innumerable worlds within an infinite universe, driven by random atomic collisions in the void. Against the singular cosmologies of Plato and Aristotle, early Atomists argued that microscopic uncuttable particles move eternally in the void. These particles collide haphazardly to form countless kosmoi that grow, age, and eventually unravel into new worlds.

Epicurus lived from 341 to 270 B.C.E. and solved a major problem regarding atomic variety. He asserted that while atoms are infinite in number, the types of atoms are finite. This guarantees the infinite recurrence of identical worlds across the infinite expanse.

Lucretius wrote De rerum natura during the first century B.C.E., living from 99 to 55 B.C.E. He proved the infinity of the universe using a famous spatial thought experiment:

• If you throw a spear at any hypothetical boundary, it will either be stopped or pass through.
• Both outcomes prove that something lies beyond the barrier.
• Nature thus renders the universe infinite.

Lucretius attacked theistic cosmogonies for fostering fear, narcissism, and denial of flaws. He highlighted moral atrocities such as Agamemnon sacrificing his innocent daughter Iphigenia because priests persuaded him the gods demanded her for safe passage to Troy.

Michel Serres reads Lucretius as describing two distinct primordial chaoses:

• a stochastic cloud of omnidirectional atomic collisions;
• a laminar flow of parallel straight falls disrupted by an uncertain swerve called the clinamen.

Stoic and Christian Receptions

Zeno of Citium began lecturing at the stoa poikile in 300 B.C.E., founding a cosmology that rejected spatial multiplicity and the void. The Stoics maintained a singular cosmos that periodically undergoes destruction and rebirth through fire. This living world is permeated by a corporeal divine reason, ending when the sun consumes everything in flames.

Nietzsche reframed the Stoic eternal return as a psychological and ontoethical possibility. A demon might steal into your loneliness to declare that life must be lived innumerable times more, testing whether you would curse or bless the return.

Origen of Alexandria lived from 185 to 254 C.E. and reconciled a cyclic cosmology of multiple successive worlds with divine eternity. He argued that God has always been active through a succession of worlds before and after our own.

Augustine of Hippo lived from 354 to 430 C.E. and fiercely rejected Stoic and Origenian cosmic cycles in The City of God. The Visigoths sacked Rome in 410 C.E., prompting Augustine to compose his masterpiece between 413 and 426 C.E. He condemned eternal recurrence out of revulsion toward endless repetition, securing linear salvation through Christ instead.

3. From Scholasticism to the Infinite Universe

Late medieval debates and Renaissance cosmologists shattered the Aristotelian boundaries, replacing a singular cosmos with an actual infinite universe and countless worlds.

Aquinas and Cusa

Aquinas maintained that all things come from God and find their end in God, establishing an ordered hierarchy known as the Great Chain of Being. Because God is one, all things must belong to one unified world. An infinity of worlds would deny providential order and imply a lack of a single final home. Question and article number 1.47.3 in the Summa theologiae addresses the plurality of worlds during the lifetime of Thomas Aquinas from 1225 to 1274.

The Paris Condemnations of 1277 declared it heretical to claim that God cannot create multiple worlds, inadvertently opening a space for late-scholastic debate on possible worlds. Bishop Etienne Tempier issued a list of 219 heretical teachings, including Condemnation 34 regarding whether the first cause can make many worlds. Richard of Middleton invoked the condemnation of Lord Etienne to argue that because God created one world ex nihilo, he could create any number of them ex nihilo.

Nicholas of Cusa discarded the geocentric model by proposing that the universe has no absolute center and that every cosmic body acts as a shifting center of its own perspective. Cusa lived from 1401 to 1464 and published De docta ignorantia in 1440, anticipating Albert Einstein who formulated aspects of special relativity in 1905.

Cusa described a traveler on a boat who cannot perceive the motion of the vessel unless observing the shore, illustrating how observers perceive themselves at rest within a moving universe.

Cusa redefined the theological metaphor of the infinite sphere, applying it to the universe as a finite-infinity whose center is nowhere and whose circumference is nowhere. He distinguished between the negative infinite belonging to God, and the privatively infinite universe.

• Enfold the center with the poles using imagination to picture an unpicturable sphere whose center coincides with its periphery.

Giordano Bruno's Infinite Multiverse

Giordano Bruno radically expanded Cusa's cosmology by asserting an actual infinite universe filled with an infinite number of independent solar systems and habitable worlds. Bruno lived from 1548 to 1600 and published The Ash Wednesday Supper and On the Infinite Universe and Worlds in 1584 before his execution at the stake in Rome in 1600.

Thomas Digges published a Copernican diagram in 1576 extending the fixed stars indefinitely outward into a boundless and populated palace of felicity.

Bruno inverted traditional hierarchies by arguing that matter is eternal, divine, and self-generative, perpetually unfolding infinite forms from within itself. He rejected the Platonic notion that form precedes matter, arguing that form comes and goes while matter remains permanent.

Bruno used the example of a clay pot breaking where the form is lost but the clay remains, or a log turning into smoke and ash while matter persists.

Bruno concluded that the universe is neither purely monistic nor pluralistic, but multimodal, remaining one substance through an infinite multiplicity of distinct worlds. He posited an immobile world soul permeating all matter. Because the infinite has no parts, every portion of the universe reflects the whole.

4. Measuring the Immeasurable Cosmos

Seventeenth and eighteenth-century pioneers balanced telescopic observation with physical laws, defining finite, indefinite, and cyclic cosmic systems.

Galileo, Kepler, and Descartes

Galileo published his telescopic discoveries in Sidereus nuncius in 1610. The Inquisition condemned Copernicanism six years later.

By showing that the moon had a surface similar to Earth, Jupiter possessed four moons, and stars were distant suns, Galileo's observations dismantled Aristotelian cosmology and sparked intense speculation regarding inhabitants on other planets. Just as theological questions arose over whether non-European humans were descendants of Adam or needed salvation, seventeenth-century thinkers anxiously debated whether beings on other planets shared human reason, fell when Adam fell, or required Christ's redemption.

Johannes Kepler was horrified by Giordano Bruno's infinite worlds and argued that astronomy must restrict itself to observable phenomena. He maintained that our sun occupied the center of an immense cavity bounded by fixed stars.

René Descartes treated space and matter as identical, rejecting both the atomist void and absolute infinity in favor of an indefinite plenum. His vortex theory explained solar systems as rotating swirls of particles winnowed by size and motion. Descartes began working on Le monde in 1629 and completed it in 1633, but he suppressed its publication upon learning of Galileo's condemnation. He later published attenuated ideas in his 1644 Principia philosophiae.

Newton and Kant

Isaac Newton reinstated absolute space and absolute time against Leibnizian relativity. In his letters to Richard Bentley during the winter of 1692/1693, Newton argued that gravity alone could not create the distinction between shining and opaque bodies, produce circular orbital motion, or prevent an infinite universe from collapsing without divine assistance. He published his Principia in 1687.

Immanuel Kant attempted a grand synthesis of Newtonian physics and Epicurean atomism in his 1755 Universal Natural History and Theory of the Heavens.

Kant proposed that a primordial chaos of distributed atoms formed worlds and galactic systems through the opposing forces of gravitational attraction and a non-Newtonian repulsive force acting as an Epicurean swerve. He published his Natural History anonymously in 1755, but the book suffered obscurity when the original publisher went bankrupt and impounded unsold copies.

Kant argued that completed worlds tend toward destruction, eventually collapsing into the sun to create a massive conflagration that dissolves everything back into elementary particles. He introduced the concept of the phoenix of nature at the conclusion of his treatise to describe this cyclical regeneration of cosmic systems from their own ashes.

5. The Big Bang and Modern Multiverse Models

Twentieth-century astrophysics replaced a static universe with an expanding big bang, string theory landscapes, and complex inflationary multiverses.

Edwin Hubble dismantled the galactocentric view in 1924 by proving that spiral nebulae are independent galaxies. This discovery increased the size of the known universe by a factor of half a million. Woody Allen's character Alvy Singer in Annie Hall gets depressed upon realizing the universe is expanding into nothing at all.

Expansion and Inflation

Arno Penzias and Robert Wilson discovered the Cosmic Microwave Background in 1965. This thermal record established that the universe had a hot beginning in time rather than existing eternally. Robert Jastrow compared the scientific realization of the big bang's beginning to climbing a mountain only to find a band of theologians waiting there.

Alan Guth solved the fine-tuning problems of the big bang by introducing inflation. Inflation is a brief burst of exponential expansion occurring right after the big bang that flattens space, thermalizes distant regions, and generates quantum fluctuations that seed galaxies. Stephen Hawking and Leonard Mlodinow illustrate inflation by comparing it to a 1 centimeter coin instantly blowing up to ten million times the width of the Milky Way.

Max Tegmark's Level I multiverse assumes that beyond our observable Hubble volume, space and matter continue infinitely. Given an infinite amount of space and a finite number of particle configurations, all possible events and historical outcomes must recur infinitely many times. You can imagine an alternate version of yourself reading this book, checking social media, or making a different number of coffee cups.

String Theory and Cyclic Alternatives

String theory yields a vast landscape of stable vacuum states, providing a physical basis for the multiverse and resolving the cosmological constant problem. Leonard Susskind asks readers to imagine a space of 500 dimensions with a topography that includes $10^{500}$ local minima.

Paul Steinhardt and Neil Turok developed the ekpyrotic or cyclic model to suggest our three-dimensional universe is a membrane separated by a tiny gap from a hidden partner brane in a higher dimension. Steinhardt and Turok map their cyclical model mathematically onto Hindu cosmology, where one cycle corresponds to a year in the life of Brahma.

Dark energy now makes up about 73 percent of the universe, with dark matter at 23 percent and visible matter at a meager 4 percent. Contemporary models of the multiverse generally fall into four major types:

• spatial multiverses;
• temporal multiverses;
• the Many-Worlds Interpretation;
• modal or ultimate multiverses.

Physicists invoke the multiverse hypothesis as a scientific mechanism to resolve fine-tuning and eliminate the need for a benevolent creator. Lawrence Krauss compares the random generation of universe parameters to throwing zillions of darts at a dartboard until some hit the bull's-eye.

6. Ascending to the Ultimate Multiverse

Contemporary theoretical models push the multiverse to its absolute limits through quantum branching, simulated realities, and mathematical universe hypotheses.

Quantum and Connected Multiverses

Hugh Everett posited the Many-Worlds Interpretation in 1957. Bryce DeWitt publicized MWI, noting that 10^100+ slightly imperfect copies of yourself constantly split. Family Guy characters Stewie and Brian traverse alternative Quahogs.

Stephen Hawking and Thomas Hertog advance a top-down, no-boundary cosmological model. This approach traces history backward from our present universe to a quantum beginning comprising all possible histories. Michel Foucault's distinction between history and genealogy serves as an analogy for top-down versus bottom-up cosmologies.

Laura Mersini-Houghton proposes a connected multiverse where our universe originates from a primordial chaotic bath. This battle explains why our universe began with an improbable low-entropy starting point estimated by Roger Penrose as 1 in 10^[(10^123)]. The Very Large Array Telescope and 2013 Planck results confirmed a giant void predicted by Mersini-Houghton's team. In 2006, her team predicted a giant void 12 degrees in size in the sky about 8 billion light-years away, which was observed in 2007. An unusual pattern in motion named dark flow discovered in 2009 involved 800 galaxy clusters.

Lee Smolin proposes a reproductive cosmogony where new baby universes are born inside the singularities of black holes. Karl Schwarzschild calculated black holes in 1916 alongside Einstein's publication of general relativity. David Hume's Philo imagined how many worlds might have been botched and bungled. Edward Harrison suggests that advanced civilizations could manufacture new baby universes in laboratories by compressing space-time into black holes. The media storm surrounding the 2008 launch of the Large Hadron Collider in Geneva, Switzerland, involved fears of creating a planet-swallowing black hole.

Simulations and Mathematical Universes

Nick Bostrom outlines a simulation argument suggesting that if posthuman civilizations can run conscious simulations, you are almost certainly living inside a computer simulation.

Brian Greene calculates that an earth-sized computer has a performance capacity of 10^33 to 10^42 operations per second. A human brain has a capacity of 10^17 operations per second and performs 10^24 operations over a hundred-year lifetime. Total human operations since Lucy reach 10^35. Simulation games range from Sim City and Second Life to military training software and Sindome.

• Live as if you are being simulated and try to participate in pivotal events.
• Be entertaining, praiseworthy, funny, outrageous, violent, sexy, strange, pathetic, or heroic so simulators do not pull the plug.
• Keep famous people around you happy and interested in you.

Max Tegmark proposes the Ultimate Multiverse or Level IV Mathematical Universe Hypothesis. Every mathematically possible structure exists physically as a parallel universe outside space and time. A massive number like 10^500 universes is nevertheless infinitesimal compared to Level IV possibilities. Examples include an empty universe with 666 spatial dimensions or a universe governed by Newton's equations populated solely by solid billiard balls.

10 Key Ideas

1. Classical antiquity established a finite, bounded, and singular universe governed by external divine ordering and natural motion rather than internal chaos.
2. Early Atomists, Stoics, and Christian theologians fiercely debated the spatial and temporal multiplicity of worlds long before the modern scientific revolution.
3. Late medieval debates and Renaissance cosmologists shattered the Aristotelian boundaries, replacing a singular cosmos with an actual infinite universe and countless worlds.
4. Seventeenth and eighteenth-century pioneers balanced telescopic observation with physical laws, defining finite, indefinite, and cyclic cosmic systems.
5. Twentieth-century astrophysics replaced a static universe with an expanding big bang, string theory landscapes, and complex inflationary multiverses.
6. Contemporary theoretical models push the multiverse to its absolute limits through quantum branching, simulated realities, and mathematical universe hypotheses.
7. Plato's Timaeus describes the birth of the cosmos not as an internal emergence from chaos, but as an external ordering performed by a divine craftsman.
8. The Paris Condemnations of 1277 declared it heretical to claim that God cannot create multiple worlds, inadvertently opening a space for late-scholastic debate on possible worlds.
9. Immanuel Kant attempted a grand synthesis of Newtonian physics and Epicurean atomism in his 1755 Universal Natural History and Theory of the Heavens.
10. Nick Bostrom outlines a simulation argument suggesting that if posthuman civilizations can run conscious simulations, you are almost certainly living inside a computer simulation.