Cosmology

• 1. Defining The Cosmos

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  The composite photo from the Hubble eXtreme Deep Field shows a speck of light that is an individual galaxy, some as old as 13.2 billion years. This image contains more than 2 trillion galaxies within the observable universe. Cosmology serves as the scientific study of this vast nature and origin of the cosmos. The term first appeared in English in 1656 within Thomas Blount's Glossographia with the meaning of speaking about the world. German philosopher Christian Wolff later used cosmologia in Latin during 1731 to describe a branch of metaphysics dealing with the physical world. Scientists including astronomers and physicists investigate these questions alongside philosophers such as metaphysicians and philosophers of space and time. Religious or mythological cosmology forms a separate body of beliefs based on creation myths and eschatology found in literature and traditions.

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• 2. Ancient Philosophical Roots

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  Greek philosopher Anaximander proposed a model where the Earth floats very still in the center of the infinite without support from anything. Aristotle described a system of hollow concentric wheels filled with fire surrounding the Earth like bark on a tree. These early models placed the Earth at the center of the universe while stars moved through holes in the celestial spheres. Parmenides argued that the universe was unchanging, uniform, perfect, necessary, timeless, and neither generated nor perishable. Plato created a complex cosmogony where static Earth sat at the center surrounded by heavenly bodies moving in perfect circles. The Almagest written by Ptolemy in the second century CE became the most successful universe model due to its longevity. Ancient thinkers debated whether the cosmos had an infinite past or a finite beginning while constructing geometric-mathematical models to explain planetary motion.

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• 3. The Scientific Revolution

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  Nicolaus Copernicus published De revolutionibus orbium coelestium during 1543 describing a heliocentric system where planets orbit the Sun. Isaac Newton released Principia Mathematica in 1687 providing the first description of universal gravitation laws. This work resolved anomalies in previous systems caused by gravitational interaction between planets. Albert Einstein published Cosmological Considerations of the General Theory of Relativity in 1917 as his final modification of general relativity. Alexander Friedmann introduced the idea of an expanding universe containing moving matter in 1922. Willem de Sitter explored astronomical ramifications of Einstein's theory while Karl Schwarzschild and Arthur Eddington studied distant objects. Physicists began changing their assumption that the universe was static and unchanging during this period of rapid theoretical development.

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• 4. The Great Debate And Expansion

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  Heber Curtis argued for the idea that spiral nebulae were star systems in their own right as island universes. Mount Wilson astronomer Harlow Shapley championed the model of a cosmos made up of the Milky Way star system only. The Great Debate took place on the 26th of April 1920 at the meeting of the U.S. National Academy of Sciences in Washington, D.C. Edwin Hubble detected Cepheid Variables in the Andromeda Galaxy during 1923 and 1924 to resolve the conflict. Their distance established spiral nebulae well beyond the edge of the Milky Way. Georges Lemaître proposed the Big Bang model in 1927 which was subsequently corroborated by Edwin Hubble's discovery of redshift in 1929. Arno Penzias and Robert Woodrow Wilson discovered cosmic microwave background radiation in 1964 providing evidence to rule out alternative cosmologies.

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• 5. The Big Bang Consensus

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  Astronomers reported on the 1st of December 2014 at the Planck 2014 meeting in Ferrara, Italy that the universe is 13.8 billion years old. This composition includes 4.9% atomic matter, 26.6% dark matter and 68.5% dark energy. Observations from COBE, WMAP and Planck satellites matched predictions of cosmic inflation theory since around 1990. The specific version known as the Lambda-CDM model represents a standard parameterization of the Big Bang with dark matter and dark energy. Alan Guth claimed modern times constitute the golden age of cosmology due to precise agreement between theory and observation. BICEP2 collaboration announced detection of gravitational waves in 2014 but this result was later found to be spurious due to interstellar dust interference.

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• 6. Modern Observational Advances

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  Large new galaxy redshift surveys including 2dfGRS and SDSS transformed cosmology into a predictive science during recent decades. Observations of distant supernovae and gravitational lensing provided data matching theoretical predictions for the first time. These advances allowed scientists to move beyond largely speculative science toward high accuracy measurements. The Planck satellite delivered detailed maps of the microwave background radiation confirming the age and composition of the cosmos. Modern physical cosmology now dominates astronomy by bringing together observational data and particle physics theories. Scientists use these tools to study the chronology of the universe and its large-scale structures and dynamics.

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