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Jai Ganesh

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Cosmology

Cosmology

Gist

Cosmology is a branch of metaphysics that deals with the nature of the universe. : a theory or doctrine describing the natural order of the universe. : a branch of astronomy that deals with the origin, structure, and space-time relationships of the universe. also : a theory dealing with these matters. cosmological.

Summary

Cosmology is a branch of astronomy involving the science of the universe's origin.

Cosmology is a branch of astronomy that involves the origin and evolution of the universe, from the Big Bang to today and on into the future. According to NASA, the definition of cosmology is "the scientific study of the large scale properties of the universe as a whole."

Cosmologists puzzle over exotic concepts like string theory, dark matter and dark energy and whether there is one universe or many (sometimes called the multiverse). While other aspects astronomy deal with individual objects and phenomena or collections of objects, cosmology spans the entire universe from birth to death, with a wealth of mysteries at every stage.

Humanity's understanding of the universe has evolved significantly over time. In the early history of astronomy, Earth was regarded as the center of all things, with planets and stars orbiting it. In the 16th century, Polish scientist Nicolaus Copernicus suggested that Earth and the other planets in the solar system in fact orbited the sun, creating a profound shift in the understanding of the cosmos, according to The Royal Society. In the late 17th century, Isaac Newton calculated how the forces between planets — specifically the gravitational forces — interacted.

The dawn of the 20th century brought further insights into comprehending the vast universe. Albert Einstein proposed the unification of space and time in his General Theory of Relativity. In the early 1900s, scientists were debating whether the Milky Way contained the whole universe within its span, or whether it was simply one of many collections of stars.

Edwin Hubble calculated the distance to a fuzzy nebulous object in the sky and determined that it lay outside of the Milky Way, proving our galaxy to be a small drop in the enormous universe, according to Scientific American(opens in new tab). Using General Relativity to lay the framework, Hubble measured other galaxies and determined that they were rushing away from the us, leading him to conclude that the universe was not static but expanding.

In recent decades, cosmologist Stephen Hawking determined that the universe itself is not infinite but has a definite size. However, it lacks a definite boundary. This is similar to Earth; although the planet is finite, a person traveling around it would never find the "end" but would instead constantly circle the globe. Hawking also proposed that the universe would not continue on forever but would eventually end.

Launched in November 1989, NASA's Cosmic Background Explorer(opens in new tab) (COBE) took precise measurements of radiation across the sky. The mission operated until 1993.

Although NASA's Hubble Space Telescope is probably best known for its astounding images, a primary mission(opens in new tab) was cosmological. By more accurately measuring the distances to Cepheid variables, stars with a well-defined ratio between their brightness and their pulsations, Hubble helped to refine measurements regarding how the universe is expanding. Since its launch, astronomers have continued to use Hubble to make cosmological measurements and refine existing ones.

Thanks to Hubble, "If you put in a box all the ways that dark energy might differ from the cosmological constant, that box would now be three times smaller," cosmologist Adam Riess of the Space Telescope Science Institute said in a statement(opens in new tab). "That's progress, but we still have a long way to go to pin down the nature of dark energy."

NASA's Wilkinson Microwave Anisotropy Probe (WMAP) was a spacecraft that operated from 2001 to 2010. WMAP mapped tiny fluctuations in the cosmic microwave background (CMB), the ancient light from the early universe, and determined that ordinary atoms make up only 4.6 percent of the universe, while dark matter makes up 24 percent.

"Lingering doubts about the existence of dark energy and the composition of the universe dissolved when the WMAP satellite took the most detailed picture ever of the cosmic microwave background," said cosmologist Charles Seife in the journal Science

The European Space Agency's Planck space mission ran from 2009 to 2013 and continued the study of the cosmic microwave background.

ESA is currently developing the Euclid mission, which should launch in 2023, according to ESA's fact sheet(opens in new tab). Euclid will study dark matter and dark energy with greater precision, tracing its distribution and evolution through the universe.

"At the heart of the mission is one of the billion pound questions of physics," the ESA's David Parker said in a statement.

Details

Cosmology is the field of study that brings together the natural sciences, particularly astronomy and physics, in a joint effort to understand the physical universe as a unified whole.

If one looks up on a clear night, one will see that the sky is full of stars. During the summer months in the Northern Hemisphere, a faint band of light stretches from horizon to horizon, a swath of pale white cutting across a background of deepest black. For the early Egyptians, this was the heavenly Nile, flowing through the land of the dead ruled by Osiris. The ancient Greeks likened it to a river of milk. Astronomers now know that the band is actually composed of countless stars in a flattened disk seen edge on. The stars are so close to one another along the line of sight that the unaided eye has difficulty discerning the individual members. Through a large telescope, astronomers find myriads of like systems sprinkled throughout the depths of space. They call such vast collections of stars galaxies, after the Greek word for milk, and call the local galaxy to which the Sun belongs the Milky Way Galaxy or simply the Galaxy.

The Sun is a star around which Earth and the other planets revolve, and by extension every visible star in the sky is a sun in its own right. Some stars are intrinsically brighter than the Sun; others, fainter. Much less light is received from the stars than from the Sun because the stars are all much farther away. Indeed, they appear densely packed in the Milky Way only because there are so many of them. The actual separations of the stars are enormous, so large that it is conventional to measure their distances in units of how far light can travel in a given amount of time. The speed of light (in a vacuum) equals 3 × {10}^{10} cm/sec (centimetres per second); at such a speed, it is possible to circle the Earth seven times in a single second. Thus in terrestrial terms the Sun, which lies 500 light-seconds from the Earth, is very far away; however, even the next closest star, Proxima Centauri, at a distance of 4.3 light-years (4.1 × {10}^{18} cm), is 270,000 times farther yet. The stars that lie on the opposite side of the Milky Way from the Sun have distances that are on the order of 100,000 light-years, which is the typical diameter of a large spiral galaxy.

If the kingdom of the stars seems vast, the realm of the galaxies is larger still. The nearest galaxies to the Milky Way system are the Large and Small Magellanic Clouds, two irregular satellites of the Galaxy visible to the naked eye in the Southern Hemisphere. The Magellanic Clouds are relatively small (containing roughly 109 stars) compared to the Galaxy (with some {10}^{11} stars), and they lie at a distance of about 200,000 light-years. The nearest large galaxy comparable to the Galaxy is the Andromeda Galaxy (also called M31 because it was the 31st entry in a catalog of astronomical objects compiled by the French astronomer Charles Messier in 1781), and it lies at a distance of about 2,000,000 light-years. The Magellanic Clouds, the Andromeda Galaxy, and the Milky Way system all are part of an aggregation of two dozen or so neighbouring galaxies known as the Local Group. The Galaxy and M31 are the largest members of this group.

The Galaxy and M31 are both spiral galaxies, and they are among the brighter and more massive of all spiral galaxies. The most luminous and brightest galaxies, however, are not spirals but rather supergiant ellipticals (also called cD galaxies by astronomers for historical reasons that are not particularly illuminating). Elliptical galaxies have roundish shapes rather than the flattened distributions that characterize spiral galaxies, and they tend to occur in rich clusters (those containing thousands of members) rather than in the loose groups favoured by spirals. The brightest member galaxies of rich clusters have been detected at distances exceeding several thousand million light-years from the Earth. The branch of learning that deals with phenomena at the scale of many millions of light-years is called cosmology—a term derived from combining two Greek words, kosmos, meaning “order,” “harmony,” and “the world,” and logos, signifying “word” or “discourse.” Cosmology is, in effect, the study of the universe at large.

Additional Information

Cosmology (from Ancient Greek (kósmos) 'world', and 'study of') is a branch of physics and metaphysics dealing with the nature of the universe. The term cosmology was first used in English in 1656 in Thomas Blount's Glossographia, and in 1731 taken up in Latin by German philosopher Christian Wolff, in Cosmologia Generalis. Religious or mythological cosmology is a body of beliefs based on mythological, religious, and esoteric literature and traditions of creation myths and eschatology. In the science of astronomy, cosmology is concerned with the study of the chronology of the universe.

Physical cosmology is the study of the observable universe's origin, its large-scale structures and dynamics, and the ultimate fate of the universe, including the laws of science that govern these areas. It is investigated by scientists, including astronomers and physicists, as well as philosophers, such as metaphysicians, philosophers of physics, and philosophers of space and time. Because of this shared scope with philosophy, theories in physical cosmology may include both scientific and non-scientific propositions and may depend upon assumptions that cannot be tested. Physical cosmology is a sub-branch of astronomy that is concerned with the universe as a whole. Modern physical cosmology is dominated by the Big Bang Theory which attempts to bring together observational astronomy and particle physics; more specifically, a standard parameterization of the Big Bang with dark matter and dark energy, known as the Lambda-CDM model.

Theoretical astrophysicist David N. Spergel has described cosmology as a "historical science" because "when we look out in space, we look back in time" due to the finite nature of the speed of light.

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