Writer's Note: 1) Most of the pages in this Section are image-intensive, so that the large number of illustrations can lead to a lengthy download time for those using modems connected to telephone lines; for such individuals, purchase of the CD-ROM is recommended; 2) Some parts or ideas presented in this Section may seem repetitious, i.e., are stated more than once; some of this reiteration is deliberate - much of the topics covered tend to be complex and unfamiliar to the non-specialist reader (those who are not astronomers, cosmologists, physicists), so that repeating is a helpful aid in reminding one of these previously developed ideas and tying them (making them relevant) to the other subjects where they later appear. Other repetition may be inadvertent owing to the writer's failure to note that an idea may be stated in different parts of the text because it was re-encountered without realizing that it or similar information had been treated earlier; for this, your indulgence - or better, your editing - is sought .

There will be no individual page summaries in Section 20 which deals with Cosmology: The Origin, Composition, Structure, Development, and History of the Universe (or Universes, if there are more than one). This is largely because of the complexity and wide range of ideas on each page: this does not lend itself easily to synopsize. The reader instead must work through the knowledge imparted on each page without the aid of a preview or reduction to a simplified digest. If the field is new to you, several readings of this Section may be needed to facilitate mastery of this ultimate subject: the Origin of Everything. Also, if a novice, you should profit from working through the excellent online "textbook" in Astronomy prepared by Dr. J. Schombert at the University of Oregon, which have been referenced in the Preface . In keeping with the Overview and the 20 Sections that have followed, every illustration will be accompanied by a synoptic caption.

Despite this absence of summaries, we will attempt to abridge the overall ideas underlying Astronomy and Cosmology in this summary as an Overview.:

ASTRONOMY deals mainly with the description of the objects, materials, structure, and distribution of what appears to exist beyond the Earth itself. Astronomy as an observing "science" traces its roots to early civilizations such as the pre-Christian era Babylonians, Egyptians, Greeks, and Chinese and the Mayans and Aztecs in the New World. Star groupings, the constellations, were established and became involved in myths that suggested deity controls of how the World (i.e., the Universe) is able to function. COSMOLOGY deals with the origin, development, and future expectations of/for the Universe, and also began in early times, with both myths and theological explanations for the meaning and cause(s) of the physical (natural) World (including and beyond the Earth) gradually being supplanted by scientifically-based observations. Key ideas that provide this basis include the postulates by such Greek philosophers as Pythagoras, Euxodus, and Aristotle, and the later (ca. 140 BCE) Ptolemaic description of epicyclic "heavenly" motions; these persisted largely as philosophical musings until the advent of Copernicus in the 16th Century CE who posited the heliocentric theory for the Solar System (but suggested by Aristarchus in 280 BCE), followed by important contributions from Tycho Brahe and Johannes Kepler soon thereafter. Galileo was the first to use the telecope for astronomical observations. Isaac Newton provided the foundation for the movements of stars and planets with his Laws of Gravity and Motion. William Herschel in the late 1700s CE provided the first proof that the Milky Way, in which the Sun is located. is an "Island Universe", namely a huge cluster of stars comprising a galaxy; Herschel surmised that other such galaxies must exist. This led to the beginning of the modern era of Cosmology stemming for work by Edwin Hubble in the 1920s.

Before the beginning of this ( there may be others) Universe there was no time nor space, no energy (in the discrete forms we know) nor matter - at least in the sense that we perceive these fundamental "qualities". What may have existed is some as yet undefined quantum state in which fluctuations in the "emptiness" - the void - led to extremely fleeting "particles" containing the essence to grow into a Universe. Essentially all such evanescent moments ended with the disappearance of these particles (still unidentified entities: energetic virtual (potential non-yet existing particles which may be those constituting the Dark energy that dominates the Universe (Pages 20-8 and 20-9) have been proposed). But the potential was there for one such particle to spring to existence at a moment that witnessed "creation" of a singularity from when our Universe sprang.

This singularity was so unstable that it "exploded" into what is known colloquially as the "Big Bang". That took place some 13.7 billion (+/- 200 million) years ago (see page 20-9 for a discussion as to how this value has been reached and has changed several times in recent years). The first minute of Universe time was the critical stage leading to the state of the Universe we observe today. We can trace theoretically events during the minute back to 10^-43 sec(onds) - an instant known as the Planck time - when the Universe was infinitesimally small. (Experimentally, astrophysicists can actually reconstruct the sequence and verify the essential physics of the Universe’s early conditions back to 10^-12 seconds and to particle sizes as small as 10^-17 meters; better yet, a significant number (most?) of the particles and forces (and fields through which they interact) have now been defined and all but a few actually found and identified under laboratory conditions.) Initially, the fundamental forces (strong; weak; electromagnetic; gravity) were unified (as is being explained through one new theory in physics called "superstrings"). But, they quickly separated systematically into the individual four prime forces. Although expansion was rapid, at about 10^-35 seconds, there was a one-time only extreme acceleration of this minute Universe through a process called Inflation.

Thereafter, in this first minute as expansion continued and the proto-Universe cooled to lower energy levels, the fermions (matter), controlled by the appropriate bosons (force), began to organize into the protons and neutrons (both composed of quarks), electrons, mesons, neutrinos, and others of the myriads of particles continually being discovered in high energy accelerator experiment in physics labs.

As the first minute ended, some particles began to associate with others (while probably all the anti-matter that should have been created was destroyed). In the first few minutes, particles began to organize into nuclei that were part of a plasma state in which the mix included electrons, photons, neutrinos and others. In the next 380,000 years or so, this particle-radiation state witnessed the beginnings of organization into atoms, mostly of Hydrogen and some helium. After that time the Universe became "transparent" so that communication through photon (light) radiation was possible between segments of the Universe close enough to exchange information at the speed of light. The Universe was almost completely homogeneous and isotropic on a grand scale but locally tiny fluctuations in the state of matter (mostly H and He), as appear in the irregularities in the Cosmic Background Radiation (greatly cooled Big Bang "afterglow'), led to gravitational clumping (into nebulas) that grew simply because these slight increases in density continued to increase the organization through the force of gravitational attraction. From this eventually, in the first billion years, stars began to form and to arrange in clusters called galaxies. These adopt specific shapes, such as spiral, elliptical, or irregular.

A star is defined as a massive, spherical astronomical body that is undergoing (or has undergone) burning of nuclear fuels (initially Hydrogen; as it evolves elements of greater atomic number are consumed as well) so as to release energy in large amounts of both luminous and non-luminous radiation (over a wide range of the EM spectrum); stars eventually change significantly in mass, size, and luminous output with some finally surviving only as very dense cores (neutron stars) of minimal luminosity. Stars burn their Hydrogen at high temperatures, during which (depending on their size) they convert this fuel to heavier elements (largest ones can produce elements up to iron in the Periodic Table). Large stars die out rapidly (a few hundred thousand to one or more billion years); small stars can persist for times that are comparable to the total life of the Universe. During their stable lifetimes, the stars hold together by a fine balance between inward contraction under gravity, involving internal heating up, and the outward pressure of the radiation produced by nuclear processes. Many stars can explode as supernovae. Various types of stars evolve over time through distinct pathways; among these are Red Giants; White Dwarfs; Brown Dwarfs, and Neutron Stars. Black Holes are another, perhaps widespread, constituent of space. As a star forms out of nebular material - gases mainly of some Hydrogen and helium, and other elements in various forms, including particulate dust), some of this material not drawn into the growing star may collect in clots that would form planetary bodies - rocks and gas balls - similar to those making up our Solar System.

The composition of the Universe has only recently been determined fairly precisely. Ordinary matter, making up the stars, galaxies, gas/dust clouds and a small fraction of the so-called empty space, accounts for about 4%. The rest is present in Dark Matter (undetected directly by any technique so far; includes the WIMPS and MACHOs discussed on page 20-9) which seemingly increases around galaxies, and makes up about 23% of a Universe that would give rise to the conditions now measured in the Cosmic Background Radiation, and Dark Energy (about 73%), tied to a still mysterious force that seems to act like the anti-gravity force first postulated by Einstein,which he called the Cosmological Constant, and is the prime candidate for causing the recent observation that the Universe now is once again expanding after slowing down for the first seven or so billion years.

The fate of the Universe depends ultimately on how much mass (and its convertible form, energy) it has. If that number is high the Universe’s expansion may slow down and eventually reverse (contract) so that all matter and energy collect again at a singularity which may undergo another Big Bang. Or the matter/energy is insufficient to slow expansion and the Universe enlarges forever. The shape of the Universe will depend on the nature of the expansion; at large scales the Universe is subject to the laws of Relativity (but equally as important is the role of matter/energy at the smallest - quantum - scales. Recent information favors endless expansion and the possibility that the rate of expansion is now increasing.

Add to all of this the theoretical (quantum-driven) possibility that there may be multiple universes, unable to communicate with one another, with new ones forming at various times and perhaps old ones dying in some way. The mind boggles at this point. But even more amazing is the realization that there is something we humans recognize as "mind" - our most valuable property and objectively the most powerful entity so far discovered in the Universe. Our minds have identified the ways in which planets form, including those suited to hosting living creatures, and the very nature of life itself.

Humankind has in the last 400 years, and especially the last 50 years, developed the skills and the will to explore our Universe. We now obtain data of great explanatory/interpretive value using telescopes that gather in radiation from all parts of the EM spectrum. Thus, there are now specialized observing systems that sample in the gamma-ray, x-ray, ultraviolet, visible, near and far infrared, and radio wavelength regions of the spectrum. Astronomy is probably the prime user of nearly all segments of that spectrum, as it gathers its information almost exclusively by remote sensing methods.

The big advance during the last 50 years has been to place astronomical telescopes into space, in orbits above the Earth's atmosphere. The most famed of these is the Hubble Space Telescope (HST) which has dazzled astronomers, other scientists, and the world public with its abundance of extraordinary images (data to the science community; art to many people without an interpretive background). There have been other great space observatories; we mention most of the best known in this Overview: the Compton Gamma-Ray Observatory (CGRO); the Chandra X-Ray Telescope; XMM-Newton; Extreme Ultraviolet Explorer (EUVE); the International Ultraviolet Explorer (IUE); the Far Ultraviolet Explorer (FUSE); the Galaxy Evolution Explorer (GALEX); the Infrared Astronomical Satellite (IRAS); the Infrared Space Observatory (ISO); the Space InfraRed Telescope Facity (SIRTF; renamed the Spitzer Space Telescope. No radio telescopes have yet been orbited but plans are underway.

This is perchance a gross simplification of the big picture. Read through this Section for more details. And watch for continual updates - so much is happening now.

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Before beginning this Section, we urge you to read through this hidden Preface (once there, hit your BACK button on the browser you use to return to this page). The Preface contains four major topics: 1) the role of remote sensing in astronomy; 2) some suitable references for additional information; and basic principles of 3) Relativity, and 4) Quantum Physics. The Preface contains a list of some very readable books and a number of Internet links to reviews or tutorials on Astronomy/Cosmology. Also, most of the illustrations in this Section were made from images and data acquired by spaceborne Observatories; for a listing of many of these with links to homepages click on this Internet site produced by astronomers at the Australian National University.

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The BIG BANG; The First Minute of the Universe; The Nature and Origin of Matter; The Early Eras

Introductory Overview

Cosmologists - those who study the origin, structure, composition, space-time relations, and evolution of the astronomical Universe - generally agree that the Universe had a finite beginning which by 1990 fe;; between 12 and 16 Ga (Ga = 1 billion years [b.y.]) ago; the current best estimate lies close to 14 Ga (13.7 is now recognized as the most accurate value [see page 20-9]). This is derived by measuring the time needed for light to have traveled from the observable outer limit of the Universe to Earth in terms of light years *, which can be converted to distances. The physical conditions that guaranteed the present Universe must have burst into existence almost instantaneously. During the first minute of the Universe's history, many of the fundamental principles of both Quantum Physics (or, as applied to this situation, Quantum Cosmology) and Relativity - the two greatest scientific discoveries of the 20th Century (see Preface, accessed by link above) - played key roles in setting up the special conditions of this Universe that have been uncovered and defined in the 20th Century. Quantum processes were a vital governing factor during the buildup and modifications of the particles and subparticles that arose in the earliest stages. Likewise, Relativity influenced the space-time growth of the Cosmos from the very start.

In the most widely accepted current model of the Universe, there is no starting place or time in the conventional sense of human experience. Space**, as now defined and constrained by the outer limits of the observable Universe, did not yet exist (see below); also, sequential events, embedded in a temporal continuum, had not begun. The observable Universe is just the visible or detectable part extending to the outermost reach of the Universe where objects or sources of radiation have sent signals traveling at the speed of light over an elapsed time not greater (usually somewhat less) than the time (age) of the start of expansion. Since now most cosmologists feel some confidence that there is something beyond the observable Universe (be it the unseen parts of our Universe or some other Universe(s)). That observed part plus the unobserved part is sometimes spoken of as the Cosmos.

Everything that exists physically is included in the Cosmos. (One can debate whether things "spiritual" are only the thought processes that have a physical basis, or these things really exist independently.) As this Section unfolds, you will come to realize that there is a hierarchy of the physical, arranged (in part) by a progression of decreasing sizes. That hierarchy, in its simplest form, is:

?? --> THE VOID --> OUR UNIVERSE (PERHAPS OTHER UNIVERSES)-->THE INTERGALACTIC MEDIUM --> GALACTIC CLUSTERS --> GALAXIES --> INTRAGALACTIC GASES --> STAR CLUSTERS --> STARS --> PLANETARY SYSTEMS --> PLANETS --> SATELLITES (MOONS) --> FIRST ORDER SURFICIAL AND INTERIOR FEATURES ON PLANETS --> LOCAL FEATURES --> INDIVIDUAL ENTITIES (FOR EXAMPLE, HUMANS) --> ATOMS AND MOLECULES --> SUBATOMIC PARTICLES --> SUPERSTRINGS -->?

The mysterious Void will be considered later in this Section. The initiating event which started our Universe from out of that Void, referred to as the Big Bang (BB), began at a point-like singularity (so small that the notion of spatial three-dimensions [3-D] has no conceptual meaning), some sort of quantum state of still-being-defined nature that marks the inception of space/time (thus, without a preceding "where/when"; philosophically "uncaused"), from which all that was to become the Universe can be mentally envisioned to have been concentrated. This singularity is thus described as not quite a point (dimensionless) condition which has extreme curvature and incredible density and where the laws of physics (including relativity) break down, i.e., do not apply. The singularity also ties in to the nearly instantaneous moment in time when the Universe is initiated after which some things can be said about the earliest behaviour of the Universe in terms of known or postulated concepts in physics). Just prior to the singularity's unfolding into the first moments of the Universe, space and time were completely joined (not distinguishable; and without any of the meaningful spacetime dimensions that would come into physical reality when the BB commences; thus the pre-BB may be without any meaningful geometric or temporal parameters).

At the very beginning of this (our) Universe, multidimensional space and time came into being and began to take on physical characteristics. But at the cosmic scale, these two fundamental properties must, according to Special Relativity, comprise the 4-dimensional spacetime Universe we now observe (according to some theories discussed below and on page 20-10, additional dimensions are possible). The exact nature (concept) of time is still not fully understood and is subject to continuing debate (for an excellent review of time, read About Time: Einstein's Unfinished Revolution by Paul Davies, 1995); also consult his Web site on "What happened before the Big Bang" at this site (the host site contains many interesting and provocative articles; click on Albert Einstein within the page that comes up to get to the parent site). There is, of course, the conventional time of everyday experience on Earth (years, days, seconds, etc.), measured fairly precisely by atomic clocks (e.g., the pulsating beat of a cesium atom, used to define the 'second') and less so by mechanical timepieces or crystal watches. There are the redefining ideas of time consequent upon Special Relativity, in which the perception of time units proceeds faster or slower depending on frames of reference moving at different relative velocities. There is the notion of "eternity" in which time just is - has no specific beginning or ending.

But, all these measures and concepts are difficult to extrapolate to that nebulous temporal state (if real) which was before the singularity of our Universe came into being. (Conceivably the singularity could have existed for some finite "time" before its inevitable instability forced the beginning we describe below as the Big Bang.) But, time had to separate at that instant and become measurable in terms we have set forth to use its property of steady progression of a temporal nature. If nothing existed prior to the singularity event, then scientists presently have no means to determine and measure the nature of the time that was involved as a prior state. If ours is not the only Universe (see the discussion of multiverses on page 20-10), and other Universes existed before the one we observe, then time in some way can be pushed backward to their inceptions. One possibility is an infinite number of Universes in time and space, with no end points for starts and finishes (read Paul Davies' book for the philosophical as well as physical implications of time, and the still unresolved dilemmas in specifying the meaning of time).

For our purposes in studying the Cosmology of the one known Universe, we will assume time started at the moment the Universe sprang into existence. Arbitrarily, we postulate that time is immutable (a second at the beginning is of the same duration as a second is defined by today); there are models that postulate variable time values but we will ignore these. We accept the subsequent progression of time as being comprehensible in the units we define for Earth living. Thus, the Universe, under this proposition, can be dated as to its age in years - the year being the present day time involved in the Earth's complete revolution around the Sun.

At the very beginning, the fundamental energy within the singularity may have been (or been related to) gravitational energy that controlled the nature of the singularity. An alternative now being investigated is some form of repulsive energy (similar to that once proposed by Albert Einstein) such as Quintessence (see page 20-10) which may prove to be related to the "Dark Energy" (page 20-9) that seemingly dominates the present Universe. At the instant of singularity, the initial energy (some of which was about to become matter) was compressed into a state of extremely high density (density = mass or amount of matter [or its energy equivalent] per specific [unit] volume), estimated to be about 10⁹⁰ kg/cc (kilograms per cubic centimeter) and extraordinary temperatures, perhaps in excess of 10³² °K (K = Kelvin = 273 + °C [C = degrees Centigrade]). Both high values are without any counterpart in the presently observed Universe. As you will see below, certain forms of matter came from the pure energy released during the first fraction of a second of the Universe's history. The famed Einstein equation E = mc² accounts for the fact that under the right conditions, energy can convert to matter, and vice-versa.

At the instant of creation, the singularity (which theory holds to have been less than 10^-33 of a centimeter in diameter), proved exceptionally unstable and proceeded to "come apart" by experiencing something akin to an "explosion", which goes under the popular name of the "Big Bang" (BB); implicit in this is the general idea of expansion (see page 20-1a, accessed through the link below on this page). This was not an explosion in the conventional sense, such as produces an incandescent gaseous fireball, but rather an extremely-violent release of kinetic energy released from the singularity that initiated the general expansion and has since (so far) exceeded the countering effect of gravity. The prime effect was to create and enlarge space itself. The explosion is described as "not into space" but "of space". No center can be found (in space today) for the BB since all points in the new finite but growing space simply draw apart more or less equally as space stretches under conditions in which pressure and density remain the same everywhere. This difference in behavior is clarified in the two illustrations (read their captions for more informaion) below taken from (Six) Misconceptions about the Big Bang, by C.H. Lineweaver and T.M. Davis, Scientific American, March 2005, cited again on pages 20-8 - 20-10.

ILLUSTRATIONS COURTESY OF ALFRED T. KAMAJIAN

Intuition suggests that the dots in the above illustration would also be expanding (enlarging). These yellow dots represent galaxies. But in fact they remain roughly the same size during the expansion and move as a unit. The star distances within the galaxies stay about the same. This is due to the strong interstellar gravitation that holds a galaxy, once formed, to a near constant size. Over time as galaxies spread apart from expansion their mutual interactive gravitational attraction weakens and this may disturb their shapes and shift the stars.

Expansion is thus continuing to the present in part because the inertial effects (evident in the observed recessional motions of galaxies, etc.) imposed at the initial push still influence how space grows and, now it is believed, in part due to the continuing action of the above-mentioned repulsive energy. After the freeing of gravity from the other fundamental forces (see below), it has since been acting on all particles, from those grouped collectively into stars and clouds making up the galaxies to individual nucleons, photons, etc. - thus at macro- to micro-scales. Gravity therefore exacts one controlling influence on the rate of expansion, serving to slow it down. But, this rate should be decreasing over time because gravity between the Universe's constituents weakens as expansion forces them further apart (Newtonian inverse square of distance r effect). As we shall elaborate later, recent evidence suggests that there are also anti-gravity forces (enabled by the repulsive energy of presently uncertain nature) that act to overcome the restraining effects of gravity which seek to slow the expansion and perhaps eventually draw matter together in a general collapse.

However, as treated on page 20-8, and again in the second part of this page, this expansion is actually a dilation (or "dilatation", a synonym) of space rather than a thrusting apart of individual matter through direct outward motion as for a familiar example the centripetal ejection of debris following a central explosion of, say, dynamite inside an automobile. Thus, the matter does not physically travel as do particles from a dynamite detonation site; space itself "travels" by progressive enlargement over time.

One cannot speak of "there" in reference to the singularity because the space that characterizes our Universe did not start to form until the moment of its beginning. It is difficult to think of any "there" since no dimensional frame of reference can be specified. At the outset of "creation" the singularity was made up of pure energy of some kind (in a "virtual" state within a "void" called the false vacuum). What might have preceded this moment at which the Universe springs into being and how the singularity came to be (become) remains speculative; theoreticians in the Sciences have proposed inventive, although somewhat abstract, solutions but the alternative and traditional views of philosophers (metaphysicians) are still taken seriously by many in the scientific community. This last idea is treated again near the bottom of Page 20-11 and a link to some of the writer's speculations.

This is an appropriate point to insert comments about what the writer has recently learned about the concept of the Instanton. This is an alternative version of the notion of the Singularity described in previous paragraphs. The Instanton is a condition that derives from Yang-Mills Gauge theory which is a part of what is known as Quantum Chromodynamics (QCD). We will not further delve into that subject but will just mention that Cosmologists such as Stephen Hawkings and Neil Turok have adapted Instanton theory to the conceptualizing of what was before and led up to the Big Bang, or any of the competing ideas for the Universe's inception. In a nutshell, they envision a process by which a quantum fluctuation in the vacuum or void prior to the initiation of the Big Bang led to the appearance of energy by a quantum tunneling process. Their "Pea Instanton", which had such high temperatures and pressures that it had to "explode", was created in this way. Rather than pursue this topic further here, we refer you to the Cambridge University link at the bottom of the Preface and to these two additional Web sites: (1) and (2).

Many scientists believe that what may have "existed" prior to the Universe was a quantum state (in a sense, analogous to the condition of "potency" in ancient Greek philosophy) which influenced a true vacuum (no matter whatsoever) that somehow possessed a high level of energy (of unknown nature but not, however, as photon radiation). Countless quantum fluctuations (which in quantum theory are said not to depend on [obey] metaphysical cause/effect controls and are not subject to time ordering) in this vacuum energy density produced sets of virtual particles and anti-particles (analogs to positrons, the positively-charged equivalent of an electron; neutrons and anti-neutrons, etc) that came into existence for very brief moments and then annihilated. But, rarely, annihilation did not occur, so that a particle could grow and trigger a 'phase transition' that led to the singularity from whence all that entails the Universe - matter, energy, space, and time - came into being. In this quantum model, it is conceivable that many such singularities could form from time to time, leading to mulitple universes that, as far as we know theoretically, cannot have any direct contact.

This is one example of prohibition by relativistic limits, in which information travelling at the speed of light cannot reach us from beyond the horizon - outer edge - of our own observable universe. The concept of the Cosmological Horizon refers to the boundary or outer limits of the Universe that we can establish contact with. This is approximated by the currently observed farthest galaxies that formed in the first billion years of cosmic time. This Horizon is also conceptualized as the surface dividing spacetime (which includes all locatable 4-dimensional points) into what we can see and measure from what is hidden and unobservable. The observable therefore must lie within our Light Cone, an imaginary surface that encloses all possible paths of light reaching us since the beginning of time. (The second illustration below is an example). Check page 20-10 for further discussion of these ideas.

The controlling factor in this "visual" awareness is just the speed of light (photons). If the Universe is about 14 billion years old, then light leaving just formed protogalaxies near the observable limit of the Universe departed some 13+ billion years ago but this radiation is only now reaching us, since it had to traverse across a Universe that was expanding (ever increasing distances) and drawing the protogalaxies away from us. (Scientists actually have detected cosmic background radiation [the "afterglow"; see page 20-9], which pervades the entire Universe, whose first confirmable appearance was only about 300,000 years since the beginning of the BB, at the time when detectable radiation could penetrate ion clouds that blocked its escape - this is the present longest-term limit to the lookback time involved, thus peering into the past to find the earliest discernible event). A distinction must be made between observed and observable: as will be discussed in detail on pages 20-8 and 20-9, there is strong reason to believe that the real Universe is (much?) larger, but part lies beyond the present limits of observation. As time moves through the future, the horizon will move into ever more of the ultimate Universe.

A corollary: In the Standard Model for the Big Bang, there have been and are parts of the Universe which cannot directly influence each other because there hasn't been enough time for light from any one part to have reached some others. Thus, the 'horizon' relative to Earth as the observing point (but any other position in the Universe is equally as valid an observing point) refers to the spatial or time limit that demarcates between what we can establish contact with in any part of the Universe and what lies beyond. This figure illustrates an extreme example of parts that cannot mutually communicate:

Let astronomers look out towards the apparent limits to the "outer" Universe, say at a distance of 13 billion light years (not quite to the farthest galaxies yet observed), in two opposite directions. As it turns out, that distance seems to be about the same no matter what direction astronomers look out at; this creates an apparent impression that Earth lies near the center of the Universe (but that will prove "false" or "meaningless" as discussed several paragraphs hence). But, if we perchance were at the center of this diagram, we'd assume that the galaxies at the opposing edges are 26 billion light years apart (the diagram is outdated and misleading since a 13.7 year old Universe [presently accepted best value] would produce a 27.4 billion light year separation). But for a 13.7 billion year old Universe, with radiation from each set of galaxies traveling at the speed of light, a signal from one galaxy group would not have had enough time to penetrate well beyond the Earth to observation points into the region of space on the other side. Thus, there has not been enough time for communication between one part of the Universe and various other parts beyond the 13.7 billion year limit. This is true throughout a Universe whose dimensions are equivalent to a 28 billion light-year diameter sphere (not necessarily the real shape of the Universe, since that is not actually known but is generally held to be flat; see page 20-9). This provides a convenient means to visualize the collection of objects in the observable part of the Universe. Within this sphere, there are thus pockets of space that are not in touch with other pockets.

This seeming paradox is called the "Horizon problem". Simply stated: how can these isolated regions have very similar properties (such as similar densities of Dark Matter, Cosmic Background Radiation, and numbers of galaxies) if they are not in contact. This appears to violate the fundamental principle of universal causality, which holds that during expansion all parts of the Universe would need to have been in communication (by light transfer or other means of exchanging energy) so that the fundamental principles of physics would have ample causal opportunity to influence each other. This is seemingly necessary if at a gross scale the Universe is to maintain uniformity (the essence of the Cosmological Principle which postulates broad homogeneity and isotropism). One explanation that accounts for the causality needed to obey this Principle is given below in the subsection dealing with Inflation.

Nevertheless the isolation of regions of the Universe from one another is a real fact, as evident in the above illustration. And, specifically there were situations whereby some parts of the Universe were not in causal contact shortly after the Big Bang, and thus not visible to one another during early cosmic history, but will eventually, as expansion proceeds, become known to each other. Consider the diagram below:

From J. Silk, The Big Bang, 2nd Ed., © 1989. Reproduced by permission of W.H. Freeman Co., New York

Start with hypothetical observers at two points A and B not then in contact in early spacetime. Over expansion time, their light cones would eventually intersect, allowing each to see (at time t₁) other parts of the Universe in common but not yet one another. At a later time, beyond t₂ ("now") in the future, the horizons of A and B (boundaries of the two light cones) will finally intersect, allowing each to peer back into the past history of the other.

These intriguing ideas just discussed actually don't tell the full story. One can arrive at a Universe whose farthest opposite points are about 46 billion light years apart. Check this diagram:

From: Misconceptions about the Big Bang, by C.H. Lineweaver and T.M. Davis, Scientific American, March 2005

ILLUSTRATIONS COURTESY OF ALFRED T. KAMAJIAN

On the left side is the model that equates the radius of the observable Universe with the age (rounded off here at 14 b.y.). This just assumes a "static" condition in which the age is determined by light speed alone. Light from the yellow spiral galaxy in the top panel left 14 b.y ago and arrives now in the bottom panel. But, in actuality, during that 14 billion years, the Universe has continued to expand. If one assumes a expansion factor of three during the 14 b.y. time interval, the situation is as pictured on the right. The light emitted from the galaxy has in 14 b.y. had to travel an ever enlarging space, so that today the galaxy is at least 42 billion years distance from Earth. Since we don't know where Earth really is in this finite Universe, it is currently impossible to determine the actual farthest points in opposing directions [on the sphere model, or on the flat model. But this diagram is important in indicating the Universe is really larger than the 28 billion light year dimensions cited above.

Commenting further on the Universe's geometry: One view holds the present Universe to be finite but without boundaries. Its temporal character is such that it had a discrete beginning but will keep on existing and growing into the infinite future (unless there is sufficient [as yet undiscovered] mass to provide gravitational forces that slow the expansion and eventually cause contraction [collapse]). A much different model considers the Universe to be infinite in time and space - it always was and always will be (philosphically, there are concepts that equate God as an "intellectual presence" distributed throughout this naturalistic Universe). These and other important ideas - whether the Universe's shape is analogous to spherical, hyperbolic, or flat; whether it is open or closed, whether it is presently decelerating or accelerating, and whether it is infinite or finite in time and space - are treated in detail on pages 20-8, 20-9, and 20-10.

So, by the end of the second quarter of the 20th Century, most models for the Universe's behavior considered expansion of some sort as an outcome. Einstein, in particular, showed that any three-dimensional expansion must also consider the effects of the fourth dimension - time - to account for the behaviour of light traveling great distances in a vast "volume" (without known boundaries) making up what we conceive of as "space". He also deduced that space must be curved (and light and other radiation will therefore follow curved paths as the shortest distance between widely separated points) and would, in his view, expand dynamically in a 4-dimensional spherical geometry (a spacetime dimensionality). (Einstein, at least in his early thinking, also considered the Universe to be finite and eternal.)

The next figure is a spacetime diagram that summarizes the history of the expanding and evolving Universe in terms of what is popularly known today as the general or Standard Big Bang (BB) model for its inception. (It received its descriptive name as a disparaging comment from the astronomer Fred Hoyle, who advocated instead a Universe of constant size as described in his Steady State model; variants of this and other models have been put forth, as described on page 20-9). Simply stated, the Standard Big Bang model holds the Universe to have expanded from a infinitesimally small point. In essence, the Big Bang is the creation event that started the Universe and determined its ultimate course of evolution through the state now observed and into its long term (perhaps infinite) future.

From J. Silk, The Big Bang, 2nd Ed., © 1989. Reproduced by permission of W.H. Freeman Co., New York

A variation of this figure with additional information appears below:

The Big Bang as an expansion theory traces its roots to ideas proposed by A. Friedmann in 1922 to counter ideas attendant to Albert Einstein's Theory of General Relativity, from which that titan had (erroneously) derived a model of a static, non-expanding, eternal universe (he eventually abandoned this model as evidence for expansion was repeatedly verified and he realized his General Relativity proved very germane to the expansion models). The Abbe George Lemaitre (a Belgian priest) in 1927 set forth another expansion model that started with his proposed "Primeval (or Primordial) Atom", a hot, dense, very small object that resembles the "singularity", a term more widely accepted. The nature of a Big Bang was refined and embellished by G. Gamow and others in the 1930s. Confirming evidence for expansion came from Edwin Hubble in the late 1920s. The Big Bang can be mentally related to the above-mentioned singularity by imagining that the expansion is run in reverse (like playing a film backwards): all materials that now appear as though moving outward (as space itself expands) would, if reversed in direction, then appear to ultimately converge on a "point of origin" that is represented by the singularity.

As described later in this Section (page 20-9), the BB concept drew its principal support from the observations by Edwin Hubble and others on radiation redshifts associated with the distribution of galaxy velocities. The Universe has been enlarging ever since this first abrupt explosion, with space expanding, and galaxies drawing apart, so that the size of the knowable part of this vast collection of galaxies, stars, gases, and dust is now measured in billions of light years (representing the distances reached by the fastest moving material [near the speed of light] since the moment of the Big Bang [~14 billion years ago]). This age or time since inception is determined from the Hubble Constant H (which may change its value) which is derived from the slope of a plot of distance (to stellar or galactic sources of light) versus the velocity of each source (see page 20-9).

Aside from quantum speculation, nothing is really known about the state of the Universe-to-be just prior to the initiation of the Big Bang (a moment known as the Planck Epoch). The Laws and the 20 or so fundamental parameters or factors that control the observed behavior of all that is seeable in the Universe become the prevailing reality at the instant of the Big Bang, but Science cannot as yet account for the "why" of their particular formulation and values, i.e., what controls their specifics and could they have come into existence spontaneously without any external originator, the "Creator" or "Designer". Among these conditions that had to be "fine-tuned" just right is this partial, but very significant list: homogeneity and isotropy of the Universe (the Cosmological Principle); relative amount of matter and anti-matter; the H/He and H/deuterium ratios; the neutron/proton ratio; the degree of chaos at the outset; the balance between nuclear attraction and electric repulsion; the optimal strength of gravity; the decay history of initial particles; the total number of neutrinos produced early on; the eventual mass density which affects the Critical Density; the specific (but varying) rates of expansion after the Big Bang; the delicate balance between Temperature and Pressure, both during the first moments, and much later during star formation; the ability within stars to produce carbon - essential to life; and much more. (See also another list at the bottom of page 20-11a.)

Some of these are interdependent but the important point is that if the observed values of these parameters/factors were to differ by small to moderate degrees, the Universe that we live in could almost certainly not have led to conditions that eventually fostered intelligent life capable of evolving during the history of the Universe as we know it. Also presumably necessary: beings that can attest to the Universe's existence and properties by making observations and deductions that lead to knowledge of the Universe. This requires the eventual appearance of "conscious reasoning" at least at the level conducted by humans on Earth, and perhaps also human-like creatures existing elsewhere in the Universe, - this concept is one of the tenets in what is referred to as the "Anthropic Principle" (page 20-11).

The First Minute of Universe History

Events in the first few fractions of a second, and subsequent time to the end of the first minute, of the Universe's existence have determined the nature and compositional makeup of the subsequent observed Universe of today. At present, that Universe consists of three prime components (in percentages determined from Cosmic Microwave Radiation data; WMAP Observatory; page 20-9), as shown in this figure:

This chart further subdivides the compositional makeup of the Universe:

At the instantaneous moment of the Universe's conception, gravity, matter, and energy all co-existed in some incredibly concentrated form (but capable of supporting fields of action) that cannot be adequately duplicated or defined by experiment on Earth since it requires energy at levels of at a minimum 10¹⁹ GeV (Giga-electron volts; "Giga" refers to a billion; one electron-volt is the energy acquired by a single electron when accelerated through a potential drop of one volt; 1 eV = 1.602 x 10^-12 ergs). A value of 10¹⁹ GeV is vastly greater than currently obtainable on Earth by any controllable process (presently, the upper limit obtained experimentally in high energy physics labs (with their large particle accelerators and colliders is ~10³ GeV). Best postulates consider the singularity (whatever its origin) at this instant to be governed by principles underlying quantum mechanics, have maximum order (zero entropy [see page 20-8]), and be multidimensional (i.e., greater than the four dimensions - three spatial and one in time - that emerged at the start of spacetime as the Big Bang got underway). Quantum theory does not rule out discrete "things" (some form of energy or matter) to have existed prior to the inception of the Planck Epoch; on the other hand, this existence is not required or necessary. But, as implied above and discussed in detail on page 20-10, "fluctuations" within possible energy fields in a pre-Universe quantum state (an abstract but potentially real condition that runs counter to philosophical notions of "being") may have been the triggering factor that started the BB.

This theory allows cosmologists to begin the Universe at a parameter called the Planck time , given as 10^-43 seconds (what happened or existed at even earlier time is not knowable [but can be inferred] with the principles of physics developed so far). At that instant, the Universe must have been at least as small at 10^-35 meters - the Planck length (about the same size as a string in superstring theory [see below]). At the initiation of the Big Bang, the four fundamental forces (gravity, and the strong [nuclear], weak [radioactivity], and electromagnetic [radiation] forces, referred to collectively as the Superforce) that held the Universe together co-existed (were unified) momentarily until about 10^-32 sec) in a special physical state that obeyed the conditions imposed by one meaning of the term Symmetry***. During this fraction of a second interval, gravity then was as strong as the other forces. Its tendency to hold the singularity together had to be overcome by the force that activated the Big Bang. The onset of fundamental force separation may have been tied to the force driving Inflation (see below).

But gravity thereafter rapidly decreased in relative strength so that today at the atomic scale it is 2 x 10^-39 weaker than the electrical force between a proton and an electron (according to one recent theory, gravity remained strong until about 10^-19 seconds). However, since the forces between protons (positive) and electrons (negative) are neutralized (balanced) in ordinary matter, the now much weaker gravitational forces are the major residual force that persists and acts to hold together collective macro-matter (at scales larger than atoms, specifically those bodies at rest or in motion subject to and described by Newton's Laws; includes those aspects of movements of planets, stars, and galaxies that can be treated non-relativistically). And gravity has the fortunate property of acting over very long distances (decreasing as the inverse square law: 1/r²). Although we think of gravity as the most pervasive force acting within the Universe, there is growing evidence that some form of gravity-like force also resides within an atom's nucleus but extends its effects over very short (atomic scale) distances.

The non-gravity forces that separated from the gravitational force are described by the still developing Grand Unified Theory or GUT, which seeks to explain how they co-existed. The GUT itself is a subset of the Theory of Everything (TOE) which, when it is finally worked out, will specify a single force or condition (or, metaphysically, a state of Being) that describes the situation at the very inception of the Universe. Thus, TOE unites the gravity field with the quantum field within the singularity that emerged as separate entities almost instantaneously at the start of the Big Bang. The TOE speculates on what may have existed or happened prior to the Big Bang, based on both quantum principles and belief that some other type of [pre-Bang] physics yet to be developed governed the pre-Universe void. At the Planck time, the four fundamental forces are said to be united (the Unified Epoch). The flow chart below (see also the third figure below) specifies the major components of each of the forces as they are assumed to exist after the first minute of the Big Bang. When unified at the outset of the Big Bang, they are presumed to exist in a state shown by the ? (whose nature and properties are still being explored theoretically; at present this condition cannot be produced experimentally because of the huge energies [way beyond present capabilities in laboratories] involved).

One model, now gaining some favor, based on Superstring theory (see last paragraph on this page) contends that at the first moment of the Big Bang (at the 10^-43 sec arbitrary starting point, before which any singularity or other state of existence cannot yet be described by any defined theory in present day Physics) the Universe-to-be consisted of 10 dimensions. As the process of the Universe's birth starts, six of those dimensions collapse (but presently exist on microscales as small as 10^-32 centimeters) and the remaining four (three spatial; one time) enlarged to the Universe of today.

The behavior of these forces in the earliest moments of the Big Bang was critical to the construction and development of the Universe as we perceive it today. Gravity in particular controls the ultimate fate of the Universe's expansion (see below) and formation of stars and galactic clusters. (According to Einsteinian Relativity, gravity, which we intuitively perceive as attractive forces between masses, is a fundamental geometric property of spacetime that depends closely on the curvature of space, such that concentrations of matter can "bend" space itself; Einstein and others have predicted the existence of gravitational waves that interact with matter; see the Preface for additional treatment). For all its importance, it is surprising that gravity is by far the weakest of the four primary forces. Its role in keeping macro-matter together and controlling how celestial bodies maintain their orbits is just that it becomes the strong, action-at-a-distance force left whenever the other forces are electrically neutral and have influence only out to very short distances.

Between 10^-36 and 10^-33 sec (a minuscule but vital interval of time - about a billionth of a trillionth of a trillionth earth seconds - referred to as the Inflationary Stage), there is evidence of a critical mechanism that explains certain fundamental properties of the Universe. Inflation was first proposed by Alan Guth, then at Princeton University, to account for some aspects of the Universe [see below] that were serious difficulties in the Standard Model. The theory holds that the nascent and still minute Universe underwent a major phase change (probably thermodynamic) in which repulsion forces caused a huge exponential increase in the rate of expansion of space. Through this brief moment the micro-Universe grew from an infinitesimal size (but still containing all the matter and energy [extremely dense] that was to become the Universe as it is now) to that of a grapefruit or perhaps even a pumpkin (an upper size limit is given as a meter). This is an expansion factor that may have been between 10⁵⁰ and 10⁷⁸ (this is the range of uncertainty, although some theoreticians choose 10⁵⁰ as the more likely number). Or, using another analogy, this is equivalent to increasing the size of the proton (~10^-13 cm) to roughly the size of a sphere 10,000,000 times the Solar System's diameter (arbitrarily, taken as the distance from the Sun to the far orbital position of Pluto, or ~5.9 x 10⁹ km).

This extreme growth determined the eventual spatial curvature of the present Universe (in the most "popular" model, tending towards "flat"). This next diagram illustrates the extreme growth of the incipient Universe during the Inflationary moment (both horizontal and vertical scales are in powers of ten); in the version shown, the Big Bang expansion is shown as decelerating over time but a vital modification which restores acceleration expansion to the Universe's progression is discussed on page page 20-10.

From Astronomica.org

Within this inflationary period, temperatures dropped drastically. During this critical moment, the physical conditions that led to the present Universe were preordained. The driving force behind this huge "leap" in size (which has happened at this extreme rate only once in Universe history) is postulated by some as a momentary state of gravity as a repulsive (negative) force (perhaps equivalent to Einstein's once-defunct Cosmological Constant but in a new form). Forces related to fundamental particles such the Higgs boson or the postulated "Inflaton" (see above) may have powered this tremendous expansion. Either particle is associated with a field (spatial region over which the force is said to operate; the force normally diminishes progressively with distance to the particle).

The source of the energy that drove Inflation has not been precisely identified but one theory ascribes this to potential energy within the quantum field of the Inflaton. Another hypothesis is that the energy was derived during the separation of gravitational force from the remaining three forces (see third diagram below). This may have released a huge amount of energy capable of bringing about the repulsion that marks the brief moments of inflation (see paragraphs on page 20-10 that describe Einstein's Cosmological Constant which depends on a similar repulsive energy related to an as yet undiscovered but apparently real Dark Energy). During this very brief inflationary period, different parts of the still "empty" surrounding void (where energy existed but into which the first particles that would form matter had not yet appeared and organized) were entered at a rate greater than the speed of light. In effect, it was this initial evolving dimensionality or space itself that was expanding. (Recent discoveries indicate that the Universe is now undergoing a second but relatively much slower rate of accelerating expansion that has turned around the post Big Bang gravitationally-mandated deceleration, beginning at some [still undetermined] stage [probably prior to the last 7 billion years] of the Universe's growth; see page 20-10.)

During inflation, as gravity began to act independently, gravitational waves were produced that had a critical bearing on the minute but vital variations in distribution of temperatures (and matter) in the subsequent history of the Universe as we know it. As time proceeded, gravity then reverted to the attractive force that took over control of further expansion. Specifically, a metastable state called the false vacuum - devoid of matter per se but containing some kind of energy - underwent a decay or phase change by quantum processes to a momentary energy density that produces the negative pressure capable of powering the inflation. Inflation continues until the false vacuum potential (which starts out as positive when its associated density field is zero), which initiated the expansion, drops to zero. The Universe thereafter has a positive density field that varies in space and time.

Advantages of the Inflationary model are that it sets the stage for the "creation" of matter, it accounts for the apparent "flatness" of the Universe's shape, and it helps to explain its large-scale homogeneity and isotropy (smoothness). Before the Inflation began this uniformity condition (homogeneity) existed, with the initial conditions in causal contact, and was subsequently "frozen in" to the Universe by the rapidity of inflationary expansion. Thus, prior to the moment of Inflation, all parts of the singularity were in communication with one another and their properties were coordinated. But, as Inflation proceeded, in which the components moved apart at a much faster rate that exceeded the speed of light, this communication was lost momentarily, whereas the previous uniformity was largely maintained during this super-expansion. Since then the components of the Universe (e.g., galaxies) in some parts of the Universe have been regaining communications with other parts. However, the model suggests that during inflation, energy may not have been perfectly uniformly distributed, producing narrow zones of greater concentration called "cosmic strings". These, during the following slower expansion, served as the irregularities which eventually led to concentrations of matter that localized into the early Universe structure around which the first galaxies formed. The slight departures from homogeneity also show up in the variations detected in the Cosmic Background Radiation (CBR, also referred to as Cosmic Microwave Radiation [CMR], see page 20-9).

Inflation also seems to solve the above-mentioned "horizon problem" (recall that horizon refers to regions of the Universe that are limited in their interactions [causal contact] by the distances photons can travel at light speed during the interval of time in which a cosmological phenomenon is being considered). This problem is illustrated by this diagram:

In this diagram parts of the Universe seem to lie outside these horizon limits (in purple). Such distant parts are not now in contact with one another (do not exchange light signals) and would seem causally independent. The Inflation model gets around this by 1) assuming these and all parts were in contact in that miniscule fraction of the Universe's first second before Inflation, and thus 2) had inherited, or "locked in" the co-ordinating physics underlying the Universe's operations that subsequently preserved general uniformity as the Universe went through its huge inflationary expansion.

A good summary of the essence and history of Inflation is at a Web site prepared by John Gribbin. This next diagram serves to show (conceptually) how inflation affected all that followed; it also previews much of what will be discussed later on this page.. Several variants of this diagram will appear throughout Section 20.

Although theoretical calculations and certain experiments seem to be confirming the essential points in the Inflation model, not every cosmoscientist has come to accept this innovative explanation of the earliest moments of the Universe and the consequences of its subsequent history that inflation seems to predict. In the past few years, some have turned their attention to alternate models. Most striking in its departure is the Varying speed of Light (VSL) model first espoused by Dr. Joao Magueijo in 1995, who later joined forces with Dr. Andreas Albrecht when they collaborated at the Imperial College in London. The essence of VSL is that during roughly the same time in the first BB second that Inflation would have operated, at this earliest moment the intense energy being release would cause the speed of light to be greater than today's value. That speed, ever decreasing, would then converge on the now constant value today, thus meeting Einstein's fundamental posit that this speed is constant. Magueijo and Albrecht have calculated that this phenomenon of rapidly dropping speed in these early instances can produce most of the same outcomes that the spatial expansion of Inflation leads to. Initially largely rejected by his colleagues, recent observations of possible light speed changes in the post BB Universe, if confirmed, have refocused attention on VSL. Like Inflation, VSL remains hard to prove since its essential characteristics occur under physical conditions that are still near-impossible to duplicate experimentally. Stay tuned.

Returning to the progression of physical events after Inflation but within the first minute of the BB. In the next paragraphs, we discuss the nature of matter and the interactions between matter and energy. Some of the ideas we present were extracted from the Internet. One major source of information on the Fundamental Particles making up matter, and of several illustrations below, is found at theContemporary Physics Education Project website. The coordinating chart that comes up after clicking on this link is reproduced here, even though unreadable (working with the link version can provide a satisfactory size):

These particles participate in the makeup of what is called an atom. The structure of an atom is shown next; discussion of the particles making up atoms then follows:

As described above, during the first fraction of a second following the Planck moment incredible events unfolded in rapid succession that led to release of kinetic energy that powered the Universe's development and created the initial stages of radiation. Matter was formed as condensed energy (an E = mc² transformation)(in the first minute some of the matter decayed back into radiation, releasing neutrinos and other particles). These primitive components of matter (or more properly, mass****) rapidly organized into a myriad of elementary particles. They fall into two broad classes:

I) the FERMIONS: all particles with quantum spins of 1/2 of odd whole numbers such as 1, 3, 5 (includes protons, electrons, neutrons); they all obey the Pauli Exclusion Principle which states that no two different particles can have the same values of the four quantum numbers. Fermions can be divided into subgroups: 1) the heavier Hadrons (minute particles, consisting of certain QUARK combinations held together by Gluons (massless force particles) permitting strong interactions within atomic nuclei), further subdivided into (a) the Baryons (combinations of three quarks [see 4th paragraph below on this page] that include the familiar protons and neutrons (each about 10^-13 cm in size [compared with diameters on the order of 10^-8 cm for the classical Bohr atom]) and (b) the Mesons (short-lived heavier particles) families, and 2) the Leptons, even tinier discrete particles that are weakly interacting (that are represented by electrons, tauons, muons, and three types of neutrinos (electron-neutrino; tau-neutrino; muon-neutrino; the discovery of the latter two imply that the neutrino may have a small mass, and if proved could account for some of the missing matter in the Universe talked about later in this Section). Some of the above is summarized in these two diagrams;

II) BOSONS, the force carrying messenger particles; these have unit [1] spins. Best known of the bosons are the 1) photons (which have zero rest mass) that are quanta ***** of radiant energy responsible for electromagnetic (EM) forces which travel at light speed as oscillatory (sinusoidal) waves and 2) the gluons that bind the nucleus by mitigating against the strong repelling forces therein. A boson that theory says exists, but as yet has not been "found" is 3) the graviton, which transfers the force of gravity (also, at the speed of light). This chart summarizes bosons:

Much of the above information is summarized in the chart below. This classification of particles and their interactions is an integral part of the Standard Model for the ways in which matter is put together, which applies to any Big Bang scenario (without the refinements of Inflation) that leads to a broadly homogeneous, isotropic large-scale Universe and is an acceptable summary of what is verifiably known now about the origin of matter and energy (with the caveat that the model is subject to continual modification or revision).

Illustration produced by AAAS, taken from The Economist, Oct. 7-12, 2000, p. 96

In this classification, the major entities are the three families: Quarks (gray), making up the Fermions, and including Baryons; Leptons (orange), and Bosons (brown). The quark particles have generally been discovered and proved to exist from high energy physics experiments using particle accelerators.

A variant of this classification which arranges the mass and force particles according to measured or estimated mass of each type of particle is shown below. In this version, Leptons are considered as classified within a more general category of Fermions. The chart emphasizes the growing belief that mass itself is governed by the relative contribution from the Higgs Boson (see footnote 4 (****). The different masses arise from different interactions of fundamental particles with the Higgs field (of which there may be different sets with different values and properties),

From The Dawn of Physics Beyond the Standard Model, by Gordon Kane, Scientific American, June 2003

Quarks were the first (sub)particles to form during the early moments of the first minute. The nomenclature for the 6 quarks are descriptive terms for convenience and carry no special physical significance. There are six types or "flavors" (Up, Strange, etc.), each subject to variants or "colors"; various combinations of quarks give rise to the different nucleons). Quarks have a baryon number of +1/3, charge numbers of +2/3(up) and -1/3(down), and a spin quantum number of 1/2. The two Baryons familiar to most are made of three Quarks: the proton consists of two up (each +2/3) and one down quark (-1/3) for a net charge of 1; the neutron two down and one up quark, for a net charge of 0 (zero). Mesons contain only two Quarks.

Quarks also can have a reverse sign, thus they can organize into anti-protons and anti-neutrons. Other combinations of Quarks lead to more exotic particles; one group includes mesons, which include members such as the pion Π^-, consisting of an anti-up quark (-u) and a (d) quark and the kaon K⁺ made up of a (u) and an (-s) quark.

According to a Higgs field-based model, protons and neutrons derive their mass from the energy of motion of the quarks and gluons flying around the nucleus.

The Leptons have much smaller masses and are single particles (not containing the quark subparticles). They are not influenced by the strong nuclear force but can interact through the weak nuclear force. Three of the Leptons (upper row) are neutrinos which have extraordinary penetrating power (one can pass through the entire Earth without interacting or changing); once thought to be massless, evidence now suggests a very small mass.

The force particles (Bosons) are involved with the individual fundamental forces mentioned above. For example, the gluon holds the nucleus of baryons together; z and w Bosons control the weak nuclear force; photons are the force carriers that are associated with electromagnetic radiation; gravitons transmit the force of gravity. The Higgs Boson has not yet actually been proved to exist (but from theory is considered almost certainly to be real); recent experiments in a European supercollider may have witnessed a few genuine Higgs particles but confirmation will likely await several new supercolliders capable of much higher energies due to come on line before the end of the first decade in 2000. The Higgs Boson is considered to be the force particle that accounts for mass in the fundamental particles that have that property.

Little has been said so far about neutrinos. But these are particles of great importance. They reside in the nucleus and are released during both radioactive decay and nuclear fusion. They are one of the four fundamental particles. They are without electric charge (with an energy of 0.001 eV) (unique in this respect; neutrons, also chargeless, actually consist of a combined proton [+] and electron [-]). Once thought to be massless, much like the photon, experiments have now shown that they travel at less than light speed and hence possess some minute mass (any particle traveling at the speed of light is without mass, i.e., all its mass is converted to energy). They are super-abundant (~100 million of them for every atom in the Universe); more than a trillion pass through your body at any one second. They are ubiquitous: they are a main constituent of cosmic rays; they are produced during the Sun's persistent fusion; they even form by collisions within the atmosphere. Yet, they pass through the full Earth almost unimpeded, rarely interacting with nuclei.

Neutrinos were first proposed in 1936 by Wolfgang Pauli of Quantum Mechanics fame. But their existence was first confirmed in 1956 through an elaborate experiment by Dr. Ray Davis who built a detector consisting of a large vat of cleaning fluid set deep within a South Dakota gold mine. Extremely rare collisions with chlorine in the fluid produced argon. Davis consistently came up with a tiny number (3 argon atoms in a set time span) that was at odds with the model proposed by Dr. John Bahcall of Princeon based on his model of thermonuclear fusion in the Sun, who detected 10 per unit time. The discrepancy was not resolved for decades until it was realized that the neutrinos, which had the three "flavors" mentioned above, actually underwent a transition process (called oscillation) of the original ν_e or electron neutrino (the only flavor produced in solar fusion) into tau and muon neutrinos, all three in about equal proportions. Since the Davis detector only could count electron neutrinos, the discrepancy was explained. A subsequent detector, a deuterium water vat in a Sudbury, Ontario nickel mine, has proved capable of counting all three flavors, so that both Davis and Bahcall were right insofar as their predictions and counting difference are now explained.

The importance of neutrinos is still not fully understood. They are essential in accounting for energy involved in nuclear processes, so that the Law of Conservation of Energy is sustained. Their role in the Big Bang, and before it, is still being investigated. They may have pre-existed the BB and may be one of the virtual particles. There is growing evidence that a type called the "sterile neutrino" (that is not influenced by the weak force) is involved (and may be the main constituent) in what is known as Dark Matter (see page 20-9). They also are possibly important in determining the imbalance between matter and anti-matter. They are important in the high temperature processes of the initial minutes of the Big Bang because they are factors in some of the possible reactions, especially in the formation of helium, and thus helped to determine the relative abundances of H, He, Li, and Be - those elements that mark the initial composition of the material Universe. The detection of neutrinos (which cannot be measured directly by instruments since they have no charge) is one of the great "detective stories" successes of Physics.

Likewise, the Standard Model is itself a great achievement in Astrophysics. When examined rigorously, it is now considered only an approximation to full reality in subatomic physics. It fails, for example, to explain and integrate gravity. Attempts to revise it are leading to what is called the Supersymmetric Standard Model (SSM), mentioned again below. Theoreticians believe that gravity must have its own Boson which they have named the Graviton. Although it most likely exists in some form, its actuality has yet to be proved. It has not been found during any of the current particle accelerator experiments (which are also looking for the Higgs Boson, but none now operating may be powerful enough).

Now, returning to the events of the first minute: By ~10^-39 sec there was a fundamental symmetry break that brought on a split between the GUT forces and the other fundamental force known as gravity, dependent on the Graviton. The history (pattern) of force dissociation during the first second is depicted in this illustration:

From The Left Hand of Creation, J. Barrow and J. Silk, 1993, Oxford Press

At 10^-35 second there was a further split of non-gravitational forces into the Strong and the Electroweak (combination of Weak and Electromagnetic) forces; the Electroweak pairing then separated into today's EM and Weak forces at about 10^-10 sec. From 10^-35 to 10^-6 sec, matter consisted of the subatomic quarks (Quark Era), and their binding particles, the gluons, present but not yet involved in producing nucleons (protons, neutrons). Temperatures were still too high (10²⁸ °K) to foster quark organization into these nucleons. By the start of this interval, at the time when energy levels dropped to about 10^-16 GeV, the GUT state underwent dissociation into the Strong nuclear force (binding nuclei) and the Electroweak force. At about 10^-9 sec, by which time temperatures had fallen to ~10¹⁵ K, the Weak nuclear force (involved in radioactive decay) and the Electromagnetic (EM) force (associated with photon radiation) separated and began to operate independently. Then, by 10^-6 seconds, the six fundamental Quarks had organized in combinations of 2 or 3 into hadrons during the brief Hadron Era.. Protons formed by this time remained stable but some neutrons produced later experienced decay into protons and electrons. This Era was followed at 10^-4 seconds, lasting up to one second or so, by the emergence of electrons, neutrinos and other Leptons (Lepton Era). Thus, prior to 10^-6 seconds, quarks had formed almost exclusively, but by the end of the first second of time they were greatly reduced in number as free (unorganized) particles, even as Hadrons, Leptons (especially neutrinos) and photons (the particle carriers of electromagnetic energy) were becoming the dominant products despite extensive electron-positron and bBryon-antibaryon annihilation. As electrons emerged, some reacted with protons to form neutrons, releasing neutrinos. From this point on, the ratio of Baryons to photons is 1 to a billion (a similar number holds for the ratio of Baryons to neutrinos).

From the GUT stage onward, both matter and antimatter were being created (baryogenesis). By 10^-4 sec both quark particles and antiparticles (with opposite charges, e.g., at the Lepton level an anti-electron or positron would have a + charge) that had earlier coexisted had now interacted by mutual annihilation. Neutrinos and antineutrinos released by proton-electron reactions also experienced this destruction. So, at this moment only a residue of elementary particles survived - (almost?) all antiparticles apparently were completely wiped out leaving only some of the numerically larger amounts of particles. Annihilation is an extremely efficient process for releasing the maximum amount of energy when positrons and electrons meet - destruction of a pair generates 10⁶ electron volts. During the annihilation phase, a great quantity of high energy gamma ray radiation and other energetic photons produced from the interactions comes to dominate the particles in the incipient Universe.

By 10^-3 seconds, the temperature had now dropped to 10¹⁴ K and the proto-Universe had a diameter roughly the size of our present Solar System. In the next few seconds, temperatures dropped below a level where further antiparticle production took place in abundance. The particles making up the Universe today represent the excess over the few surviving antiparticles. Most of the latter would have concentrated in near empty space outside any cluster of matter (the stars, galaxies, gas clouds, etc.) - if antiparticles still co-exist in significant amounts with the particles we deal with on Earth or in the denser cosmic world, the effects of destruction might be detectable; no evidence that this is going on to a noticeable degree has been found.

At the one second stage, the Universe had already expanded ****** to a diameter of about 1 to 10 light years even as its density had decreased to ~10 kg/cc (kilograms per cubic centimeter), and its temperature had dropped to about 10¹⁰ K. By this time all the fundamental particles (essential matter) now in the Universe had be created, largely from the vast quantities of photons (energy "fuel") released during the first second. As of the first minute, about 1 free neutron existed for every six protons, although all of these neutrons would eventually combine with protons in isotopes and heavier elements. The general excess of protons persisted, making those Hydrogen atom nuclei then and still the most prominent atomic species in the Universe. Neutrinos by now had appeared in abundance as the principal energy released when protons combined with electrons and protons fused with other protons. These neutrinos thereafter became decoupled from other matter.

Much of what is known about events, conditions, and sequences during the first minute of the Universe has been surmised from theoretical hypotheses and calculations together with high energy experiments. One focus is on the strong force between Quarks, examined using the theory of Quantum Chromodynamics (QCD). Experimental verification of Quark behavior requires building of Particle Accelerators or Colliders that are major undertakings in terms of costs and technical "know-how". In February, 2000 an announcement from CERN in Geneva claims to have reproduced conditions equivalent to the first ten microseconds (10^-6 sec) of the Big Bang. In effect, a "mini-Big Bang" is generated that lasts for much less than a trillionth of a second. To achieve this, the SPS-CERN Accelerator hurls Lead atoms (heavy) in a beam that strikes Lead or Gold targets at tremendous velocities. Momentarily, temperatures at the collision point reach 100,000 times that of the Sun's interior (~1.5 billion °C), at which the physicists interpreting the experiment postulated production of a plasma (electrically-charged "gas") emanating from the contact zone that is composed, for a very brief instant, of Quarks and gluons. These quickly recombine into protons, neutrons, and electrons as the heated material dissipates.

New colliders, generating at least 10 times more energy, are coming on line since 2000, so that relevant new experiments will likely confirm the theoretical models that describe the history of the later part of the first minute. Now active is the Relativistic Heavy Ion Collider (RHIC) operating at the Brookhaven Laboratory on Long Island. Using high speed Gold nuclei that are driven in opposite directions, collisions now duplicate the conditions representing the first microsecond. At that moment it now appears that the quark-gluon "soup" was liquidlike rather than a gas plasma. Some parameters at this moment are: Energy released = 20000 GeV; Temperature = approaching 6 trillion °C; Pressure at impact = 10³⁰ atmospheres; Duration of event = 10^-23 sec.

Next up is the Large Hadron Collider (LHC) at CERN that will approach conditions equivalent to the first 0.1 microsecond in the Big Bang sequence. Energies comparable to those extant during the first moments (earlier than 10^-11 sec) are so great that no appropriate experimental setup is feasible for the foreseeable future, and may never be attainable in physics labs on Earth.

There is one fundamental topic that we haven't yet treated on this page in any detail: the three main categories of constituents of the physical Universe - Ordinary Matter (4%), Dark Matter (23%), and Dark Energy (73%) - which comprise all that is present in the observable Universe. Suffice to say here that the current distribution, percentage-wise, of these categories was established during the first minute. The treatment of the two "Dark" types is deferred until page 20-9 and 20-10 in order to develop other cosmological concepts needed to plumb the meaning and implications of the categories.

We close this part of the page by commenting on some other topics in Big Bang expansion. Newer models treating aspects of the physics and mechanisms of expansion during the first fraction of a second of the Big Bang have been proposed (see below) and the theory behind each is currently being tested experimentally. We will cite and briefly describe three of the most intriguing at the moment, but will forego any in-depth explanation:

1) Primordial Chaos: which postulates that in the earliest stages of the Big Bang the distribution and behavior of matter and energy in the incipient Universe was notably disordered and inhomogeneous, irregular, and turbulent, with variations in temperature and other scalar (non-directional) properties, anisostropic expansion rates, and other disturbances in the initial conditions within various parts of the rapidly changing microverse (a variant, called the Mixmaster model, considers the expansion to oscillate into a few momentary contractions at the outset). As the Universe grew both during Inflation and afterwards, these irregularities were smoothed out, leading to the gross isotropy of the present Universe; one version assumes a cold rather than very hot initial state;

2) Supersymmetry: a symmetry property which states that for every Fermion (quantum spin of 1/2) there must be a corresponding force-carrying Boson (quantum spin of 1), called a sparticle of the appropriate kind; likewise each Boson has a corresponding Fermion sparticle; thus, in this model the number of particles that exist is doubled; the concept predicts that there must be some subatomic particles still to be discovered if this pairing is valid); these supersymmetric particles are heavier than normal particles and may be a major constituent of Dark Matter (page 20-9). The Supersymmetry Standard Model (SSM) is proving to be a plausible means for simplifying the broken symmetry problems that beset the Standard Model;

3) Extra Dimensions: Such as those associated with Superstring theory; (last paragraph).

Big Bang Eras after the First Minute

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 a misnomer 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. Its existence is equated with that of the Cosmic Background Radiation, the remnant of the initial (and small) 'fireball' consisting of the radiation and matter of the first eras.

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). 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.

From Astronomica.org

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 higher N 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 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". 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 predominantly 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). The time that lasted from after the first few minutes to about 300,000 years (cosmic time, i.e., since the moment of the Big Bang) is known as the Radiation Era (connoting the dominance of electromagnetic radiation). Appreciable numbers of solid atoms had formed by 100,000 years during this Era. As expansion proceeded, the mass-equivalent radiation density (E = mc² equivalency) 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 ~10000 years but temperatures remained too hot for electrons to combine with nuclei. The Universe during this stage was opaque (in the sense that no visible light passes from one point to the next) because, even with decreasing photon density, detectable radiation at these wavelengths was prevented from traversing or leaving the enlarging primitive Universe's confines owing to internal scattering by free electrons.

This era of first opaqueness ended roughly 380,000 years after the Big Bang (some recent estimates put this termination at closer to 500,000 years after the B.B.) with the onset of the Decoupling Era, at which stage cooling had dropped below 3,000° K, allowing protons and helium nuclei to start combining with electrons to form stable Hydrogen and helium atoms - a process known as Recombination). As this era began, the Universe was about 1/200th its present size. Thereafter for a time, the extreme decrease in numbers of free electrons (today there are about one free proton and electron for every 100,000 atoms) drastically reduced scattering (not by direct collision as occurs when sunlight hits dust but by close interaction between the photon and electron or proton fields). The Decoupling Era lasted until approximately the first million years of Universe history.

This atomic Hydrogen absorbs radiation at various wavelengths. In the Visible range, for example, the Universe would appear as though it consisted primarily of a dark mist. For about 400,000 years, this Hydrogen acted as a kind of atomic "fog" which kept the Universe opaque (often referred to as a cosmic Dark Age). At this time, any radiation within the fog would have extended into the Ultraviolet. A glow would be apparent at those wavelengths, since at that time the Cosmic Background Radiation would give off UV light as it continued to redshift from preceding shorter wavelengths enroute to its present-day microwave emission wavelengths brought on by continuing expansion of space. The Cosmic Background Radiation (CBR)(discussed in detail on page 20-9) represents the residual "afterglow" of the Big Bang - the once very hot thermal radiation that has cooled thermodynamically to its present 2.73...°K value (detectable in the microwave region). This radiation seems nearly isotropic in all directions from which we observe the Universe. However, it does show tiny, but extremely important deviations in temperature; the diagram below shown on page 20-9 is reproduced here to illustrate this.

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). 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 difference.

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:

From Scientific American, February 2004

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. 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.

As the first stars and protogalaxies began to develop towards the end of the first half million years, their strong outputs of electromagnetic radiation caused a Re-ionization (removal of electrons) of the Hydrogen that increased to the extent that the earlier opaque (at Visible wavelengths) Universe now became rather rapidly transparent to radiation spanning those wavelengths. 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). This transparency facilitates free passage from external sources of visible wavelengths within any region of the Universe.

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 formed in this period. 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 participates in the appearance of the first galaxies. As the first stars formed, their UV radiation 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 UniverseScientific American, November 2006.)

The Decoupling Era is estimated to have lasted to perhaps as long as the first million years, although most of the Baryon-Lepton recombination took place in the beginning years. The end of the Decoupling Era was thus the end of the Dark Ages in Cosmology. As we will see in the next page, during this period 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.

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 object in the Universe. Stars began to form around the end of 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 1,000,000 degrees centigrade, 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 20-2ff 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 20-3ff.

Let us summarize several of the above ideas on this page, plus several 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. Labeled on his site 21st Century Science, specifically the section entitled "The Birth of the Universe".

This diagram serves to summarize much of what has been already introduced on this page, but introduces the idea that Black Holes may have form at the very moment of inception of matter. Black Holes (in this Section often abbreviated "B.H.") are ubiquitous objects found mostly within galaxies (but some may exist in intergalactic space). They are extremely dense, so much so that their extraordinarily intense gravitational pull prevents radiation from escaping them (exception: Hawking radiation) but also causes material around them to be pulled into them, commonly generating huge amounts of energy release that can be detected over the entire spectrum. (Quasars are one manifestation of this energy release.) They range in size from very small (centimeters) to sizes on planetary scales (these latter are referred to as Supermassive B.H.'s. Black Holes commmonly form from ultimate collapse of very massive stars. Black Holes play an important - perhaps critical - role in getting galaxies started and are thought to lie in the central region of most (possibly all) galaxies.

The preceding diagram gives the intergalactic temperature history of the Universe on the ordinate. For emphasis, that history is singled out in this table:

Three additional comments are appropriate here, now that the above ideas have given you a background 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.

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 I_s) - 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 I_s 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 it. 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. 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.

Note to reader: Before proceeding to the second page (covering Stars),some may wish to acquire a broader framework at the outset that describes a General Model for the SpaceTime expansion of the Universe that has continued after the first eras of the Big Bang. This and related subjects are considered in more detail on page 20-8, 20-9, and 20-10. You are given the option of skipping it by going directly to page 20-2 (click on Next below) or if you wish to build up this background now; you can access it at page 20-1a. If you choose the latter, check especially the paragraph in red at the bottom of page 20-1a.

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_{*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.) The parts of the Universe now visible 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}