Cosmology in the 21st Century

A set of flashcards covering key concepts from the lecture on cosmology, including definitions and significant theories.

Cosmology

The scientific study of the large scale properties of the universe as a whole.

Superclusters

Massive groups of galaxies that are held together by gravity, representing the largest known structures in the universe.

Cosmological Principle

A fundamental assumption stating that the universe is isotropic and homogeneous when viewed on a large enough scale.

Redshift

The phenomenon where light from distant galaxies is shifted towards longer wavelengths, indicating that they are moving away from us.

Hubble's Law

The statement that the velocity at which a galaxy is receding from an observer is proportional to its distance from the observer.

Olbers's Paradox

The contradiction between the expectation of a bright night sky if the universe is infinite and eternal and the actual darkness of the night sky.

Cosmic Expansion

The observation that the universe is expanding, with galaxies moving away from each other over time.

Critical Density

The density at which the universe is flat; it determines the overall geometry and fate of the universe.

Dark Energy

A mysterious form of energy causing the acceleration of the universe's expansion.

Observable Universe

The portion of the universe that we can see or detect, limited by the distance that light has traveled since the Big Bang.

Big Bang

The leading explanation for the origin of the universe, describing the expansion from an extremely hot and dense state.

Cosmological Redshift

The redshift caused by the expansion of space itself, rather than the Doppler effect of galaxies moving through space.

Hubble Constant (H0)

The rate of expansion of the universe, usually expressed in kilometers per second per megaparsec.

Vesto Melvin Slipher

An astronomer who first noticed the redshift in the spectral lines of galaxies, providing early evidence for cosmic expansion.

Galaxy Clusters

Groups of galaxies held together by gravity, often found at the junction of cosmic filaments.

Galaxy formation sites

Regions of high gas density that serve as the birthplace for galaxies in the universe.

Structure of the Universe

The arrangement of galaxies and matter in the universe, characterized by clusters, superclusters, and voids.

Cosmological Theories

Various models and explanations that describe the dynamics, evolution, and structure of the universe.

General Relativity

Einstein's theory of gravity that describes how matter and energy influence the curvature of space-time.

Einstein's Cosmological Constant

A term introduced by Einstein in his equations to allow for a static universe, later abandoned after Hubble's discovery of cosmic expansion.