Earth & Life Science – Universe & Solar System Study Notes

Content Standards, Competencies & Intended Outcomes

• Content Standard – Learners must demonstrate an understanding of the formation of the Universe.
• Learning Competency ($11/12ES! -! 1a! -! e! -! 1$)
  • State the different hypotheses and theories explaining the origin of the Universe.
• Specific Learning Outcomes
  • Describe the structure & composition of the Universe.
  • Enumerate hypotheses that preceded the Big Bang Theory.
  • Explain red-shift and why it is evidence of an expanding Universe.
  • Explain the Big Bang Theory and the observations that support it.

Key Terms & Fundamental Concepts

• Baryonic Matter – ordinary matter (protons, neutrons, electrons) making up atoms, planets, stars, galaxies.
• Dark Matter – non-luminous matter that exerts gravity; helps bind galaxies.
• Dark Energy – mysterious “anti-gravity” that accelerates universal expansion.
• Protostar – early stage of a star formed by gravitational collapse of gas.
• Thermonuclear Reaction – nuclear fusion that powers stars.
• Main-Sequence Stars – stars fusing H → He in their cores; hydrostatic equilibrium between fusion pressure & gravity.
• Light-Year – distance light travels in a year: $1\ \text{ly}=9.4607\times10^{12}\ \text{km}$.

Structure, Composition & Age of the Universe

• Universe = totality of space–time, matter, energy.
• Current mean composition:
  • $4.6\%$ baryonic matter
  • $24\%$ cold dark matter
  • $71.4\%$ dark energy
• Abundant elements: H, He, Li.
• Stars form inside cold gas–dust clouds → collapse → rotation → heating → protostar → fusion ignition.
• Main-sequence lifetime: Sun burns H for ~$10^{10}$ yr; massive stars burn faster.
• Large-scale matter distribution:
  • Stars → Galaxies (billions of stars)
  • Galaxies → Clusters → Superclusters → Cosmic web; appears clumpy on small scales, homogeneous & isotropic on very large scales.
• Measured parameters:
  • Age ≈ $13.8\ \text{billion yr}$.
  • Observable diameter ≥ $91\ \text{billion ly}$ (may be infinite).
  • Mean density $\rho=4.5\times10^{-31}\ \text{g\,cm}^{-3}$.

Observational Evidence for Expansion

• Red-Shift (1929, Edwin Hubble)
  • Spectral lines shift toward longer wavelengths (red) ⇒ recessional motion.
  • Greater distance → greater red-shift ⇒ $v \propto d$ (Hubble’s law).
  • Confirms Einstein’s General Relativity prediction of dynamic Universe.
• Cosmic Microwave Background (CMB)
  • Discovered accidentally (1964, Penzias & Wilson); uniform black-body glow at $T≈2.7\ \text{K}$.
  • Remnant radiation from early hot Universe; highly isotropic with tiny anisotropies.

Non-Scientific & Mythological Accounts (Context)

• Ancient Egyptians: world rose from infinite sea at dawn’s first light.
• Kuba (Central Africa): creator god Mbombo/Bumba vomited stars, Sun, Moon.
• Indian myth: gods sacrificed Purusha – parts became sky, Earth, Sun, Moon.
• Judaism–Christianity–Islam: supreme being created Universe ex-nihilo.

Scientific Theories on the Origin of the Universe

• Creationist Theory – literal divine creation; cites Biblical scripture (non-testable scientifically).
• Oscillating / Cyclic Universe (George Gamow)
  • Expansion slows, reverses into contraction; ends in “Big Crunch” then new Bang; Universe cycles eternally.
• Steady-State Theory (Bondi, Gold, Hoyle)
  • Universe has no beginning or end; average density constant via continuous matter creation.
  • Two versions:
  • Evolutionary – density decreases.
  • Classic steady-state – density constant.
  • Falsified by CMB & observational evolution of galaxies.
• Big Bang Theory (accepted model)
  • $13.8\ \text{Gyr}$ ago a tiny, hot, dense state expanded and cooled to present-day conditions.
  • Supported by:
  1. Universal red-shift of galaxies.
  2. Predicted primordial abundances: H (~75 %), He (~25 %), trace Li.
  3. CMB as relic radiation.

The Big Bang in Detail

• Timeline Highlights
  • t<10^{-43}\ \text{s} (Planck era) – quantum gravity unknown.
  • $10^{-36}!\text{–}!10^{-32}\ \text{s}$ – Inflation: exponential expansion enlarges Universe from atomic to grapefruit size; quantum fluctuations stretched to macroscopic scales.
  • $10^{-6}\ \text{s}$ – Quark–gluon plasma cools; quarks combine into protons & neutrons.
  • $3\ \text{min}$ – Big-Bang nucleosynthesis forms nuclei of H, He, Li.
  • $380,000\ \text{yr}$ – Recombination: electrons bind to nuclei ⇒ atoms; photons decouple → CMB; temperature ≈ $10^4\ ^\circ\text{C}$ dropping to $\sim3000\ ^\circ\text{C}$.
  • $400\ \text{million yr}$ – First stars ignite; end of “Dark Ages”.
  • $\sim1\ \text{Gyr}$ – First galaxies & heavy-element synthesis.
  • $9.8\ \text{Gyr}$ – Solar system forms.
  • Present (13.8 Gyr) – Dark-energy dominated, accelerated expansion.
• Einstein’s mass–energy equivalence: $E = mc^2$ – early high energy “froze” into matter (protons, neutrons, electrons).
• Inflation Analogy –
  • "Raisin-bread" model: as dough (space) rises, raisins (galaxies) move apart; individual raisins don’t expand.

Post–Big Bang Evolution (Events Sequence)

1. Formation of basic elements – $p+n \rightarrow$ H; $2H \rightarrow$ He; trace Li; process = nucleosynthesis.
2. Radiation Era (first $\sim10,000$ yr) – energy dominated by radiation; CMB originates.
3. Matter Domination – atoms form; Li appears; neutral atoms allow structure formation.
4. Birth of Stars & Galaxies ($\sim300\ \text{Myr}$) – stellar clusters merge into galaxies.
5. Stellar Evolution – heavy elements forged in stars/supernovae recycle into new stars & planets.

Solar System Context & Overview

• Located in Milky Way spiral galaxy (≥100 billion stars); lies on Orion Arm.
• Galaxy parameters:
  • Diameter ≈ $\sim100,000\ \text{ly}$ (slide mis-quotes 100 million ly).
  • Rotates around central super-massive black hole every $\sim240\ \text{Myr}$.
• Part of Local Group → Virgo Supercluster.
• Meteorite radiometric ages ⇒ Solar System & Earth $\sim4.6\ \text{Gyr}$.

Large-Scale Features of the Solar System

• $\approx99.8\%$ of mass in the Sun; outer planets hold most angular momentum.
• Planetary orbits:
  • Nearly elliptical, coplanar.
  • All planets revolve counter-clockwise (as viewed from north of ecliptic).
  • Orbital period ↑ with distance (Kepler’s 3rd law).
  • Planet spacing approximately regular.

Small-Scale Features

• Planetary rotation: most rotate prograde; exceptions – Venus (retrograde), Uranus (axial tilt).
• Inner (terrestrial) planets: silicates + Fe/Ni, high melting points, thin/no atmospheres, dense, volatile-poor.
• Outer (gas giants): H, He, ices; low density, rapid rotation, thick atmospheres, fluid/ice interiors.

Historical Theories for Solar-System Formation

1. Nebular Hypothesis (Pierre-Simon de Laplace, 1796)

   • Slowly rotating gas cloud contracts → flattens into disk (via conservation of angular momentum) → rings detach → condense into planets; central mass → proto-Sun.
   • Shortcoming: difficulty explaining present angular-momentum distribution.

2. Encounter (Catastrophic) Hypotheses

   • G.-L. Buffon (1749) – Sun–comet near-collision ejects matter → planets.
   • James Jeans (1917) – Near pass of another star pulls solar material.
   • Chamberlain & Moulton (1904) – Planetesimal Hypothesis – massive star glances Sun, drawing filaments that cool into planetesimals.
   • Ray Lyttleton (1940) – Sun’s binary companion collides with third star, forming proto-planet that fragments into Jupiter & Saturn.
   • Problems: extremely improbable stellar encounters; cannot account for planet compositions.

3. Protoplanet (Modern) Hypothesis

   • $\sim4.6\ \text{Gyr}$ ago a molecular cloud (rich in H & He) collapsed.
   • Most mass → central proto-Sun; residual disk → proto-planetary disk.
   • Dust grains coalesced → km-sized planetesimals → gravitational accretion into protoplanets.
   • Composition gradient: inner disk hot → refractory silicates/metals; outer disk cool → volatiles & ices.
   • Giant impacts:
     • High-speed collisions strip Mercury’s mantle.
     • Retrograde rotation of Venus.
     • Mars-sized impactor hits Earth → ejecta coalesce into Moon (Moon’s chemistry ~Earth’s mantle).
   • Solar wind from young Sun clears light gases from inner Solar System; volatiles driven outward, aiding gas-giant formation.

Expansion Analogy & Non-Expanding Systems

• Galaxies recede because space itself expands; gravitationally bound systems (galaxies, solar system, atoms) remain intact within local non-expanding patches.

Numerical / Statistical References & Formulae

• Hubble relation (qualitative): $v = H_0 d$.
• Energy–mass conversion: $E = mc^2$.
• Observable radius ≥ $45.5\ \text{billion ly}$ ⇒ diameter ≥ $91\ \text{billion ly}$.
• Universe density: $4.5\times10^{-31}\ \text{g\,cm}^{-3}$.
• Light-year conversion: $1\ \text{ly}=9.4607\times10^{12}\ \text{km}$.

Ethical, Philosophical & Practical Implications (Embedded in Lecture)

• Scientific models evolve with new data; theories (e.g., Steady State) are discarded when evidence (CMB, red-shift) contradicts them.
• Creation myths underscore humanity’s quest to explain origins; science seeks testable, predictive explanations.
• Understanding cosmic origins informs our place in the Universe and drives technological advances (telescopes, satellites, particle physics).