Origin and Formation of the Universe – Vocabulary Review

These vocabulary flashcards review key terms and definitions related to the composition, history, and theoretical models of the universe as presented in the lecture notes.

Universe (Cosmos)

The total cosmic system of all matter and energy, including Earth and everything beyond it.

Cosmology

The scientific study of the origin, evolution, and structure of the universe.

Ordinary Visible Matter

The stars, planets, and hot intergalactic gas that make up about 0.4% of the universe.

Normal Non-Luminous Matter

Objects such as black holes and cold intergalactic gas that do not emit light, totaling roughly 3.6% of the universe.

Dark Matter

Invisible matter that neither emits nor reflects light yet behaves gravitationally; constitutes about 21% of the universe.

Dark Energy

Unknown, uniformly distributed energy causing the accelerated expansion of the universe; about 75% of the cosmic content.

Nucleosynthesis

The process that formed light elements (H, He) after the Big Bang and heavier elements in supernova explosions.

Hydrogen

The most abundant element in the universe, comprising 70–75% of normal matter atoms.

Helium

The second-most abundant element, produced during Big Bang nucleosynthesis.

Supernova

A massive star’s explosive death, providing energy to form elements heavier than helium.

Cosmic Microwave Background (CMB)

Relic radiation from the early universe that confirmed the existence of dark energy and supports the Big Bang model.

Philolaus

Ancient Greek (480–385 B.C.) who proposed that Earth orbits a ‘Central Fire,’ challenging geocentrism.

Aristotle

Greek philosopher (384–322 B.C.) who taught geocentrism, placing Earth at the center of the universe.

Aristarchus

Greek astronomer (310–230 B.C.) who first suggested a heliocentric solar system with the Sun at the center.

Claudius Ptolemy

Greco-Roman astronomer (100–170 A.D.) who developed the geocentric Ptolemaic system of circular orbits.

Geocentric Model

Cosmological view that Earth lies at the universe’s center with all celestial bodies orbiting it.

Heliocentric Model

Model placing the Sun at the center of the solar system with Earth and planets orbiting it.

Epicycle

Small circular path used in the Ptolemaic system to explain planetary motion around a deferent.

Deferent

The large circular orbit in Ptolemy’s geocentric model around which an epicycle’s center moves.

Eccentric (Astronomy)

An offset circle in geocentric theory, explaining non-uniform planetary speed.

Equant

A point in the Ptolemaic model about which planets appear to move at uniform angular speed.

Big Bang Theory

Most accepted explanation that the universe began ~13.8 billion years ago from a hot, dense state followed by rapid expansion.

Inflation

Brief period of exponential expansion moments after the Big Bang during which space grew enormously.

Planck Era

Earliest epoch (to 10⁻⁴³ s) when all fundamental forces were unified as a ‘super force’ and the universe was smaller than an atom.

Grand Unified Theory (GUT) Era

Period when gravity separated from the GUT force, and the strong force froze out, releasing energy that triggered inflation.

Electroweak Era

Epoch when electromagnetic and weak forces separated, leaving all four fundamental forces distinct (age ≈10⁻¹⁰ s).

Particle Era

Time of rapid particle–antiparticle creation and annihilation; quarks combined into protons and neutrons by ~1 ms after the Big Bang.

Era of Nucleosynthesis

Stage when protons and neutrons fused to form light nuclei such as deuterium and helium.

Era of Nuclei

Phase when the universe cooled to ~3000 K, allowing nuclei to capture electrons and form neutral atoms.

Era of Atoms and Galaxies

Period in which atoms clumped into protogalactic clouds, leading to the first stars and galaxy formation.

Central Fire

Philolaus’s hypothetical object around which Earth and other bodies revolved.

Fundamental Forces

Gravity, strong nuclear, weak nuclear, and electromagnetic forces governing interactions in the universe.

Super Force

Unified single force of nature believed to have existed during the Planck Era before separating into individual fundamental forces.

Composition of the Universe

Approximately 0.4 % visible matter, 3.6 % normal non-luminous matter, 21 % dark matter, and 75 % dark energy.

Cosmic Expansion

The ongoing increase in distance between galaxies, accelerated by dark energy.