Constraints On Cosmic Dynamics

Observationally, the universe appears virtually critical. Yet, there is no simple explanation for this state. In this article we advance and explore the premise that the dynamics of the universe always seeks equilibrium conditions. Vacuum-induced cosmic accelerations lead to creation of matter-energy modes at the expense of vacuum energy. Because they gravitate, such modes constitute inertia against cosmic acceleration. On the other extreme, the would-be ultimate phase of local gravitational collapse is checked by a phase transition in the collapsing matter fields leading to a de Sitter-like fluid deep inside the black hole horizon, and at the expense of the collapsing matter fields. As a result, the universe succumbs to neither vacuum-induced run-away accelerations nor to gravitationally induced spacetime curvature singularities. Cosmic dynamics is self-regulating. We discuss the physical basis for these constraints and the implications, pointing out how the framework relates and helps resolve standing puzzles such as "why did cosmic inflation end?", "why is Lambda small now?" and "why does the universe appear persistently critical?". The approach does, on the one hand, suggest a future course for cosmic dynamics, while on the other hand it provides some insight into the physics inside black hole horizons. The interplay between the background vacuum and matter fields suggests an underlying symmetry that links spacetime acceleration with spacetime collapse and global (cosmic) dynamics with local (black hole) dynamics.Comment: 11 page

Matter fields from a decaying background Lambda vacuum

We suggest an alternative framework for interpreting the current state of the visible universe. Our approach is based on a dynamical ``Cosmological Constant'' and the starting point is that a decaying vacuum produces matter. As we point out, such a dynamical Lambda is not incompatible with the general requirements of general relativity. By assuming inflation and big bang nucleosynthesis we can solve for the present fractional densities of matter Omega_{m,0} and vacuum Omega_{Lambda, 0} in terms of only one parameter which we call the vacuum domination crossing redshift, z_c. We put constraints on z_c to obtain a universe that is presently vacuum dominated and with characteristic densities consistent with observations. The model points to the possible existence of newly formed dark matter in the inter-cluster voids. We argue that some of this matter could be accreting onto clusters through the latter's long range gravitational potentials. If so, then cluster dark matter halos may not manifest clear cut-offs in their radial density profiles. Furthermore, if a substantial amount of this newly produced matter has already drained onto the clusters, then the CMB power spectrum may favor lower dark matter density values than is currently observed bound in the clusters. A final feature of our approach relates to the combined effect of the matter production by a decaying vacuum and the different rates at which matter and the vacuum will dilute with the scale factor. Such combination may create conditions for a universe in which the vacuum and matter densities dilute and evolve towards comparable amplitudes. In this sense the model offers a natural and conceptually simple explanation to the Coincidence Problem.Comment: 22 pages, 1 figure, accepted for publication in Int. J. Mod. Phys. Lett.

Can gravitational collapse sustain singularity-free trapped surfaces?

In singularity generating spacetimes both the out-going and in-going expansions of null geodesic congruences $\theta ^{+}$ and $\theta ^{-}$ should become increasingly negative without bound, inside the horizon. This behavior leads to geodetic incompleteness which in turn predicts the existence of a singularity. In this work we inquire on whether, in gravitational collapse, spacetime can sustain singularity-free trapped surfaces, in the sense that such a spacetime remains geodetically complete. As a test case, we consider a well known solution of the Einstien Field Equations which is Schwarzschild-like at large distances and consists of a fluid with a $p=-\rho$ equation of state near $r=0$. By following both the expansion parameters $\theta ^{+}$ and $\theta ^{-}$ across the horizon and into the black hole we find that both $\theta ^{+}$ and $\theta ^{+}\theta ^{-}$ have turning points inside the trapped region. Further, we find that deep inside the black hole there is a region $0\leq r<r_{0}$ (that includes the black hole center) which is not trapped. Thus the trapped region is bounded both from outside and inside. The spacetime is geodetically complete, a result which violates a condition for singularity formation. It is inferred that in general if gravitational collapse were to proceed with a $p=-\rho$ fluid formation, the resulting black hole may be singularity-free.Comment: 17 pages, 3 figures, accepted for publication in International Journal of Modern Physics

Evolution of evaporating Black Holes in a higher dimensional inflationary universe

Spherically symmetric Black Holes of the Vaidya type are examined in an asymptotically de Sitter, higher dimensional spacetime. The various horizons are identified and located. The structure and dynamics of such horizons are studied. © 1999 American Institute of Physics.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87523/2/161_1.pd

The Big Bang: Origins and initial conditions from Self-Regulating Cosmology (SRC) model

Generating appropriate initial conditions for the Universe is key to discussing cosmic evolution constructively. In standard cosmology the traditional approach assumes an early Universe that emerges from an infinite density, spacetime singularity. It then undergoes inflationary expansion, followed by a matter-creating "reheat" period. This approach produces results generally in agreement with observations. However, to date it is not known how (or even whether) a true past-directed spacetime singularity can generate a regular spacetime that becomes the observed Universe. It has been suggested that an appropriate approach should involve initial conditions that emerge naturally from existing physics. In this paper we generate initial conditions predicated on the Self-Regulating Cosmology (SRC) model recently presented [1]. In SRC, the dynamics leads to a universe that also self-regenerates from one evolutionary cosmic phase or (hereafter) kalpa to another. Within each such kalpa cosmic dynamics evolves between two different scales of de Sitter-like horizons. The end of a kalpa and the beginning of the next interface through a phase transition whose features naturally set all initial conditions for the new phase, including sourcing entropy. The SRC Universe satisfies Poincare Recurrence Theorem, with specified recurrence time. This facilitates a consistent co-application of Boltzmann Anthropic Hypothesis with the Past Hypothesis (hence with the Second Law of Thermodynamics). The issue of whether or not the early Universe undergoes inflation becomes naturally self-manifest in this scenario. The framework discusses two standing issues in cosmology: the old Cosmological Constant Problem, and the new issue of over-mature structures observed by JWST at high redshifts.Comment: 26 pages, 2 diagrams. To appear in Eur. Phys. J.

Is cosmic dynamics self-regulating?

In this paper we discuss a cosmological model for a universe with self-regulating features. We set up the theoretical framework for the model and determine the time evolution of the scale-factor $a(t)$. It is shown that such a universe repeatedly goes through alternate periods of matter and dark energy domination. The resulting dynamics oscillates about the would-be ideal time-linear or coasting path, with monotonic expansion. When compared to dynamics of the observed physical Universe, the model recovers the observationally-established evolutionary features of the latter, from the big bang to the current acceleration, and farther. It suggests a universe that initially emerges from a non-singular state, associated with a non-inflationary acceleration, and which acceleration it exits naturally with matter-energy generation. The model does not have a horizon problem or a flatness problem. It reproduces the observed current values of standard cosmic parameters, including the age $t_{0}$, the current Hubble parameter $H_{0}$ and dark energy $\Omega_{de}\$and matter $\Omega_{m}$ density parameters. We find the dark matter density-profile generated by the model naturally leads to flat rotation curves in galaxy halos. The model is falsifiable. It makes predictions that can be tested, as suggested. Finally, we discuss the dimensionless age $(H_{0}t_{0}\simeq1)$ paradox as an example of the model's ability to address standing puzzles. The findings suggest dynamics of the physical Universe may be self-regulating and predictable.Comment: Updated version submitted for review, 5 figure

A non-singular black hole model as a possible end-product of gravitational collapse

In this paper we present a non-singular black hole model as a possible end-product of gravitational collapse. The depicted spacetime which is type [II,(II)], by Petrov classification, is an exact solution of the Einstein equations and contains two horizons. The equation of state in the radial direction, is a well-behaved function of the density and smoothly reproduces vacuum-like behavior near r=0 while tending to a polytrope at larger r, low density, values. The final equilibrium configuration comprises of a de Sitter-like inner core surrounded by a family of 2-surfaces of matter fields with variable equation of state. The fields are all concentrated in the vicinity of the radial center r=0. The solution depicts a spacetime that is asymptotically Schwarzschild at large r, while it becomes de Sitter-like for vanishing r. Possible physical interpretations of the macro-state of the black hole interior in the model are offered. We find that the possible state admits two equally viable interpretations, namely either a quintessential intermediary region or a phase transition in which a two-fluid system is in both dynamic and thermodynamic equilibrium. We estimate the ratio of pure matter present to the total energy and in both (interpretations) cases find it to be virtually the same, being 0.83. Finally, the well-behaved dependence of the density and pressure on the radial coordinate provides some insight on dealing with the information loss paradox.Comment: 12 Pages, 1 figure. Accepted for publication in Phys. Rev.

Possible Limits on Photon Propagation from Quantum Gravity and Space-time Foam

Many quantum gravity theories imply that the vacuum is filled with virtual black holes. This paper explores the process in which high energy photons interact with virtual black holes and decay into gravitons and photons of lower energy. The effect requires violation (or modification) of Lorentz invariance and implies that high energy photons cannot propagate over arbitrarily large distances. For the standard Planck mass and the likely form for the interaction cross section, this quantum foam limit becomes \dist \u3c 450 Mpc (\egam/10^7 {\rm GeV})^{-5}. (Refer to PDF file for exact formula.) For quantum gravity theories that posit a lower Planck scale, the interaction rate is larger and the limit is stronger. This paper uses extant observations of gamma rays from cosmological sources to constrain this process for varying values of the Planck mass and a range of forms for the interaction cross sections