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Astrophysics — Cosmology

Structure, origin, and evolution of the universe

C
cosmic_fabric 25 terms Nov 22, 2025
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Terms 25

1
Big Bang Theory
Universe began ~13.8 billion years ago from extremely hot, dense state; has been expanding since
2
Cosmic Microwave Background (CMB)
Thermal radiation from ~380,000 years after Big Bang; first light of universe; 2.7 K today
3
Hubble's Law
v = H₀d; galaxies recede at speed proportional to distance; H₀ ≈ 70 km/s/Mpc
4
Redshift
Stretching of light wavelength from receding source; cosmological redshift due to space expansion
5
Dark Matter
~27% of universe; interacts gravitationally but not electromagnetically; detected via galaxy rotation curves, lensing
6
Dark Energy
~68% of universe; drives accelerated expansion; cosmological constant Λ; nature unknown
7
Cosmological Constant (Λ)
Einstein's term representing vacuum energy density; drives accelerated expansion
8
Inflation
Exponential expansion ~10⁻³⁶–10⁻³² s after Big Bang; solves horizon and flatness problems
9
Flatness Problem
Universe appears geometrically flat; fine-tuning problem solved by inflation
10
Horizon Problem
CMB is uniform even in regions causally disconnected; solved by inflation
11
Nucleosynthesis (BBN)
Protons and neutrons formed H, He, Li in first ~3 minutes; ~75% H, ~25% He
12
Stellar Nucleosynthesis
Elements heavier than Li formed in stars; heaviest forged in supernovae and neutron star mergers
13
Friedmann Equations
Govern expansion of universe; derived from GR with cosmological principle
14
Scale Factor (a)
Relative expansion of universe; a = 1 today; redshift z = 1/a − 1
15
Critical Density (ρ_c)
Density for flat universe; ρ_c = 3H²/8πG; actual density ≈ ρ_c
16
Density Parameter (Ω)
Ratio of actual to critical density; Ω = 1 for flat; Ω_total ≈ 1.00 observed
17
Large-Scale Structure
Cosmic web of filaments, voids, sheets, and galaxy clusters; formed from primordial fluctuations
18
Gravitational Lensing
Light bent by massive objects; strong (Einstein rings), weak (distorted shapes), microlensing
19
Gravitational Waves
Ripples in spacetime from accelerating masses; detected by LIGO from merging black holes
20
Chandrasekhar Limit
1.4 M☉ max mass of white dwarf; exceeding causes Type Ia supernova
21
Tolman-Oppenheimer-Volkoff Limit
~2–3 M☉ max mass of neutron star; above causes collapse to black hole
22
Hawking Radiation
Black holes slowly emit thermal radiation due to quantum effects near event horizon; eventually evaporate
23
Anthropic Principle
Universe's constants must permit observers to exist; weak form observational, strong form predictive
24
Multiverse
Hypothetical ensemble of universes; different physical constants possible; testable predictions difficult
25
Baryonic Matter
Ordinary matter (protons, neutrons, electrons); ~5% of universe's energy density