For the first few hundred thousand years following the Big Bang, radiation was predominant over matter (Radiation Era). Later, as the Universe cooled matter was ascendant, becoming increasingly important (Matter Era).
The extremely hot, dense "soup" of matter and energy that began in the first minute is often described as the "primeval fireball". It has been likened to something akin to a thermonuclear fusion event, yielding a detonation-like release of energy on a grandiose scale that is just hinted at by a Hydrogen bomb's explosion. (This is how the Big Bang is usually depicted, as a reddish flame, on TV shows about the Universe. This is erroneous because Hydrogen atoms did not exist as such in the earliest Universe - only Hydrogen nuclei. The energy release would not be visible [such radiation is characteristic of much lower temperature processes] but the fireball "glow" would radiate at very short wavelengths [gamma rays among them]). This so-called invisible fireball (i.e., consisting of shortwave energy outside the visible spectrum) cooled as the Universe expanded. As stated earlier, the fireball's existence has been perpetuated as the Cosmic Background Radiation, which is the Universe-filling remnant of the initial (and small) 'fireball'.
Over the next 10 to 100 seconds after the first minute, during the first stage of the Nucleosynthesis Epoch, the predominant process was the production of stable nuclei (nucleons) of Hydrogen and helium. Some of the protons (p+) and electrons (e-) that survived initial annihilation combined to produce new neutrons (n) by weak force interactions, which added to the supply of remaining hadronic neutrons. During this stage, at first the dominant atomic nucleus was just a single proton (Hydrogen of A=1). Temperatures during this phase were a few billion degrees Kelvin. The basic fusion processes that formed Hydrogen and Helium isotopes are shown in this diagram:
As temperatures dropped below 109 °K (at ~ 3 minutes), some of the neutrons started combining with available protons (Hydrogen nuclei) to form Deuterons (heavy Hydrogen or H2 nuclei) plus Gamma (γ) rays (resulting from the conservation of the binding energy released in the reaction). When a neutron is captured at lower temperatures, the assemblage is a Deuterium atom. Today there is ~1 such H2 atom per 30000 Hydrogen atoms - the survival ratio; since deuterium is not produced in most stars, the deuterium we find on Earth (in heavy water molecules) is thought to be a remnant from the first seconds of the Big Bang. The amount detected provides a good theoretical control on the nuclear processes acting during the early Big Bang. A much smaller fraction of the Deuterium can capture a second neutron to form the more unstable H3 or Tritium.
Reaction between a Deuteron and and a proton can produce helium (He3). The much more abundant He4 (two protons; two neutrons) is generated in several ways: by reactions between two Deuterons, between H3 and a proton (rare), between He3 and a neutron, or between two He3 nuclei plus a released proton. Two other elements are also nucleosynthesized in this early stage in very small quantities: Lithium (Li; 3 protons; 4 neutrons): He4 + H3 --> Li7 + γ and Beryllium (Be; 4 protons + 3 neutrons): He4 + He4 --> Be8 + e- (under the still high temperatures during nucleosynthesis, most of this highly unstable Be decays to Li).The general time line for formation of these elements during primary nucleosynthesis appears in this next diagram which plots mass numbers of the primordial isotopes. For calculation purposes, the abundance of the Hydrogen proton is arbitrarily set at 1 - but it actually does not remain constant in the ensuing processes in which the other nucleons develop as temperatures drop in the relative abundances shown (the numbers on the ordinate have a hard to see lowered minus sign in front of the exponent). Note that the number of neutrons drop as these become part of the forming elements. The nucleosynthesis for He, Be, and Li was finished at less than 1000 seconds.
Formation of the elements heavier than Helium generally takes place within the stars as they burn their Hydrogen fuel (see page 20-7 for further details). Elements with higher atomic numbers (symbol = Z, whose value is the unique number of protons in the nucleus of a given element) are not produced at all during this initial nucleosynthesis because of energy barriers at Z = 5 (Boron) and Z = 8 (Oxygen); also the statistical probability of two nucleons of just the right kind meeting is quite low. This stability gap is overcome in stars by the fusion of 3 He4 nuclei into a single C12 nucleus. The higher atomic number elements through Iron are created in more massive stars as they contract and experience rising temperatures by a complexity of fusion processes such as Helium nuclei capture, proton capture, and reactions between resulting highee Z nuclei themselves.
Thus, this brief era witnessed the synthesis of the primordial nuclear constituents -- ~90% Hydrogen/Deuterium and ~10% Helium by numbers of particles and 75-25% by mass -- that make up the two elements subsequently dominating the Universe, along with minute amounts of Lithium and Boron. Most Helium was produced at this early time, but younger Helium is also the product of Hydrogen burning in stars; the ratio of He/H has remained nearly constant because about as much new He is then created in star fusion as is converted to heavier elements during stellar evolution. The Hydrogen and Helium nuclei generated in this critical time span during the original nucleosynthesis later became the basic building materials for stars, which in turn are the sites of the internal stellar nucleosynthesis (fusion) that eventually spawned the elements with atomic numbers Z up to 26 (Fe or Iron); these account for the dominant elements, in terms of both mass and frequency, in the Universe (elements with Z > 26 are produced in other ways, such as neutron capture and neutron decay, that require energy input rather than release [as occurs for elements of Z < 26], as described later). (More about the creation [formation] of the heavier elements is covered on page 20-7.)
(An astounding fact, worthy of prominent insertion at this point: The vast majority of the Hydrogen atoms in your body and mine, present as Hydrogen-bearing substances, including water and various organic compounds, throughout the Earth [and extrapolated in scale up to the full content of the Universe] is primordial, that is, consists of the same individual protons that formed in the first minute of the Big Bang and then the nucleons of H during nucleosynthesis and the H atoms [single electron] soon thereafter. The additional elements in our bodies, O, C, N, Ca, Na, Mg, K, Al, Fe and others, were generated exclusively in stars, as we shall see later. We therefore consist of truly old matter, billions of years in age, and are in a sense "immortal" or "eternal" with respect to the future. Although seemingly far-fetched, some of an individual's atoms can conceivably end up in another human's body - reincarnation of sorts - as atoms released during decay may migrate into the food chain [although actual tracing of specific atoms through the transferrence is next to impossible]; or a more direct path by cannabalism is an alternative means.)
As the fireball subsided with continuing Universe expansion, the matter produced was dispersed in a still very dense "soup" of photon radiation, H and He nuclei, and free electrons. The radiation started out as predominantly gamma rays and then X-ray photon radiation along with neutrinos plus nucleons and other elementary particles. This mix of radiation, ionized H and He nuclei, and free electrons is called a plasma. With increasing expansion, the plasma progressively cooled so that the peak radiation wavelengths moved successively through longer values through the ultraviolet. The time that lasted from after the first few minutes to about 380,000 years (cosmic time, i.e., since the moment of the Big Bang) is known as the Radiation Era (connoting the dominance of electromagnetic radiation in the form of photons). As expansion proceeded, the mass-equivalent radiation (E = mc2 equivalency) density decreased as mass density increased (today, mass density significantly exceeds radiation energy density even though the number of photons is much larger [in a ratio of ~1 billion photons to every Baryon]). Matter began to dominate after ~57000 years but temperatures remained too hot (above 3000 °K) for electrons to combine with nuclei. The Universe during this stage was opaque because, even with decreasing photon density, detectable radiation at any wavelengths was prevented from traversing or leaving the enlarging primitive Universe's confines owing to internal scattering by free electrons in the radiation "fog".
This era of opaqueness ended roughly 380,000 years after the Big Bang (some recent estimates put this termination at closer to 500,000 years after the BB) with the onset of the Decoupling Era, at which stage cooling had dropped below 3,000° K. When this temperature was reached, protons and Helium nuclei could start combining with electrons to form stable Hydrogen and Helium atoms - a process known as Recombination). Prior to that the photons intermixed with the H and He nuclei had been more energetic, so that they would destroy any atoms that resulted from electron capture. But, by 3,000° K the H and He could retain captured electrons. Thus, the number of free (unattached) electrons in the plasma dropped significantly so that their scattering effect on the photons diminished to the extent that the photons could have been seen as visible light "if any observer had been around to witness the radiation". (Today there are about one free proton and electron for every 100,000 atoms.) As this era began, the Universe was about 1/200th its present size. The Decoupling Era lasted until approximately the first million years of Universe history.
Since that time this glow is represented by the Cosmic Background Radiation (CBR). The general term CBR refers to the photon radiation distributed throughout the Universe at any time (including the times older than Recombination). However, it would be first detectable after the start of the Decoupling Era. This glowing radiation has continued to redshift (brought on by continuing expansion of space) from the initial short wavelengths enroute to its present-day microwave emission wavelengths, thus it is known today as the Cosmic Microwave Radiation (CMR, a synonym for the more general CBR but with the connotation of describing the current peak wavelengths that fall within the microwave region of the EM spectrum). The Cosmic Background Radiation (discussed in detail on page 20-9 and also treated effectively in this Wikipedia website) represents the residual "afterglow" (sometimes referred to as "leftover radiation") of the Big Bang - which started out as gamma radiation characteristic of very hot thermal radiation (billions of °K) that has now cooled thermodynamically (from expansion) to its present 2.73...°K (for this temperature, the radiation is detectable in the microwave region). This radiation seems nearly isotropic in all directions towards which we observe the Universe. However, it does show tiny, but extremely important deviations in temperature; the diagram below (shown again on page 20-9) is reproduced here to illustrate these variations.
A small strip within this diagram shows in more detail the distribution of these temperature variations.
These variations become crucially important for the subsequent development of the Universe. Just how they formed is still not fully known (again, check page 20-9 for speculations). But they seem to have developed during or just after Inflation. As the inflationary moments took place and a Universe of very small but definite size resulted, variations in energy density - which led to the temperature variations - resulted when the expansion produced acoustic waves (analogous to the familiar sound waves but at much, much longer wavelengths [lower frequencies]). These waves behave like acoustic waves because they were propagated as alternating compressions and rarefactions of the particles that had come into existence and spread out after the Inflation. Like a traveling acoustic wave, those in the early expansion moved outward over times at cosmic scales. Since the medium through which they moved was comparitively tenuous (thin), their action required very high levels of energy (or power, to use the term that includes time). Interferences led to the slight differences in energy density that translate into the observed temperature differences.
Assuming then that this acoustic behavior describes the wave action in this expansion, then the spatial distribution of the temperature variations can lead to what is known as a power spectrum. Here is one derived from the WMAP data:
The horizontal axis plots the size of the sky (celestial sphere; essentially the imagined hemisphere above us as we look up from the horizon all about) in terms of angular frequency. The vertical axis shows variations of temperature in the millionths of a degree scale. At larger scales (c) (angular frequency equivalent to 30° but calculated in radians), the deviations from an average are moderate. At the scale of (d), about 1°, the variations are maximum. At smaller angular distances, the amount of temperature variations decreases progressively. The entire curve has the shape of a power spectrum plot. From an acoustic standpoint, the peak (d) is equivalent to the acoustic "fundamental tone"; successive peaks towards (e) are overtones.
The effect of this acoustical behavior (influenced and modified by gravity waves), up through Recombination, was to redistribute Baryons and photons produced after Inflation such that they tended to concentrate in the acoustical troughs (analogous to rarefactions in sound waves). This leads to very small, but higher temperatures in the peaks compared with lower temperatures in the troughs. Dark Matter also was of greater density in the peaks. The net result was that both energy and matter densities became spatially distributed into regions of highs and lows (but still very small variations from the overall norm) as seen in the CBR diagram (interferences may account for the non-uniform patterns). The higher density regions became the sites where the first stars and later galaxies preferentially formed. These regions were also sites of slightly greater gravitational energy; thus, they preferentially attracted more hydrogen atoms and other matter which in turn raised the gravitation state even more, bringing in still more matter and allowing gases to accumulate in huge "clouds" that in time organized into galaxies. The time interval when this occurred is narrow and critical; the material that would make up stars and galaxies had to be condensed and yet not too far apart to escape the collecting ability of gravity.
From about 5 to about 200 million years, as temperatures fell through 3000 to 600° K, the CBR photons dispersed throughout the Universe were emitting in the infrared. If any mammalian observer could have looked about the expanding Universe during this stage, this radiation would have been invisible and nothing could be envisioned since galaxies and stars had not heated up enough to be luminous. This period is referred to as the Dark Age, which gradually moderated until about a billion years after the BB. The atomic Hydrogen that dominated baryonic matter during this time began to clump up in denser pockets that became the small haloes (also containing more dark matter) which, as the gas built up, condensed into the first stars, a few of which may be as old as 200 million years after the BB.
As these first stars and protogalaxies began to develop, their strong outputs of electromagnetic radiation caused a Re-ionization (removal of electrons) of some of the Hydrogen in the still largely "empty" space. When Hydrogen protons and electrons are separate, they cannot capture (absorb) energy in the form of photons. Photons may be scattered, but scattering interactions are infrequent if the density of the plasma is low. Thus, a universe full of low density ionized hydrogen will be relatively translucent. The net effect of these new sources of ionizing radiation (in the galaxies) was that the Universe now became rather rapidly transparent to radiation. This allowed visible light photons to pass through interstellar space, which is an almost perfect vacuum and by itself is black, i.e., does not give off luminous self-radiation but does contain very low densities of photons and other particles (about 3 atoms per cubic meter of near-empty space). This transparency facilitates free passage from external sources of visible wavelengths within any region of the Universe. This next diagram, which incorporates the phase transition called Re-ionization, was taken from this Wikipedia web site.
Evidence for this re-ionization has been found so far not from visible light but by using UV radiation to "see" quasars (huge energy sources) that frequently formed in the first billion years. Early massive galaxies and stars produce an abundance of Ultraviolet radiation. Thus, as stars and galaxies began to form, their thermal and other energy outputs would ionize the interstellar Hydrogen, allowing their light to appear as now detectable in the visible range, so that the Universe at this stage started to show the stars as individuals and clusters. This did not happen "all at once" but gradually as galaxies formed and made their regions transparent; thus "holes" appeared intermittently in the opaque early Universe letting light from the reionizing process in galactic neighborhoods begin to spread through their surroundings as the opaqueness progressively dissipated. Ionized Hydrogen is today commonplace in intergalactic space; also present in the "vacuum" is neutral Hydrogen (detectable using its 21 cm wavelength radiation in the microwave region; this diagnostic wavelength can be longer owing to the redshift of EM frequencies that result from expansion of the Universe [page 20-9]).
Reionization is a consequence of the appearance of the first galaxies. As the first billion years ensued, conditions turned favorable for the the clustering of matter into stars (slight increases in density) that eventually gave rise to groupings that underwent organization into galaxies. As the first stars formed, especially supermassive ones, their radiation (particularly strong in the UV) began to ionize the neutral Hydrogen gas in space, forming huge "bubbles" of now ionized gas. These bubbles served as regions where more stars formed into clusters that became the initial smaller dwarf galaxies. The bubbles grew and interconnected into the larger galaxies now widely distributed. Enough neutral Hydrogen was left over to provide the material that continued to condense into stars. (For more details of this process, see Abraham Loeb, The Dark Ages of the Universe, in Scientific American, November 2006.)
We have mentioned "stars" several times earlier on this page (a star is defined in red in the Overview at the beginning of this page): just what is a star? It is indubitably the most fundamental large single object in the Universe. Stars began to form around sometime during the Decoupling Era. At this time, most neutral atoms in the Universe were Hydrogen. Irregularities in atom densities led to clotting of Hydrogen which continued to grow because the gravitational attraction of a clot becomes ever stronger, pulling in matter, mostly Hydrogen. Eventually, clots of Hydrogen - in spherical shapes because of the uniform pull of gravity in larger bodies - reached millions of kilometers in size. As such sizes are attained, gravity causes contraction of the bodies thereby increasing the pressures within their interiors. Temperatures increase concurrently.
At about 10,000,000 degrees Kelvin, star-interior temperatures together with the contraction pressures in the bodies can act on individual Hydrogen nuclei, which heretofore being positively charged had tended to repel each other. Under these new conditions the T-P factors are able to cause nuclei pairs to join rather than break apart. This is fusion, the basic process that ignites Hydrogen bombs, releasing the energy left over after the nuclear uniting that is experienced as an explosion. Helium is the result of two Hydrogen nuclei being fused. At higher temperatures and pressures elements of higher atomic numbers are produced (page 20-7). Of those elements, Carbon, Oxygen, and Nitrogen are vital as the building blocks of life; as mentioned above they all are produced within stars.
Stars are the objects that we see in galaxies - organized collections of stars held in a grouping determined by mutual gravitational attractions. Galaxies began to form during the first half billion years of the Universe's life. The total life of a star itself will depend on the amount of mass (mainly Hydrogen) it contains. Small stars live for many billions of years. During the stages in its lifetime in which it is stable before it has consumed its fuel, a star maintains a balance (equilibrium) between inward contraction powered by gravity and outward expansion as gases and radiation are generated from nuclear processes. Large stars die (usually violently) much earlier as they rapidly convert Hydrogen to heavier elements and use up this fuel. These big (shorter-duration lives) stars can destroy themselves by explosions termed Supernovae, which may leave behind some of the mass as Black Holes. Stars 1 to 10 times the mass of the Sun shed material with their cores becoming white dwarfs.
We will consider (next) on page 20-2 and 20-2a the nature of stars, how they form, how they produce heavier elements (covered in more detail on page 20-7), and how they end their existence. Galaxies will be treated in detail on page 20-3 and 20-3a. All we will say at this stage about galaxies is that they started out as mostly irregular in shape, then elliptical structures developed, while the familiar spiral galaxies formed later with most having organized by about 7 billion years ago, and collisions among galaxies have occurred throughout Universe time (when spiral galaxies collide elliptical types result) but were more common when the Universe was smaller (more dense).
For a review of many of the ideas in this subsection, consult this Wikipedia website: "Timeline of the Big Bang".
Let us summarize several of the above ideas on this page, plus some others introduced in the next pages, with two diagrams. The first is a variant of the above Silk diagram for the development of the Universe after the Big Bang; it is largely self-explanatory:
The second diagram has been reproduced from one of the Websites mentioned in the Preface, the course developed by Dr. J. Schombert of the University of Oregon, labeled on his site 21st Century Science site, specifically the section entitled "The Birth of the Universe".
The preceding diagram gives the intergalactic temperature history of the Universe on the ordinate. For emphasis, that history is singled out in this table:
The general pattern of development of the Universe since its first billion years has been one of increasing maturity of galaxies, destruction of some stars and formation of others, collisions among some galaxies, and in its second half the overall increase in expansion rate.
Three additional comments are appropriate here, now that the above ideas have given you a basic understanding within which they become relevant:
First, The terms "mass density" and "energy density" have appeared several times in the above paragraphs. In the initial moments of the Universe, radiation (photon) energy density was dominant. By the time temperatures had fallen to ~10000 °K, when the Universe was about 1/10000 its present size, radiation mass density (remember the E = mc2 equivalency) became about equal to matter density. After the first second or so, the mass density has come to exceed radiation density, despite the aforementioned preponderance of photons over Hadrons and Leptons. In terms of numbers of particles, there are about a billion photons for every proton and electron in the Universe. In terms of matter, hydrogen is dominant: if spread uniformly throughout the observable Universe, the number of hydrogen atoms has a density of about 1 x 10-30 g/cu.meters. Estimates of the actual numbers of hydrogen atoms averaged out (dispersed from galaxies and stars) in space range from about 1 to 6 per cubic meters.
Second, some recent hypotheses contained in the concepts of Hyperspace consider the Universe at the Planck time to have consisted of 10 dimensions [other models begin with as many as 23 dimensions but these reduce to fewer dimensions owing to symmetry and other factors]. The chief advantage of this multidimensionality lies in its mathematical "elegance" which helps to simplify and unify the relevant equations of physics. As the Big Bang then commenced, this general dimensionality split into the 4 dimensions of the extant macro-Universe that underwent expansion and 6 dimensions that simultaneously collapsed into quantum space realms having dimensions of around 10-32 centimeters in size. This rather abstruse concept is explored in depth in the book Hyperspace by Michio Kaku (Anchor Books).The third comment considers that the ultimate physical entities that make up both matter and energy may be smaller than Quarks and Leptons; these are known as Superstrings - one dimensional subparticles (of minimum lengths estimated to be 10-34 meters - the so-called irreducible quantum of length (given the symbol Is) - that vibrate at different frequencies and combine in various ways (straight to looped; in bundles) to then make up the many different fundamental particles. Each species of particle has its characteristic vibrational frequency or harmonic. While a mathematical description of superstrings can be reasonably postulated, proof of their existence has yet been to be verified but theory favors their existence and they are consistent with quantum physics. Moreover, superstrings account well for some of the fundamental ideas and properties of matter, including its behavior before, at, and after the Big Bang (see page 20-11). Thus, superstrings constitute the core makeup of particles that are obvious to us as the inhabitants of 3-dimensional space. (Whether superstrings themselves are further reducible to constituent entities or are the smallest finite entities is not known.) This diagram may help to visualize a bit of the idea.
In addition to the 4th dimension and implications for the nature of time, superstrings are tied to 6 (or in some models 7) more curled dimensions whose spatial arrangement around a particle is expressed by a curvature of radius R (probably very small - in the range of Is or somewhat larger but one recent model allows R to be up to 1 millimeter). (The idea that physical entities at subatomic sizes can have more than 3 spatial dimensions was first put forth early in the 20th Century by Theodor Kaluza [a German] and Oskar Klein [a Swede] to explain aspects of electromagnetism.) Superstrings therefore exist in hyperspace. If superstring theory proves to be valid, it will be one of the greatest achievements ever in physics. It is currently the most promising way to reconcile quantum theory and relativity. A more recent variant accounts for the graviton and contributes to an explanation of the role of gravity, the pervasive but weak force that is critical to the development and maintenance of our Universe. This is the so-called M-theory (M stands for multidimensional "membranes" (commonly spoken of as "branes" by superstring theorists). This theory postulates an 11th dimension (the membrane); when added to the dimensional mix, the result permits gravitons to fit in the general picture.
The original idea for superstrings is traced to a model proposed in 1968 by the Italian physicist Gabriele Veneziano (now at CERN) that at first ran into many difficulties, most being overcome as theoreticians began to seriously consider the concept. An outstanding review of what is up to today known or surmised about superstrings, in the context of its importance to Cosmology, has been summarized in a book (which reached best seller status) by Brian Greene, The Elegant Universe, 1999, W.W. Norton & Co.). Greene has apparently replaced Carl Sagan as the "guru" of Science whose personality favors an ability to popularize such hard concepts to master (his rival is Neil DeGrasse Tyson). Public Broadcasting (PBS) through its Nova program has aired a 3 hour special called "The Elegant Universe" (beautifully done!). I am attaching this PBS website address (assuming they retain it online for future times) that summarizes the fundamentals of superstring theory a la Greene. There is also a web page covering the basic concepts that purports to be the official site for a survey of Superstring Theory. And Wikipedia has several Web sites that deal with these topics; they are:Superstring theory; M-theory; Hyperspace web references; Hyperspace in Science Fiction.
Having originated the Universe through the preferred Big Bang Model and then considering the first few hundred million years of its early history, you will now embark on a systematic review of the major aspects of Cosmology, beginning with a survey of "stars" (after a brief "detour" to examine the Hubble Space Telescope - the space observatory that revolutionized our understanding of the Cosmos). However, it is useful now to consider succinctly the topic of "Structure of the Universe" as an Introduction to these other topics.
From an astronomical perspective, the Universe beyond Earth can be considered to have this hierarchy of major components, arranged by size: Cosmic dust and gas; Asteroids and Comets; Planets and their Moons; Stars (with the Sun as the prime model); Galaxies and Black Holes; Galaxy Clusters; Superclusters; the Cosmic Web (Filaments and Voids); the Universe itself (which embraces all its matter and energy); (and the possibility that there may be multiple Universes or Multiverses). As a preview of what will follow [mainly in the subsection on Galaxies], here are three illustrations, showing a Supercluster, a model of Filaments, and the structure of the "local" region of the Universe:
A comment before closing this page: Humans are the most highly developed assemblages of ordinary matter (this must be qualified by stating that other, more advanced thinking creatures may reside elsewhere in the Universe). But, as you saw in a diagram near the middle of this page, ordinary matter makes up only about 4% of all entities (matter and energy) in the Universe. One is tempted to claim that stars and galaxies are the principal manifestations of ordinary matter. But recent studies, utilizing data from the interactions of quasar (extreme luminous energy sources surrounding Black Holes), show that the majority of baryonic matter resides in inter- and intra-galactic space. This matter is probably unevenly distributed, with most found within the filaments just described. The matter is presumed to be composed of ionized hydrogen and some ionized heavier elements.
We have now reached the close of this first, largely overview page dealing with Cosmology. Heady stuff!! Perhaps you need to review the main ideas behind the Big Bang using another source. To do that, check this Wikipedia website that deals with the Big Bang And, in the interests of fairness (by trying to eliminate a bias favoring the Big Bang concept), the writer will here in this paragraph, give several Internet connections to websites that dispute the "correctness" of the Big Bang, i.e., critique the concept and suggest alternatives. These were found as Google sites by typing this topic: "Proof of the Big Bang". These three are typical of the pros and cons that topic elicited: Big Bang skeptic (this review traces the conversion of Richard Carrier from a negative to a positive view of the Big Bang); What Big Bang (the discreditation of the Big Bang by Alexander Shulgin); and The Big Bang is challenged (by an unidentified author). Suffice to say that the writer is among the majority of scientists who currently accept the general tenets of the Big Bang as described on this page as being "a reasonable hypothesis" that better explains the Universe than any other competing model; but aspects of the present Big Bang concept are likely to be modified, or perhaps rejected, and new variations or components of the hypothesis will be "discovered" in the future.
This has been a lengthy page. The remaining pages in this Section are also long. We will start with a diversion that describes the most important astronomical observatory ever constructed by humans - the Hubble Space Telescope. Then a page pair on stars, followed by two pages on galaxies, both topics centered on observations in visible light. A page follows that treats observations of heavenly bodies in other regions of the electromagnetic spectrum. A page dealing with special features of galaxies then ensues. After that, a page considers supernovae, pulsars, quasars, and black holes. The next page examines how the elements came to exist. The following page looks at the nature of spacetime and expansion. Evidence for the Big Bang is then treated, along with a discussion of CBR and Dark Matter/Energy. Page 20-10 looks at some recent ideas including the newly discovered idea of an accelerating Univers. Then, models for planetary formation are treated. A page is devoted to the nature of life in the Universe; this includes a "mini-course" on Biology and a history of life on Earth. The last page includes some philosophical musings about "the meaning of it all".
*A measure of cosmic distance to any object beyond our Sun is the light year (l.y.), defined as the distance (~ 9.46 x 1012 or 9,460,000,000,000 km or ~5.9 quadrilion miles) traveled by a photon moving at the speed of light (2.998.... x 108 m/sec, usually rounded off and expressed as 300,000 km/sec) during a journey of 1 Earth year; another distance parameter is the parsec, which is the distance traversed in 3.3 l.y. Keep in mind that this is an arbitrary and anthropomorphic parameter in that the year is strictly valid only for the Solar System, and more particularly applies to just that time determined by the number of days in which Earth takes to travel one complete orbital cycle around the Sun. Another comment: The parts of the Universe now visible in terms of maximum measurable light year distances are thought to be a region within a (possibly much) larger Universe of matter and energy, with light from these portions beyond the detectable limits having not yet arrived at Earth.
** It is often difficult to find a clear definition of the term "space" in most textbooks (just look for the word in their index - it is almost always absent). We tend to think first of the "out there" that has been reached and explored by unmanned probes and by astronauts as the "space" of interest. One definition recently encountered describes space as "the dimensionality that is characterized by containing the universal gravity field". The writer (NMS) has tried to think up a more general definition. It goes like this: Space is the totality of that entity that contains all real particles of matter/energy, both dispersed and concentrated (in star and galaxy clots), which fill, and are confined to, spatial dimensions that appear to be changing (enlarging) with time. Anything one can conceive that lies outside this has no meaning in terms of a geometric framework but can be conceptualized by the word "total vacuum". This vacuum would contain no energy whatsoever (therefore, no mass), and would be devoid of spatial dimensions and time. In the quantum world a false vacuum is hypothesized as occupied by virtual particles capable of creating new matter and space if a fluctuation succeeds in making a (or perhaps many) new Universe(s).
*** Symmetry in everyday experience relates to geometric or spatial distribution of points of reference on a body that repeat systematically when the body is subjected to specific regular movements. When rotated, translated, or reversed as a reflection, the points after a certain amount of movement are repeated in their same relative positions as it returns to its initial position. For example, a cube rotated 360° around an axis passing through the centers of two opposing faces will repeat the square initially facing the observer four times [90° increments. The concept of symmetry as applied to subatomic physics has other, although related, meanings that depend on conservation laws as well as relevance to spatial patterns. In general terms, this mode of symmetry refers to any quantity that remains unchanged (invariant) during a transformation. Implied are the possibilities of particle equivalency and interchangeability (the term "shuffled" may be used to refer such shifts).
Expressed mathematically, certain fundamental equations are symmetrical if they remain unchanged after their components (terms) are shuffled or rotated. In quantum mechanics, gauge (Yang-Mills) symmetry involves invariance when the three non-gravitational forces (as a system) undergo allowable shifts in the values of the force charges. At the subatomic level in the first moments of the Big Bang, symmetry is applied to a state in which the fundamental forces and their corresponding particles are combined, interchangeable, and equivalent; during this brief time, particles can "convert" into one another, e.g., hadrons in leptons or vice versa. When this symmetry is "broken", after the GUT state, the forces and their corresponding particles become separate and distinct. The progressive breaking of symmetry during the first minute of the Big Bang has been likened (analogous) to crystallization of a magma (igneous rock) by the process of differentiation. At some temperature (range), a crystal of a mineral with a certain composition precipitates out; if it can leave the fluid magma (crystal settling), the remaining magma has changed in composition. At a lower temperature, a second mineral species crystallizes, further altering the magma composition. When the last mineral species crystallizes, at still lower temperatures, the magma is now solidified. All the minerals that crystallized remain, each with its own composition. In the Big Bang, as temperatures fall, different fundamental particles become released, altering the energy state of the initial mix, as specific temperatures are reached (and at different times) until the final result is the appearance of all these particles, which as the Universe further expands and cools become bound in specific arrangements (e.g., neutrons and protons forming H and He nuclei; later picking up electrons to convert to atoms) that ultimately reorganize in stars, galaxies, and the inter- and intra-galactic medium of near empty space.
**** The familiar term "mass" needs some explanation. The Newtonian definition simply refers to the quantity of matter, in terms of its density and bulk. The relativistic quantum concept of matter considers mass to arise whenever a particle interacts with the Higgs quantum field. When a particle such as a Quark or a W Boson reacts to the Higgs field (as yet only a postulate awaiting verification of its existence), which is held to be omnipresent in empty space, in current theory this gives rise to the Higgs particle (the Boson that fosters its interaction as a force; see other references to this elswhere on this page). In so doing, the particle acquires the property called "mass". The different particles shown in the classification table in the text on this page gain their different masses because of variations in strength of interaction. In the SuperSymmetric Standard Model, there are two kinds of Higgs fields and five species of Higgs Bosons. The quantum Higgs field differs from gravitational and electromagnetic fields in that the latter assume 'zero field strength' in their lowest energy states whereas the Higgs field is 'non-zero' at its minimum energy state. The Higgs field (if it existed before the Big Bang) therefore has a finite (negative) value in a Universe-to-be that may not yet have formed discrete mass particles; as particles are created just after the singularity event they quickly react with the Higgs field to evolve into states where mass becomes a real property. For further information, we refer you to "The Mysteries of Mass" by Gordon Kane, Scientific American, July 2005.
***** Energy can be said to be quantized, that is, is associated with quanta (singular, quantum) which are discrete particles having different units of energy (E) whose values are given by the Planck equation E = hc/λ where h = Planck's constant, c = speed of light (~300,000 km/sec), and λ = the wavelength of the radiation wave for the particular energy state of the quantum being considered; the energy values vary with λ as positioned on the electromagnetic spectrum (a plot of continuously varying wavelengths).
******This extremely rapid enlargement reflects the earlier influence of Inflation with its initially very high expansion rates. Keep in mind that many of the parametric values cited in cosmological research are current estimates or approximations that may change as new data are acquired and/or depend on the particular cosmological model being used (e.g., standard versus inflationary Big Bang models). Among these, the most sought-after parameter is H, the Hubble Constant (discussed later in this review), being one of the prime goals for observations from the Hubble Space Telescope.