From time immemorial mankind has been struggling with the problems that how this Universe has come into existence. How the harmony and order of the Universe has developed. Why the sun rises, where we have come from, where we go etc. and to resolve this curiosity, they had to increase their intellectual power. Philosophy and science are the result of this intellectual process. cosmology is the study of the structure of the universe as a whole. It means an understanding of the universe, reflection on, and account of it. It should explain the underlying structure or the embodiment and its purpose; how the cosmos came to appearance and an orderly form came up and to what extent
According to the Big Bang model, the universe expanded from an extremely dense and hot state and continues to expand today. A common and useful analogy explains that space itself is expanding, carrying galaxies with it, like raisins in a rising loaf of bread. General relativistic cosmologies, however, do not actually ascribe any physicality to space. Cosmological ideas are the basis of cultural thoughts of all religions. However it has been observed in every religion that no single account, based on scientific, and cosmological approach has been forwarded as to the origin and nature of Universe. It has been seen that more often, they have been contradicting in their approaches.
According to Modern Science, our Universe was born about 13-14 billion years ago. It got created with a Big bang, an incredible explosion of an unimaginable magnitude, a fiery explosion scattering mammoth amounts of matter and energy and debris from the big bang are the raw material for the birth of billions of stars and galaxies.
Physicists and cosmologists are close to proving that there is only one source behind the physical universe, what they call a unified-field of Physics. Underneath it is the interplay of an abstract substance called energy. Albert Einstein attempted to solve this puzzle, namely, if everything is normally made up of one single substance i.e. energy, does nature provide different types of fields for energy to work its magic Physicists now realize that these divisions of fields are nothing but different aspects of a single entity, the Unified Field.
The questions like, ???How old is our Universe Where have we come from??? have engaged astronomers across the world for millennia. Using the Hubble Space telescope an International team of astronomers recently deduced that the Universe is 13.7 billion years old. The Vedic faith believes that even the cosmos is not exempt from the cycle of birth, death and rebirth. Cosmic time scales are well beyond our imagination, but our ancients ventured to measure ???This nebulous concept??™.
According to the Vedas, a day and a night of Brahma (demigod of consciousness) is 8.64 billion years long. ???This??™ said Carl Sagan, the renowned scientist-writer, ???is longer than the age of the earth or the sun, and is a little more than half the time since big bang occurred???.
The big bang theory accepted by many scientists for decades, holds that the Universe was born some 14 billion years ago when an unimaginably small dense entity blew up sowing the seeds of every bit of matter and energy.
Soon after that first explosion the Universe expanded rapidly in a phenomenon which astronomers call inflation, and then continued to spread out at varying speeds, until the present day. According to the big bang theory, time begins but never ends, as the Universe will continue to expand.
The Vedic sages derived their insights into the nature of reality without benefit of sophisticated scientific instruments. They simply looked inside themselves, and discovered the secrets of the universe within their own physical beings and their consciousness. Their understanding of the world in terms of five great elements is at once simple and profound. Though this perspective is of ancient origin, the concepts are relevant to our current understanding of reality, and can even illuminate our understanding of Western scientific principles.
Vedic seers were absolutely scientific in their thinking. They perfectly understood the fact that our Universe is ???Ordered??™ and ???harmonious??™ not a chaotic or anarchic mass. Looking at Nature and its fantastic variety, we notice how everything is orderly and harmonious.
A century ago the creation of the universe was a concept that astronomers as rule ignored. The reason was the general acceptance of the idea that the universe existed in infinite time. Examining the Universe, scientists supposed that it was just a conglomeration of matter and imagined that it had no beginning. There was no moment of creation ??“ a moment when the universe and everything in it came into being.
This idea of ???eternal existence??™ fit in well with European notions stemming from the philosophy of materialism. This philosophy originally advanced in the world of the ancient Greeks, held that matter was the only thing that existed in the universe and the universe existed in infinite time and will exist endlessly. This philosophy survived in different forms during Roman times but in the later Roman Empire and middle ages, materialism went into decline as a result of the influence of the Catholic Church and Christian philosophy. It was after renaissance that materialism began to gain broad acceptance among European scholars and scientists, largely because of their devotion to ancient Greek philosophy.
The earliest attempts at explaining the origins of the universe were generally centered in religion. The gods were commonly assumed to have created the known world and the heavens above it. It was also a common belief that they were responsible for the movement of the stars and planets and other heavenly bodies. Ancient civilizations, Greek, Roman etc. and even more recent people had their creation stories, or myths. This notion was sufficient to satisfy their curiosity so far.
In the beginning the earth was assumed to be flat. At least it appeared so to its first observers, hunters and gatherers, and members of primitive civilizations. This assumption was the result of the people??™s ignorance of the fact that the earth??™s surface is in the shape of curvature. This assumption again generates corollary that the earth must end somewhere if it is not infinite. Infinite is a rather unfathomable conception and hence right down to the Middle Ages people were afraid of the possibility of falling off from the earth??™s boundaries. What lies beyond these boundaries was largely unknown and open to speculation. The starry heavens were a source of endless wonder and inspiration. People from all parts of the world created their own myths, inspired by the skies and the celestial bodies. These myths can be speculated as an attempt to explain their own place in the Universe. Six thousand years ago, the Sumerians believed that the earth was at the center of the cosmos. This belief was later accepted by the Babylonians and Greeks.
History tells us that it was the Greeks who first put forward the idea that our planet is a sphere. Around 340BC, the Greek philosopher Aristotle made a few good points in favour of this theory in ???On the Heavens??? such as he argued that one first sees the sails of a ship coming over the horizon and only later its hull, which indicates that the surface of the ocean is curved.
The influence of Aristotle was significant. Around 150 AD Claudius Ptolemaeus (Ptolemy) elaborated Aristotle??™s ideas into a complete cosmological model. Ptolemy assumed that perfect motion should be in circles, so the stars and planets, being heavenly objects, moved in circles. He thought that the earth was stationary at the centre of the Universe and that the sun, stars and all planets revolved round it in circular orbits. Hence the model is sometimes referred to as the geocentric system. Ptolemy was aware that the postulation of perfect circular orbits contradicted observations, since the planets motion, size and brightness varied with time. In order to account for the observed derivations he introduced the idea of epicycles, smaller circular orbits around the earth. This enabled astronomers to make reasonably accurate predictions about the movement of the celestial bodies, and consequently the Ptolemic model was a great success. The system was later adopted by the Christian church and became the dominant cosmology until the 16th century.
In 1514, the polish Astronomer Nicolaus Copernicus (1473 ??“ 1543) put forward an alternative model, referred to as the heliocentric system, in which the sun is at the centre of the Universe, and all planets, including earth, revolve around it. The further apart a planet is from the Sun, the longer it takes to complete a revolution. Unfortunately the Copernican system was not inherently simpler than the geocentric system and it did not immediately render more accurate calculations of the planet??™s motion. So the observational evidence of the time favoured the Ptolemic system.
There were other practical reasons why many astronomers of the time rejected the Copernican notion that the earth orbited the sun. Tycho Brahe (December 14, 1546 ??“ October 24, 1601), a Danish nobleman from the region of Scania (in modern-day Sweden), best known today the greatest astronomer of the sixteenth century, though in his lifetime he was also well known as an astrologer and alchemist offered a third alternative in the year 1599 in which he suggested that the various planets, with the exception of the earth, orbited the sun and the sun in turn orbited a stationary earth which was at the centre of the then known universe. He realized that if the earth was moving about the sun, then the relative positions of the stars should change as viewed from different parts of the earth??™s orbit. But there was no evidence of this shift, from different parts of the earth??™s orbit.
It was only with the aid of the newly invented telescope in the early seventeenth century (Around 1608) that Galileo, an Italian Scientist, could deal fatal blow to the notion that the earth was at the centre of the universe and the Ptolemic theory was discarded.
With the help of telescope Galileo Galilei (1564 ??“ 1642) discovered the four largest moons orbiting the planet Jupiter. The existence of these moons demonstrated beyond doubt that not all celestial bodies revolve around the earth. Galileo established the truth of the Copernican model which created a tremendous revolution in the world of thought. This discovery of Galileo infuriated the contemporary Church authority. Consequently Galileo struggled with church authorities during much of his time. He was placed on house arrest and forbidden to publish his theory.
In 1594, the German astronomer Johnnes Kepler (1571 -1630) once an assistant to Tycho Brahe, refined the heliocentric model in his work ???Mysterium Cosmographicum??™ (1596; ???Cosmographic Mystery???) by showing that planets move on elliptical rather than circular orbits and gave us the means for calculating their individual distance from the Sun. Kepler also prepared the idea of gravity by explaining that the sun exerts a force on planets that diminishes inversely with distance and causes them to move faster on their orbits, the closer they come to the sun. This theory finally allowed predictions that matched observations.
Kepler??™s model remained the accepted one till 17th century. In about 1687 an English Scientist Isaac Newton discovered the force of gravity and further refined Kepler??™s motion of the forces between celestial bodies. Newton postulated the law of universal gravitation that applied to all bodies, whether in space or on earth, and he supplied the mathematical foundation for it. According to Newton bodies attract each other proportionally with their size and inversely with the square of the distance between them. He went on to demonstrate that according to this law, planets move on elliptical orbits, as previously assumed by Kepler. Unfortunately one consequence of this theory is that the stars of the universe attract each other and thus must eventually collapse on to each other. Newton was not able to give a plausible explanation for this phenomenon.
To counter this paradox it was inferred that the universe is infinite in space, and thus contains an infinite number of evenly distributed stars, which would on the whole create a gravitational equilibrium. This assumption however would still imply instability. If the balance is disturbed in one region of space, the nearest stars collapse and the gravitational pull of the resulting more massive body draws the next cluster of stars. Clusters would collapse and eventually draw the entire universe. Today we know that this is not the case, because the universe is not static as Newton thought.
The question of whether the universe has boundaries in time and space has captivated the imagination of mankind. Some would say the universe has been existed eternally, while others would say that the universe was created and thus had a beginning in time and space. The second thesis immediately raises the question what exists beyond its temporal and spatial bounds. Could it be nothingness But then, what is nothingness, the absence of matter or the absence of space and time itself The German philosopher Immanuel Kant dealt intensively with this question. In his book ???Critique of Pure reason??™ he came to the conclusion that the question cannot be answered reliably within the limits of human knowledge.
Despite Kant??™s doubt thereto, it appears that modern astronomy has answered the above question. The universe we observe is finite. It has a beginning in space and time, and prior to this beginning the concept of space and time has no meaning, because space ??“time itself is a property of the universe.
It was only during the nineteenth century that the astronomer and mathematician Bessel finally measured the distance to the stars by parallax. The nearest star other than the sun turned out to be about 25 million.
Most of the stars we can see are contained in the Milky Way ??“ the bright band of stars that stretches across our night sky. Kant and others proposed that our Milk way was in fact a lens shaped ???island universe??? or galaxy, and that beyond our own Milky Way there must be other galaxies.
Besides stars and planets, astronomers have noticed fuzzy patches of light on the night sky, which they call nebulae. Some astronomers thought these could be distant galaxies. It was only in the 1920s that American astronomer Edwin Hubble established that some of these nebulae were indeed distant galaxies comparable in size to our Milky Way galaxy.
Edwin Hubble, the stalwart of Modern Physics, also made the remarkable discovery that these galaxies seemed to be moving away from us, with a speed proportional to their distance from us. In this connection his formula stands as follows:
Where V is the speed at which galaxy moves away from us, and d is its distance. The constant of proportionality H0 is now called the Hubble constant.
Hubble observed shifts in the spectra of light from different galaxies, which are proportional to distance from us. The farther away the galaxy, the more its spectrum is shifted towards the low (red) end of the spectrum, which is in some way comparable to the Doppler Effect. This red shift indicates recession of objects in space. Today there is convincing evidence for Hubble??™s observation. Projecting Galaxy trajectories backward in time means that they converge to high density state i.e. the initial fireball.
It was soon realized that this had a very natural explanation in terms of Einstein??™s recently discovered General theory of relativity:our universe is expanding ! This discovery marked the beginning of the modern age of cosmology.
In fact Einstein might have predicted that the universe is expanding after he first proposed his theory in 1915. Matter tends to fall together under gravity. So it was impossible to have static universe. However, Einstein realized he could introduce an arbitrary constant into his mathematical equations, which could balance the gravitational force and keep the galaxies apart. This became known as the cosmological constant. Afterwards it was discovered that the universe is actually expanding; Einstein declared that introducing the cosmological constant was the greatest blunder of his life!
The Russian Physicist Alexandra Friedman had realized in 1917 that Einstein??™s equations could describe an expanding universe. He produced computation showing that the universe had been born at one moment, about ten thousand million years ago in the past and the galaxies were still travelling away from us after that initial burst. All the matter, indeed the universe itself was created at just one instant. The Belgian Astronomer George Lemaitre was the first to recognize what Friedman work is meant. The British astronomer Fred Hoyle dismissively called it the Big bang and the name stuck. Hubble??™s discovery that the universe is expanding leads to the emergence of another model that if the universe is getting bigger as time advances, going back in time means that it is getting smaller, and if one goes back enough, everything would shrink and converge at a single point. The conclusion to be derived from this model was that at some time, all the matter in the universe was confined in a single point mass that had ???zero volume??™ because of its immense gravitational force. Lemaitre referred to this state of the universe as the primeval atom and assumed that it was self existing or self created. The model of the universe stemming from the proposal of Lemaitre as modified later by others is commonly called the big-bang universe. Our universe came into being as the result of the explosion of this point mass that had zero volume. This explosion has come to be called the ???The big bang??™ and its existence has repeatedly been confirmed by observational theory about the early development and current shape of the universe.
There was a rival model called steady state model advocated by Bondi, Gold and Hoyle developed to explain the expansion of the universe. This required the continuous creation of matter to produce new galaxies as the universe expanded, ensuring that the universe could be expanding but still unchanging in time.
For many years it seemed a purely academic point of view whether the universe was eternal and unchanging or had only existed for a finite length of time. But a decisive blow was dealt to the steady state model when in 1965 Arno Penzias and Robert Wilson discovered a cosmic microwave background radiation. This was interpreted as the faint afterglow of the intense radiation of a Hot big bang, which had been predicted by George Gamow in 1948 and later by Ralph Alpher and Robert Hermann back in 1950.
Following this earlier work by Gamow, Alpher and Herman in the 1940??™s, theorists calculated the relative abundances of the elements hydrogen and helium that might be produced in a hot big bang found it was in good agreement with the observations. When the abundance of other light elements was calculated these too were consistent with the values observed. Since the 1970??™s almost all cosmologists have come to accept the hot big bang model and have begun asking more specific, but still fundamental, questions about our universe. How did the galaxies and clusters of galaxies that we observe today form out of the primordial expansion What is most of the matter in the universe made of General theory of relativity tells us that matter curves space??“time. This raises another question what is the shape of the universe Is there a cosmological constant after all
We are only beginning to find answers to some of these questions. The cosmic microwave background radiation plays a key role as it gives a picture of the universe as it was only a hundred thousand years after the Big bang. It turns out to be remarkably uniform, that it was only in 1992 that NASA??™s cosmic background explorer satellite detected the first anisotropies in this background radiation. There is slight fluctuation in the temperature of the radiation, about one part in a hundred thousand, which may be the seeds from which galaxies formed. Since the early 1980s there has been an explosion of interest in the physics of the early universe. The detection of cosmic microwave background radiation has powerfully attracted the attention of the Physicists towards searching for the early state of the universe. New technology and satellite experiments such as the Hubble space telescope have brought us an ever improving picture of our universe, inspiring theorists to produce ever more daring models.
Throughout the twentieth century the researches on Modern physics about the origin of the universe have steadily accumulated evidences that the Universe had a beginning. This is based on the principles of Edwin Hubble who found the observational evidence for the Big bang theory of the universe prophesized by the Belgian scientist George Lemaitre, which strongly advocates that all matter in the Universe was compact in a single point mass due to its immense gravitational force that had zero volume and the Universe was created from that primeval atom.
Numerous texts are to be found in the Vedic texts, of extraordinary diversity and incomparable richness, which seek unworriedly to penetrate the mystery of the beginnings and to explain the immensity and the amazing harmony of the universe.
In Vedic texts the creation of the Universe is discussed from many angles and in scientific world scientists are also trying their best to explain the creation of the Universe from scientific point of view along with experimental evidences in respect of creation of the universe. In some cases it is found that science and philosophy converges and in some cases it is seen that science and philosophy going in parallel.
The Big Bang is the cosmological model of the universe that is best supported by all lines of scientific evidence and observation. The essential idea is that the universe has expanded from a primordial hot and dense initial condition at some finite time in the past and continues to expand to this day. The framework for the model relies on Albert Einsteins General Relativity as formulated by Alexander Friedmann. After Edwin Hubble discovered in 1929 that the distances to far away galaxies were generally proportional to their red shifts, this observation was taken to indicate that all very distant galaxies and clusters have an apparent velocity directly away from our vantage point. The farther away, the higher the apparent velocity. If the distance between galaxy clusters is increasing today, everything must have been closer together in the past. This idea has been considered in detail back in time to extreme densities and temperatures, and large particle accelerators have been built to experiment on and test such conditions, resulting in significant confirmation of the theory. But these accelerators can only probe so far into such high energy regimes. Without any evidence associated with the earliest instant of the expansion, the Big Bang theory cannot and does not provide any explanation for such an initial condition. The theory accurately explains the general evolution of the universe since that instant.
A major success of the theory is its ability to account for the comparative abundance of the elements we find around us, which if you look beyond Earth is mostly hydrogen and helium. The observed abundances of the light elements throughout the cosmos closely match the calculated predictions for the formation of these elements from nuclear processes in the rapidly expanding and cooling first minutes of the universe, as logically and quantitatively detailed according to Big Bang nucleosynthesis and well described in Steven Weinbergs classic The First Three Minutes.
The term Big Bang was apparently first coined by Fred Hoyle in a derisory statement seeking to belittle the credibility of the theory that he did not believe to be true. Ironically, Hoyle helped considerably in the effort to figure out the nuclear pathway for building certain heavier elements from lighter ones. At any rate, after the discovery of the cosmic microwave background in 1964, and especially when its collective frequencies sketched out a blackbody curve, most scientists were fairly convinced by the evidence that some Big Bang scenario must have occurred.
1.2 HISTORY OF THE BIG BANG THEORY
The history of the Big Bang theory began with the Big Bangs development from observations and theoretical considerations. Much of the theoretical work in cosmology now involves extensions and refinements to the basic Big Bang theory.
Prior to the 20th Century
In 1610, Johannes Kepler used the dark night sky to argue for a finite universe. Seventy-seven years later, Isaac Newton described large-scale motion throughout the universe. In 1791, Erasmus Darwin gave the first description of a universe that expanded and contracted in a cyclic manner.
Though not recognized as scientific by either the scientific community or the author himself, who wished his work to be considered a “prose poem”, Edgar Allan Poe proposed a system very similar to the Big Bang theory in his 1848 essay titled Eureka: A Prose Poem. He proposed a finite universe which begins as a single “primal particle”, which expands outwards from “divine volition”, a repulsive force which Poe described as one of the two forces which make up all matter in the universe??”repulsion and attraction (gravity). Matter spreads evenly throughout space, but begins to clump together due to gravity, forming stars and star systems. The material universe is then drawn back together by gravity, eventually returning to the Primal Particle stage in order to begin the process of repulsion and attraction once again.
Early 20th Century
Observationally, in the 1910s, Vesto Slipher and later Carl Wilhelm Wirtz determined that most spiral nebulae were receding from Earth. Slipher used spectroscopy to investigate the rotation periods of planets, the composition of planetary atmospheres, and was the first to observe the radial velocities of galaxies. Wirtz observed a systematic redshift of nebulae, which was difficult to interpret in terms of a cosmology in which the Universe is filled more or less uniformly with stars and nebulae. They werent aware of the cosmological implications, nor that the supposed nebulae were actually galaxies outside our own Milky Way.
Also in that decade, Albert Einsteins theory of general relativity was found to admit no static cosmological solutions, given the basic assumptions of cosmology described in the Big Bangs theoretical underpinnings. The universe was described by a metric tensor that was either expanding or shrinking, a result that Einstein himself considered wrong and he tried to fix by adding a cosmological constant. The first person to seriously apply general relativity to cosmology without the stabilizing cosmological constant was Alexander Friedmann. Friedmann discovered the expanding-universe solution to general relativity field equations in 1922. Friedmanns 1924 papers included “Uber die Moglichkeit einer Welt mit konstanter negativer Krummung des Raumes” (About the possibility of a world with constant negative curvature) which was published by the Brussels Academy of Sciences on the 7 January 1924. Friedmanns equations describe the Friedmann-Lemaitre-Robertson-Walker universe.
In 1927, the Belgian Catholic priest Georges Lemaitre made one of the first modern proposition of the occurrence the Big Bang theory for the origin of the universe, although he called it his “hypothesis of the primeval atom”. He based his theory, published between 1927 and 1933, on the work of Einstein, among others, as well as ancient cosmological-philosophical traditions. Einstein, however, believed in a steady-state model of the universe. Lemaitre independently derived the Friedmann-Lemaitre-Robertson-Walker equations and proposed, on the basis of the recession of spiral nebulae, that the universe began with the “explosion” of a “primeval atom”??”what was later called the Big Bang. Lemaitre took cosmic rays to be the remnants of the event, although it is now known that they originate within the local galaxy.
In 1929, Edwin Hubble provided an observational basis for Lemaitres theory. Hubble discovered that, relative to the Earth, the galaxies are receding in every direction at speeds directly proportional to their distance from the Earth. In 1929 Hubble and Milton Humason formulated the empirical Redshift Distance Law of galaxies, nowadays known as Hubbles law, which, once the redshift is interpreted as a measure of recession speed, is consistent with the solutions of Einstein??™s General Relativity Equations for a homogeneous, isotropic expanding space. This led to the concept of the expanding universe. The law states that the greater the distance between any two galaxies, the greater their relative speed of separation. This discovery later resulted in the formulation of the Big Bang theory.
Given the cosmological principle whereby the universe, when viewed on sufficiently large distance scales, has no preferred directions or preferred places, Hubbles law suggested that the universe was expanding. This idea allowed for two opposing possibilities. One was Lemaitres Big Bang theory, advocated and developed by George Gamow. The other possibility was Fred Hoyles steady state model in which new matter would be created as the galaxies moved away from each other. In this model, the universe is roughly the same at any point in time. It was actually Hoyle who coined the name of Lemaitres theory, referring to it sarcastically as “this big bang idea” during a radio broadcast on March 28, 1949, on the BBC Third Programme. Hoyle repeated the term in further broadcasts in early 1950, as part of a series of five lectures entitled The Nature of Things. The text of each lecture was published in The Listener a week after the broadcast, the first time that the term “big bang” appeared in print.
Late 20th Century
Comparison of the predictions of the standard Big Bang model with experimental measurements. The power spectrum of the cosmic microwave background radiation anisotropy is plotted in terms of the angular scale (or multipole moment) (top).
For a number of years the support for these theories was evenly divided. However, the observational evidence began to support the idea that the universe evolved from a hot dense state. The discovery of the cosmic microwave background radiation in 1965 , although, as Big Bang skeptics point out, this prediction was only qualitative, and failed to predict the actual temperature of the CMB. After some reformulation, the Big Bang has been regarded as the best theory of the origin and evolution of the cosmos. Before the late 1960s, many cosmologists thought the infinitely dense and physically paradoxical singularity at the starting time of Friedmanns cosmological model could be avoided by allowing for a universe which was contracting before entering the hot dense state and starting to expand again. This was formalized as Richard Tolmans oscillating universe. In the sixties, Stephen Hawking and others demonstrated that this idea was unworkable, and the singularity is an essential feature of the physics described by Einsteins gravity. This led the majority of cosmologists to accept the notion that the universe as currently described by the physics of general relativity has a finite age. However, due to a lack of a theory of quantum gravity, there is no way to say whether the singularity is an actual origin point for the universe or whether the physical processes that govern the regime cause the universe to be effectively eternal in character.
1.3 Future of the theory
Much of the current work in cosmology includes understanding how galaxies form in the context of the Big Bang, understanding what happened at the Big Bang, and reconciling observations with the basic theory. In the past there was much discussion as to whether the Big Bang would need to be completely abandoned as a description of the universe, but such proponents of non-standard cosmology have become fewer in number over the last few decades. Cosmologists continue to calculate many of the parameters of the Big Bang to a new level of precision and hypothesized an expansion of the universe appears to be accelerating.
Huge advances in Big Bang cosmology were made in the late 1990s and the early 21st century as a result of major advances in telescope technology in combination with large amounts of satellite data, such as that from COBE and the Hubble Space Telescope. In 2003, NASAs WMAP takes more detailed pictures of the universe by means of the cosmic microwave background radiation. The image can be interpreted to indicate that the universe is 13.7 billion years old (within one percent error) and that the Lambda-CDM model and the inflationary theory is correct. No other cosmological theory can yet explain such a wide range of parameters, from the ratio of the elemental abundances in the early Universe to the structure of the cosmic microwave background, the observed higher abundance of active galactic nuclei in the early Universe and the observed masses of clusters ofgalaxies.
1.4 Big bang theory assumptions
The Big Bang theory depends on two major assumptions: the universality of physical laws, and the Cosmological Principle. The cosmological principle states that on large scales the universe is homogeneous and isotropic.
These ideas were initially taken as postulates, but today there are efforts to test each of them. For example, the first assumption has been tested by observations showing that largest possible deviation of the fine structure constant over much of the age of the universe is of order 10?5. Also, General Relativity has passed stringent tests on the scale of the solar system and binary stars while extrapolation to cosmological scales has been validated by the empirical successes of various aspects of the Big Bang theory.
If the large-scale universe appears isotropic as viewed from Earth, the cosmological principle can be derived from the simpler Copernican Principle, which states that there is no preferred (or special) observer or vantage point. To this end, the cosmological principle has been confirmed to a level of 10?5 via observations of the CMB. The universe has been measured to be homogeneous on the largest scales at the 10% level.
1.4a. Physical law:-
A physical law or scientific law is a scientific generalization based on empirical observations of physical behavior (i.e. the law of nature ). Laws of nature are observable. Scientific laws are empirical, describing the observable laws. Empirical laws are typically conclusions based on repeated scientific experiments and simple observations, over many years, and which have become accepted universally within the scientific community. The production of a summary description of our environment in the form of such laws is a fundamental aim of science.
Laws of nature are distinct from religious and civil law, and should not be confused with the concept of natural law. Nor should physical law be confused with law of physics – the term physical law usually covers laws in other sciences (e.g. biology) as well.
Several general properties of physical laws have been identified (see Davies (1992) and Feynman (1965) as noted, although each of the characterizations are not necessarily original to them. Physical laws are:
??? True, at least within their regime of validity. By definition, there have never been repeatable contradicting observations.
??? Universal. They appear to apply everywhere in the universe. (Davies, 1992:82)
??? Simple. They are typically expressed in terms of a single mathematical equation. (Davies)
??? Absolute. Nothing in the universe appears to affect them. (Davies, 1992:82)
??? Stable. Unchanged since first discovered (although they may have been shown to be approximations of more accurate laws??”see “Laws as approximations” below),
??? Omnipotent. Everything in the universe apparently must comply with them (according to observations). (Davies, 1992:83)
??? Generally conservative of quantity. (Feynman, 1965:59)
??? Often expressions of existing homogeneities (symmetries) of space and time. (Feynman)
??? Typically theoretically reversible in time (if non-quantum), although time itself is irreversible. (Feynman)
Often those who understand the mathematics and concepts well enough to understand the essence of the physical laws also feel that they possess an inherent intellectual beauty. Many scientists state that they use intuition as a guide in developing hypotheses, since laws are reflection of symmetries and there is a connection between beauty and symmetry. However, this has not always been the case; Newton himself justified his belief in the asymmetry of the universe because his laws appeared to imply it.
Physical laws are distinguished from scientific theories by their simplicity. Scientific theories are generally more complex than laws; they have many component parts, and are more likely to be changed as the body of available experimental data and analysis develops. This is because a physical law is a summary observation of strictly empirical matters, whereas a theory is a model that accounts for the observation, explains it, relates it to other observations, and makes testable predictions based upon it. Simply stated, while a law notes that something happens, a theory explains why and how something happens.
1.4b. Cosmological Principle:-
The Cosmological Principle is a principle invoked in cosmology that, when applied, severely restricts the large variety of possible cosmological theories. It follows from the observation of the Universe on a large scale, and states that: On large spatial scales, the Universe is homogeneous and isotropic. Or simply put, the universe is the same everywhere on a large scale
The properties of homogeneity and isotropy assumed by the Cosmological Principle suggest that Earth is not at a preferred place (see the Copernican principle), and that at very large scales the Universe is smooth (i.e. not fractal).
One implication of the cosmological principle is that the largest discrete structures in the universe are in mechanical equilibrium. Homogeneity and isotropy of matter at the largest scales would suggest that the largest discrete structures are parts of a single indiscrete form, like the crumbs which make up the interior of a cake. At extreme cosmological distances, the property of mechanical equilibrium in surfaces lateral to the line of sight can be empirically tested; however, under the assumption of the cosmological principle, it cannot be detected parallel to the line of sight.
Observations of the cosmos reveal a higher density and lower metallicity in the population of galaxies at further distances with respect to Earth. To account for this scientists applying the cosmological principle suggest the unfalsifiable notion that a change in the population of galaxies along the line of sight translates into change of the homogeneous universe as a whole. Cosmologists agree that in accordance with observations of distant galaxies, a universe must be non-static if it follows the cosmological principle. To their benefit, a non-static universe is also implied, independent of these observations of distant galaxies, as the result of applying the cosmological principle to General Relativity.
1.5 Observational evidence:-
The earliest and most direct kinds of observational evidence are the Hubble-type expansion seen in the redshifts of galaxies, the detailed measurements of the cosmic microwave background, and the abundance of light elements (see Big Bang nucleosynthesis). These are sometimes called the three pillars of the big bang theory. Many other lines of evidence now support the picture, notably various properties of the large-scale structure of the cosmos which are predicted to occur due to gravitational growth of structure in the standard Big Bang theory.
1.5a. Hubbles law
Hubbles law is the statement in physical cosmology that the redshift in light coming from distant galaxies is proportional to their distance. The law was first formulated by Edwin Hubble and Milton Humason in 1929 after nearly a decade of observations. It is considered the first observational basis for the expanding space paradigm and today serves as one of the pieces of evidence most often cited in support of the Big Bang. The most recent calculation of the proportionality constant used 2003 data from the satellite WMAP combined with other astronomical data, and yielded a value of 70.1 ?± 1.3 (km/s)/Mpc. In August, 2006, a less precise figure was obtained independently using data from NASAs orbital Chandra X-ray Observatory: 77 (km/s)/Mpc or about 2.5?10?18 s?1 with an uncertainty of ?± 15%.
A decade before Hubble made his observations, a number of physicists and mathematicians had established a consistent theory of the relationship between space and time by using Einsteins field equations of general relativity. Applying the most general principles to the nature of the universe yielded a dynamic solution that conflicted with the then prevailing notion of a static universe.
In 1922, Alexander Friedmann derived his Friedmann equations from Einsteins field equations, showing that the universe might expand at a rate calculable by the equations. The parameter used by Friedmann is known today as the scale factor which can be considered as a scale invariant form of the proportionality constant of Hubbles Law. Georges Lemaitre independently found a similar solution in 1927. The Friedmann equations are derived by inserting the metric for a homogeneous and isotropic universe into Einsteins field equations for a fluid with a given density and pressure. This idea of an expanding spacetime would eventually lead to the Big Bang and Steady State theories of cosmology.
Shape of the universe
Before the advent of modern cosmology, there was considerable talk about the size and shape of the universe. In 1920, the famous Shapley-Curtis debate took place between Harlow Shapley and Heber D. Curtis over this issue. Shapley argued for a small universe the size of the Milky Way galaxy and Curtis argued that the universe was much larger. The issue was resolved in the coming decade with Hubbles improved observations.
Combining redshifts with distance measurements
Combining his measurements of galaxy distances with Vesto Sliphers measurements of the redshifts associated with the galaxies, Hubble discovered a rough proportionality of the objects distances. Though there was considerable scatter (now known to be caused by peculiar velocities), Hubble was able to plot a trend line from the 46 galaxies he studied and obtain a value for the Hubble constant of 500 km/s/Mpc (much higher than the currently accepted value due to errors in his distance calibrations). (See cosmic distance ladder for details.)
In 1958, the first good estimate of H0, 75 km/s/Mpc, was published by Allan Sandage, but it would be decades before a consensus was achieved.
The cosmological constant abandoned
After Hubbles discovery was published, Albert Einstein abandoned his work on the cosmological constant (which he had designed to allow for a static solution to his equations). He later termed this work his “greatest blunder” since the assumption of a static universe had prevented him from predicting the expanding universe. Einstein made a famous trip to Mount Wilson in 1931 to thank Hubble for providing the observational basis for modern cosmology.
The discovery of the linear relationship between redshift, interpreted as recessional velocity, and distance yields a straightforward mathematical expression for Hubbles Law as follows:
??? v is the recessional velocity, typically expressed in km/s.
??? H0 is Hubbles constant and corresponds to the value of H (often termed the Hubble parameter which is a value that is time dependent) in the Friedmann equations taken at the time of observation denoted by the subscript 0. This value is the same throughout the universe for a given comoving time.
??? D is the comoving proper distance from the galaxy to the observer, measured in megaparsecs (Mpc), in the 3-space defined by given cosmological time. (Recession velocity is just v = dD/dt).
Observability of parameters
Strictly speaking, neither v nor D in the formula are directly observable, because they are properties now of a galaxy, whereas our observations refer to the galaxy in the past, at the time that the light we currently see left it.
For relatively nearby galaxies (redshift z much less than unity), v and D will not have changed much, and v can be estimated using the formula v = zc where c is the speed of light. This gives the empirical relation found by Hubble.
For distant galaxies, v (or D) cannot be calculated from z without specifying a detailed model for how H changes with time. The redshift is not even directly related to the recession velocity at the time the light set out, but it does have a simple interpretation: (1+z) is the factor by which the universe has expanded while the photon was travelling towards the observer.
Expansion velocity vs relative velocity
In using Hubbles law to determine distances, only the velocity due to the expansion of the universe can be used. Since gravitationally interacting galaxies move relative to each other independent of the expansion of the universe, these relative velocities, called peculiar velocities, need to be accounted for in the application of Hubbles law.
The Finger of God effect is one result of this phenomenon discovered in 1938 by Benjamin Kenneally. In systems that are gravitationally bound, such as galaxies or our planetary system, the expansion of space is (more than) annihilated by the attractive force of gravity.
Idealized Hubbles Law
The mathematical derivation of an idealized Hubbles Law for a uniformly expanding universe is a fairly elementary theorem of geometry in 3-dimensional Cartesian/Newtonian coordinate space, which, considered as a metric space, is entirely homogeneous and isotropic (properties do not vary with location or direction). Simply stated the theorem is this:
Any two points which are moving away from the origin, each along straight lines and with speed proportional to distance from the origin, will be moving away from each other with a speed proportional to their distance apart.
In fact this applies to non-Cartesian spaces as long as they are locally homogeneous and isotropic; specifically to the negatively- and positively-curved spaces frequently considered as cosmological models (see shape of the universe).
The Ultimate fate and age of the universe
The ultimate fate of the universe and the age of the universe can both be determined by measuring the Hubble constant today and extrapolating with the observed value of the deceleration parameter, uniquely characterized by values of density parameters (?). A so-called “closed universe” (?>1) comes to an end in a Big Crunch and is considerably younger than its Hubble age. An “open universe” (??1) expands forever and has an age that is closer its Hubble age. For the accelerating universe that we inhabit, the age of the universe is coincidentally very close to the Hubble age.
The value of the Hubble parameter changes over time either increasing or decreasing depending on the sign of the so-called deceleration parameter q which is defined by
In a universe with a deceleration parameter equal to zero, it follows that H = 1/t, where t is the time since the Big Bang. A non-zero, time-dependent value of q simply requires integration of the Friedmann equations backwards from the present time to the time when the comoving horizon size was zero.
It was long thought that q was positive, indicating that the expansion is slowing down due to gravitational attraction. This would imply an age of the universe less than 1/H (which is about 14 billion years). For instance, a value for q of 1/2 (once favoured by most theorists) would give the age of the universe as 2/(3H). The discovery in 1998 that q is apparently negative means that the universe could actually be older than 1/H. In fact, estimates of the age of the universe are, by coincidence, very close to 1/H.
The expansion of space summarized by the Big Bang interpretation of Hubbles Law is relevant to the old conundrum known as Olbers paradox: if the universe were infinite, static, and filled with a uniform distribution of stars (notice that this also requires an infinite number of stars), then every line of sight in the sky would end on a star, and the sky would be as bright as the surface of a star. However, the night sky is largely dark. Since the 1600s, astronomers and other thinkers have proposed many possible ways to resolve this paradox, but the currently accepted resolution depends in part upon the Big Bang theory and in part upon the Hubble expansion. In a universe that exists for a finite amount of time, only the light of finitely many stars has had a chance to reach us yet, and the paradox is resolved. Additionally, in an expanding universe distant objects recede from us, which causes the light emanating from them to be redshifted and diminished in brightness. Although both effects contribute, the redshift is the less important of the two; remember the original paradox was couched in terms of a static universe.
Determining the Hubble constant
The value of the Hubble constant is estimated by measuring the redshift of distant galaxies and then determining the distances to the same galaxies (by some other method than Hubbles law). Uncertainties in the physical assumptions used to determine these distances have caused varying estimates of the Hubble constant. For most of the second half of the 20th century the value of H0 was estimated to be between 50 and 90 (km/s)/Mpc.
Disputes over Hubbles constant
The value of the Hubble constant was the topic of a long and rather bitter controversy between Gerard de Vaucouleurs who claimed the value was around 100 and Allan Sandage who claimed the value was near 50.
In 1996, a debate moderated by John Bahcall between Gustav Tammann and Sidney van den Bergh was held in similar fashion to the earlier Shapley-Curtis debate over these two competing values.
This difference was partially resolved with the introduction of the ?CDM model of the universe in the late 1990s.
The ?CDM model
With the ?CDM model observations of high-redshift clusters at X-ray and microwave wavelengths using the Sunyaev-Zeldovich effect, measurements of anisotropies in the cosmic microwave background radiation, and optical surveys all gave a value of around 70 for the constant.
Using Hubble space telescope data
In particular the Hubble Key Project (led by Dr. Wendy L. Freedman, Carnegie Observatories) gave the most accurate optical determination in May 2001 with its final estimate of 72?±8 (km/s)/Mpc, consistent with a measurement of H0 based upon Sunyaev-Zeldovich effect observations of many galaxy clusters having a similar accuracy.
Using WMAP data
The most precise cosmic microwave background radiation determinations were 71?±4 (km/s)/Mpc, by WMAP in 2003, and 70.4+1.5?1.6 (km/s)/Mpc, for measurements up to 2006. The five year release from WMAP in 2008 finds 71.9+2.6?2.7 (km/s)/Mpc.These values arise from fitting a combination of WMAP and other cosmological data to the simplest version of the ?CDM model. If the data is fitted with more general versions, H0 tends to be smaller and more uncertain: typically around 67?±4 (km/s)/Mpc although some models allow values near 63 (km/s)/Mpc.
Using Chandra X-ray Observatory data
In August 2006, using NASAs Chandra X-ray Observatory, a team from NASAs Marshall Space Flight Center (MSFC) found the Hubble constant to be 77 (km/s)/Mpc, with an uncertainty of about 15%. The consistency of the measurements from all these methods lends support to both the measured value of H0 and the ?CDM model.
Hubbles law has two possible explanations. Either we are at the center of an explosion of galaxies??”which is untenable given the Copernican Principle??”or the universe is uniformly expanding everywhere. This universal expansion was predicted from general relativity by Alexander Friedman in 1922 and Georges Lemaitre in 1927, well before Hubble made his 1929 analysis and observations, and it remains the cornerstone of the Big Bang theory as developed by Friedmann, Lemaitre, Robertson and Walker.
The theory requires the relation v = HD to hold at all times, where D is the proper distance, v = dD / dt, and v, H, and D all vary as the universe expands (hence we write H0 to denote the present-day Hubble “constant”). For distances much smaller than the size of the observable universe, the Hubble redshift can be thought of as the Doppler shift corresponding to the recession velocity v. However, the redshift is not a true Doppler shift, but rather the result of the expansion of the universe between the time the light was emitted and the time that it was detected.
That space is undergoing metric expansion is shown by direct observational evidence of the Cosmological Principle and the Copernican Principle, which together with Hubbles law have no other explanation. Astronomical redshifts are extremely isotropic and homogenous, supporting the Cosmological Principle that the universe looks the same in all directions, along with much other evidence. If the redshifts were the result of an explosion from a center distant from us, they would not be so similar in different directions.
Measurements of the effects of the cosmic microwave background radiation on the dynamics of distant astrophysical systems in 2000 proved the Copernican Principle, that the Earth is not in a central position, on a cosmological scale. Radiation from the Big Bang was demonstrably warmer at earlier times throughout the universe. Uniform cooling of the cosmic microwave background over billions of years is explainable only if the universe is experiencing a metric expansion, and excludes the possibility that we are near the unique center of an explosion.
1.5b. Cosmic microwave background radiation
In cosmology, the cosmic microwave background radiation (most often referred as acronyms as CMB but occasionally CMBR, CBR or MBR, also referred to as relic radiation) is a form of electromagnetic radiation discovered in 1965 that fills the entire universe. It has a thermal black body spectrum at a temperature of 2.725 kelvin. Thus the spectrum peaks in the microwave range at a frequency of 160.2 GHz, corresponding to a wavelength of 1.9 mm. Most cosmologists consider this radiation to be the best evidence for the Big Bang model of the universe.
The cosmic microwave background spectrum measured by the FIRAS instrument on the COBE satellite is the most precisely measured black body spectrum in nature. The data points and error bars on this graph are obscured by the theoretical curve.The cosmic microwave background is isotropic to roughly one part in 100,000: the root mean square variations are only 18 ?µK. The Far-Infrared Absolute Spectrophotometer (FIRAS) instrument on the NASA Cosmic Background Explorer (COBE) satellite has carefully measured the spectrum of the cosmic microwave background. FIRAS compared the CMB with a reference black body and no difference could be seen in their spectra. Any deviations from the black body form that might still remain undetected in the CMB spectrum over the wavelength range from 0.5 to 5 mm must have a weighted rms value of at most 50 parts per million (0.005%) of the CMB peak brightness. This made the CMB spectrum the most precisely measured black body spectrum in nature.
The cosmic microwave background, and its level of isotropy, are both predictions of Big Bang theory. In the theory, the early universe was made up of a hot plasma of photons, electrons and baryons. The photons were constantly interacting with the plasma through Thomson scattering. As the universe expanded, adiabatic cooling caused the plasma to cool until it became favourable for electrons to combine with protons and form hydrogen atoms. This happened at around 3,000 K or when the universe was approximately 379,000 years old (z=1088). At this point, the photons scattered off the now neutral atoms and began to travel freely through space. This process is called recombination or decoupling (referring to electrons combining with nuclei and to the decoupling of matter and radiation respectively).
The photons have continued cooling ever since; they have now reached 2.725 K and their temperature will continue to drop as long as the universe continues expanding. Accordingly, the radiation from the sky we measure today comes from a spherical surface, called the surface of last scattering. This represents the collection of points in space (currently around 46 billion light-years from the Earth??”see observable universe) at which the decoupling event happened long enough ago (less than 400,000 years after the Big Bang, 13.7 billion years ago) that the light from that part of space is just reaching observers.
The big bang theory suggests that the cosmic microwave background fills all of observable space, and that most of the radiation energy in the universe is in the cosmic microwave background, which makes up a fraction of roughly 5?10-5 of the total density of the universe.
Two of the greatest successes of the big bang theory are its prediction of its almost perfect black body spectrum and its detailed prediction of the anisotropies in the cosmic microwave background. The recent Wilkinson Microwave Anisotropy Probe has precisely measured these anisotropies over the whole sky down to angular scales of 0.2 degrees. These can be used to estimate the parameters of the standard Lambda-CDM model of the big bang. Some information, such as the shape of the Universe, can be obtained straightforwardly from the cosmic microwave background, while others, such as the Hubble constant, are not constrained and must be inferred from other measurements.
Relationship to the Big Bang
Measurements of the CMB have made the inflationary Big Bang theory the standard model of the earliest eras of the universe. The standard hot big bang model of the universe requires that the initial conditions for the universe are a Gaussian random field with a nearly scale invariant or Harrison-Zeldovich spectrum. This is, for example, a prediction of the cosmic inflation model. This means that the initial state of the universe is random, but in a clearly specified way in which the amplitude of the primeval inhomogeneities is 10-5. Therefore, meaningful statements about the inhomogeneities in the universe need to be statistical in nature. This leads to cosmic variance in which the uncertainties in the variance of the largest scale fluctuations observed in the universe are difficult to accurately compare to theory.
The cosmic microwave background radiation and the cosmological red shift are together regarded as the best available evidence for the Big Bang (BB) theory. The discovery of the CMB in the mid-1960s curtailed interest in alternatives such as the steady state theory. The CMB gives a snapshot of the Universe when, according to standard cosmology, the temperature dropped enough to allow electrons and protons to form hydrogen atoms, thus making the universe transparent to radiation. When it originated some 400,000 years after the Big Bang ??” this time period is generally known as the “time of last scattering” or the period of recombination or decoupling ??” the temperature of the Universe was about 3,000 K. This corresponds to an energy of about 0.25 eV, which is much less than the 13.6 eV ionization energy of hydrogen. Since then, the temperature of the radiation has dropped by a factor of roughly 1100 due to the expansion of the Universe. As the universe expands, the CMB photons are redshifted, making the radiations temperature inversely proportional to the Universes scale length. For details about the reasoning that the radiation is evidence for the Big Bang, see Cosmic background radiation of the Big Bang.The power spectrum of the cosmic microwave background radiation temperature anisotropy in terms of the angular scale (or multipole moment). The data shown come from the WMAP (2006), Acbar (2004) Boomerang (2005), CBI (2004) and VSA (2004) instruments.
Microwave background observations
Subsequent to the discovery of the CMB, hundreds of cosmic microwave background experiments have been conducted to measure and characterize the signatures of the radiation. The most famous experiment is probably the NASA Cosmic Background Explorer (COBE) satellite that orbited in 1989??“1996 and which detected and quantified the large scale anisotropies at the limit of its detection capabilities. Inspired by the initial COBE results of an extremely isotropic and homogeneous background, a series of ground- and balloon-based experiments quantified CMB anisotropies on smaller angular scales over the next decade. The primary goal of these experiments was to measure the angular scale of the first acoustic peak, for which COBE did not have sufficient resolution. These measurements were able to rule out cosmic strings as the leading theory of cosmic structure formation, and suggested cosmic inflation was the right theory. During the 1990s, the first peak was measured with increasing sensitivity and by 2000 the BOOMERanG experiment reported that the highest power fluctuations occur at scales of apporoximately one degree. Together with other cosmological data, these results implied that the geometry of the Universe is flat. A number of ground-based interferometers provided measurements of the fluctuations with higher accuracy over the next three years, including the Very Small Array, Degree Angular Scale Interferometer (DASI) and the Cosmic Background Imager (CBI). DASI made the first detection of the polarization of the CMB and the CBI provided the first E-mode polarization spectrum with compelling evidence that it is out of phase with the T-mode spectrum.
In June 2001, NASA launched a second CMB space mission, WMAP, to make much more precise measurements of the large scale anisotropies over the full sky. The first results from this mission, disclosed in 2003, were detailed measurements of the angular power spectrum to below degree scales, tightly constraining various cosmological parameters. The results are broadly consistent with those expected from cosmic inflation as well as various other competing theories, and are available in detail at NASAs data center for Cosmic Microwave Background (CMB) (see links below). Although WMAP provided very accurate measurements of the large angular-scale fluctuations in the CMB (structures about as large in the sky as the moon), it did not have the angular resolution to measure the smaller scale fluctuations which had been observed using previous ground-based interferometers.
A third space mission, the Planck Surveyor, is to be launched in 2008. Planck employs both HEMT radiometers as well as bolometer technology and will measure the CMB on smaller scales than WMAP. Unlike the previous two space missions, Planck is a collaboration between NASA and ESA (the European Space Agency). Its detectors got a trial run at the Antarctic Viper telescope as ACBAR (Arcminute Cosmology Bolometer Array Receiver) experiment ??“ which has produced the most precise measurements at small angular scales to date ??“ and at the Archeops balloon telescope. Additional ground-based instruments such as the South Pole Telescope in Antarctica and the proposed Clover Project, Atacama Cosmology Telescope and the QUIET telescope in Chile will provide additional data not available from satellite observations, possibly including the B-mode polarization.
VEDIC EXPOSITIONS ON CREATION OF THE UNIVERSE
The Vedic Seers present several cosmogonies in explaining the creation of the Universe. The Nasadiya hymns (RV.X.129) have discussed the objective aspect of the creation of the Universe.
In the beginning, things undoubtedly began but what about the beginning itself ???before??? the actual ???beginning??? The beginning is precisely the beginning, because it has no ???before,??? because it is itself begi