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Physics LibreTexts

15: Cosmology

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“The scientific issues that engage people most are the truly fundamental ones: is the universe infinite? Is life just a sideshow in the cosmos? What happened before the Big Bang? Everyone is flummoxed by such questions, so there is, in a sense, no gulf between experts and the rest. ”

Dr. Martin Rees, The Lord Rees of Ludlow
Astrophysicist
(1942- )

Learning Objectives

Upon completion of this module, the student will be able to:Upon completion of this module, the student will be able to:

  • Describe the Big Bang Theory, including the theory’s strengths and weaknesses
  • Describe different cosmological views of the Universe

This module presents an overview of our home galaxy, the Milky Way Galaxy, its characteristics, satellite galaxies, and how it compares to other galaxies.

  • 15.1: What do you think?
    This page emphasizes the magnificent qualities of the Universe and discusses the pivotal event of the Big Bang as its starting point, encouraging readers to contemplate their emotions regarding this extraordinary occurrence.
  • 15.2: In the beginning…
    This page discusses cosmogony, which investigates the Universe's origin through science, philosophy, theology, and religion, questioning the nature of creation. It differentiates between physical cosmology, rooted in scientific inquiry, and religious cosmology, based on beliefs.
  • 15.3: Physical Cosmology
    This page discusses the Big Bang theory, which explains the Universe's origin from a hot, dense state that expanded and cooled over time, resulting in the formation of particles, atoms, stars, and galaxies. Proposed by Georges Lemaître in 1927, the phrase "Big Bang" was coined by Sir Fred Hoyle in 1949 as a critique. Despite efforts to find a different term, "Big Bang" has persisted as the accepted name for the theory.
  • 15.4: The Big Bang in Eras
    This page details the development of the Universe after the Big Bang, categorizing it into eras: Planck, Grand Unification Theory, Electroweak, Particle, Nucleosynthesis, Nuclei, Atoms, and Galaxies. It describes the evolution from a hot event to the creation of particles, four fundamental forces, atomic structures, stars, galaxies, and life, culminating in the present. Ongoing data continues to enhance this understanding.
  • 15.5: The Planck Era
    This page describes the Planck era, a brief phase of extreme heat and energy in the Universe's early moments without matter. As it expanded and cooled, atomic nuclei formed within three minutes. Inflation at the end of the Grand Unification Theory era significantly shaped the Universe's structure and density. Subsequently, the four fundamental forces—gravity, electromagnetic, strong, and weak—emerged from an initial unified force.
  • 15.6: Big Bang Evidence
    This page outlines evidence for the Big Bang theory, highlighting three major points: the Cosmological Redshift indicating the Universe's expansion, cosmic background radiation from the Big Bang, and the predicted Helium abundance matching observations. Additional supporting evidence includes the uniformity of Cosmic Microwave Background Radiation, large-scale homogeneity of the Universe, light element abundance, and stellar ages.
  • 15.7: Recent Data on the Universe
    This page discusses the Wilkinson Microwave Anisotropy Probe (WMAP), a satellite that enhances cosmological studies by estimating the Universe's age at about 13.7 billion years. It reveals that 73% of the Universe's composition is dark matter, with 23% as cold dark matter, and only 4% being conventional matter. This indicates that ordinary matter is a small portion of the Universe, prompting inquiries about dark matter's nature and whereabouts.
  • 15.8: Issues with the Big Bang
    This page discusses the Big Bang Theory, highlighting that physical cosmologists see issues related to it as largely solvable. They prioritize events following the Big Bang over its origins and identify three significant problems that are complex and not covered in the current course.
  • 15.9: Beyond the Big Bang
    This page discusses alternative theories to the Big Bang, including the Oscillating Universe, Steady State theory, Modification of Newtonian Dynamics (MOND), and Tired Light. These theories propose cyclical expansion, a constant universe with ongoing matter creation, evolving Newton's laws, and light losing energy over time, respectively. However, they receive limited support and serve mainly as counterarguments to the Big Bang theory.
  • 15.10: What is Next for the Big Bang Theory?
    This page discusses the ongoing data collection from the Hubble Space Telescope until it stops functioning, while highlighting improvements in Earth-based telescope technology. It mentions the importance of other satellites, particularly the James Webb Space Telescope, set to launch in 2018, which will focus on capturing data across different wavelengths like infrared and gamma-ray.
  • 15.11: Questions Regarding the Eventual Fate of the Universe
    This page discusses the nature of the Universe, emphasizing that it is not expanding into anything measurable and has no observable edge. Its future expansion is contingent on its density, likely leading to indefinite expansion. Matter will eventually convert to energy, leaving a dark Universe in about 100 trillion years. It also addresses Dark Matter and Dark Energy as currently undetectable but potentially revealable through technological advancements.
  • 15.12: Religious or Philosophical Cosmology
    This page examines the term "creation" in the context of the Big Bang Theory and other origin theories of the universe. It defines "creation" as bringing something into existence, citing American Heritage and Encarta dictionaries, and questions the suitability of the term in this scientific context.
  • 15.13: Views on Creation
    This page examines diverse religious views on the universe's creation, highlighting the limitations of scientific explanations. Buddhism promotes non-attachment, while Daoism indicates a shift from unity to diversity. Hinduism credits Brahmā as the creator, and Islam outlines a systematic creation by Allāh. Judeo-Christian accounts, especially Genesis, are analyzed, notably the interpretation of "day" affecting perceptions of the universe's age.


This page titled 15: Cosmology is shared under a CC BY 4.0 license and was authored, remixed, and/or curated by Lumen Learning via source content that was edited to the style and standards of the LibreTexts platform.

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