Cosmology
From the Big Bang to Galaxies
One box of the universe, followed from a split second after the Big Bang to today. Drag through 54 orders of magnitude in time and watch quarks become protons, protons and neutrons become helium, the glowing fog clear into the light we still see, and the seeds left by inflation grow into the cosmic web.
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Box
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Numbers
Time since the start—
Temperature—
Typical particle energy—
Size compared with today—
Redshift z—
Density—
This box, then—
By mass: H / He—
Deuterium per H—
Free electrons per H—
Light travels between hits—
Data and models
- Expansion: Planck 2018 densities, with the number of particle species g*(T) of the Standard Model in the radiation era.
- Inflation is drawn as 60 e-folds ending at 10⁻³² s; when it really happened, and how, is still open.
- Nuclei: neutrons freeze out at 0.79 MeV and decay until deuterium survives at 0.07 MeV; the curves are tuned to standard nucleosynthesis codes (helium 24.7% by mass, D/H = 2.5×10⁻⁵).
- Recombination: a fit to RECFAST. Reionization: Planck’s tanh model centred on z = 7.7.
- Structure: a Gaussian field with the Planck power spectrum (σ8 = 0.81) in a box 150 Mpc across, 262,144 particles moved by the Zel’dovich approximation. Stars light up in the densest places first.
What to observe
- There is no centre and no edge: the box is a piece of a universe that is the same everywhere. The Big Bang happened everywhere at once. In 10⁻³² s inflation stretches this piece by 10²⁶, and quantum ripples become the faint blue and red seeds.
- Above 2 trillion degrees, quarks cannot stay inside protons. At about 10 microseconds the soup cools enough for them to lock into protons and neutrons, three at a time.
- After three minutes, every surviving neutron is swept into helium. When the dust settles the universe isa quarter helium by mass, which is just what old stars and gas clouds show today.
- For 380,000 years light cannot get anywhere: it keeps bouncing off free electrons. Then the gas cools to 3,000 K, electrons settle into atoms, and the fog clears. That light, stretched 1,100 times, is the microwave background.
- The seeds were only one part in 100,000. Gravity grows them through the dark ages, and the first starslight up in the densest knots after about 100 million years, then ionize the gas around them.
- Today the same seeds have become filaments of galaxies around empty voids: the cosmic web, grown in place from the pattern inflation left.
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