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Cosmic inflation is a theory that proposes a rapid exponential expansion of the universe during its first few moments after the Big Bang, solving several problems in cosmology such as the horizon and Flatness Problems. This brief period of inflationary expansion set the initial conditions for the universe's large-scale structure and uniformity observed today.
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Dark matter is a form of matter that does not emit, absorb, or reflect light, making it invisible and detectable only through its gravitational effects on visible matter. It is believed to constitute approximately 27% of the universe, influencing the structure and evolution of galaxies and galaxy clusters.
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Gravitational instability refers to the process by which regions of a self-gravitating fluid become unstable and collapse under their own gravity, leading to the formation of structures such as stars, galaxies, or planetary systems. It plays a crucial role in astrophysics, explaining how large-scale structures in the universe form from small initial density fluctuations.
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Hierarchical clustering is an unsupervised learning method used to build a hierarchy of clusters by either iteratively merging smaller clusters into larger ones (agglomerative) or dividing larger clusters into smaller ones (divisive). It is particularly useful for visualizing data structure and relationships through dendrograms, allowing for flexible and interpretable clustering solutions without needing to pre-specify the number of clusters.
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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.
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Density fluctuations refer to the variations in density within a medium, which can significantly affect the behavior and properties of that medium, such as sound propagation, light scattering, and phase transitions. These fluctuations are crucial for understanding phenomena in fields ranging from cosmology, where they influence the distribution of matter in the universe, to material science, where they impact the stability and characteristics of materials.
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Galaxy formation is the process by which gas, dark matter, and stars come together under the influence of gravity to create the diverse structures observed in the universe. This process is influenced by a combination of cosmological parameters, initial conditions, and feedback mechanisms, leading to the wide variety of galaxy types seen today.
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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.
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Baryonic matter is the 'normal' matter that makes up the atoms in the universe, including protons, neutrons, and electrons, and constitutes only about 5% of the universe's total mass-energy content. It is distinct from dark matter and dark energy, which together account for the Remaining 95% and are not composed of baryons.
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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.
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Weak lensing is a subtle effect of gravitational lensing where the light from distant galaxies is slightly distorted by the gravitational field of large-scale structures like galaxy clusters, allowing astronomers to map the distribution of dark matter in the universe. This phenomenon is crucial for understanding cosmic structure formation and provides insights into the nature of dark energy and the overall geometry of the universe.
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The Large Scale Structure of the universe refers to the organization and distribution of matter on the largest scales, encompassing galaxies, galaxy clusters, and the vast cosmic web of filaments and voids. It is crucial for understanding the universe's evolution, the nature of dark matter and dark energy, and the initial conditions set by the Big Bang.
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Baryon density refers to the number of baryons, such as protons and neutrons, per unit volume in the universe, which plays a crucial role in understanding the matter content and evolution of the cosmos. It is a fundamental parameter in cosmology, influencing the formation of structures and the synthesis of elements in the early universe.
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The baryon-to-photon ratio is a critical parameter in cosmology that quantifies the relative abundance of baryonic matter to photons in the universe, providing insights into the conditions of the early universe and the processes of nucleosynthesis. This ratio is instrumental in understanding the evolution of the universe, as it influences the formation of cosmic structures and the cosmic microwave background radiation.
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The matter density parameter, often denoted as Omega_m, is a dimensionless quantity that represents the ratio of the actual matter density of the universe to the critical density needed for the universe to be flat. It plays a crucial role in cosmology, helping to determine the overall geometry and fate of the universe, influencing models of cosmic expansion and structure formation.
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.
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The Lambda-CDM model, or the 'Lambda Cold Dark Matter' model, is the prevailing cosmological model that describes the evolution of the universe from the Big Bang to its current state, incorporating both dark energy (Lambda) and Cold Dark Matter. It provides a comprehensive framework that explains the observed large-scale structure of the cosmos, cosmic microwave background radiation, and the accelerating expansion of the universe.
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Cosmic strings are theoretical one-dimensional topological defects that may have formed during phase transitions in the early universe, potentially influencing cosmic structure formation. They are predicted to be extremely thin yet incredibly dense, with significant gravitational effects that could be observed through phenomena like gravitational lensing or gravitational waves.
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The early universe refers to the period immediately following the Big Bang, characterized by rapid expansion and cooling that led to the formation of fundamental particles and eventually atoms. This era set the stage for the development of cosmic structures such as galaxies, stars, and planets through processes governed by fundamental forces and cosmic inflation.
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The Cold Dark Matter (CDM) model is a theoretical framework that explains the structure formation of the universe, where dark matter is composed of slow-moving particles that clump together under the influence of gravity. It successfully accounts for the observed large-scale structure of the universe, such as galaxy clusters and cosmic microwave background anisotropies, while predicting the existence of unseen matter that interacts weakly with ordinary matter and radiation.
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A dark matter halo is a theoretical, invisible mass surrounding galaxies, believed to account for the majority of a galaxy's mass and influence its gravitational behavior. It plays a crucial role in the formation and evolution of galaxies, providing the necessary gravitational pull to hold them together and affecting their rotation curves.
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Cosmological perturbations are small deviations from the perfect uniformity of the universe's density and temperature, crucial for understanding the formation of large-scale structures like galaxies and galaxy clusters. They arise from quantum fluctuations in the early universe and evolve under the influence of gravity, providing the initial seeds for structure formation as described by the inflationary model and observed in the Cosmic Microwave Background radiation.
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The Cosmic Web is the large-scale structure of the universe, consisting of interconnected filaments of galaxies and dark matter that form a vast network. It is the result of gravitational forces shaping matter over billions of years, revealing the distribution of matter and the underlying structure of the cosmos.
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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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