Before beginning this subsection, we urge you to read through this hidden Preface.

Cosmologists - those who study the origin, structure, space-time relations, and evolution of the astronomical Universe - generally agree that the Universe had a finite beginning between 10 and 18 Ga (Ga = 1 billion years [b.y.]) ago; the current best estimate lies near 15 Ga. The physical conditions that guaranteed the present Universe burst into existence almost instantaneously. During the first millisecond, incredible events unfolded in rapid succession that led to release of the energy that powered the Universe's development and created the initial stages of matter which eventually organized into a myriad of elementary particles, the FERMIONS, the best known of which are:

These fall into two general classes: HADRONS (minute particles, themselves made up of fundamental subnucleonic particles, called quarks [of which there are six types; various combinations of three give rise to the different nucleons] held together by gluons permitting strong interactions within atomic nuclei), that include the familiar protons and neutrons (both being heavy particles called baryons that are the principal nucleons) and the less well-known mesons (short-lived heavier particles); and LEPTONS (even tinier particles with weak nuclear interactions) that are represented by electrons, tauons, muons, and three types of neutrinos. Other infinitesimally small particles that also originated within this fraction of a second are the gravitons (responsible for gravitational forces) and the photons (one of several force/energy-carrying particles in the group known as bosons) that are quanta * of radiant energy responsible for electromagnetic (EM) forces which travel at light speed as oscillatory (sinusoidal) waves (photons have zero rest mass). 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 - played key roles in setting up the special conditions of this Universe that have been uncovered and defined in this century. Quantum processes governed the buildup and modifications of the particles and subparticles that arose in the earliest stages whereas 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 since space, as now defined and constrained by the outer limits of the observable Universe and by Einsteinian distances within these limits, and sequential events, represented in a temporal continuum, did not yet exist. The initiating event began at a point-like singularity, a 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 conceptualized to have been concentrated. What may have "existed" prior to the Universe was a quantum state (analogous to the condition of "potency" in ancient Greek philosophy) which was an absolute vacuum that somehow possessed a high level of energy. A fluctuation in vacuum energy grew and triggered a 'phase transition' that led to the singularity from whence all that entails the Universe - matter, energy, space, and time - came into being.

Although this singularity does not have a set of dimensions in the conventional sense (it is described as a point [dimensionless] condition in which a region of space has infinite curvature and incredible density where the normal laws of physics [including relativity] break down [do not apply]), whatever was "there" at the outset was pure energy of some kind. The famed Einstein equation E = mc² guaranteed the potential of this energy (as photons) to be converted to some degree into matter (some of the energy remains) which began to be accomplished in the first second of the Universe's coming into existence. This energy-matter equivalent was compressed into a state of extremely high density (density = mass or amount of matter 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. What might have existed before this moment of "creation" and how the singularity came to be 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.

The next figure summarizes the history of the evolving Universe in terms of what is popularly known today as the general Big Bang model for its inception (variants of this and other models have been put forth, as described on page Cosmo-5). 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

The Big Bang as an expansion theory is generally attributed to ideas proposed by G. Lemaitre and G. Gamow around 1939. (As described later in this subsection, the concept drew its principal support from the observations by Hubble and others on radiation redshifts associated with the distribution of galaxy velocities). Simply stated, the model holds the Universe to have expanded from a point (the singularity) where initial physical conditions were that of extremely high temperatures (thus, accounting for the "hot" that prefixes any reference to "Big Bang" in the standard model) accompanied by immense gravitational forces that had compressed matter/energy to an incredible density (mathematical theory holds these conditions to be at or approaching infinite values). This singularity is located "nowhere" in conceptual non-space (a vacuum "nothingness") but as expansion progressed, space was "created" and continues to "enlarge". One view holds the present Universe to be finite but without boundaries; its temporal character is such that it had no discrete beginning and 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).

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". This was not an explosion in the conventional sense (such as produces an incandescent gaseous fireball) but rather an ultra-violent release of kinetic energy that initiated the general expansion. The K.E. greatly exceeded gravitational energy but the latter has since been acting on all particles from galactic to nucleons, photons, etc. scales to influence the rate of expansion; in effect, so far anti-gravity forces have overcome the restraining effects of gravity seeking to slow the expansion and perhaps eventually drawing matter together in a general collapse. However, as elaborated on page Cosmic-4, this expansion is actually a dilation 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 detonation site; space itself "travels" by progressive enlargement over time.

Nothing is yet 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) since the Laws of Physics did not themselves exist as such inasmuch as there was no Universe yet in which they could apply and operate. (The Laws and the 20 or so fundamental parameters that control the observed behavior of all that is 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, i.e., what controls their specifics and could they come into existence spontaneously without any external originator, the "Creator" or "Designer".) But, at the moment of 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 (requires energy at levels on the order of 10¹⁹ GeV [Giga-electron volts],vastly greater than currently obtainable on Earth by any controllable process). Best postulates consider the singularity (whatever its origin) at this instant to be governed by pure quantum mechanics, have maximum order (zero entropy [see page Cosmo-5]), 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 permits nothing physical, i.e., discrete matter, to have existed prior to the inception of the Planck Epoch, but a "fluctuation" 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.

This theory allows cosmologists to begin the knowable Universe at the Planck time , given as 10^-43 seconds, At the initiation of the Big Bang, the four fundamental forces (gravity, and the strong, weak, and electromagnetic forces, referred to as the Superforce) that hold the Universe together existed momentarily in a single state under the condition of Supersymmetry. The non-gravity forces are grouped by the still developing Grand Unified Theory or GUT (a subset of the Theory of Everything [TOE] which seeks to specify a single force or condition that describes the situation at the very inception of the Universe) in which these forces are said to be united (the Unified Epoch). These forces were 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 space-time 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).

By ~10^-35 sec there was 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). Between 10^-37 and 10^-32 sec (a minuscule but vital interval of time referred to as the Inflationary Stage). During this inflation several Big Bang models consider that the minute Universe expanded at an incredible rate (~10³⁰ increase in dimensions), far greater than at any time since. Through this brief moment (a trillionth 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 pea. By way of analogy, this is equivalent to increasing the size of a 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 [the effects of gravity and the solar wind, and the location of the Oort cloud of comets extend the system's influence to much greater distances]). This extreme growth determined the eventual spatial curvature of the present Universe (in the most "popular" model, tending towards "flat"). Within this inflationary period, temperatures dropped drastically, only to rise sharply immediately thereafter and then continue its fall. Within 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 only once in Universe history) is postulated by some as a momentary state of gravity as a repulsive force that forced this tremendous expansion; as time proceeded, gravity then reverted to the attractive force that took over control of further expansion.

From 10^-35 to 10^-6, matter consisted of the subatomic particles known as quarks (Quark Era) and electrons. Temperatures were still too high (10²⁸ K) to foster quark organization into nucleons. During this interval, 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 begun to organize in combinations of 2 or 3 into hadrons during the brief Hadron Era.. This was followed at 10^-4 seconds by the emergence of electrons 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, even as hadrons, leptons (especially neutrinos) and photons were becoming the dominant products despite extensive electron-positron annihilation. 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).

During the earliest phases, 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. At this moment only a residue of elementary particles survived (all antiparticles apparently were completely wiped out leaving only some of the numerically larger amounts of particles), together with a great quantity of high energy gamma ray radiation and other energetic photons produced from the interactions. By 10^-2 seconds, the temperature had now dropped to 10¹³ K and the proto-Universe had a diameter roughly the size of our present solar system.

At the 1 second stage , the Universe had already expanded ** to a diameter of about 1 to 10 light years (a light year [l.y.] is the distance [~ 9.46 x 10¹² or 9,460,000,000,000 km] traveled by a photon moving at the speed of light [300,000 km/sec] during a journey of 1 Earth year) 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.

(Two parenthetical comments are appropriate here: 2) 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 dimensionality split into the 4 dimensions of the extant Universe that underwent expansion and 6 dimensions that simultaneously collapsed to a second entity having the dimension of a speck 10^-32 centemeters in size; and 2) The physical entities that make up both matter and energy may be smaller than quarks; these are known as one-dimensional superstrings- one dimensional subparticles that vibrate at different frequencies and combine in various ways to then make up the many different fundamental particles that are now known to exist or can be reasonably postulated; proof of superstrings existence has yet been to be verified but theory favors their existence and they are consistent with quantum physics.)

_{* Energy can be said to be quantized, that is, is associated with quanta (singular, quantum) which are discrete particles having different units of energy (E) whose values are given by the Planck equation E = h c/ where h = Planck's constant, c = speed of light (300,000 km/sec), and = the wavelength of the radiation wave for the particular energy state of the quantum being considered; the energy values vary with as positioned on the electromagnetic spectrum (a plot of continuously varying wavelengths).}

_{** This extremely rapid enlargement reflects the earlier influence of inflation with its initially higher expansion rates. Keep in mind that many of the parametric values cited in cosmological research are current estimates or approximations that may change as new data are acquired and/or depend on the particular cosmological model being used (e.g., standard versus inflationary Big Bang models). Among these, the most sought after parameter is H, the Hubble Constant (discussed later in this review), being one of the prime goals in observations from the Hubble Space Telescope.}

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