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The Lambda Cold Dark Matter (ΛCDM) model is the prevailing cosmological model that describes the universe as composed of approximately 70% dark energy (Λ), 25% Cold Dark Matter, and 5% ordinary matter. It successfully explains a wide range of astronomical observations, including the cosmic microwave background radiation, large-scale structure, and the accelerating expansion of the universe.
Dark energy is a mysterious form of energy that is hypothesized to be responsible for the accelerated expansion of the universe, accounting for approximately 68% of the total energy content of the cosmos. Its nature remains one of the biggest unsolved problems in physics, with various theories suggesting it could be a property of space itself or a new dynamic field.
Cold Dark Matter (CDM) is a theoretical form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects. It is believed to constitute a significant portion of the universe's mass, playing a crucial role in the formation and structure of galaxies and the large-scale structure of the universe.
The cosmic microwave background (CMB) is the thermal radiation left over from the Big Bang, providing a snapshot of the infant universe approximately 380,000 years after its birth. It serves as a critical piece of evidence for the Big Bang theory and offers insights into the early universe's conditions, composition, and large-scale structure.
Large-Scale Structure refers to the organization of matter on the grandest scales in the universe, encompassing galaxy clusters, superclusters, filaments, and voids. It reveals the cosmic web pattern formed by dark matter and baryonic matter, providing insights into the universe's formation and evolution governed by gravitational forces and dark energy.
The cosmological constant, denoted by the Greek letter Lambda (Λ), was introduced by Albert Einstein in his equations of General Relativity to allow for a static universe, but it is now understood as a measure of the energy density of empty space, or dark energy, that is driving the accelerated expansion of the universe. This constant plays a crucial role in the current Lambda Cold Dark Matter (ΛCDM) model, which is the standard model of Big Bang cosmology.
Structure formation refers to the process by which small initial density fluctuations in the early universe grow over time to form galaxies, clusters, and larger cosmic structures. It is driven by gravitational instability, with dark matter playing a crucial role in the hierarchical clustering of matter.
Hubble's Law states that the velocity at which a galaxy recedes from an observer is directly proportional to its distance from the observer, implying that the universe is expanding. This relationship is fundamental to cosmology and provides evidence for the Big Bang theory, as it suggests that galaxies were once closer together in the past.
The Friedmann Equations are fundamental in cosmology, describing how the Universe expands over time based on general relativity and the matter-energy content of the cosmos. They provide critical insights into the dynamics of the Universe, including its age, geometry, and ultimate fate, by relating the scale factor to the density and pressure of cosmic components.
Dark matter halos are theoretical structures that surround galaxies and galaxy clusters, providing the gravitational framework that holds these systems together despite their apparent lack of visible mass. They are crucial for understanding the universe's large-scale structure and dynamics, as they account for the majority of the gravitational influence in galaxies, despite being composed of non-luminous material that does not emit or interact with electromagnetic radiation.
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