What is Cosmology? Cosmology Definition, Terms, Facts & Theories

Cosmology Definition, New terms, Facts & Theories


Introduction to Cosmology

Cosmology is the study of the origin, evolution, and structure of the universe. 

This science grew out of simple observations and evolved along with mathematical theories, technological advances and space exploration.

Below is an attempt to describe the universe by one Arthur Dent (i.e., someone certified scientifically declined in space matters).

Okay…the present universe is a bunch of ashes, dust, and bits leftover from a phenomenally big bang.

The universe is mainly made up of dark matter and exotic particles that cannot be observed. (Sounds very feminine to me.)

It is dotted with black holes, which suck in streams of dying stars. (Sounds like a corporation I once worked for.)

It is threaded by cosmic strings, which are tears in the fabric of space itself. (I had a pair of jeans like that once.)

Some cosmologists will have us believe the universe’s future is grim: it’s either going to end in a big crunch and collapse into a universal black hole or expand and decay into the nothingness of eternal night.

How long has Man studied cosmology?

What were early cosmologists hoping to find?

How did cosmology begin to understand the universe accurately?

What difference did the invention of the telescope make to cosmology?

How did Newton and his ‘falling apple’ observation advance cosmology?

How did the discovery of Uranus further cosmology?

Who is the father of modern cosmology, relatively speaking?

What does cosmology say about the creation of the universe?

So, what’s new in cosmology terms?

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How long has man studied cosmology?

From about 2200 B.C to about A.D, 1200 ancient astronomers put forward notions of the universe. Observations were recorded from Babylon, China, Greece, Italy, India and Egypt – all without the assistance of sophisticated instruments.

When asked to name a philosopher and astronomer, Aristotle (384-322 B.C) is usually first to spring to mind for many. And if we don’t remember Aristotle from our school science lessons, we may recall him getting a less than savory mention in the lyrics of Monty Python’s Philosophers’ Drinking Song.

Plato, they say, could stick it away

Half a crate of whiskey every day.

Aristotle, Aristotle was a bugger for the bottle.

Hobbes was fond of his dram,

And René Descartes was a drunken fart.

‘I drink, therefore I am.’

Need I go on?

While Aristotle (384-322 B.C) is widely considered one of the world’s earliest and greatest philosophers, his teachings in the area of astronomy were far from correct. Thus, many historians feel that Aristotle’s theories, supported as they were by the Catholic Church, did more to hinder the understanding of the cosmos than to advance it.

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Aristotle wrote in his book, De caelo (On the Heavens) that the Earth sits at the center of a great celestial sphere made up of fifty-five successively smaller spheres. Each sphere carries a celestial body around the heavens in a perfectly circular motion around the rotating Earth. The closest sphere to the Earth contains the moon. The area below the moon’s sphere had five components: Earth, air, fire, water and the ‘quintessence,’ a transparent element from which the spheres are formed.

Aristotelian theories denominated scientific thought for nearly two thousand years.

Read more: Study of Galaxy, Stars and Constellations

What were early cosmologists hoping to find?

First up – determining the Earth’s place in the universe. Two competing theories vied for supremacy regarding this question.

The Geocentric model:

The Earth is at the center of the universe with other heavenly bodies revolving around it.

The Heliocentric model:

The Sun is at the center of the solar system with the Earth and other planets in orbit around it.

Aristarchus (260 B.C), proposed the heliocentric theory.

Ptolemney (100 A.D), suggested everything in the solar system revolves around the Earth. Ptolemney’s theory was more widely accepted and remained unchallenged for 1,300 years.

How did cosmology begin to understand the universe accurately?

In 1543 Polish astronomer Nicolas Copernicus published De Revolutionibus Orbium Coelestium (Revolution of Heavenly Spheres). His works drew mass attention to the heliocentric model of the universe.

A generation later, Danish astronomer, Tycho Brahe, and his successor, Johannes Kepler, offered proof supporting Copernicus’s model by carefully assessing the positions of planets.

In early 1600, Kepler announced his laws of planetary motion, demonstrating that the planets follow oval-shaped paths around the Sun.

What difference did the invention of the telescope make to cosmology?

The first astronomer to work with a telescope was an Iranian, Galileo Galilei.

Galileo revealed never-before-known details about the surface of the Sun and moon. He observed Jupiter’s moons and Saturn’s rings and discovered many stars too faint to be seen with the naked eye. Galileo’s observations gave strong support to the heliocentric concept of the universe. This position made him unpopular with church officials, and he was placed under house arrest for the last nine years of his life.

How did Newton and his falling apple advance cosmology?

Isaac Newton was born in 1642; Galileo died the same year. English born Newton introduced theories of gravity and mass, and explained how they are responsible for an apple’s falling to the ground, for the moon orbiting the Earth, and for the motion of the planets around the Sun.

How did the discovery of Uranus further cosmology?

In 1781, when English astronomer, William Herschel, discovered a new planet (Uranus), he also studied our galaxy (the Milky Way). He suggested that the universe contained other galaxies and other solar systems.

The early 1800s saw the discovery of asteroids, the first of these being Ceres, discovered by Father Guiseppe Piazzi. He was one of the many astronomers searching for a planet between Mars and Jupiter.

By the mid-1800s, Gustav Kirchhoff and Johann Doppler developed the technique of spectroscopy. This technique, a method of breaking downlight into components, made it possible for astronomers to determine the chemical composition of the Sun and other stars, and prove they were moving.

Who is the father of modern cosmology?

relatively speaking?

Arguably Albert Einstein. Why? 

In 1915 Einstein developed the general theory of relativity, which states that the speed of light is a constant and that the curvature of space and the passage of time are linked to gravity. He inserted a mathematical device known as a “cosmological constant” into his calculations to make them fit the concept of an unchanging universe.

In 1917, Dutch astronomer, Willem de Sitter (1872 -1934), discarded the cosmological constant and used the theory of relativity to show that the universe may always be expanding.

By 1920, American astronomer, Harlow Shapley, had calculated the size of the Milky Way galaxy and theorized the Sun was not at its center.

When American astronomer, Edwin Powell Hubble, discovered in 1920 that the spiral-shaped objects other astronomers had recorded seeing in the sky were other galaxies, he revolutionized the view of the universe.

At about the same time, Vesto Melvin Slipher discovered galaxies were expanding outward. Not only did he prove the universe was much bigger than first thought, but that it was still growing, thus confirming de Sitter’s theory.

What does cosmology say about the creation of the universe?

Have you heard of the Big Bang theory? What about the Steady State theory?

These are the two most popular modern theories about how the universe was created.

The Big Bang theory

In the 1920s, Georges Henri Lemaitre, a Belgian born astronomer and Jesuit priest, suggested that fifteen to twenty billion years ago, the universe came together with a big explosion. Almost immediately, gravity came into being, followed by atoms, stars, and galaxies. The solar system formed four and one-half billion years ago from a cloud of dust and gas.

The Steady State theory

By contrast, this theory suggests that all matter in the universe has been created continuously at a constant rate from the beginning of time. Structurally, the universe is the same as it has been forever.

By 1963, however, this theory had been discredited mainly due to the discovery of Quasars – very distant, bright, star-like objects. If the steady-state theory were correct, objects and matter would be distributed evenly throughout the universe, but quasars exist only in places far from the Earth.

So what’s new in cosmology terms?

While recent discoveries favor the Big Bang theory, today’s astronomers are continually revising their notions, especially about the size of the universe.

In 1991, astronomers making maps of the universe discovered that great “sheets” of galaxies in clusters and superclusters, fill areas hundreds of millions of light-years in diameter. Vast, empty spaces of darkness measuring up to four hundred light-years across, separate them.

Dark Matter

Astronomers assume that dark matter is a “cosmic glue” that keeps rapidly moving galaxies together and regulates the rate the universe expands at.

You cannot touch it or taste it, and, for the most part, you can’t see it; yet the dark matter is thought to make up 90 percent of the mass of the universe.

I recommend you check out some books if you seriously want to know more.

White Dwarf

Finally in 1996, after decades of hunting, astronomers announced that they had discovered the composition of about half the mysterious dark matter in our galaxy: white dwarfs

For a real mind spin and a sci-fi laugh, I recommend you watch Red Dwarf instead.

Cosmic string

In the television series, Star Trek: The Next Generation, the Starship Enterprise rescues two-dimensional people who have wandered too far from their home on a cosmic string. The Trekking cosmic string is portrayed as a long strand of matter in space with a phenomenal gravitational pull.

Astronomers’ cosmic string is similar to the fictional Trekkian version, but with two differences. First, the cosmic string is still a theoretical concept. Second, cosmic strings, if they do exist, are unable to support life.

Black holes

A black hole is a place where space and time meet and stretch out for infinity. In other words, the remains of a massive star that has used up its nuclear fuel and collapsed under the enormous gravitational force into a single point. Black holes are impossible to see, yet they may account for 90 percent of the universe’s content.

If the concept of a black hole has caught your imagination – for it indeed must be the strangest and most mysterious element of the cosmos – I recommend reading the two titles listed below, written by Steven Hawkins (1942)

Dying stars

Every star ends its life by collapsing to a small, dense, glowing object known as a white dwarf, or this was the theory put forward by British astronomer Arthur Stanley Eddington (1882 – 1944).

Indian-born American astronomer, Subrahmanyan Chandrasekhar, later amended Eddington’s theory by showing, through a series of calculations, that a more massive dying star would be crushed by its own gravity and become either a neutron star or a black hole.


The neutrino is an undetectable sub-atomic particle that has no electrical charge or mass. Yet neutrinos contain a sizable amount of energy and have the ability to penetrate and pass through any substance without interference.

American physicists Clyde L. Cowan Jr. and Frederick Reines first detected this tiny, elusive particle in 1956. They built a neutrino detector in a nuclear reactor at Savannah River, South Carolina.

Neutrinos are detected in a massive tank of water. When a neutrino enters the tank, it produces a tiny flash of blue light.

If you seriously need to know more about neutrinos >>>


Hands up who has seen Ghostbusters? While Hollywood used dramatic license to create gooey paranormals, plasma, in strict scientific terms, is not a solid, a liquid, or a gas. It is an entirely different state of matter. Plasma is made of ions (electrically charged atoms) and electrons. The particles within plasma appear to move at random and are affected by electric and magnetic fields.

Plasma charged particles spiral along the lines of a magnetic field, but cannot cross those lines. This creates an electric current, which carries along a magnetic field, effectively “freezing” them together.

(Just visualize the classic scene in Ghostbusters I where they cross-match the particle beams from their lasers to create a greater force to rid their clients of pesky paranormals.)

If you’re serious about plasma, check out these books.

If you’re curious about paranormal plasma, then this might be the book for you.


MACHOs are an acronym for “massive compact halo objects.” Besides sounding like the reason an angel would give God for turning up late for heavenly duties, the term is generic and encompasses black holes, giant planets, and brown dwarfs.

WIMPs is an acronym for “weakly interacting massive particles” and includes particles of elements that have minimal effect on ordinary matter. (Sounds like a grade school teacher I once had.)

You don’t seriously want a link for this, do you?

The Big Crunch

In simple terms, the big crunch is a consequence of the big bang. The theory suggests that very far in the future, the matter will reverse direction and crunch back to the single point at which it began. (Think of a bungee jump gone wrong.)

Astronomers who subscribe to this dim forecast believe that the fate of the universe is in the hands of a mysterious substance called dark matter (not, as previously stated, to be confused with anyone’s mother-in-law).

The Big Bore

It is so named because it has nothing exciting to forecast, except that all matter will continue to move away from all other matters, and the universe will expand forever.

What are the planets?

A planet is defined as a body that orbits the Sun (or another star) and produces no light of its own but reflects the light of the Sun or a star. Planets are grouped into three categories: the solid, terrestrial planets, the giant gaseous (also known as Jovian) planets, and Pluto. In recent years astronomers have speculated about the existence of 2 other planets in the solar system: Vulcan, between Mercury and the Sun, and Planet X, beyond Pluto.

What are moons?

If it’s a natural body that orbits a planet, then it is classed a moon. (Naturally, this excludes human-made satellites and nursery rhyme cows that jump over the moon.)

Seven of our solar system’s planets are accompanied on their journey around the Sun by moons, sixty-one in total. However, this number will probably change as new findings come to light, like the recent unconfirmed sighting of four additional moons around Saturn.

What are asteroids?

Asteroids are like feral chunks of rock in orbit around the Sun. They’re too small to be planets, yet they’re similar in many other ways. Astronomers often refer to them as minor plants for this reason.

The most widely accepted theory about the origin of asteroids is that they’re old pieces of matter left over from the Big Bang. They did not come together to form a planet for one reason, or another. Astronomers estimate one million asteroids exist in our solar system alone. Ceres is the largest of the asteroids measuring 584 miles (940) kilometers in diameter. The smallest asteroid is hardly more giant than a speck of dust.

What are comets?

Comets are made up of dust and rocky material mixed with frozen methane, ammonia, and water. If you’re thinking the ingredients sound similar to frozen confectionery, you’ll be pleased to know Astronomers refer to them as ‘dirty snowballs.’ For this reason, comets are perhaps the most unique members of the solar system. A comet speeds within an elongated orbit around the Sun. It consists of a nucleus, a head, and a gaseous tail. The tail is formed when some of the comet’s tail melts as it nears the Sun, and the resulting gas is pushed away by the solar wind.

Recommended Books:

1. Cosmology’s Century: An Inside History of Our Modern Understanding of the Universe

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2. The Little Book of Cosmology

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3. Cosmology for the Curious

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