• Introduction
• Temperature Maps
  • Earth
  • Monopole
  • Dipole
  • COBE
  • Power
  • Precision
  • Features
• Thermal History
  • Expansion
  • Plasma
  • Glue
  • Pressure
  • Thermal
• Acoustic Oscillations
  • Gravity
  • Plane Waves
  • Harmonics
  • Extrema
• Angular Peaks
  • Spatial/Angular
  • Oscillation
  • Freeze Frame
  • Streaming
  • Soundscape
• First Peak
  • Data
  • Curvature
  • Flatness
  • Dark Energy
  • Summary
• Second Peak
  • Data
  • Inertia
  • Baryonmeter
  • Power
  • Dark Baryons
  • Summary
• Higher Peaks
  • Driving Force
  • Power
  • Summary
• Damping Tail
  • Diffusion
  • Ruler
  • Consistency
  • Summary
• Parameter Estimation
  • Parameters
  • Degeneracy
• Polarization
  • What and Why
  • Scattering
  • Projection
  • Power
  • Quadrupoles
  • B-modes
  • Gravity Waves
• Summary

Brief Thermal History

Key Concepts

• Ionization/Recombination
• Tightly-coupled photon-baryon fluid
• Compression results in acoustic oscillations or sound waves

Let's review the basic elements of the thermal history of the CMB.

Ionization/Recombination: Going backwards in time, the CMB photons get hotter and hotter until they can ionize hydrogen.

Photon-Baryon Fluid: Thomson scattering and electromagnetic interactions glue the photons to the baryons.

Sound Waves: Radiation pressure resists any attempt to compress the fluid setting up acoustic oscillations.

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