The journey
Eight thresholds, one future, 60 lessons
Each threshold is a moment when the universe crossed into a new kind of complexity: stars, elements, planets, life, minds, farms, machines. The last chapter looks past the present. Read them in order, or jump to the one you are curious about.
Threshold 1: The Big Bang · 13.8 billion years ago · 13.8 billion years ago to the first atoms
- 1.1 Was the Big Bang an explosion?Draft
The Big Bang was not a blast at a point in empty space. It was the whole universe, everywhere at once, hot and dense and beginning to expand.
- 1.2 The first three minutesDraft
How quarks became protons and neutrons, and how the first nuclei formed before the universe was twenty minutes old.
- 1.3 Why is the night sky dark?Draft
A dark night sky is evidence that the universe has a finite age and is expanding.
- 1.4 The afterglowDraft
The cosmic microwave background, the oldest light there is, and what its faint ripples tell us.
- 1.5 How we knowDraft
The three pillars of evidence for the Big Bang, and how each one could have proved it wrong.
- 1.6 The Dark Ages and the first lightDraft
A hundred million years of darkness, and then the first stars switch on.
- 1.7 Open questionsDraft
Dark matter, dark energy and inflation: what the standard model of cosmology cannot yet explain.
Threshold 2: Stars light up · 13.6 billion years ago · About 13.6 billion years ago onward
- 2.1 Gravity versus pressureDraft
How a cloud of gas collapses, heats and ignites.
- 2.2 What a star isPlanned
Fusion in the core balanced against gravity: the equilibrium that lets a star shine for billions of years.
- 2.3 The lives of stars, sorted by massDraft
Why a star's mass decides everything: how long it lives, how it dies and what it leaves behind.
- 2.4 GalaxiesPlanned
Cities of stars, dark matter and the cosmic web.
- 2.5 Reading starlightPlanned
Spectra, distances and the cosmic distance ladder: how we measure things we can never visit.
- 2.6 The Sun, a typical starPlanned
Our own star as an ordinary star, with Aditya-L1 as India's eye on it.
- 2.7 One chart for every starPlanned
The Hertzsprung–Russell diagram, which organises every star by brightness and temperature.
Threshold 3: New chemical elements · 13.5 billion years ago · From the first supernovae onward
- 3.1 Where the elements come fromDraft
Stellar nucleosynthesis: how stars build carbon, oxygen and iron.
- 3.2 Making goldPlanned
Supernovae and neutron-star mergers, the violent events that make the heaviest elements.
- 3.3 The periodic table as a history bookPlanned
Every element has an origin story; the periodic table arranged by where each one was made.
- 3.4 Why carbon?Planned
Bonding, chains and rings: why carbon chemistry is the chemistry of complexity.
- 3.5 Molecules in spacePlanned
Dust, ice and organic molecules between the stars.
- 3.6 From quarks to the HiggsDraft
The fundamental particles and the four forces that shape matter.
- 3.7 Are you really made of stardust?Planned
The famous claim, tested element by element.
Threshold 4: Earth and the solar system · 4.57 billion years ago · 4.57 billion years ago onward
- 4.1 From nebula to planetsDraft
How the solar system assembled from a disc of gas and dust.
- 4.2 Earth's violent birthPlanned
The Moon-forming impact and the magma ocean.
- 4.3 Core, mantle, crustDraft
Differentiation: how the Earth sorted itself into layers.
- 4.4 Plate tectonics and the HimalayaPlanned
The engine of a living planet, told through the Indian plate and the rise of the Himalaya.
- 4.5 Oceans and airPlanned
Where the water and the atmosphere came from.
- 4.6 Deep timePlanned
Radiometric dating: how we know the age of a rock.
- 4.7 Earth as a systemPlanned
Rock, water, air and life as one connected machine.
Threshold 5: Life on Earth · 3.5 billion years ago · At least 3.5 billion years ago onward
- 5.1 What is life?Planned
Definitions of life, and the last universal common ancestor of everything alive today.
- 5.2 How chemistry became biologyDraft
The hypotheses and evidence for the origin of life.
- 5.3 Evolution by natural selectionPlanned
The mechanism, stated precisely, and the evidence that it works.
- 5.4 The Great Oxidation EventPlanned
How microbes remade the planet's atmosphere.
- 5.5 The complex cellPlanned
Endosymbiosis and the origin of the eukaryotic cell.
- 5.6 The Cambrian explosionPlanned
Animal body plans appear in the fossil record.
- 5.7 Mass extinctionsPlanned
Five great dyings and the age of reptiles.
- 5.8 Mammals in the shadowsDraft
How small mammals survived the dinosaurs and inherited the Earth.
Threshold 6: Collective learning · 300,000 years ago · About 7 million years ago to 12,000 years ago
- 6.1 Primates and homininsDraft
The family tree from the first primates to the hominins.
- 6.2 From habilis to sapiensDraft
Homo habilis, Homo erectus and the arrival of our species.
- 6.3 Fire, tools and cookingPlanned
Stone tools, controlled fire and the cooking hypothesis.
- 6.4 Language and symbolic thoughtPlanned
The evidence for language and the first art.
- 6.5 Collective learningPlanned
Why humans, alone among species, accumulate knowledge across generations.
- 6.6 Out of Africa, into IndiaPlanned
The peopling of the world, including the early routes into the subcontinent.
- 6.7 Foraging lifewaysPlanned
How people lived for most of human history.
Threshold 7: Agriculture · 12,000 years ago · About 12,000 years ago to 1500 CE
- 7.1 Why farm?Draft
Climate, population and the Holocene: why farming began where and when it did.
- 7.2 DomesticationPlanned
How wheat, rice, cattle and dogs were remade by people, and people by them.
- 7.3 Villages to citiesDraft
Surplus, hierarchy, writing and the first states.
- 7.4 The Indus Valley civilisationPlanned
Cities, water engineering and a script still unread.
- 7.5 The price of farmingPlanned
Disease, inequality and shorter lives: what agriculture cost.
- 7.6 Empires and exchangePlanned
Agrarian empires, the Silk Road and the Indian Ocean world.
Threshold 8: The modern revolution · 275 years ago · About 1500 CE to the present
- 8.1 The Columbian ExchangePlanned
1492 and the joining of the world's biological and human systems.
- 8.2 The Scientific RevolutionPlanned
A new way of knowing: evidence, instruments and doubt.
- 8.3 Fossil fuels and the Industrial RevolutionPlanned
Coal, steam and the release of stored sunlight.
- 8.4 The Great AccelerationPlanned
Population, energy and information since 1950.
- 8.5 The AnthropocenePlanned
Humans as a geological force.
What comes next · The present to the deep future
- 9.1 The next century: climatePlanned
What the climate models say, what is settled, what is not, and what is still up to us.
- 9.2 Energy after fossil fuelsPlanned
Sun, wind, atoms and storage: the transition that decides what the next century looks like.
- 9.3 Machines that learnPlanned
Artificial intelligence, and whether it counts as a new kind of collective learning.
- 9.4 Editing lifePlanned
Biotechnology, from vaccines to gene editing, and what it means to steer evolution on purpose.
- 9.5 Leaving EarthPlanned
Space as a place to live, and the physics that makes it hard.
- 9.6 The deep futurePlanned
From the year 3000 to the death of the Sun and the fate of the universe.