God and the Univers

God and the Universe.--To the superficial reader it may appear at first sight, that the theory of the Aether suggested in this work leaves no place in the Universe for the operations and existence of an Infinite and living Spirit, a God. It may be objected, that if all matter and all modes of motion find their physical origin in one common and primordial medium, the electromagnetic Aether, where is the necessity for the existence of an Eternal and Infinite Spirit?

At first sight there appears some force in the objection, but it loses its point when we come to view the Universe from the standpoint of spirit phenomena. The purpose of the writer in this work has been to deal with natural phenomena only, purely from the philosophical and scientific standpoint. Spirit phenomena (which is equally as real and obvious as natural phenomena) have no part or place in a work which deals with scientific facts and data, but demand and will receive in a future work equal consideration and philosophic treatment. A man must indeed be lacking in vision who cannot see behind all things the evidence of a richer and fuller truth than that which merely lies on the surface, or who fails to read and learn the greatest truth that circles the Universe in its ultimate unity, which indisputably points to the existence of an Eternal and ever-living Spirit, a God. I affirm that there is no scientific truth, even including the law of the conservation of matter and motion, which has been enunciated in this work, but what is reconcilable with the existence of an Eternal and Infinite Spirit; and although such a statement may seem a paradox, yet I am convinced that before many more years have passed, the reconciliation of natural with spiritual phenomena will be an accomplished fact. The fool to-day may say in his heart, there is no God, but ere long not only religion, but Science herself, shall expose his lack of wisdom and his folly.

Begin of the Univers

The noted scientific cosmologist, P. James E. Peebles, summed up the current state of this field by saying that at its heart is the solidly established big bang theory. But Peebles immediately cautioned, "That the universe is expanding and cooling is the essence of the big bang theory. You will notice I have said nothing about an "explosion" – the big bang theory describes how our universe is evolving, not how it began." To the big bang, he tells us, scientists are trying to add the theory of inflation, that is, that early in its life the universe expanded rapidly. There is also strong evidence that most of the mass of the universe cannot be accounted for by the things we see, but there must be some sort of unknown dark matter. Further, it appears that something, some dark energy or quintessence, is making the universe accelerate.

By 1929, however, the picture was changing. Edwin Hubble was discovering other galaxies, and found that the farther away they were, the more the light from them was shifted towards the red end of the spectrum, indicating that they were moving away and the universe was therefore expanding. And physicists like Alexander Friedmann and George Lemaître and others had uncovered Einstein’s apparent mistake. In 1965, two Bell Laboratory scientists, Arno Penzias and Robert Wilson, while trying to eliminate radio interference, discovered cosmic background microwave radiation left over from the big bang.
Now we are faced with a universe so big and so old that it defies our imaginations to grasp it. It appears to have begun 15 billion years ago. Our galaxy, alone, has some 100 billion stars, and it is just one of perhaps a 100 billion galaxies, and this immense universe is expanding at an ever increasing rate.

This is an awe-inspiring picture, but what does it say about the origin of the universe? Let’s imagine that the scientific cosmologists have been creating an ever more detailed and vivid movie of the structure and movement of the universe, and this film, when it is played backwards, makes the universe appear as if it is coming together and beginning in an intensely hot and dense state. But the real question is whether this movie takes us back to the absolute beginning, or very origin of the universe. It doesn’t appear to do so because the basic laws of nature, as described by Einstein’s relativity, break down as we approach this beginning. It is as if the film runs out and just before we reach the beginning we are dazzled with a blinding white light. And we are faced with the very difficult question: can science find a way to talk about the very beginning of the universe, or is this simply outside its scope?

About meteor

Can there be any one upon the Earth who has not been struck by the phosphorescent lights that glide through the somber night, leaving a brilliant silver or golden track—the luminous, ephemeral trail of a meteor?

Sometimes, when Night has silently spread the immensity of her wings above the weary Earth, a shining speck is seen to detach itself in the shades of evening from the starry vault, shooting lightly through the constellations to lose itself in the infinitude of space.

These bewitching sparks attract our eyes and chain our senses. Fascinating celestial fireflies, their dainty flames dart in every direction through space, sowing the fine dust of their gilded wings upon the fields of Heaven. They are born to die; their life is only a breath; yet the impression which they make upon the imagination of mortals is of the profoundest.

The young girl dreaming in the delicious tranquility of the transparent night smiles at this charming sister in the Heavens . What can not this adorable star announce to the tender and loving heart? Is it the shy messenger of the happiness so long desired? Its unpremeditated appearance fills the soul with a ray of hope and makes it tremble. It is a golden beam that glides into the heart, expanding it in the thrills of a sudden and ephemeral pleasure.... The radiant meteor seems to quit the velvet of the deep blue sky to respond to the appeal of the imploring voice that seeks its succor.

What secrets has it not surprised! And who bears malice against it? It is the friend of the betrothed who invoke its passage to confide their wishes, and associate it with their dreams. Tradition holds that if a wish be formulated during the visible passage of a meteor it will certainly be fulfilled before the year is out. Between ourselves, however, this is but a surviving figment of the ancestral imagination, for this celestial jewel takes no such active part in the doings of Humanity.... Besides, try to express a wish distinctly in a second.

It is a curious fact that while comets have so often spread terror on the Earth, shooting stars should on the contrary have been regarded with benevolent feelings at all times. And what is a shooting star? These dainty excursionists from the celestial shores are not, as is supposed, true stars. They are atoms, nothings, minute fragments deriving in general from the disintegration of comets. They come to us from a vast distance, from millions on millions of miles, and circle in swarms around the Sun, following a very elongated ellipse which closely resembles that of the cometary orbit. Their flight is extremely rapid, reaching sometimes more than 40 kilometers (25 miles) per second, a cometary speed that is, as we have seen, greatly above that of our terrestrial vehicle, which amounts to 29 to 30 kilometers (about 19 miles).

These little corpuscles are not intrinsically luminous; but when the orbit of a swarm of meteors crosses our planet, a violent shock arises, the speed of which may be as great as 72 kilometers (45 miles) in the first second if we meet the star shower directly; the average rate, however, does not exceed 30 to 40 kilometers (19 to 25 miles), for these meteors nearly always cross our path obliquely. The height at which they arrive is usually 110 kilometers (68 miles), and 80 kilometers (50 miles) at the moment of disappearance of the meteor; but shooting stars have been observed at 300 kilometers (186 miles).

The friction caused by this collision high up in the atmosphere transforms the motion into heat. The molecules incandescence, and burn like true stars with a brilliancy that is often magnificent.

But their glory is of short duration. The excessive heat resulting from the shock consumes the poor firefly; its remains evaporate, and drop slowly to the Earth, where they are deposited on the surface of the soil in a sort of ferruginous dust mixed with carbon and nickel. Some one hundred and forty-six milliards of them reach us annually, as seen by the unaided eye, and many more in the telescope; the effect of these showers of meteoric matter is an insensible increase in the mass of our globe, a slight lessening of its rotary motion, and the acceleration of the lunar movements of revolution.

Although the appearance of shooting stars is a common enough phenomenon, visible every night of the year, there are certain times when they arrive in swarms, from different quarters of the sky. The most remarkable dates in this connection are the night of August 10th and the morning of November 14th. Every one knows the shooting stars of August 10th, because they arrive in the fine warm summer evenings so favorable to general contemplation of the Heavens. The phenomenon lasts till the 12th, and even beyond, but the maximum is on the 10th. When the sky is very clear, and there is no moon, hundreds of shooting stars can be counted on those three nights, sometimes thousands. They all seem to come from the same quarter of the Heavens, which is called the radiant, and is situated for the August swarm in the constellation of Perseus, whence they have received the name of Perseids. Our forefathers also called them the tears of St. Lawrence, because the feast of that saint is on the same date. These shooting stars describe a very elongated ellipse, and their orbit has been identified with that of the Great Comet of 1862.

The shower of incandescent asteroids on November 14th is often much more abundant than the preceding. In 1799, 1833, and 1866, the meteors were so numerous that they were described as showers of rain, especially on the first two dates. For several hours the sky was furrowed with falling stars. An English mariner, Andrew Ellicot, who made the drawing we reproduce , described the phenomenon as stupendous and alarming (November 12, 1799, 3 A.M.). The same occurred on November 13, 1833. The meteors that scarred the Heavens on that night were reckoned at 240,000. These shooting stars received the name of Leonids, because their radiant is situated in the constellation of the Lion.
This swarm follows the same orbit as the comet of 1866, which travels as far as Uranus, and comes back to the vicinity of the Sun every thirty-three years. Hence we were entitled to expect another splendid apparition in 1899, but the expectations of the astronomers were disappointed. All the preparations for the appropriate reception of these celestial visitors failed to bring about the desired result. The notes made in observatories, or in balloons, admitted of the registration of only a very small number of meteors. The maximum was thirteen. During that night, some 200 shooting stars were counted. There were more in 1900, 1901, and, above all, in 1902. This swarm has become displaced.

The night of November 27th again is visited by a number of shooting stars that are the disaggregated remains of the Comet of Biela. This comet, discovered by Biela in 1827, accomplished its revolution in six and a half years, and down to 1846 it responded punctually to the astronomers who expected its return as fixed by calculation. But on January 13, 1846, the celestial wanderer broke in half: each fragment went its own way, side by side, to return within sight from the Earth in 1852. It was their last appearance. That year the twin comets could still be seen, though pale and insignificant. Soon they vanished into the depths of night, and never appeared again. They were looked for in vain, and were despaired of, when on November 27, 1872, instead of the shattered comet, came a magnificent rain of shooting stars. They fell through the Heavens, numerous as the flakes of a shower of snow.

The same phenomenon recurred on November 27, 1885, and confirmed the hypothesis of the demolition and disaggregation of Biela's Comet into shooting stars.

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Giant Jupiter

And now let us bow respectfully before Jupiter, the giant of the worlds. This glorious planet is indeed King of the Solar System.

While Mercury measures only 4,750 kilometers (2,946 miles) in diameter, and Mars 6,728 kilometers (4,172), Jupiter is no less than 140,920 kilometers (87,400 miles) in breadth; that is to say, eleven times larger than the Earth. He is 442,500 kilometers (274,357 miles) in circumference.

In volume he is equivalent to 1,279 terrestrial globes; hence he is only a million times smaller than the Sun. The previously described planets of our system, Mercury, Venus, the Earth, and Mars combined, would form only an insignificant mass in comparison with this colossus. A hundred and twenty-six Earths joined into one group would present a surface whose extent would still not be quite as vast as the superficies of this titanic world. This immense globe weighs 310 times more than that which we inhabit. Its density is only the quarter of our own; but weight is twice and a half times as great there as here. The constituents of things and beings are thus composed of materials lighter than those upon the Earth; but, as the planet exerts a force of attraction twice and a half times as powerful, they are in reality heavier and weigh more. A graceful maiden weighing fifty kilograms would if transported to Jupiter immediately be included in the imposing society of the "Hundred Kilos."

Jupiter rotates upon himself with prodigious rapidity. He accomplishes his diurnal revolution in less than ten hours! There the day lasts half as long as here, and while we reckoned fifteen days upon our calendar, the Jovian would count thirty-six. As Jupiter's year equals nearly twelve of ours, the almanac of that planet would contain 10,455 days! Obviously, our pretty little pocket calendars would never serve to enumerate all the dates in this vast world.

How stars are formed ?

Stars are born from compact knots within dark molecular clouds that are refrigerated by dust that blocks heating starlight. If the random knots, compressed by supernovae or other means, are dense enough, they can contract under their own gravity.

Conservation of angular momentum demands that as they collapse they must spin faster. Star formation requires that angular momentum be removed such that the new “young stellar objects” do not completely tear themselves apart before they can become fully developing protostars. High-speed particles (cosmic rays) from exploding stars partially ionize the dusty knots.

The ions grab onto the weak magnetic field of the Galaxy and, as a result of their physical interaction with neutral atoms and molecules, provide the initial means to slow the rotation. If the rotation is still too fast, the contracting body may split into a double (or more complex) star, though the origins of doubles are not clearly solved. A contracting protostar still indeed rotates progressively faster until the part of its mass not accreted by the star itself is spun out into a dusty disk, from which planets might later accumulate. From the disk shoot powerful molecular flows that slow the star still more .

When the protostar’s interior reaches about 106 K (1.8 × 106 ◦F), it can fuse its internal deuterium. That and convection, which brings in fresh deuterium from outside the nuclear-burning zone, bring some stability, and a star can now be said to be born. Stars like the Sun shrink at constant temperature until deuterium fusion dies down. Then they heat at roughly constant luminosity until the full proton-proton chain begins, which provides the stars’ luminosity and stops the contraction. The stars settle onto the zero-age main sequence (from which they will later evolve). At the same time, the surrounding dusty cloud is clearing, allowing new, accreting, and highly active T Tauri stars to be seen flocking around their birthclouds . The whole process takes only 10 or so million years, the mature stars then leaving their birthplaces, destined both to age and to orbit the Galaxy. High-mass stars proceed similarly, but at such a great pace that the death process begins even as the birth process is ending.

What is Black Holes ?

Hypothetical black holes are regions of space that can not be directly observed, characterized by high density and an intense gravitational field that catches the light and matter in surrounding space.A black hole is a dead star shape.

Black hole concept was developed by German astronomer Karl Schwarzschild (1873-1916) in 1916 based on Einstein's relativity theory.Proof of existence of black holes in the Universe was only made in 1994 by browsing or using the Hubble Space Telescope, mounted on hostage space orbit around the Earth. By measuring the gas around the center of M87 Galatia was inferred the existence of a mass of about 3 billion solar masses. In 1995 were also found two other black holes in the universe.A star who dies condense to reach a so-called "White dwarf star, with a diameter of several thousand kilometers, close to the diameter of Earth. If the star is compressing more it becomes a "neutron star". Neutron star has a density of about one million tonnes per a cubic centimeter. If the star is compressed as it reaches the size and density close off huge and they entitle properties called black hole.

If a star has a mass of less than three solar masses when the exclusion principle will prevent the collapse of quantum gravity. Black holes and cosmic guts absorb any radiation over a large distance around them.
It implies that our sun will cease to exist over a few billion ani. Astronomers believe today that a black hole continues to evolve, and its end will be a huge explosion equivalent to the detonation of several million thermonuclear bombs.

Galaxy formation and evolution

How the diverse array of galaxies that are now observed originated and evolved into their present form is a topic of intense speculation.Evidence from structural properties. Some clues can be discerned in certain structural properties of galaxies. The most plausible explanation for the smooth and round light distribution of an elliptical galaxy is that the stars formed out of a collapsing gas cloud.

The rapidly changing gravitational pull experienced by different stars as the collapse proceeds has been shown by computer simulations to rearrange the stars into the observed shape.
The highly flattened disks of spiral galaxies must have formed during a similar collapse, but it is believed that most star formation did not occur until the rotating gas cloud had already flattened into a pancakelike shape. Had the stars formed at an earlier stage of the collapse, their rapid motions would have led to the formation of an elliptical galaxy. However, if the cloud stays gaseous until it flattens, much of the kinetic energy of the collapse is radiated away by gas atoms. Subsequent star formation is found to maintain a highly flattened, disklike shape, characteristic of spiral galaxies.

The flattening occurs in part because of the centrifugal forces in the rotating cloud. A confirmation of this picture has come from the discovery that elliptical galaxies rotate much less rapidly than spiral galaxies. This raises the question of the origin of the rotation itself. A natural explanation seems to lie in the action of the gravitational torques exerted by neighboring protogalaxies.
Evidence from composition. Another aspect of galaxies that has evolutionary significance is their composition, and, in particular, the distribution of heavy elements. The amount of heavy-element enrichment can be inferred from the color of the starlight, blue stars being metal-poor. Galaxies are found to be significantly bluer in their outermost regions and redder toward their central nuclei. The explanation seems to be that galaxies formed out of collapsing gas clouds that formed stars in a piecemeal fashion. As stars formed, they evolved, underwent nuclear reactions, produced heavy elements, and eventually shed enriched material (some stars even exploding as supernovae). Successive generations of stars formed out of the debris of earlier stars, and in this way the stellar content of galaxies systematically became enriched. The greatest enrichment would naturally occur toward the center of a galaxy, where the gaseous stellar debris tended to collect.

Interactions. Observations reveal many systems of interacting galaxies and close pairs ofgalaxies, which are possible candidates for later interactions. As galaxies move about within clusters, they will occasionally pass very near one another or even collide directly. Possible outcomes include loss of material from the galaxies' outer regions, transfer of material from one galaxy to another, merger of the two galaxies, modification of the galaxies' forms by tidal perturbations, and loss of gas and dust due to collisional heating. Whether a merger occurs mainly depends on the relative velocity difference of the two galaxies. If they pass each other too fast, the gravitational drag between them will not be efficient enough to change their trajectory and the passage does not result in merging.

Observations show an increase of interactions in the last few 109 years. The random velocity of a galaxy inside an association of galaxies increases with the mass connected to that association. Once the association forms and the galaxies within it start moving under its gravitational influence, the relative velocities in encounters of galaxies will become too high for mergers to occur and the number of mergers decreases. Looking backin time, the increase ofinter-actions is stronger in clusters of galaxies than in environments with few galaxies. This is a consequence of the higher number density of galaxies, which increases the probability of having an encounter.
Galaxies undergoing mergers experience dramatic morphological changes. Due to tidal forces the merging galaxies start deforming and develop very prominent features, most notably the so-called tidal arms. Mergers can trigger periods of intense star formation. Gas which was available in the disks of the progenitor spiral galaxies will be driven to the centers of the remnant galaxies and start forming stars in a starburst. It has been proposed that ultraluminous infrared galaxies like the Antennae galaxies are just galaxies undergoing mergers in which an extensive starburst occurs. Theoretical considerations suggest that the outcome of the interaction between two galaxies of similar size will be an elliptical galaxy. This is one of the most favored formation mechanisms for elliptical galaxies.

Origin. An outstanding and unresolved issue concerns the origin of the primordial gas clouds out of which the galaxies evolved. The cosmic background radiation yields a glimpse of the universe prior to the epoch of galaxy formation. The universe is now completely transparent to this radiation. However, about 500,000 years after the big bang, the radiation was sufficiently hot that matter was ionized, and the matter was also sufficiently dense to render the universe completely opaque to the radiation. To observe the background radiation now (some 1010 years later) is to see back to this early epoch, known as the decoupling epoch: at earlier times, matter and radiation were intimately linked, and subsequently the radiation propagated freely until the present time.

Theory of formation from fluctuations. The cosmic background radiation is very uniform, but fluctuations were discovered in 1992 by the Cosmic Background Explorer (COBE) satellite. These are at a level of 1 part in 105, and are on angular scales of several degrees. The precursor fluctuations of the primordial inhomogeneities that gave rise to the observed structures in the universe would be on scales of degrees, for the largest superclusters and voids, to arc-minutes, for galaxy clusters. A definitive measurement is not yet available for these angular scales, but without such primordial fluctuations galaxies could not have formed. The mutual action of gravity exerted between these infinitesimal fluctuations results in their gradual enhancement. Eventually, great gas clouds develop that will collapse to form galaxies. The required amplitude for these primordial seed fluctuations must be of the order of 1 part in 105, precisely what is measured on larger scales, to within uncertainties of at most a factor of 2.

Numerical simulations of galaxy clustering have enabled the spectrum of fluctuation length scales and amplitudes to be inferred. Galaxies are not randomly distributed, as would be "white" noise; rather, they are correlated. Given a galaxy at an arbitrary position, at a distance away, there is an excess probability, above random, of finding another galaxy. These correlations are large on scales less than 5 mega-parsecs (1.0 x 1020 mi or 1.5 x 1020 km), and are measured out to 20 Mpc (4 x 1020mior6 x 1020km). The parent fluctuations that gave rise to the galaxies must be similarly correlated, although the amplitude of the effect was much less.
A theory of the very early universe, first proposed in 1980, provides an explanation of the distribution of amplitudes of the fluctuations with scale, but accounts only qualitatively for their strength. According to this theory, the initial stages of the big bang were characterized by a period of rapid inflation during the first 10-35 sof the expansion. One consequence of an inflationary epoch is that quantum-statistical fluctuations are amplified up to scales of galaxies and of clusters of galaxies.

The predicted distribution of fluctuations is initially the same, on all scales, from that of galaxy clusters to the observable universe. On the largest scales, where there has been little time to develop deviation from the initial conditions, the distribution ofcosmic microwave background fluctuations measured by COBE in 1992 and in many subsequent experiments, especially the Wilkinson Microwave AnisotropyProbe (WMAP),is approximately consistent with that predicted by the simplest inflationary cosmological model. Thus, the most simple of cosmologies may contain the nascent seeds of future galaxies.
Isothermal and adiabatic fluctuations. The possible fluctuations in the early universe can be categorized into distinct varieties. Of particular importance for galaxy formation are density fluctuations that are found to generally be a combination of two basic types: adia-batic and isothermal.

Primordial adiabatic fluctuations are analogous to a compression of both matter and radiation. They are generic to almost all models of the early universe. In the absence of weakly interacting dark matter, the diffusive tendency of the radiation tends to smooth out the smaller adiabatic fluctuations. This process remains effective until the decoupling epoch, and galaxy formation occurs only relatively recently. However, the dominant presence of dark matter that does not interact with the radiation other than by gravity allows fluctuations to survive on all scales in the weakly interacting dark matter. The theory of fluctuation origin does not specify the strength of the fluctuations. However, the observations of the cosmic microwave background demonstrate that some 300,000 years after the big bang when the radiation was last scattered by the matter, the amplitude of the density fluctuations amounted to only a few parts in 104 on galaxy cluster scales. This means that massive galaxies and galaxy clusters formed relatively recently, although small galaxies could have formed when the universe was just a tenth of its present size. Galaxies form when the gaseous matter cools and condenses in the gravity field of the dark matter, forming gas clouds that subsequently fragment into stars.

In some variations of the standard model for structure formation, primordial isothermal fluctuations were also present in the very early universe. These consist of variations in the matter density, without any corresponding enhancement in the radiation density. Consequently, in the radiation-dominated early phase of the big bang, isothermal fluctuations neither grow nor decay, as the uniform radiation field prevents any motion. Once the universe becomes transparent, the matter fluctuations respond freely to gravity and grow if they are above a certain critical size. The smallest isothermal fluctuations that can become enhanced and form gas clouds contain about 106 solar masses. Galaxy formation occurs very early in this case.
Role of dark matter. The presence of weakly interacting dark matter is almost universally accepted by astronomers in order to account for the rotation curves of galaxies. The baryonic component of matter in the universe is known from calculations of the abundances of the light elements to amount to about 3% of the critical density for closing the universe. There is at least 10 times as much dark matter, which constitutes at least 90% of the mass of the universe. Consequently, dark matter dominates the growth of the primordial density fluctuations. The gravitational influence of this dark matter greatly aids this growth.

Baryon fluctuation growth is suppressed by interactions with the radiation prior to the epoch of decoupling of matter and radiation, whereas weakly interacting particles are able to cluster freely as long as the dominant form of density is ordinary matter rather than radiation. Since the density in the very early universe was dominated by radiation, fluctuation growth in the presence of dark matter is enhanced by about a factor of 10, equivalent to the expansion factor between the epochs of ordinary matter dominance when fluctuation growth first commences and the last scattering of the radiation. The associated fluctuations in the cosmic microwave background required in order to form structures by a given epoch are reduced by a corresponding factor. The detection of cosmic microwave background temperature fluctuations at a level of about one part in 105, initially by the COBE satellite and subsequently by more than 20 experiments, means that the precursor fluctuations of the largest structures, such as galaxy clusters, have been identified, in a statistical sense, in the sky. Dark matter plays an essential role in reconciling the level of the observed fluctuations with the limited growth period available since the universe was first matter-dominated, approximately 10,000 years after the big bang. This matter consists of massive weakly interacting particles whose existence is predicted by the theory of supersymmetry .

The implications of particle dark matter for structure formation are considerable. If the particles are massive, they are slowly moving at the onset of fluctuation growth, when the universe is first matter-dominated. Such particles are called cold dark matter. As structure develops, cold dark matter clusters, first on the smallest scales, then on progressively larger scales. This leads to a bottom-up scenario of hierarchical clustering. Unique predictions are made for both the microwave background fluctuations and the density fluctuations that are measured in large-scale structure studies.
Reconciliation of large-scale structure and galaxy formation with cold dark matter has proven remarkably successful on the largest scales. Most data point to a universe in which the density of cold dark matter is about 30% of the critical value. The cosmic microwave background temperature fluctuations demonstrate that the universe is at critical temperature to account for the locations of the observed angular peaks in the fluctuation distribution observed on the microwave sky. In a universe that has a near-Euclidean geometry, the positions of these peaks are displaced because of the bending of the light rays that have traversed the universe since the epoch when the microwave background photons were last scattered by the matter. A Euclidean geometry requires that the universe must be at critical density, if most of the energy density is in the form of the vacuum energy that is associated with the cosmological constant term introduced by Albert Einstein. One prediction of such a cosmological model is that the expansion of the universe is currently accelerating as a consequence of the nature of the additional energy. Data from use of distant supernovae to measure the deceleration of the universe suggest that the universe is indeed accelerating. Large-scale structure still provides asevere constraint on the nature of the dark matter.

In a universe with a critical density of dark matter, excessively strong clustering of galaxies occurs. Dark energy, which is uniform and smooth, does not participate in gravitational clustering. Three independent observational results contribute to make a strong case for a standard model of the modern universe. These are the cosmic microwave background temperature fluctuation peaks, the acceleration of the universe as inferred from the distances to remote supernovae, and the large-scale structure of the galaxy distribution. The standard model of the universe consists of 30% dark matter, 65% dark energy, and 5% baryons. Variations in the standard model introduce a component of hot dark matter. This matter consists ofneutrinos that are assumed to have a small mass, sufficient to account for about one-quarter of the critical density. However, the resulting mixture of hot and cold dark matter gives poor agreement with the astrophysical data on fluctuations at all scales. According to a much less accepted alternative viewpoint, the dark matter is entirely baryonic. It consists of very low mass stars or of burnt-out stars such as white dwarfs. In this case, the matter density of the universe is only about one-tenth of the critical density, with the rest of the critical density being made up of dark energy. One then finds that adiabatic fluctuations in a baryon-dominated universe, supplemented by a subdominant admixture of hot dark matter, can result in temperature fluctuations that agree with the observational constraints.

A further possible advantage of this interpretation is that by reducing the Hubble constant to about two-thirds of the currently preferred value, it is also possible to dispense with dark energy if one ignores the evidence for acceleration of the universe inferred from distant supernovae. The universe would then contain a critical density of baryons, along with some hot dark matter. Another scenario appeals to warm dark matter, for which a massive neutrino is the expected candidate. However, this option requires an admixture of isothermal fluctuations in order to allow early structure formation. The isothermal fluctuations are consistent with the cosmic microwave background data, provided they are subdominant. In this case, a complex baryon genesis scenario is required, in which matter is created with spatial inhomogeneities in the number of baryons relative to the number of photons. By far the simplest model is one in which the observed structure is seeded by primordial adia-batic density fluctuations generated during inflation.
Reference : McGraw - Hill Encyclopedia of Science and Technology

Milky Way Galaxy - Our Galaxy

Milky Way Galaxy The large disk-shaped aggregation of stars, gas, and dust in which the solar system is located. The term "Milky Way" is used to refer to the diffuse band of light visible in the night sky emanating from the Milky Way Galaxy.

Although the two terms are frequently used interchangeably. Milky Way Galaxy, or simply the Galaxy, refers to the physical object rather than its appearance in the night sky.
Structure and contents. The Milky Way Galaxy contains about 2 x 10^11 solar masses of visible matter. Roughly 96% is in the form of stars, and about 4% is in the form of interstellar gas. The gas both inside the stars and in the interstellar medium is primarily hydrogen and helium with a small admixture of all of the heavier atoms.

The mass of dust is about 1 % of the interstellar gas mass and is an insignificant fraction of the total mass of the Galaxy. Its presence, however, limits the view from the Earth in the plane of the Galaxy to a small fraction of the Galaxy's diameter in most directions.
The Milky Way Galaxy contains four major structural subdivisions: the nucleus, the bulge, the disk, and the halo. The Sun is located in the disk about half way between the center and the indistinct outer edge of the disk of stars. The currently accepted value of the distance of the Sun from the galactic center is 8.5 kiloparsecs, although some measurements suggest that the distance may be as small as 7 kpc.

The nucleus of the Milky Way is a region within a few tens of parsecs of the geometric center and is totally obscured at visible wavelengths. The nucleus is the source of very energetic activity detected by means of radio waves and infrared radiation.
At the galactic center, there is a very dense cluster of hot stars observed by means of its infrared radiation. In 1997. astronomers confirmed the existence of a black hole with a mass of about 2.5 million times the mass of the Sun at the position of an unresolved source of radio emission known as Sgr A* in the middle of the central star cluster. The black hole appears to be the dynamical center of the Milky Way.

The bulge is a thick distribution of stars centered on the nucleus which extends to a distance of about 3 kpc from the center. It contains a relatively old population of stars, nearly as old as the Milky Way itself. Direct imaging with infrared satellites has demonstrated that the bulge is actually an elongated barlike structure with a length about two to three times its width. The Milky Way is thus classified as a barred spiral galaxy, a classification that includes about half of all disk-shaped galaxies.
The disk is a thin distribution of stars and gas orbiting the nucleus of the Galaxy. The disk of stars begins near the end of the bar and can be identified to about 16 kpc from the center of the Galaxy; the disk of gas can be identified to about twice this distance, about 35 kpc from the center. The faint low-mass stars make up most of the mass of the disk. There is also a thick disk of stars and gas. The thin disk of stars contains most of the mass and has a thickness relative to its diameter similar to that of a commercial compact disk. The disk is the location of the spiral arms that are characteristic of most disk-shaped galaxies, as well as most of the present-day star formation.

The halo is a rarefied spheroidal distribution of stars nearly devoid of the interstellar gas and dust that surrounds the disk. The stars found in the halo are the oldest stars in the Galaxy. The stars are found individually as "field" stars as well as in globular clusters: spherical clusters of up to about a million stars with very low abundances of elements heavier than helium. The extent of the halo is not well determined, but globular clusters with distances of about 40 kpc from the center have been identified.

Dynamical evidence suggests that the halo contains nonluminous matter in some unknown form, commonly referred to as dark matter. The dark matter contains most of the mass of the Galaxy, dominating even that in the form of stars.
Evidence suggests that the ages of the oldest stars in the Milky Way are within about 10% of the age of the universe as a whole; thus parts of the Milky Way must have formed early in the history of the universe, about 12-16 billion years ago. There is increasing evidence that the Milky Way formed as a result of the coalescence of small galaxies and protogalaxies, objects with the masses of small dwarf galaxies that are thought to have been among the first objects to form in the Univers.

The Big Bang theory

The Big Bang is actually not a "theory" at all, but rather a scenario or model about the early moments of our universe, for which the evidence is overwhelming.

It is a common misconception that the Big Bang was the origin of the universe. In reality, the Big Bang scenario is completely silent about how the universe came into existence in the first place. In fact, the closer we look to time "zero," the less certain we are about what actually happened, because our current description of physical laws do not yet apply to such extremes of nature.
The Big Bang scenario simply assumes that space, time, and energy already existed. But it tells us nothing about where they came from or why the universe was born hot and dense to begin with.

But if space and everything with it is expanding now, then the universe must have been much denser in the past. That is, all the matter and energy (such as light) that we observe in the universe would have been compressed into a much smaller space in the past. Einstein's theory of gravity enables us to run the "movie" of the universe backwards—i.e., to calculate the density that the universe must have had in the past.
The result: any chunk of the universe we can observe—no matter how large—must have expanded from an infinitesimally small volume of space.
By determining how fast the universe is expanding now, and then "running the movie of the universe" backwards in time, we can determine the age of the universe.The result is that space started expanding 13.7 billion years ago. This number has now been experimentally determined to within 1% accuracy. It's a common misconception that the entire universe began from a point. If the whole universe is infinitely large today (and we don't know yet), then it would have been infinitely large in the past, including during the Big Bang. But any finite chunk of the universe—such as the part of the universe we can observe today—is predicted to have started from an extremely small volume.

Part of the confusion is that scientists sometimes use the term "universe" when they're referring to just the part we can see ("the observable universe"). And sometimes they use the term universe to refer to everything, including the part of the universe beyond what we can see. It's also a common misconception that the Big Bang was an "explosion" that took place somewhere in space. But the Big Bang was an expansion of space itself. Every part of space participated in it. For example, the part of space occupied by the Earth, the Sun, and our Milky Way galaxy was once, during the Big Bang, incredibly hot and dense. The same holds true of every other part of the universe we can see. We observe that galaxies are rushing apart in just the way predicted by the Big Bang model. But there are other important observations that support the Big Bang.

Astronomers have detected, throughout the universe, two chemical elements that could only have been created during the Big Bang: hydrogen and helium. Furthermore, these elements are observed in just the proportions (roughly 75% hydrogen, 25% helium) predicted to have been produced during the Big Bang. This is the nucleosynthesis of the light elements. This prediction is based on our well-established understanding of nuclear reactions—independent of Einstein's theory of gravity. Second, we can actually detect the light left over from the era of the Big Bang. This is the origin of the cosmic microwave background radiation. The blinding light that was present in our region of space has long since traveled off to the far reaches of the universe. But light from distant parts of the universe is just now arriving here at Earth, billions of years after the Big Bang. This light is observed to have all the characteristics expected from the Big Bang scenario and from our understanding of heat and light.

The standard Hot Big Bang model also provides a framework in which to understand the collapse of matter to form galaxies and other large-scale structures observed in the Universe today. At about 10,000 years after the Big Bang, the temperature had fallen to such an extent that the energy density of the Universe began to be dominated by massive particles, rather than the light and other radiation which had
predominated earlier. This change in the form of matter density meant that the gravitational forces between the massive particles could begin to take effect, so that any small perturbations in their density would grow. Thirteen point seven billion years later we see the results of this collapse in the structure and distribution of the galaxies.