Events in the first few fractions of a second, and subsequent time to the end of the first few minutes, 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:
Thus, ordinary matter (Fermions) is only 4% of all particles in the Universe. Although the two "Darks" comprise the remaining 96%, not much concrete knowledge has accrued about the nature of either Dark Matter or Dark Energy. Both presumably exist but proof of this is still lacking. Dark Matter is inferred to keep galaxies from flying apart. Dark Energy is inferred to be causing the renewed expansion of the Universe. Much effort is underway to prove their reality and determine their essential characteristics. Particle Accelerators are probing matter at high energies to gain a better understanding of their possible physical makeup. Dedicated cosmological observatories of the future may provide important insights.
This chart further subdivides the compositional makeup of the Universe:
Both matter and energy are said to consist of particles, such as atoms, electrons, etc. for the former and photons and bosons for the latter. There are an estimated billion photons for every atom in the Universe. The total mass of the Universe - consisting of matter particles and photon energy particles converted to mass (E = mc2) is approximately 1053 kg. If elemental matter (dominated by hydrogen) is expressed as the number of atoms uniformly dispersed (redistributed from galaxies and stars) per cubic meter, the average density of atomic matter is (estimates vary) between about 2 and 6 atoms of H per m3.
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 Big Bang (whatever its origin) at its singularity 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 - the Planck Era - is not currently knowable [but can be inferred] with the principles of physics developed so far). At that instant, the Universe which sprang forth must have been at least as small at 1.6 x 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 10-36 sec) in a special physical state - GUT; see below - 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 point 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).
(As a momentary aside: The Planck length, although exceedingly small, is nevertheless an allusion to dimensions. Dimension in turn implies space. It refers to the size of the Universe at the inception of the Planck Epoch. It is calculated in the framework of quantum cosmology using the speed of light c, the Planck constant h, and the Universal Gravitational Constant G as inputs. The Big Bang did two really important things 1) it released pent-up energy to power the expansion and creation of matter, and 2) it made the starting point for space into which particles emerged as energy cooled and these started to separate. From the first moment until now the main theme of the Univere's history has been the expansion of space and the redistribution and repositioning of its constituent particles.)
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 force is the primary one 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 fields associated with the other forces 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 united fundamental forces make up the Unified Epoch. The flow chart below specifies the major components of each of the forces as they are assumed to exist after the first minute of the Big Bang; the arrows proceed timewise to more fundamental states at the very beginning. 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; note that the involvement of Inflation is not considered.
The history of these forces during the first second of the Big Bang is discussed in more detail later on this page.
One model, now gaining some favor, based on Superstring theory (discussed near the bottom of this page) contends that at the first moment of the Big Bang (at the 10-43 sec arbitrary starting point), 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.
The first fundamental change during the Big Bang is known as the GUT transition, occuring at 10-36 seconds, when the strong and electroweak forces began to separate. 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 (now, at MIT), to account for some aspects of the Universe's growth [see below] that faced serious difficulties in the Standard Model. This has come to be known as the Inflationary Model for the Big Bang. The Inflation theory holds that the nascent and still minute Universe underwent a major phase transition (probably thermodynamic; water is a commonly cited example of such transition, as when it goes from liquid to solid [ice] or liquid to gas [steam]) in which repulsion forces caused a huge exponential increase in the rate of expansion of space. In fact, during the Inflation stage, the Special Relativity restriction which states that nothing can move faster than the speed of light was violated such that whatever was released during the Big Bang drew apart at rates greater than light speed. Through this brief moment of Inflation the micro-Universe grew from an infinitesimal size estimated to be about 10-28 meters (but still potentially 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 has not yet been agreed upon by cosmologists. A commonly cited value is 1078, but estimates in the literature for the growth in this minute span of inflation range from about 1030 to as high as 1090. To get a sense of the effect of such a factor, consider this analogy: the expansion 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 extraordinary growth determined the eventual spatial curvature of the present Universe (in the most "popular" model, tending towards [or perhaps equal to] "flat"). It also accounts for the overall uniformity found in the Universe today because initial irregularities would be stretched so thin by the magnitude of inflation that they would act as though "invisible". 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.
At the inception of Inflation, the temperature was ~ 1028 °K. Within this inflationary period, temperatures dropped drastically to ~1012 ° K by 10-10 sec. During this critical moment, the (preordained ??) physical conditions that led to the present Universe were established. 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 (possibly the vacuum energy that is 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).
Still 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 extreme 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). (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; again, see page 20-10.)
However, as of 2008 a newer explanation as to what powered the expansion has become ascendant. Since no matter yet existed, the cause of the Inflation state is postulated to be a quantum fluctuation in an extremely dense vacuum. The source of the vacuum energy that drove Inflation has not been precisely identified but theory ascribes this to potential energy within the quantum field of the Inflaton. During this very brief inflationary period, the "empty" surrounding Cosmos (the "beyond", where only energy existed but into which virtual particles come and go but usually fail to initiate any surviving Big Bang event) is entered by the activated particle at a rate greater than the speed of light. 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.
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. The Universe thereafter has a positive density field that varies in space and time. Inflation probably ended at 10-34 sec, after which the vacuum energy transitioned into real energy. Thereafter, particles began to appear as the Standard Hot Big Bang per se commenced.
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 incipient Universe 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. These irregularities may have been quantum fluctuations. The slight departures from homogeneity also show up in the variations detected in the Cosmic Background Radiation (CBR, see page 20-9).
Inflation also seems to solve the above-mentioned "horizon problem" (recall that in one meaning horizon refers to regions of the Universe that are limited in their interactions [causal contact between regions] 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.
Inflation also has been invoked to account for the possibility of matter and energy, perhaps even galaxies, being distributed beyond the 13.7 billion year horizon that limits what telescopes could potentially observe. Since the very earliest constituents of the first moments of the Big Bang were traveling faster than light speed, some of these constituents were flung beyond what cosmologists are restricted to in their observations.
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. Note the very large increase in the Universe's size shown on the left, followed by expansion at a decreasing rate, and then slow but steady reversal leading to an increasing rate (which occurs when the vacuum energy [negative or dark energy] of the Universe begins to exceed the positive gravitational energy), shown on the right.
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 released 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.