Formation of the Universe, Solar System, and Earth

Vocabulary flashcards summarizing key terms and concepts about the origin of the universe, solar system, and Earth.

Cosmology

The branch of science that studies the origin, structure, and evolution of the universe.

Big Bang Theory

The prevailing model stating the universe began 13.8 billion years ago from an extremely hot, dense state and has been expanding ever since.

Cosmic Microwave Background (CMB)

The oldest detectable light—thermal radiation released about 380,000 years after the Big Bang—that permeates the universe as a faint microwave glow.

Cosmic Inflation Theory

Alan Guth and Andrei Linde’s idea (1980s) that the early universe underwent a brief, exponential expansion, solving puzzles such as homogeneity and flatness.

Vacuum Energy

Energy inherent in ‘empty’ space; in inflation theory, it drove the rapid expansion of the early universe.

Steady State Theory

Now-obsolete model claiming the universe has no beginning or end, remains unchanged in appearance, and continuously creates new matter as it expands.

Homogeneity (in cosmology)

The observation that matter is distributed almost uniformly on the largest scales across the universe.

Star System (Stellar System)

A small group of stars that gravitationally orbit one another; the solar system is a type because the Sun is a star.

Nebular Hypothesis

Kant and Laplace’s 18th-century model proposing the Sun and planets formed from a rotating cloud of gas and dust (nebula) about 4.5 billion years ago.

Planetesimal Theory

Victor Safronov, T.C. Chamberlin, and F.R. Moulton’s idea that planets formed by accretion of small solid bodies (planetesimals) within the protoplanetary disk.

Tidal Theory

James Jeans and Harold Jeffreys’ 1917 proposal that a close-passing star’s gravity pulled material from the Sun, which later condensed into planets.

Accretion

The gradual growth of celestial bodies through gravitational attraction and collision of smaller particles or planetesimals.

Gas Giants

Outer planets (Jupiter, Saturn, Uranus, Neptune) composed mainly of hydrogen and helium, remaining gaseous because they formed beyond the frost line.

Terrestrial (Telluric) Planets

Inner rocky planets (Mercury, Venus, Earth, Mars) characterized by silicate rocks and metal cores.

Cosmic Microwave Background Age

The CMB light dates to about 380,000 years after the Big Bang, offering clues to the universe’s composition and age.

Hydrogen Plasma

Hot, charged gas consisting of protons and electrons; filled the young universe before atoms formed.

Neutron, Proton, Electron

Subatomic particles present in the early universe; as expansion cooled, they combined to form neutral atoms.

Pure Vacuum Bubble

In inflation theory, the early universe state composed solely of vacuum energy, devoid of matter or radiation.

Density Fluctuations

Small variations in matter distribution during cosmic inflation that allowed gravity to pull gas together, forming stars and galaxies.

CMB Sky Map

An image of microwave temperature variations across the sky, used to study the universe’s structure and origins.

Star Formation

Process in which gravity causes dense regions of gas and dust to collapse, igniting nuclear fusion in cores to create stars.

Galaxy Formation

The assembly of stars, gas, and dark matter into large gravitationally bound systems following density fluctuations after inflation.

Frost Line Temperature

The low temperature region beyond which volatile gases condense; crucial for giant planet evolution.