Cosmological Arrow Of Time Research Articles

The Cosmological Arrow of Time and the Retarded Potentials

We demonstrate that the cosmological arrow of time is the cause for the arrow of time associated with the retarded radiation. This implies that the proposed mathematical model serves to confirm the hypothesis of Gold and Wheeler that the stars radiate light instead of consuming it only because the universe is expanding—just like the darkness of the night sky is a side-effect of the global cosmological expansion.

Fidelity Mechanics: Analogues of the Four Thermodynamic Laws and Landauer's Principle.

Fidelity mechanics is formalized as a framework for investigating critical phenomena in quantum many-body systems. Fidelity temperature is introduced for quantifying quantum fluctuations, which, together with fidelity entropy and fidelity internal energy, constitute three basic state functions in fidelity mechanics, thus enabling us to formulate analogues of the four thermodynamic laws and Landauer’s principle at zero temperature. Fidelity flows, which are irreversible, are defined and may be interpreted as an alternative form of renormalization group flows. Thus, fidelity mechanics offers a means to characterize both stable and unstable fixed points: divergent fidelity temperature for unstable fixed points and zero-fidelity temperature and (locally) maximal fidelity entropy for stable fixed points. In addition, fidelity entropy behaves differently at an unstable fixed point for topological phase transitions and at a stable fixed point for topological quantum states of matter. A detailed analysis of fidelity mechanical-state functions is presented for six fundamental models—the quantum spin- XY model, the transverse-field quantum Ising model in a longitudinal field, the quantum spin- XYZ model, the quantum spin- XXZ model in a magnetic field, the quantum spin-1 XYZ model, and the spin- Kitaev model on a honeycomb lattice for illustrative purposes. We also present an argument to justify why the thermodynamic, psychological/computational, and cosmological arrows of time should align with each other, with the psychological/computational arrow of time being singled out as a master arrow of time.

When scale is surplus

We study a long-recognised but under-appreciated symmetry called dynamical similarity and illustrate its relevance to many important conceptual problems in fundamental physics. Dynamical similarities are general transformations of a system where the unit of Hamilton’s principal function is rescaled, and therefore represent a kind of dynamical scaling symmetry with formal properties that differ from many standard symmetries. To study this symmetry, we develop a general framework for symmetries that distinguishes the observable and surplus structures of a theory by using the minimal freely specifiable initial data for the theory that is necessary to achieve empirical adequacy. This framework is then applied to well-studied examples including Galilean invariance and the symmetries of the Kepler problem. We find that our framework gives a precise dynamical criterion for identifying the observables of those systems, and that those observables agree with epistemic expectations. We then apply our framework to dynamical similarity. First we give a general definition of dynamical similarity. Then we show, with the help of some previous results, how the dynamics of our observables leads to singularity resolution and the emergence of an arrow of time in cosmology.

The Arrow of Time: Can Time be Reversed?

In the year 1928, Arthur Eddington, a British physicist, first introduced the word “time’s arrow” to physics. He believed that the arrow of time is vividly recognized by consciousness and insisted that the reversal of this arrow would render the physical world nonsensical. It is widely known that the laws of physics remain unchanged under the combination C, P, and T and that the laws of physics do not change with the flow of time but that is not the case under the operation T alone. This paper focuses on mainly three arrows of time, the thermodynamic arrow of time, the psychological arrow of time and the cosmological arrow of time and discusses the reversal of the arrow of time and its implications.

Defining Arrow of Time at the Start of Inflation by Expansion of Entropy in a Taylor Series and Examining Initial Conditions

First, we do a Taylor series expansion of Entropy. Afterwards we define the arrow of time. After that, we define what terms we will analyze in the Taylor series expansion of entropy to help in finding initial conditions which may allow for the earliest possible identification of the Arrow of Time in cosmology. Definition of the arrow of time will allow choosing different initial starting points. That is, that in the actual equations of classical GR, there is no reason to have time asymmetry after given initial conditions. Time asymmetry is built into initial conditions and we start to explore which initial conditions may assist in evaluating contributions to Entropy via an analysis of which terms in a Taylor series survive, and what their sign and contribution values are.

Initial Conditions for Defining an Arrow of Time at the Start of Inflation?

This investigation sets forth initial conditions for a start of the arrow of time in cosmology based upon the idea that of having initial degrees of freedom set as g*~ 1000 initially, instead of a maximum value of g*~ 100-120 for the number of degrees of freedom during the electro weak era.

The Time-symmetric Gold Universe Reconsidered

ABSTRACTThe present article proposes to re-examine the parity-of-reasoning or double-standard fallacy argument, which favours a time-symmetric Gold universe model over a cosmological arrow of time. There are two reasons for this re-examination. One is empirical: the recent discovery of an expanding and accelerating universe questions the symmetry assumption of the Gold universe on empirical grounds. The other is theoretical: the argument from t-symmetry fails to take into account some important aspects of the topology of phase space and recently developed typicality arguments. If the parity-of-reasoning argument, which depends on the t-symmetry of probability, is reconsidered in terms of the topology of phase space and typicality arguments, the double-standard fallacy argument loses much of its appeal. The Gold universe model itself suffers from unexplained dynamic asymmetries. The upshot of this article is that the Gold universe model is implausible or far less plausible than asymmetric models.

Arrow of time in dissipationless cosmology

It is generally believed that a cosmological arrow of time must be associated with entropy production. Indeed, in his seminal work on cyclic cosmology, Tolman introduced a viscous fluid in order to make successive expansion/contraction cycles larger than previous ones, thereby generating an arrow of time. However, as we demonstrate in this letter, the production of entropy is not the only means by which a cosmological arrow of time may emerge. Remarkably, systems which are dissipationless may nevertheless demonstrate a preferred direction of time provided they possess attractors. An example of a system with well defined attractors is scalar-field driven cosmology. In this case, for a wide class of potentials (especially those responsible for inflation), the attractor equation of state during expansion can have the form , and during contraction . If the resulting cosmology is cyclic, then the presence of cosmological hysteresis, during successive cycles, causes an arrow of time to emerge in a system which is formally dissipationless. An important analogy is drawn between the arrow of time in cyclic cosmology and an arrow of time in an N-body system of gravitationally interacting particles. We find that, like the N-body system, a cyclic Universe can evolve from a single past into two futures with oppositely directed arrows of time.

Cosmology and time

Time has always played a crucial role in cosmology. I review some of the aspects of the present cosmological model which are more directly related to time, such as: the definition of a cosmic time; the existence of typical timescales and epochs in an expanding universe; the problem of the initial singularity and the origin of time; the cosmological arrow of time.

Why does the universe expand?

The purpose of the paper is five-fold: (a) Argue that the question in the title can be presented in a meaningful manner and that it requires an answer. (b) Discuss the conventional answers and explain why they are unsatisfactory. (c) Suggest that a key ingredient in the answer could be the instability arising due to the `wrong' sign in the Hilbert action for the kinetic energy term corresponding to expansion factor. (d) Describe how this idea connects up with another peculiar feature of our universe, viz. it spontaneously became more and more classical in the course of evolution. (e) Provide a speculative but plausible scenario, based on the thermodynamic perspective of gravity, in which one has the hope for relating the thermodynamic and cosmological arrows of time.

DIMENSIONAL REDUCTION AND THE TCP THEOREM IN THE SUPERSTRING THEORY

Previously, we have shown that the Kasner solution [Formula: see text] to the D = (M+N+1)-dimensional vacuum Einstein theory [Formula: see text], where dx2 and dy2 are flat spaces of dimensionality M and N, respectively, exists only for (M - N)2 = M + N, that is D = 2+4K(K + 1), 1 + 4L2. The first three quantum numbers K = 0, 1, 2 for even D correspond to the three superstring dimensionalities D = 2, 10, 26 and are also given by the condition D = 2 mod 8 for the existence of Majorana–Weyl fermions. Here, we explain this result in terms of world-sheet symmetry and the TCP theorem applied to the superstring theory, the no-scale metric exhibiting T non-invariance which compensates the CP non-invariance due to the fermions, whose chirality thus gives the cosmological arrow of time its sense of direction.

Arrows of time and chaotic properties of the cosmic background radiation

We advance a new viewpoint on the connection between the thermodynamical and cosmological arrows of time, which can be traced via the properties of cosmic microwave background (CMB) radiation. We show that in the Friedmann–Robertson–Walker universe with negative curvature there is a necessary ingredient for the existence of the thermodynamical arrow of time. It is based on the dynamical instability of motion along null geodesics in a hyperbolic space. Together with special (de-correlated) initial conditions, this mechanism is sufficient for the thermodynamical arrow, whereas the special initial conditions alone are able to generate only a pre-arrow of time. Since the negatively curved space will expand forever, this provides a direct connection between the thermodynamical and cosmological arrows of time. The structural stability of the geodesic flows on hyperbolic spaces and hence the robustness of the proposed mechanism is especially stressed. We then point out that the main relations of equilibrium statistical thermodynamics (including the second law) do not necessarily depend on any arrow of time. Finally we formulate a curvature anthropic principle, which stipulates the negative curvature as a necessary condition for the time-asymmetric universe with an observer. CMB has to carry the signature of this principle as well.

Quantum string cosmologies

AbstractDifferent models of quantum string minisuperspaces for both isotropic and anisotropic geometries are presented. As for the isotropic case the general model of axion‐dilaton cosmology of arbitrary curvature is studied and solved explicitly. In the anisotropic case Bianchi type I and IX and Kantowski‐Sachs geometries are investigated. A short review of string cosmology is given with the emphasis on its “graceful‐exit” problem. The problems of boundary conditions, wave packets in minisuperspace and possible implications for the arrow of time in cosmology are briefly discussed.

Vacuum structure for expanding geometry

We consider gravitational wave modes in the Friedmann-Robertson-Walker metrics in a de Sitter phase and show that the state space splits into many unitarily inequivalent representations of the canonical commutation relations. Non-unitary time evolution is described as a trajectory in the space of the representations. The generator of time evolution is related to the entropy operator. The thermodynamic arrow of time is shown to point in the same direction as the cosmological arrow of time. The vacuum is a two-mode SU(1,1) squeezed state of thermo-field dynamics. The link between an expanding geometry, squeezing and thermal properties is exhibited.

Models for intermediate time dynamics with two-time boundary conditions

The consequences of conditioning a stochastic process at two times are examined, in particular with regard to the behavior at intermediate times. These results clarify discussions on the relation between the thermodynamic and cosmological arrows of time.

Violation ofCPT invariance in the typical universe

We show that the understanding of the problem of time asymmetry can be reached proceeding from the hypothesis of typicalness of the Universe. We come to the following consequences: 1) the cosmological arrow of time, in general, should not coincide with the thermodynamic one; 2) the thermodynamic arrow should not change its direction, while the Universe turns from the expanding phase to the contracting one; 3) CPT-invariance has to be violated. The last prediction, in principle, allows experimental verification.

Magnetic charges, inertia, and arrow of time

The prerelativistic concept of inertial mass (as opposed to gravitational mass) is reconsidered in view of a possible relationship between inertia and magnetic (mass) monopoles. Assuming that such “fictitious” (topological) charges could have developed in the chaotic early cosmology, a physical principle is suggested, based on dissipation of topological charges and decoupling of interactions, which could have governed the onset of inertia and of the arrow of time, and controlled the critical balance between mass density and expansion rate in the FRW universe. In view of the recent accomplishments in the detection of Dirac monopoles, a generalization of the Eotvos experiment is proposed which could shed light on the grand unification regime. A comment is given on the issue of relating the psychological and the cosmological arrows of time.

Two-dimensional quantum cosmology: Directions of dynamical and thermodynamic arrows of time.

Two-dimensional quantum cosmology is studied to clarify the issue associated with the arrow of time. We introduce a density-matrix description for the minisuperspace by projecting out nonzero modes of the wave function of the whole Universe. Thermodynamic time is determined by the direction in which the quantum coherence of minisuperspace variables decreases. This arrow of time is compared with that of dynamical time which is determined by the semiclassical approximation for the density matrix. We reconfirm that the global time cannot properly be defined for the thermodynamic times as well as for the dynamical time in a closed universe. The arrows of dynamical and thermodynamic times coincide with the cosmological arrow of time.

Arrow of time in cosmology.

The usual proof of the CPT theorem does not apply to theories which include the gravitational field. Nevertheless, it is shown that CPT invariance still holds in these cases provided that, as has recently been proposed, the quantum state of the Universe is defined by a path integral over metrics that are compact without boundary. The observed asymmetry or arrow of time defined by the direction of time in which entropy increases is shown to be related to the cosmological arrow of time defined by the direction of time in which the Universe is expanding. It arises because in the proposed quantum state the Universe would have been smooth and homogeneous when it was small but irregular and inhomogeneous when it was large. The thermodynamic arrow would reverse during a contracting phase of the Universe or inside black holes. Possible observational tests of this prediction are discussed.

TCP, quantum gravity, the cosmological constant and all that...

We study cosmology from the point of view of quantum gravity. Some light is thrown on the nature of time, and it is suggested that the cosmological arrow of time is generated by a spontaneous breakdown of TCP. Conventional cosmological models in which quantum fields interact with a time-dependent gravitational field are shown to describe an approximation to the quantum gravitational wave function which is valid in the long-wavelength limit. Two problems with initial conditions are resolved in models in which a negative bare cosmological constant is cancelled by the classical excitation of a Bose field η with a very flat potential. These models can also give a natural explanation for the observed value of the cosmological constant.