GEOL 105 Origin of the Universe

Ptolemy

Proposed the Ptolemaic geocentric system placing Earth at the center.

Geocentric

Earth-centered; a model in which Earth is at the center of the system.

Aristotle

Ancient Greek philosopher who acknowledged two “worlds”: Earth and the Moon.

Retrograde motion

The apparent backward motion of a planet that helped distinguish planets from stars.

Planet

The word comes from the Ancient Greek meaning “wandering star.”

Nicolaus Copernicus

Proposed a heliocentric model in which planets circle the Sun rather than Earth.

Heliocentric

Sun-centered; planets orbit the Sun rather than Earth.

Copernican Revolution

The shift from an Earth-centered to a Sun-centered model of the solar system.

Epicycles

Circles within circles used in the Copernican system to help describe planetary orbits.

Galileo Galilei

Used a telescope to observe the Sun Moon and planets and showed that planets were worlds in their own right.

Galileo's observations

Revealed mountains and craters on the Moon and challenged the idea that the heavens were fundamentally different from Earth.

Giordano Bruno

Supported some Copernican ideas and believed the Universe was infinite in age and extent.

Milky Way

Our galaxy containing approximately 100–400 billion stars.

Sagittarius A*

The black hole at the center of the Milky Way.

Melvin Slipher

Discovered galaxies beyond the Milky Way and observed their redshift.

1913

Year Slipher's galaxy observations showed redshift indicating galaxies were moving away.

Redshift

A shift in light toward longer wavelengths associated with objects moving away.

Doppler effect

A change in observed wave frequency caused by relative motion between the source and observer.

Edwin Hubble

Observed that galaxies are moving away from each other and that more distant galaxies move away faster.

Hubble's observation

The farther away a galaxy is the greater its recession velocity.

Standard Cosmological Model

The model of the Universe supported by observations including cosmic expansion and the CMB.

Cosmic Microwave Background (CMB)

The oldest electromagnetic radiation coming from everywhere in the sky.

Arno Penzias and Robert Wilson

Discovered the cosmic microwave background radiation in 1965.

1965

The year Penzias and Wilson discovered the CMB.

Cosmic distance ladder

A series of astronomical distance-measuring methods in which each technique calibrates the next.

Standard candle

An object whose intrinsic luminosity is known and can be used to calculate distance.

Inverse-square law

The relationship showing that observed brightness decreases as distance increases.

Cepheid variables

Luminous pulsating giant stars whose periods are related to their intrinsic brightness.

Henrietta Swan Leavitt

Discovered that the longer a Cepheid's pulsation period the brighter it is intrinsically.

Cepheid period-luminosity relationship

The relationship in which longer Cepheid pulsation periods correspond to greater intrinsic brightness.

Type Ia supernovae

Supernovae with predictable peak luminosities that can be used as standard candles.

Chandrasekhar limit

The approximate 1.4-solar-mass limit associated with the explosion of a white dwarf in a Type Ia supernova.

1.4 solar masses

The approximate Chandrasekhar mass limit for a white dwarf.

Expanding Universe

The idea that galaxies are moving away from one another as space expands.

Primordial Singularity

The extremely concentrated early state obtained by rewinding the expansion of the Universe.

Age of the Universe

Approximately 13.8 billion years.

Age of Earth

Approximately 4.5 billion years.

Universe's age when Earth formed

Approximately 9.3 billion years.

Visible Universe

The portion of the Universe whose light has had time to reach us.

Theoretical limit of the visible Universe

Approximately 13.8 billion light-years according to the lecture.

Lookback time

The idea that observing distant objects means seeing them as they existed further in the past.

Cosmic Microwave Background origin

The liberation of light occurred when the Universe was about 380

380

000 years

Density fluctuations

Variations in the density of early hydrogen-helium gas that helped gravity form clouds and galaxies.

Formation of galaxies

Density fluctuations led to gravitational attraction concentration of matter into clouds and eventually stars and galaxies.

First stars

Formed approximately 300 million years after the Primordial Singularity.

Peak galaxy formation

Occurred roughly 1–3 billion years after the Primordial Singularity.

Galaxy

A cluster of stars that orbit around a common center.

Galaxy shapes

Can include elliptical disk and spiral shapes.

Barred galaxy

A flat galaxy that appears to spin around a central mass such as the Milky Way and Andromeda.

Supermassive black hole

A massive black hole found at the center of galaxies.

Dark Matter

Invisible mass within galaxies that accounts for a large amount of galactic mass not contained in observed stars.

General relativity

Einstein's theory in which mass and energy curve spacetime.

Spacetime

The combined structure of space and time that is curved by mass and energy.

Geodesics

The straightest possible paths that objects follow through curved spacetime.

Matter tells spacetime how to…

Curve.

Spacetime tells matter how to…

Move.

Cosmological constant (Λ)

A term in Einstein's equations associated with spacetime curvature empty-space energy and cosmic expansion.

Dark energy

The energy associated with empty space that drives the accelerated expansion of the Universe.

Main sequence

The stage on the Hertzsprung-Russell diagram containing about 85% of stars including the Sun.

Hertzsprung-Russell (H-R) diagram

A diagram relating stars' properties such as temperature/color and luminosity.

Red giants

Large cooler stars.

White dwarfs

Dying stars whose fuel for fusion reactions is being exhausted.

Star lifetime relationship

Smaller stars generally live longer than larger stars.

Sun-like star lifetime

A 1-solar-mass star lives about 10 billion years according to the lecture.

Binary star system

A system of two stars orbiting around a common center of mass.

Binary or multiple-star systems

Approximately 50–85% of stellar systems according to the lecture.

Supernova

The explosion marking the end of the life of a massive star.

Massive star life cycle

A massive star can end in a supernova spreading matter into the surrounding galaxy.

Black hole

A collapsed object so dense that light cannot escape.

Event Horizon Telescope

In 2019 produced an image of the black hole at the center of Messier 87.

Messier 87

The galaxy containing the black hole imaged by the Event Horizon Telescope in 2019.

Nucleosynthesis

The process of creating new atomic nuclei from pre-existing protons and neutrons.

Primordial nucleosynthesis

The creation of elements in the early Universe beginning about three minutes after the Primordial Singularity.

Hydrogen from primordial nucleosynthesis

Approximately 75%.

Helium from primordial nucleosynthesis

Approximately 24%.

Lithium from primordial nucleosynthesis

Approximately 1%.

Stellar nucleosynthesis

The creation of chemical elements through nuclear fusion reactions within stars and novas.

E = mc²

The relationship between mass and energy presented in the lecture.

Scales of matter

The range from approximately 10^-35 meters for the smallest quantum structures to 10^27 meters for the visible Universe.

Smallest quantum structures

Approximately 10^-35 meters.

Visible Universe scale

Approximately 10^27 meters.

Matter scale sequence

Quarks → nucleus → atom → cell → human → Earth → Sun → Solar System → nearest star → galaxy → cluster of galaxies.

Planck time

Approximately 10^-43 seconds.

Meaning of Planck time

A timespan below which no meaningful length can be measured because of indeterminacy related to Heisenberg's uncertainty principle.

Age of Universe in seconds

Approximately 10^17 seconds.

Human reaction time

Approximately one-tenth of a second.

Average human lifespan

Approximately 10^10 seconds.

Speed of light

299792458 meters per second.