Cosmology

Cosmologyis a branch of astronomy and of metaphysics committed to the study of the universe as a whole, of the contents, structure, and evolution of the universe from the beginning of time to the future.

As a branch of two very old endeavours of humanity, the study of the sky and the origins of the world, it embraces numerous related inquiries concerned with the world we live in and, to the extent it could be imagined and observed, the universe. As a branch of metaphysics it attained some prominence when Christian von Wolffe published Discursus Praeliminaris de Philosophia in Genere (1728). Von Wolff placed cosmology in his classification scheme of the main areas of philosophy, distinguishing cosmology from ontology, theology and psychology, essentially making it a distinctive field of philosophy unto itself. As a philosphy, its nature has been disputed over time since von Wolff but it can be said that generally, it is thought to encompass humanity's experience in, and the nature of, the physical world. As a science, it encompasses the work of observational astronomy and theoretical physics as scholars in both fields attempt to describe and explain the physical universe. Cosmology, as a science, attempts to construct models of the physical universe from observational data which are then tested. Cosmology, as metaphysics, involves a priori investigations of a rational cosmology and the conceptual and categorical analyses of the speculative philosopher.

Ancient cosmology

Any attempt to understand cosmology, or simply what humanity thought about the universe whenever that might have occurred to them prior to the last few millennium would be largely guess work. Their understanding would have been inextricably interwoven with their impressions and their imagination. Impressions would have been made in a facile manner, what ever they could see where ever they were, their immediate circumstance, their fears and attempts at explaining the mysterious, all would have come together in a variety of concepts about the nature of the universe.

What we consider cosmology today, if we are addressing explanations from observations and precise measurements that can be duplicated--the scientific approach--or at least its basic and most primitive roots, it would have been fraught with almost anything but what we consider scientific. Simple deduction about how fire is made and food accessed and shelter constructed would have been within the reach of prehistoric and ancient humanity, but how close they came to an understanding, no matter how fragmented or trivial, of the universe as we know it today, is simply beyond us to ever know. That they observed that things seemed to be regular and predictable is evident from stone circles and other constructions that indicated they knew the sun would strike a certain point on the ground at a certain time every year, the moon would change appearance on a regular basis--any number of possible conclusions could be reached about these clues that have been left. Burial customs going back as far as the last twenty millennium might indicate a belief in the after life, possibly an eternal existence—but that too is reaching and can not be safely concluded.

Since prehistoric people left only fragments of their impressions in relics and documents and instruments of most ancient sources have long since disappeared, prehistoric and ancient humanity's understanding will always be a fragmented picture to us today. In fact, if the definition of cosmology would be constructed around what it was meant to achieve, if it was meant to explain things, it would not necessarily follow that those explanations would be tested as we expect scientific theories to be tested today. The result of such explanations would be extraordinary people, monsters, places and events which would not be verifiable, such as monsters at the edge of the world as mariners sometimes believed as late as the 15th century.

Creation stories

Creation stories represent some of the earliest attempts to explain the origins of the world.

Mesopotamia

The Babylonian vision of the universe describes a world of fresh water, oceans and mists. It was featureless otherwise without solid land. Each had a god, Apsu, Tiamat and Mummu repectively and these gods eventually begat other gods who begat other gods and so forth. Eventually the god Ea, the cleverest, came forth and became the most powerful ruling over all the other gods. As the population of gods increased Apsu grew tired of the other gods and plotted to slay their off spring. However, Ea beat him to it, killed him and built a palace on the fresh waters and with another god fathered Marmaduke or Marduk, a giant who became the god of rain and storms. Ea’s crime did not go unpunished and Tiamat raised up an army of monsters which was more than Ea could withstand so he called forth Marmaduke to fight. Marmaduke agreed, with the condition that upon winning he would assume absolute power over all the other gods. His condition was met and he prevailed over Tiamat’s host. After the ensuing carnage, Marmaduke took the body of Tiamat and used half for the sky and the other half for land. One of the defeated gods was later slain and his body was used to create humans.

The themes of wars between supernatural beings, a world with few features, employing the bodies of gods slain in battle or dead by other means to create additional features of the world are very common. As such there is no attempt to correlate the explanation with precise measurements, duplicated results, nothing even vaguely scientific. It was a world of imagination and evidently remained that way for millennium.

China

The Chinese creation myth from an anthology, The Classic of Mountains and Seas, collected in the first century B.C., contains some details vaguely reminiscent of how modern cosmology views the beginning of the universe today. At the beginning, heaven and earth were not separate and contained in an egg-shaped cloud wherein all matter existed in chaos. The giant Pan Gu, grew in the chaos, sleeping and developing for 18,000 years. When he awoke and stretched, the egg broke releasing the matter of the universe. The lighter purer elements rose to make the sky and heavens, and the heavier impure elements settled to make the earth. Pan Gu lived another 18,000 years holding the sky and the earth separate to a distance of 30,000 miles. When Pan Gu died his body became parts of the world: His arms and legs became the four directions and the mountains; his blood became the rivers; his sweat, the rain and dew.; his voice, the thunder; his breath, the winds; his hair, the grass; his veins, the roads and paths; teeth and bones, the minerals and rocks; his flesh became the soil; his left eye the sun, and his right the moon.

Sometime later a goddess named Nü Wa comes into the picture, and being lonely she made humans out of mud. Seeing that humans would not live forever, she divided them into male and female so they could procreate. Her first creations made by hand were the rulers and aristocrats, others she made from mud slung from a vine become the common folk.

Eventually there was some kind of geological upheaval and the heavens collapsed creating holes in the sky and a deluge ensued, then the earth cracked from which poured fire. Beasts appeared in the forests and attacked humans. She drove the beasts away, placed river stones to patch the holes in the sky and put a turtle in place to hold the earth and sky separate. She used molten rock to fill the holes in the earth. Upon her death, her body became more parts of the world

Many creation stories contain a vision of the universe as formless or without land and other features. People are often made from the soil itself.

Physical Cosmology

"ALL men by nature desire to know.

(Aristotle Metaphysics, 350 B.C. )

At various points throughout history, there is evidence of the attempt to provide a meaningful explanation of the origin of the physical world that corresponds to both observation and description of the physical world by measuring it and idea that the explanation should predict what will happen next. Early attempts at discerning such things as the shape of Earth, the cycles of the Moon, and the distance from Earth to other celestial bodies have been recorded and passed down to us. They indicate a move toward a more precise understanding of the cosmos and in some cases show a surpising degree of insight that is still respected today.

The first solid evidence of a cosmological model that would explain observations come to us from the Greeks of the 4th century B.C.. Babylonians in the 4th millennium B.C. were making accurate observations of the planets, the moon, the stars and the Sun and were providing reasonable predictions of their motions, but they did not leave us with a model to explain these motions as the Greeks did.

The Greeks over time developed a cosmological perspective that the stars were placed firmly and unchangingly in the sky in a sphere that rotated around the Earth every 24 hours. Likewise, the planets, the Sun and the Moon, everything not on the Earth moved in a zone of aether between the Earth and the stars.

This model had many contributors and some detractors, unfortunately the records of their thoughts and work are often fragmentary at best and some we know of only through the comments of others. By the second century, Ptolemy of Alexandria (he may have been Egyptian or he may have been Greek) set down a system to account for the motion of the planets and the Sun and the Moon and the stars around the Earth, a model that was based on perfect circles and epicycles to explain loops observed in planetary motions, loops that were actually retrograde motion caused by the motion of the Earth's movement around the Sun along with the other planets. It was a very complicated system and it stood for a long time. Its demise was posited by quite a number of people over the centuries, even before Ptolemy. but it was not seriously rejected until Galileo. Even the concept of aether lasted until the late 19th century when the Michelson-Morley Experiment failed to account for the aether wind.

Medieval cosmology

The Medieval period is generally cast as that time when the Roman Empire withdrew from the West and the coming of the Renaissance, a period of approximately 476 to 1453 A.D. In this period the work of Ptolemy held sway, the universe was geocentric, it moved about the Earth which was the center of the universe.

Renaissance cosmology

A number of things had to develop to firmly establish the field of physical cosmology as distinct from the traditional cosmologies embracing philosophical and religious perspectives: the development of scientific enquiry and methodology; the attitude that would compel people to challenge the status quo; the means to make more precise observations and reveal the vast extent of the universe; and the means to measure and analyse data to arrive at rational, mathematically derived models. Eventually astronomers took issue with the problems Ptolemy's model presented when compared with the data they gathered.

William Gilbert

One of the first, if not the first scientist, was a man named William Gilbert (1544-1603). Gilbert's world was infused with the mystical and the world had been seen through mystical perspectives long before Aristotle posited a "Prime Mover" to explain how the world was set in motion. Gilbert had the attitude, the drive to simply say, "Is that true?" and then test the idea to reveal its credibility. Galileo credited Gilbert as the first true scientist.

Georg Peurbach

Georg Peurbach (1423-1461) challeneged errors in astronomy texts that predated Ptolemy and wrote a new textbook and guide to Ptolemy’s Almagest. Peurbach's New Theory of the Planets (published 1454) addressed problems encountered in earlier models employing descriptive geometrics to predict planetary motions.

Johannes Regiomontanus

Johannes Regiomontanus (1436-1476), a student of Georg Peurbach, continued his work of observation and critique, improving translations of the ancient Greek works, and openly pointing out the discrepancies between observations and current astronomical theory.

Nicolaus Copernicus

Nicolaus Copernicus (1473-1543) established, at long last, the heliocentric theory putting the solar system in orbit around the sun and thereby resolving many of the problems that Ptolemy and others had striven to answer with increasingly complicated models of the universe.

Leonard Digges

Leonard Digges (1520-1559) invented the theodolite, the telescope, the reflecting telescope and possibly the refractive telescope providing cosmology with the means to an end--practical and precise observations to serve the theoretical.

Thomas Digges

Thomas Digges (1543-1595), son of Leonard, continued his work, attempted to resolve questions with observations with the telescope and posited the infinite universe.

Galileo Galilei

Galileo Galilei (1564-1642) supported the heliocentric model, employed practical observations with telescopes of his own construction, made precise measurements and first introduced concepts of inertia and relativity of motion.

Johannes Kepler

Johannes Kepler (1571-1630) was instrumental in marrying the best observational data of the time (that of Tycho Brahe) and the most plausible cosmological model of the time (that of Copernicus). Kepler abandoned the Aristotelian perfection of circular orbits and posited the elliptical, and resolved the problems of period and area of orbits.

Robert Hooke

Robert Hooke (1635-1703) posited some major theories and invented or improved practical apparatus that would enhance methods of analyses of cosmological phenomena.

He developed more accurate time keeping devices by inventing a spring control for the balance wheel in watches, enhancing the accuracy of measuring movement of celestial bodies as well as improving navigation. He was possibly the first to stress the need for resolving power and point out the advantages of using hair lines in place of silk or metal wire. He built the one of first reflecting telescopes, observed and described the rotation of Mars, was the first to infer the rotation of Jupiter, and described one of the earliest examples of a double star.

Hooke’s wave theory of light was an essential step forward in spectrum analysis.

Hooke was the first to propose that the motions of astronomical bodies were a matter of dynamics. He published, Attempt to Prove the Motion of the Earth (1674), in which he offered a theory of planetary motion. employing the correct principle of inertia and a balance between an outward centrifugal force and an inward gravitational attraction to the Sun. He proffered three principles of gravity in a lecture entitled “System of the World,” given in 1674

• . . .all Coelestial Bodies whatsoever have an attraction or gravitating power towards their own Centers, whereby they attract not only their own parts, and keep them flying from them . . . but they do also attract all the other Coelestial Bodies that are within the sphere of their activity
• . . . all bodies whatsoever that are put into a direct and simple motion, will continue to move forward in a straight line, till they are by some other effectual powers deflected and bent into a Motion describing a Circle, Ellipses, or some other more compounded Curve Line.
• In that same lecture, he also posited the strength of the attraction but wrongly suggested that gravity decreases inversely with distance from the object.

${\frac {1}{X}}$

where X is the distance

He later corrected this in 1679, in a letter to Newton in which he suggested that this attraction would vary inversely as the square of the distance from the Sun.

${\frac {1}{X^{2}}}$

where X is the distance

Hooke's theory was qualitatively correct. However he did not have the mathematical skills to provide exact and quantitative definition.

Modern Cosmology

A seminal project in the advancement of cosmology was COBE. With COBE, the extent and precision of the data gathered shifted the entire field of cosmology prompting the Nobel Foundation (Royal Swedish Academy of Sciences) to comment, "the COBE-project can also be regarded as the starting point for cosmology as a precision science: For the first time cosmological calculations (like those concerning the relationship between dark matter and ordinary, visible matter) could be compared with data from real measurements. This makes modern cosmology a true science (rather than a kind of philosophical speculation, like earlier cosmology)."

Leading theoretical focus

The Big Bang

The Big Bang, a label bestowed derisively by its leading critic, Fred Hoyle in the early part of the 20th century, is basically a theory of the universe with a beginning, and possibly an end. Until the Big Bang, cosmology was established on an immutable, everlasting and unchanging universe, the Aristotelian model.

Until Georges Lemaître, the idea of a beginning was hotly rejected, even by those whose evidence best supported this theory, people such as Einstein and Hubble.

In essence the Big Bang is about a moment--an extremely short moment--wherein all the matter and energy of the universe is condensed into a space smaller than the subatomic components of an atom, and then are released in a sudden moment. The problem with this model of the cosmos is that prior to the moment of the Big Bang, it is not possible to actually investigate what happened, to scientifically research the nature of things, a problem that nearly lead Einstein to ultimately reject this theory.