Structure and Composition of the Universe – Comprehensive Study Notes

Universe: Definition & Scope

• Encompasses everything that exists:

  • All of space, time, matter, and energy

  • Includes Earth, the Moon, all other planets and their moons, stars, galaxies, and the observer ("you")

• Filipino terms used in the transcript:

  • “Sansinukob”

  • “Kalawakan”

• Age of the universe: $13.7\text{ \ billion years}$ (occasionally rounded to $13.8\text{ \ billion years}$ in later slides)

Overall Composition of the Universe

• Three broad constituents:

  • Baryonic (Ordinary) Matter

  • Made of baryons (e.g.

    • Protons

    • Neutrons)

  • Includes familiar astronomical objects (planets, stars, comets, meteoroids, asteroids, etc.)

  • Dark Matter

  • Consists of particles that do not absorb, emit, or reflect light → invisible through electromagnetic observation

  • Detected only via gravitational effects on baryonic matter and light

  • Example given: stellar black hole

    • Forms when the core of a very massive star collapses under its own gravity

    • Collapse triggers a supernova (exploding star) that ejects outer layers into space

  • Dark Energy

  • A mysterious force driving the accelerating expansion of the universe

  • Presence inferred from

    • Behavior of baryonic matter

    • Observed acceleration rate of cosmic expansion

Most Abundant Chemical Elements

• Hydrogen (H) and Helium (He) dominate cosmic elemental abundance

  • Both created soon after the Big Bang during an early nucleosynthesis epoch

• Helium reference data (periodic-table style excerpt):

  • Atomic number: $2$

  • Atomic mass: $4.002602$

  • Electron configuration: $1s^{2}$

  • Melting point: < -272.2\ ^\circ\text{C}

  • Boiling point: $-268.93\ ^\circ\text{C}$

• Origin explanation:

  • Immediately post–Big Bang the universe was a hot, dense “particle soup” (protons, neutrons, electrons)

  • Cooling allowed fusion of protons & neutrons → ionized hydrogen; further fusion produced some helium

Variety of Astronomical Bodies & Continued Expansion

• Universe hosts diverse bodies beyond planets and stars:

  • Moons, asteroids, comets, meteors/meteoroids, black holes, galaxies, clusters, etc.

• Star definition:

  • Astronomical body composed of plasma (4th state of matter)

  • Generates heat & emits light via nuclear fusion

• Ongoing cosmic expansion observable via red-shift of galaxies

Theories on the Origin of the Universe

• Transcript lists Big Bang Theory as the key (and most accepted) model

Big Bang Theory (BBT) – Core Ideas

• First formulated by Georges Lemaître (1927)

• Universe began as a singularity (infinitely small, hot, dense point)

  • Timestamp: $\approx 13.8\text{ \ billion years ago}$

• A massive “bang” initiated rapid expansion (not an explosion into space, but an expansion of space itself)

• Expansion led to cooling → allowed structure formation over time:

  1. Fundamental forces appeared in sequence (gravity, electromagnetic, strong & weak nuclear)

  2. Nucleosynthesis created the first atoms → mainly H & He

  3. Gas clouds collapsed → first stars & galaxies

  4. Subsequent stellar processes produced heavier elements → planets, comets, and other celestial bodies

• Tagalog summary (from slides):

  • “Ang uniberso ay nagsimula bilang isang napakaliit at napakainit na punto (‘singularity’)… nagkaroon ng ‘Big Bang’… uniberso ay patuloy na lumalawak at lumalamig… nabuo ang iba’t ibang bagay tulad ng mga bituin, planeta, at mga galaxy.”

Evidence Supporting Big Bang Theory

• Cosmic Microwave Background (CMB)

  • Omnipresent electromagnetic radiation—relic heat from ~380,000 years after the Big Bang

  • Extremely uniform but exhibits slight anisotropies matching early density fluctuations

• Galactic Red-shift (Hubble–Lemaître Law)

  • Distant galaxies observed moving away → implies uniform expansion of space

• Consistency with abundances of light elements (H, He, trace Li) predicted by Big-Bang nucleosynthesis models

Key Terminology & Concepts Recap

• Baryons: Heavy sub-atomic particles (protons, neutrons)

• Plasma: Ionized gas, 4th state of matter; constituent of stars

• Supernova: Explosive stellar death, disperses elements and can create black holes

• Black Hole (stellar type): Region where gravity is so strong that not even light escapes; end-state of massive stars

• Nucleosynthesis: Formation of new atomic nuclei; two main epochs addressed

  1. Big-Bang nucleosynthesis: Early universe (first few minutes), formed H & He

  2. Stellar nucleosynthesis: Inside stars, forms heavier elements

Practical / Philosophical Implications Highlighted

• Universe’s accelerating expansion driven by dark energy raises questions about ultimate fate (Big Freeze, Heat Death, etc.)

• Observation of dark matter & dark energy illustrates limits of human detection—large portions of reality are inferred, not directly seen

• Big Bang Theory’s success demonstrates interplay of theory, observation, and technological advancement (e.g., CMB detection, red-shift spectroscopy)