Introduction to Cosmology

The universe as a physical system with a history

About this course

Modern cosmology: the expanding universe and its dynamics, the thermal history and the microwave background, dark matter and dark energy.

What you will be able to do

  • Describe the observational evidence for an expanding universe
  • Use the FRW metric and the Friedmann equations to relate content to expansion
  • Recount the thermal history from the hot Big Bang to recombination
  • Explain what the CMB and its anisotropies measure
  • Summarise the evidence for dark matter and dark energy, and what inflation solves

What this course covers

  • The Scale Factor and Uniform Expansion
  • Comoving Coordinates and Proper Distance
  • Cosmological Redshift vs. Doppler Motion
  • The FRW Metric
  • Redshift as a Direct Read of the Scale Factor
  • Kinematics vs. Dynamics — Preview of Friedmann Equations
  • Scale and structure of the universe
  • The cosmological principle
  • Olbers' paradox
  • The observable universe and resolution of Olbers' paradox
  • Estimating the number of stars in the observable universe
  • The spine of cosmology: clause one
  • Galaxy rotation curves and dark halos
  • Galaxy cluster velocities and missing mass
  • Gravitational lensing as a mass map
  • The Bullet Cluster: mass separated from gas
  • Why dark matter cannot be ordinary dim matter
  • Nature and identity of dark matter: the open frontier
  • Why the early universe was opaque
  • Recombination and the surface of last scattering
  • Redshifting the CMB to 2.7 degrees — the central result
  • The CMB fills the whole sky and is smooth to 1 part in 100,000
  • Discovery history of the CMB
  • Clause nine and the CMB as proof of the hot Big Bang
  • Temperature scales as one over the scale factor
  • The cooling curve of the universe
  • Why compression heats the universe (Jessica's question)
  • The thermal timeline of cosmic epochs
  • The Big Bang as expansion of space, not explosion in space
  • The two fossils: light elements and the CMB
  • Worked example: temperature at recombination
  • Kinematics to Dynamics: Course Framing
  • First Friedmann Equation: Newtonian Derivation
  • Critical Density and Density Parameter Ω
  • Fluid (Continuity) Equation and Density Scaling
  • Three Fates of the Universe
  • Acceleration Equation and Impossibility of a Static Universe
  • Critical Density Numerical Calculation
  • The flat-sky problem and distance ladder strategy
  • Standard candles and the inverse-square law
  • Parallax and the parsec
  • Why parallax cannot reach galaxies
  • Cepheid variables and the period-luminosity law
  • Type Ia supernovae as cosmological standard candles
  • Course spine clause three and lecture synthesis
  • Neutron freeze-out and the 1:7 ratio
  • Free neutron decay and the nucleosynthesis race
  • Quarter-helium mass fraction from counting
  • The deuterium bottleneck
  • Predicted light-element abundances and observational confirmation
  • Deuterium as a baryometer and the dark-matter implication
  • CMB Temperature Anisotropies
  • Frozen Sound: Photon-Baryon Oscillations
  • The Power Spectrum and Acoustic Peaks
  • Reading the Peaks: Geometry and Cosmic Composition
  • Ripple Depth: The 10⁻⁵ Figure
  • Clause Ten and the Cosmic Spine
  • Gravitational instability: the runaway amplifier
  • Growth of structure in an expanding universe
  • Dark matter's head start
  • Hierarchical (bottom-up) assembly and the cosmic web
  • From dark scaffold to luminous galaxies
  • Quantifying amplification and Clause 11 of the course spine
  • Why a matter-filled universe must decelerate
  • The 1998 supernova discovery of accelerating expansion
  • Negative pressure as the driver of accelerated expansion
  • Einstein's cosmological constant as the simplest dark energy candidate
  • The cosmological constant problem
  • The cosmic energy budget and the coincidence of dark energy dominance
  • Critical Density and Omega Parameters
  • The Cosmic Budget Equation
  • The Cosmic Inventory
  • Dilution Laws for Each Ingredient
  • The Eras of the Universe
  • Clause Six: The Filled-In Cosmological Recipe
  • Redshift as a measure of recession
  • Hubble's Law: V = H₀D
  • Expanding space and the absence of a center
  • Cosmological redshift as stretching of space
  • Hubble time and the age of the universe
  • Course spine clause two and lecture synthesis
  • The Horizon Problem
  • The Flatness Problem
  • Inflation: The Core Idea and Its Engine
  • Inflation: Scale, Duration, and the Two-Problem Fix
  • Quantum Fluctuations as Seeds of Structure
  • Inflation's Predictions, Confirmation, and Open Questions
  • The Planck Wall and Quantum Gravity Frontier
  • Matter–Antimatter Asymmetry and Baryogenesis
  • The Five Great Open Questions of Cosmology
  • The Fate of the Universe: Eternal Accelerating Expansion
  • The Complete Cosmological History as a Single Arc
  • Cosmological Scale of Time in Powers of Ten

Syllabus

  1. Observing the Universe

    1. L1 · The Universe at Large
    2. L2 · Measuring the Cosmos
    3. L3 · The Expanding Universe

  2. The Dynamics of Expansion

    1. L4 · The Scale Factor and the FRW Universe
    2. L5 · The Friedmann Equations
    3. L6 · What the Universe Is Made Of

  3. Thermal History

    1. L7 · Cosmic History - The Hot Big Bang
    2. L8 · The First Three Minutes

  4. The Microwave Background

    1. L9 · The Cosmic Microwave Background
    2. L10 · Ripples in the CMB

  5. Structure, Darkness and Origins

    1. L11 · Dark Matter
    2. L12 · Building Galaxies
    3. L13 · Dark Energy and the Accelerating Universe
    4. L14 · Inflation
    5. L15 · First Instants and the Fate of the Universe