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 with slow modems; 2) Some parts or ideas presented in this Section may seem repetitious, i.e., are stated more than once; 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.
ASTRONOMY AND COSMOLOGY:
THE DESCRIPTION, ORIGIN, AND DEVELOPMENT OF THE UNIVERSE
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:
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, which deals with the origin, development, and future expectations for the Universe, also began in early times, with both myths and theological explanations for the meaning and cause(s) of the phyical (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”, or galaxy and surmised that other such galaxies must exist. This lead to the beginning of the modern era of Cosmology stemming for work by Edwin Hubble in the 1920s.
Before the beginning of the (this) Universe there was no time nor space, no energy (in the discrete forms we know) nor matter. What may have existed is some as yet undefined quantum state in which fluctuations in the “emptiness” led to extremely fleeting “particles” containing the essence to grow into a Universe. Essentially all such evanescent moments ended with the disappearance of the ???. But the potential was there for one such moment to see “creation” of a singularity from when the Universe sprang.
This singularity was so unstable that it “exploded” into what is known colloquially as the “Big Bang”. That took place some 14 billion or so years ago. 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), when the Universe was infinitesimally small. (Experimentally, astrophysicists can actually reconstruct the sequence and verify the essential physics of the Universe�s early condition back to 10-12 seconds and to particle sizes as small as 10-17 meters; better yet, 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 the new theory in physics called “superstrings”). But, they quickly separated systematically into the individual 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 (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 (and 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 300,000 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) 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.
Stars burn their hydrogen at high temperatures, during which (depending on their size) they convert the fuel to heavier elements. Large stars die out rapidly (a few billion years to much less); small 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; 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 fate of the Universe depends ultimately on how much mass it has. If that number is high the Universe�s expansion will 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. 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.
This is perchance a gross simplification of the big picture. Read through this Section for more details. And watch for updates - so much is happening now.
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.
The Nature and Origin of Matter; The Early Eras
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 between 12 and 16 Ga (Ga = 1 billion years [b.y.]) ago; the current best estimate lies close to 14 Ga. 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 unobserved part plus the observed part is sometimes spoken of as the Cosmos.
The initiating event, referred to as the Big Bang, 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) but without any meaningful geometric or temporal value.
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 there is no means to determine and measure the time 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 a start to the time accompanying the moment of its existence and its subsequent progression 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.
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 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 far 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” (B.B); 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”. 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. As we shall elaborate later, recent evidence suggests that anti-gravity forces (enabled by the repulsive energy of presently uncertain nature) have overcome the restraining effects of gravity seeking 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) <http://stripe.colorado.edu/~yulsman/Instanton1.html>`__ and `(2) <http://web.uvic.ca/~jtwong/>`__.
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 (in terms of our terrestrial perception of time, based on a complete revolution of Earth around the Sun), 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. (We actually have detected cosmic background radiation [see page 20-9], which pervades the entire Universe, whose first appearance was only about 300,000 years since the beginning of the B.B. - 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 one part to have reached the other. 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, in two opposite directions. We, at the center of this diagram, would assume that the galaxies at the opposing edges are 26 billion light years apart. But for a 14 billion year old Universe, and 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 US into the region of space on the other side. Thus, there is no (time for) communication between one part of the Universe and various other parts. 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, but an adequate means to visualize the collection of objects in the observable part of the Universe). Within this sphere, there are pockets of space that are not in touch with other pockets. (A pocket of the pervasive Cosmic Background Radiation, for example, that covers about 2° of the sky hemisphere above us on Earth does not interact with radiation beyond it as the Universe continues to expand.)
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.
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.
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 (B.B.) model for its inception. (It received its descriptive name as a derisive comment from the astronomer Fred Hoyle, then precept of expansion, 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 which gives a summary of energy levels and temperatures for the evolutionary history of the Universe is too big for this page. You can access it by clicking here. Note that most temperatures are expressed in energy equivalents as eV’s or electron volts (GeV refers to Giga-electron volts). To return to the present page, you will need to hit the X button on the upper right of the screen that comes up with your browser.
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 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 B.B. 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 to 15 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”).
The First Minute of Universe History
At the 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); 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 B.B.
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 with the principles of physics developed to this day). 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 existed 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 remains 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). 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 mark; before which any singularity or other state of existence cannot yet be described by present 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) a mechanism to explain certain properties of the Universe was first proposed by Alan Guth, then at Princeton University), to explain 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 (approximately a trillionth of a trillion of a trillionth [10:sup:-36] of a second), 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. 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:sup:-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 is discussed on page page 20-10.
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 such as the Higgs boson or the postulated “inflaton”) that forced this tremendous expansion.
The source of the energy that powered Inflation has not been precisely identified but the separation of gravitational force from the remaining three forces (see third diagram below) may have released a huge amount of energy capable of bringing about the repulsion that marks 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 the brief inflationary period, different parts of the still “empty” void (energy existed but the first particles that would form matter had not yet appeared and organized) separated at a rate greater than the speed of light - in effect, it was this initial evolving dimensionality or space 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 (now with a positive field that has varied 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 helps to explain its large-scale homogeneity and isotropy (smoothness). Before the Inflation began this uniformity condition existed, with the initial conditions in causal contact, and was subsequently “frozen in” to the Universe by the rapidity of inflationary expansion. Theory suggests that during inflation, energy may not have been pefectly 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.
Inflation also seems to solve the above-mentioned “horizon problem” (recall that horizon refers to the sections 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 present in this diagram:
In this diagram parts of the Universe seem to lie outside these horizon limits. This simple diagram may help to better visualize this:
Such distant parts are not now in contact with one another (do not exchange light signals) and would seem causally independent. But this isolation, which appears to defy causality, in 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.
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 B.B. 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 B.B. 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 B.B.: 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. From the radiation associated with this energy, matter was formed (an E = mc2 transformation)(in the first minute some of the matter decayed back into radiation, releasing neutrinos and other particles). These primitive forms of matter 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 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), and
II) *BOSONS*, the force carrying messenger particles; these have unit  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).
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 fermions composed of quarks (elementary particles with fractional charge that comprise protons, neutrons, and mesons), the leptons (including the electron), and the bosons, force particles with finite (but very small) mass. The gray field containing the quarks is the Baryon group. 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. The chart emphasizes the growing belief that mass itself is governed by the relative contribution from the Higgs Boson.
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 (of which 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) are descriptive terms for convenience and carry no special physical significance. 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. As a visual aid, this is summarized in this diagram:
|Quark components of protons, neutrons, and mesons. |
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.
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.
The Standard Model, when examined rigorously, is now considered only an approximation to full reality in subatomic physics. It fails, for example, to explain and integrate gravity. 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).
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 (an infinitesimal particle which has yet to be “discovered” or verified by physicists). The history (pattern) of force dissociation during the first second is depicted in this illustration:
during the first minute of the Big Bang.|
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 particles known as quarks (Quark Era), and their binding particles, the gluons, present but not yet involved in producing nucleons (protons, neutrons). Temperatures were still too high (10:sup:28 °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 (itself an interactive composite of the electromagnetic and weak forces). 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 baryon-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 (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 1 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 energy released when protons combined with electrons. These thereafter were decoupled from other matter.
The search goes on for convincing proof of the full nature of the neutrinos that are often the energy particle released from weak force nuclear reactions that took place at very high temperatures. They are abundant today (~100 million of them for every atom in the Universe), with most coming from production during the first minute, and some from stellar reactions. Being without charge (and with an energy of 0.001 eV) and massless or nearly so, these particles do not readily interact with matter. They pass easily through your body, or even through the entire Earth, because the likelihood of collisions is very small. They are thus very hard to detect (and thus prove their existence); elaborate experiments using huge tanks containing water or other hydrogen compounds have so far recorded only a few possible neutrino interactions. However, 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.
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. Experimental verification, particularly during the earlier moments in this critical minute, has been limited because, as they were taking place, the energies involved were huge - well beyond the capabilities of even the most powerful particle accelerators and other means of directly observing particle behavior. However, in February, 2000 an announcement from CERN in Geneva claims (as yet unverified by other labs) to have reproduced conditions equivalent to the first microsecond (10:sup:-6 sec) of the Big Bang. Accelerators hurled lead atoms in a beam that struck lead or gold targets at tremendous velocities. Momentarily, temperatures at the collision point reached 100,000 times that of the Sun’s interior (~1.5 billion °C), at which the physicists interpreting the experiment believe the plasma emanating from the contact zone was composed, for a very brief instant, of quarks and gluons. These quickly combined into protons, neutrons, and electrons as the heated material dissipated. New colliders, generating at least 10 times more energy, will be coming on line by 2000 and subsequent years, so that relevant new experiments will likely confirm the theoretical models that describe the history of the later part of the first minute. Energies comparable to those extant during the first moments are so great that no appropriate experimental setup is feasible for the foreseeable future, and may never be attainable in physics labs on Earth.
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 is doubled; the concept predicts that there must be some subatomic particles still to be discovered if this pairing is valid); it also aids in simplifying the broken symmetry problems that beset the Standard Model; and
3) Extra Dimensions : such as those associated with Superstring theory; (last paragraph).