Threshold 1 · The Big Bang
The Beginning
The universe begins hot, dense and everywhere at once, then expands and cools until the first atoms can form.
This is the chapter with the fewest characters and the highest stakes. There are no stars yet, no planets, no chemistry beyond hydrogen and helium; there is only space, time, energy and the rules. Everything that follows in the other seven chapters is written in those rules, so it pays to learn them first.
The story runs from the earliest moment our physics can describe, a fraction of a second after whatever came first, through the first three minutes in which the lightest nuclei were forged, to the moment 380,000 years later when the universe became transparent and released the afterglow we still detect today. Along the way we take apart the most common picture of the Big Bang, the explosion in empty space, and replace it with the real one.
The chapter ends in darkness. For a hundred million years there is nothing to see, and then the first stars switch on.
Lessons
- 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.