Step by Step
1
The Planck epoch and inflation
Before 10⁻⁴³ seconds (the Planck epoch), our understanding of quantum gravity breaks down entirely — this period remains unknown. At around 10⁻³⁶ seconds, cosmic inflation begins.
2
Particle formation
At about 10⁻¹² seconds, the electroweak phase transition occurs. By about 10⁻⁶ seconds, quarks combine to form protons and neutrons.
3
Neutrino decoupling and nucleosynthesis
At about 1 second, neutrinos decouple from other matter, and nearly all antimatter is annihilated, leaving behind a slight excess of matter (which is why the universe today is made of matter rather than antimatter). By about 3 minutes, Big Bang nucleosynthesis produces roughly 75% hydrogen and 25% helium-4, with trace amounts of deuterium, helium-3, and lithium.
4
Recombination and first stars
At about 380,000 years, recombination occurs and the CMB is released. Roughly 200 million years later, the very first stars — Population III stars — ignite, ending the cosmic "Dark Ages" that followed recombination.
Applied Walkthrough
1
In the universe's first fraction of a second — before 10⁻⁴³ seconds — physics as currently understood simply breaks down, an era called the Planck epoch that remains genuinely unknown.
2
By around 10⁻³⁶ seconds, cosmic inflation begins its brief but dramatic exponential expansion, and by 10⁻⁶ seconds, quarks have combined to form the first protons and neutrons.
3
At about 1 second, neutrinos decouple and nearly all antimatter is annihilated against matter, leaving behind the small excess of matter that makes up everything we see today; by about 3 minutes, Big Bang nucleosynthesis has locked in the universe's initial composition — roughly 75% hydrogen, 25% helium.
4
Hundreds of thousands of years later, at about 380,000 years, recombination finally releases the CMB, and after a further roughly 200 million years of cosmic darkness, the very first stars ignite — Population III stars, ending the cosmic Dark Ages and bringing light back to the universe for the first time.
Exam Application
Exams test whether you can correctly sequence the major events of the early universe's timeline (Planck epoch → inflation → particle formation → nucleosynthesis → recombination → first stars), and whether you know the approximate timing of each stage.
⚠ Common Trap
The most common trap is confusing the timing of nucleosynthesis (about 3 minutes) with recombination (about 380,000 years) — these are two entirely different events separated by an enormous gap in time, with nucleosynthesis setting the initial elemental composition and recombination later releasing the CMB.
✓ Quick Self-Check
1. What is the Planck epoch, and why is it significant?
The period before 10⁻⁴³ seconds after the Big Bang, where current physics (quantum gravity) breaks down and remains unknown.
Tap to reveal / hide
2. When did Big Bang nucleosynthesis occur, and what did it produce?
About 3 minutes after the Big Bang; produced roughly 75% hydrogen and 25% helium-4, with trace deuterium, helium-3, and lithium.
Tap to reveal / hide
3. When did recombination occur, and what did it release?
About 380,000 years after the Big Bang; released the CMB.
Tap to reveal / hide
4. What happened to antimatter in the early universe?
It was nearly all annihilated against matter at around 1 second, leaving a slight matter excess.
Tap to reveal / hide
5. When did the first stars form, and what era did they end?
About 200 million years after recombination; they ended the cosmic "Dark Ages."
Tap to reveal / hide