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

---