Several methods are used to determine the composition of the universe. Results of the Wilkinson Microwave Anisotropy Probe (WMAP) satellite studies [7] gave the composition shown in Table 1 soon after the Big Bang and at present.

The composition during the cosmic evolution has also been documented [4] [5] [6]. Table 2 shows this as a function of temperature (T) at various times and Cosmic Epochs, together with the cooling information (Composition vs T, P,t).

At temperatures above 10¹² K and time <10⁻¹² sec, the universe was a primeval hot gas of spaceons and presumably radiation, in equilibrium. Upon expansion and cooling, fundamental particles (quarks, leptons, hadrons, protons, neutrons, electrons) were created. On further cooling to about 10⁹ K, nucleosynthesis occurred to produce nuclei of H, He Li and D. At about 10⁸ K, a plasma phase was formed which consisted of electrons and positive ions of H and He. Radiation

(photons, neutrinos) was ever present and dominated the early epoch of the universe. Further cooling of the plasma until about 3 × 10³ K resulted in recombination of electrons with positive ions of H and He, converting the plasma to gaseous elements. As the universe continued to expand and cool, matter continued to form and grow through the action of gravity to become stars, galaxies, and clusters. The universe cooled to 2.7 K as indicated by the Cosmic Microwave background (CMB). The primary constituents of the universe are: gases (H, He), plasma of electrons, protons, and He ions, ordinary matter (gasses, solids, dust, in stars, galaxies, clusters, intergalactic space), radiation, and spaceons (gas at all temperatures).

Thermodynamics is a very powerful method for obtaining compositional information [3] [8]. The timeline of the universe is shown in Table 2. We also show its cooling rate, i.e., composition as a function of temperature, pressure, and time, which we have derived. From the latter, together with WMAP data on the constituents of the universe (Table 1), we constructed a thermodynamic phase diagram [3] [8] for our model universe. Such diagrams are routinely used in Chemistry, Metallurgy and Geophysics; though normally confined to the components of matter. The equivalence of matter and energy, allows us to do the same for the universe as a whole system with matter, energy and radiation as components.

The result for our model universe is shown in Figure 1. Note that the figure is schematic and the temperature is not drawn to scale in order to highlight the phases formed. We only emphasized the points at which the phases are formed because the exact pressure dependence is not fully known. The major phases are: radiation, matter (IV, solid, gasses, plasma formed in galaxies, stars, clusters), a plasma phase (III) formed immediately after nucleosynthesis, dark energy (V) and spaceons (gas). The broken lines indicate the overlap between various phases during the process of formation. While dark energy (spaceons) were present at the beginning of the universe, it’s phase transition is indicated only at the time when it became the major component of the universe. Dark matter is underlined since its nature is still unknown and unassigned. All phases are in contact with spaceons at all epochs of cosmic evolution, as indicated. This is as it should be since space is in contact with all elements of the universe at all times. This results in an isotropic and homogeneous universe so that there is no need for an inflationary stage. At extremely high temperatures and pressures (right end), fundamental particles and radiation are indistinguishable from the hot spaceons. At low temperature/pressure (left end), dark energy overlaps with the cold spaceons which may further transition to another phase. These end points are critical points, where 2 phases co-exist. (For water, at the critical temperature of 647 K and pressure of 2.2064 × 10⁷ Pa, liquid water is indistinguishable from its vapor phase).

Dark energy constitutes 71% of our universe. It is hypothesized to be an unknown form of energy that permeates all of space uniformly. It is invisible and difficult to study because it does not interact with radiation, hence cannot be investigated spectroscopically. It only interacts with gravity. Its density is very low, less than ordinary and dark matter; it converts to dark matter, was less in the past than at present, and it is thought to function like an anti-gravity force which causes the accelerated expansion of the universe [9] [10] [11].

Based on our model, the expansion of the universe could be thought of as the expansion of spaceons into the Void (“nothingness”). It can be thought of as driven by the pressure and temperature differential of the hot high energy state (high T, short λs) and the cold state in the Void (T ≈ 0K,λ ≈ ∞). It is an inherent property of space that it needs to expand in order to attain a lower energy state. The expansion may be viewed from the standpoint of Quantum Field Theory [12], as arising from a force that is associated with a field. We call the latter the space field from which emanate space quanta, the spaceons. It is a scalar field, often referred to in the literature as “Quintessence”. It has been theorized to be the substance which comprises Dark Energy [10].

One can see from our thermodynamic phase diagram (Figure 1) that dark energy is a phase that overlaps with the new entity that we have introduced as a component of the universe, i.e., the spaceons; the two phases are indistinguishable. Hence, dark energy can be associated with spaceons, the energy of space. The amount of dark energy soon after the Big Bang was relatively small (Table 1) because most of the energy of space was converted to radiation, fundamental particles, dark matter and ordinary matter. Its density remains low as the universe expands.

The behavior of our model universe with spaceons is well suited to mathematical treatment using the Friedmann-Lemaitre-Robertson-Walker (FLRW) metric [11]. (Note: It is worthwhile to recall that in deriving his equations, Friedmann used an ideal gas as a model for his cosmic fluid.) The second Friedmann equation [10] [11] delineates the contributions of the various components of the universe (matter, radiation, and spaceons) to the accelerated expansion of the universe, i.e.,

d 2 a / d t 2 = − ( 8 π G a / 3 ) { ( 1 / 2 ) ρ m + ρ r − Λ / 8 π G } (4)

We have set the curvature term,k = 0, normally appearing in Equation (4), which corresponds to a Euclidean universe with a flat spacetime curvature. In the above equation, a is the scale parameter, G the gravitational constant; ρ_m is the mass-energy density of matter, ρ_r that of radiation, and Λ, the cosmological constant which represents the energy of the vacuum [10]. “Vacuum energy ” is not a good term to use with our model, where the vacuum state is now the Void (“absolutely nothing”); it is preferable to use the term “energy of space”. The cosmological constant will then be replaced by the energy density of space, ρ_s, i.e.

d 2 a / d t 2 = − ( 8 / 3 ) π G a / 2 ρ m + ρ r + ( ρ s + 3 P s ) (5)

andρ_s is the energy density of space. It is related to the pressure P_s via the equation of state P_s = w_sρ_s where w_s is the equation of state parameter. A negative pressure would give rise to a positive ρ_s that can cause an acceleration of the expansion.

For the purpose of fitting the observed data (Table 1), it is preferable to use another form of the Friedmnan equation. It is common to utilize one involving the Hubble constant, H, which is measured in experiments and use velocity, da/dt, rather than acceleration [9] [10] [11]. Thus,

a H 2 = ( d a / d t ) 2 a 2 = ( H 0 ) 2 [ Ω m a − 3 + Ω r a − 4 + Ω s a − 3 ( 1 + w s ) ] (6)

H = ( d a / d t ) ⋅ a , H₀ its value at the present time; ϱ_i is the density parameter for component i, ϱ_c is the critical energy density of the universe (the density of the universe at the present time) and Ω_i = ϱ_i/ϱ_c = f, the fractional energy density.

A plot of fractional energy density as a function of of “a” can be constructed to fit the measured composition of the universe at about the time of the Big Bang and at the present time (see Table 1). The plot in Figure 2 shows the evolution of the composition of the universe. The dominance of radiation, matter, and dark energy at different times are amply illustrated. As can be seen there is good fit of the data summarized in Table 1 at time t = 13.8 billion years (a = 1) and at the time of the Big Bang, at about t = 380,000 years (a= 5.25 × 10⁻³, redshift z = 1089), with an equation of state parameter, w_s = −0.7. Dark Energy is very small in the early universe as most of the energy is used in the creation of radiation and fundamental particles. As the universe expands, however, the energy densities of radiation and matter continue to dilute and are eventually overcome by the

energy density of Dark Energy. This occurs at around 7 billion years at which time the expansion of the universe starts to accelerate. We call this the transition time, t_r. This result has been established by Baryon Acoustic Oscillation measurements in the Baryon Oscillation Spectroscopic Survey (BOSS) project [13] [14] and supernova measurements [15]. Figure 3 lends support to these findings. One sees that the fractional energy density of Dark Energy (DE1) crosses that of total matter (TM1) at t_r with a= 0.65 (t = 7.25 × 10⁹ years). Siegel [16] has made a similar fit using a cosmological constant of −1, but did not give a value for the transition time. Our calculation with a cosmological constant (w = −1) yielded a time of 8.75 × 10⁹ years (a= 0.74) for the dominance of dark energy (Figure 3), broken line, DE2, TM2). Result for the so-called Phantom Energy model [17] gives w= −1.2 for the transition time, t_r, and a later transition time of 9.2 × 10⁹ years (DE3, TM3). The measurement of transition time, t_r, appears to be a good test for the suitability of models for Dark Energy.

The concept of a constant energy density for space leads to some difficulties. The cosmological constant is considered to be equal to the energy of the vacuum. Calculations give a 120 orders of magnitude for the calculated value of the density of dark energy; this is obviously wrong. Moreover, the constancy of dark energy in the course of cosmic evolution is thought to be unlikely [18]. It also poses difficulties in answering the question of where the energy comes from during the expansion of the universe. It is more reasonable to expect that the

energy density would dilute as the universe expands for all forms of energy. Quintessence [18], with spaceons as the cosmic fluid that is a component of the universe, appears to be the better explanation for dark energy.

In our model, the universe started with a finite amount of energy. It was assumed to be an isolated system and expansion was adiabatic, with no energy transfer in and out of the universe. From thermodynamics,

Q = d E + P d V = 0 , (7)

where Q is the energy flowing into or out of the system, dE the change in internal energy, P the pressure, and dV the change in volume during the expansion. The work to create space, PdV, is done at the expense of the internal energy, i.e. dE = −PdV or

d E / d V = − P , (8)

the slope of the dE/dV plot is negative. One can also derive the relation,

H = ( 1 / 4 π r 3 ) ( d V / d E ) ( d E / d t ) or (9)

d E / d t = 4 π r 3 H [ d V / d E ] (10)

where, r, is the radius of the universe, and H is the Hubble constant, proportional to expansion velocity. To a first approximation, a decrease in H indicates a decrease in internal energy of the universe with time, t. BOSS studies of Busca et al. [ref [13], Figure 21], shows the expansion of the universe to be slowing down during the first 6 billion years after the Big Bang. A better plot is shown in Figure 4, from unpublished work by a Berkeley Group [14] who were collaborators in the Sloan Digital Sky Survey (SDSSIII) of the BOSS project. It showed that the expansion velocity reached a minimum around 7.5 billion years (t_r). This is consistent with our model universe with the expansion being adiabatic initially, i.e. dE/dt = negative. Turner and Riess [15] have also shown that the universe

changed from deceleration (during the matter dominated epoch) to acceleration at a redshift, z= 1 or t= 7 × 10⁹ years. The expansion velocity increased thereafter. The slope dE/dV (and that of dE/dt) became positive at large z (longer time, Figure 4(b)).

Thermodynamically,

d E / d V = ( d Q / d V ) − P = + (11)

that is, Q is no longer zero. The expansion has become non-adiabatic. This means an ingress of energy from outside the universe. Thermodynamics leaves the possibility that the accelerated expansion of the universe could occur with an “injection” or “leak” of energy from outside the universe, if it is open. However, there is no evidence at the present time that “something” exists outside the universe to support this. Thus, we take the universe to be closed and the expansion must remain adiabatic. Thermodynamics then demands that for the accelerated expansion to continue, the Pressure, P, in Equation (11) must be negative. It is interesting to note that this is just what is required by the Theory of Relativity and Friedmann’s equation (Equation (4)). It is also the negative pressure associated with Dark Energy. This seems like a coincidence, but it is also required by the law of Conservation of Energy on which the Friedmann’s equation is based [10]. Thus our model is totally consistent and most satisfying. It is important to note that the negative pressure cannot be taken as due to a repulsive form of gravity, as is often theorized.

We next try to answer the question of where the energy comes from to sustain the accelerated expansion by dark energy. The negative pressure means work is done on the system and energy is added to it. A likely source is the gravitational field through the action of gravity. The gravitational force is an attractive force. It exerts this force on all matter to clump together resulting in a decrease in gravitational potential energy, i.e., the negative potential energy becomes more negative. The gravitational energy lost in turn goes to increase the energy of space and the expansion to accelerate. A simple analogy is to imagine a rubber hose filled with running water. Squeezing the hose momentarily shrinks its diameter and causes water to squirt out. Figure 5(a) shows schematically the state of the universe during the period of deceleration (5 - 7 × 10⁹ yrs) in the matter dominated epoch. Consider the cosmic fluid flowing through a tube (dash lines) within the universe. The Hubble flow (HF) is slowing down. The pressure of the universe is outward (P_s = +) due to the inherent property of space (the spaceons) to expand into the Void; the slope dE/dV is negative (Equation (7)). In Figure 5(b), at the transition point, the attractive force of gravity starts to dominate with a pressure inward (P_g = −); dE/dV becomes positive. In the process, the “cosmic fluid” contained in the tube is squeezed out much like that of the rubber hose. The fluid velocity or the Hubble flow increases, manifesting itself as an accelerated expansion of the universe.

During the expansion of the universe, following the Big Bang, matter (mostly atomic H gas) proceeded to consolidate and clump together to form stars, galaxies,

clusters, and superclusters. Through the action of gravity they eventually form black holes, neutron stars, and other massive compact objects. These grow by mergers and accretion of nearby materials (gas, dust, etc) which get compressed by gravity resulting in smaller volume of matter whose mass approaches infinite density, i.e., a Black Hole/neutron star. Chapline [19] [20] has questioned the reality of Black Holes and proposed an alternative theory where matter infalling into the event horizon, undergoes a phase transition into dark energy [20]. The theory resolves questions associated with black holes, one of which is the loss of information when matter is swallowed by the black hole singularity. It also explains other cosmic phenomena not explained by black holes. He suggested the name “Dark Energy Stars” for Black Holes. Likewise, Mazur and Mottola [21], as well as Barcelo et al. [22], have proposed similar theories and suggested the name Gravastars and Black Stars respectively. Rovelli et al. [23] [24], used Loop Quantum Gravity to show that a singularity can be prevented via a “big bounce” mechanism by which the gravitational pressure acting on matter is balanced by an opposite degeneracy-like pressure of the core. The latter eventually explodes, releasing energy and hence the information it contains; this solves the information loss paradox.

It is not really known what the real state of matter is in Planck stars; we theorize that further compression by gravity should ultimately transform “particulate” matter to quarks, gluons, and finally to spaceons (dark energy), per the theories of Chapline [19] [20] and Barcelo, et al. [22]. (This is consistent with our phase diagram in Figure 1, tracing the curve from low to high T). We will adopt a hybrid model incorporating features of the models of Chapline, Barcelo et al. and Rovelli. We suggest to use the more descriptive names “Quantum Stars”, and “Space Well” for the singularity”. Moreover, the singularity cannot be real but maybe just an artifact in the mathematics of General Relativity; such state cannot exist due to the fact that the volume of space must be finite and cannot be less than the Planck volume. (Our model indicates this as mentioned later in Section 5.) In any case, Black Holes or Quantum Stars will have an “equivalent mass-energy” of M. The gravitational potential energy of the universe becomes more negative due to much greater “masses” of the clumped massive compact objects compared to H atoms. One can calculate the total gravitational potential energy change between the present time t_p and that at the time of transition, t_r, at the beginning of the accelerated expansion (7.25 × 10⁹ years), for all pairs of compact and other objects (“masses”) in the universe. The total energy at the present time, t_p, is

U p = − G [ M i ⋅ M j / R + m k ⋅ m l / r + M i ⋅ m k / s + ⋯ ] , (12)

summed over pairs of all other masses, m i , j , k , l , ⋯ (atoms, stars, etc) and Quantum Stars, other compact object, etc, M i , j , k , l , ⋯ in the universe; R , r , s , ⋯ are their respective distances of pair separation. Similarly, we can calculate the total potential energy just before the transition time, t_r, to give U_r. The difference in potential energy, Δ U = U p − U r , provides the energy that feed the further expansion of the universe. The calculation is unwieldy and is best done by simulation techniques.

Our proposed mechanism is supported by recent observations on the merger of 2 black holes or neutron stars. As the two massive bodies come together, their distance of separation decreases and in the process gravitational energy is released as gravitational waves [25]. The latter causes the perturbation of space that increases the energy of space and accelerates the expansion of the universe. This example explains the observed increase in internal energy vs time (slope, dE/dt = +) as shown in Figure 4.