Physics · Cosmology
Cosmos: Big Bang to Now
Zoom from your bedroom to the edge of the observable universe, stretch space until galaxies fly apart, and weigh the dark matter that holds them together.
The course
7 worlds · 29 lessons
World 1 · Your Cosmic Address
FREEFrom your room to the edge of what we can see- 01Zooming out: powers of tenTwenty-seven steps from your room to the universe · 11 min
- 02Light-years and look-back time: seeing the pastWhy far away means long ago · 12 min
- 03Neighbours: from the Milky Way to the cosmic webWhere Earth sits in the structure of the universe · 12 min
- 04The observable universe: how far can we see?Why the edge of sight is 46 billion light-years away · 13 min
World 2 · The Expanding Universe
PROA ruler that stretches- 01No centre, no edge: the raisin-bread universeExpansion is the stretching of space itself · 11 minPRO
- 02The scale factor: a ruler that stretchesHow to write expansion in one number · 12 minPRO
- 03The age of the universe: running the film backwardsWhat the expansion rate tells us about time · 12 minPRO
- 04Accelerating: dark energyThe surprise of 1998 · 12 minPRO
World 3 · Redshift and Hubble's Law
PROHow light shows that the universe expands- 01Stretched light: Doppler vs cosmological redshiftTwo ways for a wavelength to grow · 12 minPRO
- 02Reading redshift in a spectrumFrom a shifted line to a redshift, a speed and a distance · 12 minPRO
- 03The Hubble-Lemaître law: v = H₀ dThe straight line that shows the universe expands · 13 minPRO
- 04The distance ladder: how do we know how far?Each rung checks the next one · 14 minPRO
- 05The Hubble tension: two numbers that disagreeAn open question, told honestly · 13 minPRO
World 4 · The First Light
PROThe afterglow of the early universe- 01A hot, glowing young universe: recombinationThe moment light became free · 11 minPRO
- 02Penzias, Wilson and the hum in the antennaA discovery that began as a nuisance · 11 minPRO
- 03Ripples: tiny differences that became galaxiesWhy the sky's oldest light is not quite smooth · 12 minPRO
- 04Reading the cosmic recipe: 5%, 27%, 68%What the microwave map says about the contents of the universe · 13 minPRO
World 5 · The Missing Mass: Dark Matter
PROGravity from something we cannot see- 01Orbits in a galaxy: how Kepler predicts the speedsThe speed of an orbit tells you the mass inside it · 12 minPRO
- 02Rubin's flat curvesThe observation that did not fit · 12 minPRO
- 03More evidence: clusters, lensing and the BulletIndependent clues that point the same way · 13 minPRO
- 04What could it be? And what we don't knowThe evidence is strong, the identity is open · 13 minPRO
World 6 · When Galaxies Collide
PROGravity at work on the largest bound systems- 01Galaxies are not alone: groups and clustersMost galaxies live in company · 11 minPRO
- 02Tidal tails and mergersWhat happens when galaxies meet · 12 minPRO
- 03Milkomeda: the Milky Way meets AndromedaA forecast, and how uncertain it is · 12 minPRO
- 04Simulating the unthinkable: how N-body worksWhat a simulation can and cannot tell you · 13 minPRO
