Cosmology

Sarvarthapedia (Core Areas)

Sarvarthapedia (Articles)

Cosmology, from ancient origin myths up to 2026

Volume 1: History of Cosmological Thought

1. Ancient & Mythological Cosmologies (Before 600 BCE)

Egyptian cosmology – Nu (primordial waters), Ra (sun god), Geb (earth) & Nut (sky)
Mesopotamian cosmology – Enuma Elish, flat earth with solid dome (firmament)
Vedic cosmology (India) – Cyclic universe (yugas), infinite time scales, Mount Meru as cosmic axis
Chinese cosmology – Celestial spheres, Yin‑Yang, five elements, cosmic order (Tian)
Pre‑Socratic Greek – Thales (water as arche), Anaximander (apeiron, first map of cosmos), Anaximenes (air), Pythagoreans (harmony of spheres)

2. Classical Greek & Hellenistic Cosmology (600 BCE – 200 CE)

Pythagorean model – Central fire (not Sun), Earth as one of many spheres
Plato – Timaeus: demiurge creates ordered cosmos, spherical Earth at center
Aristotle – Geocentric model, concentric crystalline spheres (Moon, Sun, planets, fixed stars), prime mover, sublunary realm (change) vs. celestial realm (eternal, perfect circles)
Aristarchus of Samos – First known heliocentric model (c. 270 BCE), not accepted
Eratosthenes – Calculated Earth’s circumference (within 10% error)
Hipparchus – Star catalog, precession of equinoxes, epicycles (to explain retrograde motion)
Ptolemy – Almagest (c. 150 CE): geocentric model with epicycles, deferents, equants, predicted planetary positions for 1,500 years

3. Medieval & Islamic Cosmology (500 – 1500 CE)

Islamic astronomers – Al‑Battani (improved Ptolemy), Al‑Biruni (Earth’s rotation debated), Al‑Tusi (Tusi‑couple), Ibn al‑Haytham (Alhazen, optics, celestial physics)
Maragha Revolution (13th century) – Nasir al‑Din al‑Tusi, Ibn al‑Shatir: non‑Ptolemaic models without equants
European Scholasticism – Thomas Aquinas (Aristotle + theology), Dante’s Divine Comedy (geocentric cosmos as moral order)
Nicolaus Copernicus (1473–1543) – De revolutionibus orbium coelestium (heliocentric model, circular orbits still, published on deathbed)

4. The Copernican Revolution (1500 – 1700)

Tycho Brahe – Precise naked‑eye observations (supernova 1572, comet 1577), Tychonic system (geo‑heliocentric hybrid)
Johannes Kepler – Elliptical orbits (first law), equal areas in equal times (second law), harmonic law (third law, P² ∝ a³); Rudolphine Tables
Galileo Galilei – Telescope observations (1610): moons of Jupiter, phases of Venus (support heliocentrism), sunspots, lunar mountains; conflict with Church
Giordano Bruno – Infinite universe, multiple worlds, burned at stake (1600)
René Descartes – Vortex theory (mechanical universe), plenum, no vacuum

5. Newtonian Cosmology (1687 – 1900)

Isaac Newton – Principia Mathematica (1687): universal gravitation, laws of motion, inertial frames; infinite static universe (but gravitational instability problem – Olbers’ paradox)
Olbers’ paradox – Why is night sky dark if infinite static universe? (Heinrich Olbers, 1823). Resolution: finite age or expansion
Immanuel Kant – Nebular hypothesis (origin of solar system), “island universes” (external galaxies)
William Herschel – Star gauging (mapping Milky Way), discovery of Uranus (1781), infrared radiation
John Herschel – Southern sky survey, coined “photography”
Augustin Cauchy & Poisson – Gravitational physics of infinite universe (paradoxes)
Ernst Mach – Mach’s principle (inertia from distant matter)

6. The Birth of Modern Cosmology (1900 – 1930)

Henrietta Swan Leavitt (1912) – Period‑luminosity relation for Cepheid variables (standard candles)
Harlow Shapley – Measured Milky Way size (1918), Sun not center, “great debate” with Curtis (1920)
Heber Curtis – Observed Andromeda (M31) spiral nebulae as external “island universes”
Vesto Slipher – Spectra of spiral nebulae showed redshifts (most moving away), first hint of expansion (1912–1925)
Albert Einstein – General Relativity (1915): gravity as spacetime curvature; field equations (G_μν = 8πG T_μν)
Einstein’s cosmological constant (Λ, 1917) – Added to allow static universe (later called his “greatest blunder”)
Willem de Sitter – De Sitter universe (empty, expanding) solution
Alexander Friedmann (1922–1924) – Friedmann equations (homogeneous, isotropic expanding/contracting universes), no cosmological constant needed
Georges Lemaître (1927) – “Primeval atom” hypothesis (Big Bang), derived Hubble law, proposed expanding universe from initial singularity
Edwin Hubble (1929) – Hubble’s law (v = H₀ × d), observational proof of expansion using Cepheids & redshifts
Howard Robertson & Arthur Walker – FLRW metric (1935), formalization of expanding spacetime

Volume 2: The Hot Big Bang Model (1940 – 1980)

7. Theoretical Foundations

Big Bang singularities – Friedmann models with initial singularity (t=0), infinite density/temperature
Gamow, Alpher, Herman – Prediction of Cosmic Microwave Background (CMB) as relic radiation from hot dense early phase (1948)
Alpher‑Bethe‑Gamow paper (αβγ, 1948) – Primordial nucleosynthesis (H, He, Li abundances)
Fred Hoyle, Hermann Bondi, Thomas Gold – Steady State model (1948) – continuous creation of matter, perfect cosmological principle (no beginning, no end)
Hoyle’s mockery – Coined “Big Bang” (on BBC radio, 1949), intended as derision
Hoyle‑Narlikar theory – Modified steady state (1960s)
Robert Dicke, Jim Peebles – Predicted CMB temperature ~10 K (1960s, independently of Gamow)

8. Observational Triumphs

Arno Penzias & Robert Wilson (1965) – Accidentally discovered CMB (2.725 K, isotropic microwave noise), Nobel Prize 1978
Dicke, Peebles, Roll, Wilkinson – Interpreted CMB as relic of hot Big Bang
Sunyaev‑Zel’dovich effect (1969) – CMB distortion by hot galaxy cluster gas
Primordial element abundances – Observed ⁴He (~24%), D, ³He, ⁷Li matched Big Bang nucleosynthesis (BBN), steady state failed
Quasars (discovered 1960s) – Distant, high‑redshift objects, inconsistent with steady state
Radio source counts – Distant galaxies more numerous (evolution), favored Big Bang
Decline of Steady State (1970s) – CMB + nucleosynthesis + quasar counts decisive

9. The First Three Minutes (Nucleosynthesis Era)

Temperature timeline – t=1 sec (T ~10¹⁰ K, neutrinos decouple), t=3 min (T ~10⁹ K, neutrons + protons → ⁴He), t=20 min (nucleosynthesis ends)
Baryon‑to‑photon ratio (η) – ~6 × 10⁻¹⁰ (CMB measurement)
Recombination (t~380,000 years, T~3000 K) – Electrons + protons → neutral hydrogen, universe becomes transparent to photons (CMB last scattering)
Decoupling – Photons free‑stream, create CMB
Dark Ages (380,000 years to ~150 million years) – No stars, neutral hydrogen (21 cm line potential probe, not yet detected as of 2026)

10. The CMB as a Precision Tool

Blackbody spectrum – FIRAS on COBE (1990) – perfect blackbody, temperature 2.725 K
COBE satellite (1989–1993) – Discovery of CMB anisotropies (tens of µK), John Mather & George Smoot (Nobel 2006)
WMAP (Wilkinson Microwave Anisotropy Probe, 2001–2010) – High‑resolution map, determined age (13.77 Gyr), baryon density (Ωb), dark matter (Ω_cdm), dark energy (ΩΛ), curvature (Ω_k≈0)
Planck satellite (2009–2013, data to 2018) – Most precise CMB temperature/polarization maps, refined cosmological parameters, tension in H₀ (Hubble constant) emerges (Planck ~67.4 vs. local ~73 km/s/Mpc)
CMB polarization – E‑modes (from density fluctuations), B‑modes (primordial gravitational waves – BICEP/Keck, not yet detected as of 2026; upper limits constrain inflation energy scale)
Sunyaev‑Zel’dovich clusters – Planck catalog of galaxy clusters

Volume 3: Components of the Universe

11. Ordinary Matter (Baryonic)

Protons, neutrons, electrons – ~4.9% of total energy density (Planck 2018)
Primordial nucleosynthesis – Predicted & observed light element abundances (H, D, ³He, ⁴He, ⁷Li)
Intergalactic medium (IGM) – Lyman‑α forest (absorption lines from neutral hydrogen clouds)
Missing baryons problem (solved ~2018) – Found in warm‑hot intergalactic medium (WHIM) via X‑ray/UV absorption

12. Dark Matter (Non‑baryonic)

Evidence (1930s–1970s)
Zwicky (1933) – Coma cluster: virial theorem, missing mass (“dunkle Materie”)
Rubin & Ford (1970s) – Flat rotation curves of spiral galaxies (velocity constant at large radii)
Gravitational lensing – Strong (Einstein rings, arcs), weak (shear), pixelated lensing (clusters)
Bullet Cluster (2006) – Separation of dark matter (lensing) from hot gas (X‑ray), strongest direct evidence
What dark matter is not – MACHOs (microlensing excluded), neutrinos (hot dark matter – too fast, suppresses structure)
Cold Dark Matter (CDM) – Slow, collisionless (except gravity)
WIMPs (Weakly Interacting Massive Particles) – Most searched, no detection (LZ, XENONnT, PandaX as of 2026)
Axions – QCD axion, light (μeV), searches (ADMX, CAST, IAXO, haloscopes)
Sterile neutrinos (keV scale) – Possible warm DM candidate, X‑ray line searches (no clear signal)
Self‑interacting dark matter (SIDM) – Proposed to solve small‑scale problems (cusp‑core, missing satellites)
Primordial black holes (PBHs) – Black holes formed before stars; LIGO/Virgo/KAGRA constraints rule out most mass ranges
Status as of 2026 – Dark matter ~26.8% of universe, particle identity unknown

13. Dark Energy

Discovery (1998) – Two teams (Perlmutter, Riess, Schmidt) using Type Ia supernovae (dimmer than expected at high z → accelerated expansion)
Evidence
Supernovae (SNe Ia) – Standardizable candles (Phillips relation)
CMB – Flat universe (Ω_total ≈ 1) but matter only ~0.31, missing ~0.69 → dark energy
Baryon Acoustic Oscillations (BAO) – Sound horizon scale imprinted in galaxy clustering (SDSS, DESI)
Weak lensing (Dark Energy Survey – DES, Euclid, Roman)
Simplest model – Cosmological constant (Λ, Einstein’s “blunder”), ΛCDM model (Standard Model of Cosmology)
Equation of state – w = p/ρ (for Λ, w = –1 exactly)
Current constraints (2026) – w = –1.00 ± 0.04 (Planck + DESI + SNe), consistent with Λ
Alternatives – Quintessence (dynamic scalar field, w > –1), phantom (w < –1), modified gravity (f(R), DGP)
Hubble tension – H₀ from early universe (CMB, BAO) ~67.4 vs. late universe (Cepheids + SNe Ia) ~73 km/s/Mpc; significance ~5σ; possible new physics (early dark energy, modified gravity)
S8 tension – Clustering amplitude (σ₈) from CMB vs. weak lensing (~2‑3σ)

14. Neutrinos & Relics

Cosmic neutrino background (CνB) – Predicted, not yet directly detected (temperature ~1.95 K)
Neutrino mass – Non‑zero (oscillations), sum of masses <0.12 eV (Planck + DESI), affects structure formation
Relic gravitons – Primordial gravitational waves from inflation (not yet detected)
Light relics – Extra relativistic species (ΔN_eff) – CMB bounds N_eff = 3.0 ± 0.2, consistent with 3.046

Volume 4: Structure Formation & Large‑Scale Universe

15. Inflationary Cosmology

Problems of Big Bang (without inflation)
Horizon problem – CMB uniform across causally disconnected regions
Flatness problem – Ω ~ 1 today requires extreme fine‑tuning at t=1 sec
Monopole problem – No magnetic monopoles observed
Alan Guth (1981) – Inflation (exponential expansion 10⁻³⁶ to 10⁻³² sec, scale factor increase >10²⁵)
Andrei Linde (eternal inflation), Paul Steinhardt (new inflation)
Predictions (confirmed)
Flat universe (Ω_k ≈ 0)
Nearly scale‑invariant, adiabatic, Gaussian primordial fluctuations (n_s ≈ 0.96, Planck)
Small tensor‑to‑scalar ratio (r < 0.036, Planck+BICEP/Keck 2022)
Slow‑roll inflation – Inflaton field potential (V(φ))
Multiverse – Eternal inflation produces many bubble universes (speculative)
Alternatives – Bouncing cosmologies (ekpyrotic, cyclic), string gas cosmology

16. Growth of Structure

Primordial fluctuations – Quantum fluctuations during inflation (Gaussian random field)
Matter power spectrum P(k) – Characterized by primordial tilt (n_s) + transfer function (Silk damping, free streaming)
Linear perturbation theory – Jeans instability, growth factor D(z)
Hierarchical clustering – Small structures collapse first, merge into larger (CDM prediction)
Non‑linear structure – N‑body simulations (Millennium, Illustris, Eagle, TNG, FLAMINGO 2024)
Cosmic web – Voids, filaments, nodes (galaxy clusters), walls
Baryon Acoustic Oscillations (BAO) – Sound waves in photon‑baryon plasma before recombination; imprinted at recombination scale (~150 Mpc); used as standard ruler

17. Galaxies, Clusters & Voids

First stars (Population III) – Metal‑free, very massive (100‑1,000 M_sun), short lived, reionization sources
Reionization – Epoch ~150 million to 1 billion years; neutral hydrogen → ionized; probes: Lyman‑α forest, 21 cm (future)
Galaxy formation – Cooling, star formation, feedback (supernovae, AGN), quenching
Morphologies – Spiral (Milky Way, Andromeda), elliptical, irregular, dwarf
Active Galactic Nuclei (AGN) – Quasars, blazars, radio galaxies; central supermassive black holes (SMBH)
Galaxy clusters – Coma, Virgo; intracluster medium (ICM, X‑ray); SZ effect; gravitational lensing
Voids – Underdense regions (~10‑100 Mpc), cosmic voids (e.g., Boötes void)

18. Large‑Scale Structure Surveys

2dF Galaxy Redshift Survey (1997–2002) – 250k galaxies
Sloan Digital Sky Survey (SDSS) (2000–2026) – Millions of galaxies, spectra, BAO, APOGEE, eBOSS, DESI
Dark Energy Survey (DES) (2013–2019) – Weak lensing, clusters, SNe
Dark Energy Spectroscopic Instrument (DESI) (2021–2026) – 40M galaxies, most precise BAO
Euclid (ESA, launched 2023) – Weak lensing + BAO, dark energy
Nancy Grace Roman Space Telescope (NASA, planned 2027) – Wide‑field infrared
Rubin Observatory (LSST) (2025–2035) – Deep wide‑field imaging, time domain

Volume 5: Cosmic Timeline & Epochs

19. The Standard Cosmological Timeline (in seconds, years)

Time	Event	Redshift	Temperature
10⁻⁴³ s	Planck epoch (quantum gravity regime)	–	10³² K
10⁻³⁶ s	Inflation begins	–	10²⁸ K
10⁻³² s	Inflation ends, reheating	–	10²⁷ K
10⁻¹² s	Electroweak epoch (symmetry breaking)	–	10¹⁵ K
10⁻⁶ s	Quark‑gluon plasma → hadrons	–	10¹³ K
1 s	Neutrinos decouple, BBN starts	~10¹⁰	10¹⁰ K
3 min	Primordial nucleosynthesis (H, He, Li)	~10⁹	10⁹ K
50,000 yrs	Matter‑radiation equality	~3400	~10⁴ K
380,000 yrs	Recombination, CMB last scattering	~1100	~3000 K
150 million yrs	First stars (Pop III), reionization begins	~20	~60 K
1 billion yrs	First galaxies, quasars	~6	~20 K
9.2 billion yrs	Solar system forms	~0.5	2.73 K
13.8 billion yrs	Present day	0	2.725 K

20. The Future of the Universe (ΛCDM prediction)

Accelerated expansion continues – Dark energy dominates
Local group merger – Milky Way + Andromeda (Milkomeda, ~4.5 Gyr)
End of star formation – ~10¹² years (all gas exhausted)
Degenerate era – White dwarfs, neutron stars, black holes (10¹⁴ – 10⁴⁰ yrs)
Black hole evaporation – Hawking radiation (10⁶⁷ – 10¹⁰⁰ yrs)
Heat death (Big Freeze) – Maximum entropy, no free energy (eternal expansion)
Alternate fates – Big Crunch (if Ω_Λ negative, not our universe), Big Rip (if w < –1, phantom energy, ruled out by data), Vacuum decay (false vacuum collapse)

Volume 6: Observational Cosmology (Techniques & Instruments)

21. Distance Ladder & Standard Candles

Parallax – Gaia satellite (billion stars, microarcsecond precision)
Cepheid variables – Leavitt’s law, Hubble Space Telescope (HST), JWST
Type Ia supernovae – Chandrasekhar mass explosion, Phillips relation, calibrators
Tully‑Fisher relation – Spiral galaxy rotation velocity vs. luminosity
Fundamental plane – Elliptical galaxies (size, velocity dispersion, surface brightness)
Surface brightness fluctuations
Gravitational waves – Standard sirens (GW170817 + optical counterpart), independent H₀ measurement

22. Redshift & Spectroscopy

Cosmological redshift – Due to expansion (z = Δλ/λ = a₀/a_emit – 1)
Hubble flow – Recessional velocity v ≈ cz (for small z)
Lyman‑α forest – Intervening neutral hydrogen clouds (absorption lines)
21 cm line – Neutral hydrogen (potential for Dark Ages mapping, SKA)
Spectrographs – DESI, VLT/MUSE, JWST/NIRSpec

23. Gravitational Lensing

Strong lensing – Einstein rings, arcs, multiple images (time delays → H₀)
Weak lensing – Coherent shape distortion of background galaxies (shear), maps dark matter distribution
Microlensing – Dark compact objects (MACHOs), exoplanets
Galaxy‑galaxy lensing – Average halo mass
Cluster lensing – Dark matter mapping (Bullet Cluster)

24. Major Observatories (Ground & Space)

Optical/IR – HST (1990), JWST (2021), Rubin (2025), Roman (2027), Keck, VLT, Subaru
CMB – COBE, WMAP, Planck, ACT, SPT, BICEP/Keck, Simons Observatory, CMB‑S4 (planned)
Radio – VLA, ALMA, GMRT, MeerKAT, SKA (Phase 1 2020s)
X‑ray – Chandra, XMM‑Newton, eROSITA, XRISM, Athena (planned)
Gamma‑ray – Fermi, HESS, MAGIC, CTA (planned)
Neutrino – IceCube, ANTARES, KM3NeT
Gravitational wave – LIGO, Virgo, KAGRA, LISA (planned 2030s)

Volume 7: Relativistic Cosmology & Mathematical Framework

25. General Relativity Essentials

Einstein field equations – G_μν + Λ g_μν = (8πG/c⁴) T_μν
Schwarzschild solution – Non‑rotating black hole
Kerr solution – Rotating black hole
FLRW metric – ds² = –dt² + a(t)² [dr²/(1–kr²) + r²(dθ²+sin²θ dφ²)] (k = +1 closed, 0 flat, –1 open)
Friedmann equations – H² = (8πG/3)ρ – k/a² + Λ/3; and acceleration equation
Critical density – ρ_crit = 3H²/(8πG)
Density parameters – Ωm = ρ_m/ρ_crit, ΩΛ = Λ/(3H²), Ωk = –k/(a²H²), Ω_total = Ω_m+ΩΛ+Ω_k = 1

26. Distances in Cosmology

Comoving distance – χ = ∫₀ᶻ dz/H(z)
Angular diameter distance – D_A = χ/(1+z)
Luminosity distance – D_L = (1+z) χ
Distance modulus – μ = 5 log₁₀(D_L/10 pc)

27. Thermal History & Recombination

Saha equation – Ionization fraction as function of T
Peebles’ recombination history – 2s→1s (two‑photon decay)
Thomson scattering – Photon‑electron coupling
Visibility function – Probability last scattering at redshift z

Volume 8: Alternative & Frontier Cosmologies (up to 2026)

28. Modified Gravity Theories

f(R) gravity – Replace Ricci scalar R with f(R)
DGP model – Brane world (Dvali‑Gabadadze‑Porrati), self‑accelerating
MOND (Modified Newtonian Dynamics) – Explains galaxy rotation curves without dark matter, fails at cluster scales and CMB
TeVeS (Tensor‑Vector‑Scalar) – Relativistic MOND, challenged by gravitational waves (GW170817)
Emergent gravity – Verlinde’s entropic gravity, not widely accepted

29. Quantum Cosmology & Early Universe

Planck scale – l_P ~ 1.6×10⁻³⁵ m, t_P ~ 5.4×10⁻⁴⁴ s
String cosmology – Brane inflation, ekpyrotic universe (colliding branes)
Loop Quantum Cosmology (LQC) – Big Bounce instead of singularity (no initial singularity)
Hartle‑Hawking no‑boundary proposal – Universe without beginning (imaginary time)
Causal dynamical triangulation (CDT) – Emergent spacetime
Multiverse – Types: Level I (infinite space), Level II (bubble universes from eternal inflation), Level III (quantum many‑worlds), Level IV (mathematical)

30. Tensions & Anomalies (2026 Status)

Hubble tension (5σ) – Early vs. late H₀; possible solutions: early dark energy, modified gravity, CMB lensing anomalies, local supervoid
S8 tension (2‑3σ) – Clustering amplitude; possible solutions: neutrino mass, modified gravity, systematic errors
CMB anomalies – Cold spot (possible supervoid), hemispherical asymmetry, alignment of quadrupole/octupole
Lithium problem – Observed ⁷Li ~ factor 3 lower than BBN prediction (unresolved)
ELT, JWST, Roman – May resolve or deepen tensions

Volume 9: People, Institutions & Key Discoveries

31. Pioneers (Alphabetical)

Arno Penzias, Robert Wilson – CMB discovery
Edwin Hubble – Expansion of universe, galaxy classification
Alan Guth – Inflation
Stephen Hawking – Hawking radiation, singularity theorems, no‑boundary
Albert Einstein – General relativity
George Gamow – Big Bang nucleosynthesis
Vera Rubin – Dark matter (rotation curves)
Saul Perlmutter, Brian Schmidt, Adam Riess – Dark energy (SNe Ia)
John Mather, George Smoot – CMB blackbody & anisotropy (COBE)
Rashid Sunyaev, Yakov Zel’dovich – SZ effect, CMB physics
Michael Turner – “Dark energy” term, cosmic acceleration
Neta Bahcall – Large‑scale structure
Margaret Burbidge – Stellar nucleosynthesis

32. Major Collaborations & Institutions

Planck, WMAP, COBE (NASA/ESA)
SDSS, DESI (ground‑based surveys)
Euclid (ESA), Roman (NASA)
LIGO/Virgo/KAGRA (gravitational waves)
IceCube (neutrino astronomy)
Simons Observatory, CMB‑S4 (CMB)
International Astronomical Union (IAU)
Institute for Advanced Study (Princeton), Perimeter Institute, Max Planck Institute for Astrophysics

Volume 10: Appendices & Reference

Appendix A: Glossary of 250+ Cosmology Terms

Angular diameter distance to Zel’dovich pancake

Appendix B: Constants & Parameters (2026 Best Values)

H₀ = 67.4 ± 0.5 km/s/Mpc (Planck 2018 + DESI 2025)
Ω_m = 0.315 ± 0.007
Ω_Λ = 0.685 ± 0.007
Ω_b = 0.049 ± 0.001
Ω_cdm = 0.266 ± 0.006
Ω_k = –0.0004 ± 0.0018
n_s = 0.965 ± 0.004
σ₈ = 0.812 ± 0.006
t₀ = 13.797 ± 0.020 Gyr
T_CMB = 2.72548 ± 0.00057 K

Appendix C: Timeline of Cosmology (30,000 BCE – 2026)

Appendix D: Major Cosmological Surveys (Table)

Appendix E: N‑Body Simulation Code Comparison (GADGET, AREPO, Enzo, RAMSES, SWIFT)

Appendix F: CMB Power Spectrum Explained (ℓ vs. D_ℓ)

Appendix G: Derivation of Friedmann Equations (Brief)

Appendix H: List of Unsolved Problems (as of 2026)

Nature of dark matter
Nature of dark energy (why Λ small, why now?)
Hubble tension resolution
S8 tension resolution
Primordial gravitational waves (B‑modes)
What happened before inflation?
Is the multiverse real?
Quantum gravity (string theory, LQG, asymptotic safety)

Appendix I: Further Reading & Resources

Books: Peebles (Principles of Physical Cosmology), Dodelson (Modern Cosmology), Weinberg (Cosmology), Ryden (Introduction to Cosmology)
Online: Ned Wright’s Cosmology Tutorial, Wayne Hu’s CMB pages, arXiv.org (astro-ph.CO)

End Matter

Subject Index – A‑Z (e.g., “Baryon Acoustic Oscillations, 245–249”, “Dark energy, 310–330”)
About the Editor – Cosmologist (20+ years)
Contributors – Observational, theoretical, computational cosmologists
Disclaimer – Some values and tensions may update after 2026