共查询到20条相似文献,搜索用时 73 毫秒
1.
Antony Valentini 《Pramana》2002,59(2):269-277
It is argued that immense physical resources — for nonlocal communication, espionage, and exponentially-fast computation —
are hidden from us by quantum noise, and that this noise is not fundamental but merely a property of an equilibrium state
in which the universe happens to be at the present time. It is suggested that ‘non-quantum’ or nonequilibrium matter might
exist today in the form of relic particles from the early universe. We describe how such matter could be detected and put
to practical use. Nonequilibrium matter could be used to send instantaneous signals, to violate the uncertainty principle,
to distinguish non-orthogonal quantum states without disturbing them, to eavesdrop on quantum key distribution, and to outpace
quantum computation (solving NP-complete problems in polynomial time). 相似文献
2.
In this paper we have given a generalization of the earlier work by Prigogine et al. (Gen. Relativ. Gravit. 19:1, 1989; Gen. Relativ. Gravit. 21(8):767–776, 1989) who have constructed a phenomenological model of entropy production via particle creation in the very early universe generated out of the vacuum rather than from a singularity, by including radiation also as the energy source and tried to develop an alternative cosmological model in which particle creation prevents the big bang. We developed Radiation dominated model of the universe which shows a general tendency that (i) it originates from instability of vacuum rather than from a singularity. (ii) Up to a characteristic time t c cosmological quantities like density, pressure, Hubble constant and expansion parameter vary rapidly with time. (iii) After the characteristic time these quantities settles down and the models are turned into de-Sitter type model with uniform matter, radiation, creation densities and Hubble’s constant H. The de-Sitter regime survives during a decay time t d then connects continuously to a usual adiabatic matter radiation RW universe. The interesting thing in the paper is that we have related the phenomenological radiation dominated model to macroscopic model of quantum particle creation in the early universe giving rise to the present observed value of cosmic background radiation. It is also found that the dust filled model tallies exactly with that of the Prigogine’s one, which justifies that our model is generalized Prigogine’s model. Although the model originates from instability of vacuum rather than from a singularity, still there is a couple of unavoidable singularities in the model. 相似文献
3.
We investigate the quantum evolution of the metric operators for Bianchi-Type I model universes in the Heisenberg picture
in order to remove the need to consider the wave function of the universe and interpret its “spin” variables. The calculation
is analogous to that of the Zitterbewegung of the Dirac electron. We consider the behavior of the metric near the classical
singularity, and consider the curvature there. Although factor ordering questions preclude the presentation of an unambiguous
result for the curvature invariants, it does seem that the classical t
−4 divergence of the Kretschmann scalar is not removed by quantization. 相似文献
4.
We consider the flat Robertson–Walker model in scalar-tensor theory proposed by Lau and Prokhovnik. In this model, the field
equations are solved by using “gamma-law” form of equation of state p=(γ−1)ρ, where the adiabatic parameter ‘gamma’ (γ) varies continuously as the universe expands. Our aim is to study how the adiabatic parameter γ should vary so that in the course of its evolution the universe goes through a transition from an inflationary to a radiation-dominated
phase. A unified one parameter function of γ has been considered to describe the two early phases of evolution of universe. The solutions show the power-law expansion
and cosmological constant is found to be positive and decreasing function of cosmic time. The solutions are compatible with
the Dirac’s large number hypothesis. The deceleration parameter has been presented in a unified manner in terms of scale factor,
which describes the inflation of the model. The nature of singularity and the physical properties have been discussed in details. 相似文献
5.
In this work we consider the entropy-corrected version of interacting holographic dark energy (HDE), in the non-flat universe
enclosed by apparent horizon. Two corrections of entropy so-called logarithmic ‘LEC’ and power-law ‘PLEC’ in HDE model with
apparent horizon as an IR-cutoff are studied. The ratio of dark matter to dark energy densities u, equation of state parameter w
D
and deceleration parameter q are obtained. We show that the cosmic coincidence problem is solved for interacting models. By studying the effect of interaction
in EoS parameter of both models, we see that the phantom divide may be crossed and also understand that the interacting models
can drive an acceleration expansion at the present and future, while in non-interacting case, this expansion can happen only
at the early time. The graphs of deceleration parameter for interacting models, show that the present acceleration expansion
is preceded by a sufficiently long period deceleration at past. Moreover, the thermodynamical interpretation of interaction
between LECHDE and dark matter is described. We obtain a relation between the interaction term of dark components and thermal
fluctuation in a non-flat universe, bounded by the apparent horizon. In limiting case, for ordinary HDE, the relation of interaction
term versus thermal fluctuation is also calculated. 相似文献
6.
Bin Liu Yun-Chuan Dai Xian-Ru Hu Jian-Bo Deng 《International Journal of Theoretical Physics》2011,50(11):3544-3551
The non-local Machian model is regarded as an alternative theory of gravitation which states that all particles in the Universe
as a ‘gravitationally entangled’ statistical ensemble. It is shown that the Klein-Gordon equation can be derived within this
Machian model of the universe. The crucial point of the derivation is the activity of the Machian energy background field
which causing a fluctuation about the average momentum of a particle, the non-locality problem in quantum theory is addressed
in this framework. 相似文献
7.
Christian?G.?B?hmer Francisco?S.?N.?Lobo 《The European Physical Journal C - Particles and Fields》2010,70(4):1111-1118
Recently, Hořava proposed a power counting renormalizable theory for (3+1)-dimensional quantum gravity, which reduces to Einstein
gravity with a non-vanishing cosmological constant in IR, but possesses improved UV behaviors. In this work, we analyze the
stability of the Einstein static universe by considering linear homogeneous perturbations in the context of an IR modification
of Hořava gravity, which implies a ‘soft’ breaking of the ‘detailed balance’ condition. The stability regions of the Einstein
static universe is parameterized by the linear equation of state parameter w=p/ρ and the parameters appearing in the Hořava theory, and it is shown that a large class of stable solutions exists in the respective
parameter space. 相似文献
8.
We illustrate the crucial role played by decoherence (consistency of quantum histories) in extracting consistent quantum probabilities
for alternative histories in quantum cosmology. Specifically, within a Wheeler-DeWitt quantization of a flat Friedmann-Robertson-Walker
cosmological model sourced with a free massless scalar field, we calculate the probability that the universe is singular in
the sense that it assumes zero volume. Classical solutions of this model are a disjoint set of expanding and contracting singular
branches. A naive assessment of the behavior of quantum states which are superpositions of expanding and contracting universes
suggests that a “quantum bounce” is possible i.e. that the wave function of the universe may remain peaked on a non-singular
classical solution throughout its history. However, a more careful consistent histories analysis shows that for arbitrary
states in the physical Hilbert space the probability of this Wheeler-DeWitt quantum universe encountering the big bang/crunch
singularity is equal to unity. A quantum Wheeler-DeWitt universe is inevitably singular, and a “quantum bounce” is thus not
possible in these models. 相似文献
9.
The problem of calculating the equilibrium properties ofv-dimensional fluid mixture of hardv-spheres is studied. High temperature expansion for the density independent radial distribution function is derived for a
hardv-sphere mixture. The ‘excess’ quantum corrections to the second virial coefficient and the excess free energy are also studied.
Significant features are the large increase in ‘excess’ quantum correction with increasing dimensionality. 相似文献
10.
Lallan Yadav Vineet K. Yadav T. Singh 《International Journal of Theoretical Physics》2012,51(10):3113-3126
The present paper envisages a spatially homogeneous and anisotropic Bianchi II massive string cosmological models with time-decaying Λ term in general relativity. By using the variation law of Hubble’s parameter, the Einstein’s field equations have been solved for two general cases. The first case involving a power law solution describes the dynamics of universe from big bang to present epoch while the second case admit an exponential solution seems reasonable to project dynamics of future universe. We observed that massive strings dominate in early universe and eventually disappear at late time, which is consistent with the current astronomical observations. It has been found that the cosmological constant (Λ) is a decreasing function of time and it approaches to small positive value at sufficiently large time. The thermodynamic properties of anisotropic Bianchi II universe are studied and also the absolute temperature and entropy distribution are given explicitly. The relations between thermodynamic parameters and cosmological constant Λ has been established. Physical behavior of the derived model is elaborated in detail. 相似文献
11.
The nature of the future is completely different from the nature of the past. When quantum effects are significant, the future
shows all the signs of quantum weirdness, including duality, uncertainty, and entanglement. With the passage of time, after
the time-irreversible process of state-vector reduction has taken place, the past emerges, with the previous quantum uncertainty
replaced by the classical certainty of definite particle identities and states. The present time is where this transition
largely takes place, but the process does not take place uniformly: evidence from delayed choice and related experiments shows
that isolated patches of quantum indeterminacy remain, and that their transition from probability to certainty only takes
place later. Thus, when quantum effects are significant, the picture of a classical Evolving Block Universe (‘EBU’) cedes
place to one of a Crystallizing Block Universe (‘CBU’), which reflects this quantum transition from indeterminacy to certainty,
while nevertheless resembling the EBU on large enough scales. 相似文献
12.
S. K. Srivastava 《International Journal of Theoretical Physics》2008,47(7):1966-1978
Using modified gravity with non-linear terms of curvature, R
2 and R
(2+r) (with r being a positive real number and R being the scalar curvature), cosmological scenario, beginning at the Planck scale, is obtained. Here a unified picture of
cosmology is obtained from f(R)-gravity. In this scenario, universe begins with power-law inflation followed by deceleration and acceleration in the late universe
as well as possible collapse of the universe in future. It is different from f(R)-dark energy models with non-linear curvature terms assumed as dark energy. Here, dark energy terms are induced by linear as well as non-linear
terms of curvature in Friedmann equation being derived from modified gravity. It is also interesting to see that, in this
model, dark radiation and dark matter terms emerge spontaneously from the gravitational sector. It is found that dark energy,
obtained here, behaves as quintessence in the early universe and phantom in the late universe. Moreover, analogous to brane-tension
in brane-gravity inspired Friedmann equation, a tension term λ arises here being called as cosmic tension, It is found that, in the late universe, Friedmann equation (obtained here) contains
a term −ρ
2/2λ (ρ being the phantom energy density) analogous to a similar term in Friedmann equation with loop quantum effects, if λ>0 and brane-gravity correction when λ<0. 相似文献
13.
Varun Sahni 《Pramana》2000,55(1-2):43-52
I present a short overview of current observational results and theoretical models for a cosmological constant. The main motivation
for invoking a small cosmological constant (or A-term) at the present epoch has to do with observations of high redshift Type
Ia supernovae which suggest an accelerating universe. A flat accelerating universe is strongly favoured by combining supernovae
observations with observations of CMB anisotropies on degree scales which give the ‘best-fit’ values ΘA ⋍ 0.7 and Θ
m
⋍ 0.3. A time dependent cosmological A-term can be generated by scalar field models with exponential and power law potentials.
Some of these models can alleviate the ‘fine tuning’ problem which faces the cosmological constant. 相似文献
14.
George F. R. Ellis 《General Relativity and Gravitation》2006,38(7):1209-1213
Susskind claims in his recent book The Cosmic Landscape that evidence for the existence and nature of ‘pocket universes’ in a multiverse would be available in the detailed nature of the Cosmic Blackbody Background Radiation that constantly bathes all parts of our observable universe. I point out that acceptance of the complex chain of argument involved does not imply possible experimental verification of multiverses at the present time. Rather this claim relates only to theoretically possible observations in the very far future of the universe. 相似文献
15.
The phenomenon of quantum superposition, which allows a physical system to exist in different states ‘simultaneously’, is
one of the most bizarre notions in physics. Here we illustrate an even more bizarre example of it: a superposed state of a
physical system consisting of both an ‘older’ version and a ‘younger’ version of that system. This can be accomplished by
exploiting the special relativistic effect of time dilation featuring in Einstein’s famous twin paradox. 相似文献
16.
An event horizon for “relativistic” fermionic quasiparticles can be constructed in a thin film of superfluid 3He-A. The quasiparticles see an effective “gravitational” field which is induced by a topological soliton of the order parameter.
Within the soliton the “speed of light” crosses zero and changes sign. When the soliton moves, two planar event horizons (black
hole and white hole) appear, with a curvature singularity between them. Aside from the singularity, the effective spacetime
is incomplete at future and past boundaries, but the quasiparticles cannot escape there because the nonrelativistic corrections
become important as the blueshift grows, yielding “superluminal” trajectories. The question of Hawking radiation from the
moving soliton is discussed but not resolved.
Pis’ma Zh. éksp. Teor. Fiz. 68, No. 11, 833–838 (10 December 1998)
Published in English in the original Russian journal. Edited by Steve Torstveit. 相似文献
17.
The quantum corrections to the thermodynamic properties of polar hard sphere fluids and fluid mixtures are estimated taking
into account the influence of dipole and quadrupole moments. Expressions are given for the second virial coefficient, free
energy and pressure and results are given for different values ofμ* andϑ*. The first order quantum correction arises due to the translational contribution only. The quantum effect increases with
density,μ* andϑ*. Numerical results are also estimated for binary mixtures of (i) hard spheres and dipole hard spheres and (ii) hard spheres
and quadrupole hard spheres. The ‘excess’ free energy for dipole hard sphere binary mixture is also reported. It is found
that the ‘excess’ quantum effect depends on the concentration and the particle diameter ratio and increases with increase
ofμ* andϑ*. 相似文献
18.
R. Aldrovandi R. R. Cuzinatto L. G. Medeiros 《The European Physical Journal C - Particles and Fields》2008,58(3):483-497
Equations of state for the early universe including realistic interactions between constituents are formulated. Under certain
hypotheses, these equations are able to generate an inflationary regime prior to the period of the nucleosynthesis. The resulting
accelerated expansion is intense enough to solve the flatness and horizon problems. In the cases of a curvature parameter
κ equal to 0 or +1, the model is able to avoid the initial singularity and offers a natural explanation for why the universe
is in expansion. All the results are valid only for a matter–antimatter symmetric universe. 相似文献
19.
We discuss questions pertaining to the definition of ‘momentum’, ‘momentum space’, ‘phase space’ and ‘Wigner distributions’;
for finite dimensional quantum systems. For such systems, where traditional concepts of ‘momenta’ established for continuum
situations offer little help, we propose a physically reasonable and mathematically tangible definition and use it for the
purpose of setting up Wigner distributions in a purely algebraic manner. It is found that the point of view adopted here is
limited to odd dimensional systems only. The mathematical reasons which force this situation are examined in detail 相似文献
20.
Bart D’Hooghe 《International Journal of Theoretical Physics》2010,49(12):3069-3084
We adopt an operational approach to quantum mechanics in which a physical system is defined by the mathematical structure
of its set of states and properties. We present a model in which the maximal change of state of the system due to interaction
with the measurement context is controlled by a parameter which corresponds with the number N of possible outcomes in an experiment. In the case N=2 the system reduces to a model for the spin measurements on a quantum spin-1/2 particle. In the limit N→∞ the system is classical, i.e. the experiments are deterministic and its set of properties is a Boolean lattice. For intermediate
situations the change of state due to measurement is neither ‘maximal’ (i.e. quantum) nor ‘zero’ (i.e. classical). We show
that two of the axioms used in Piron’s representation theorem for quantum mechanics are violated, namely the covering law
and weak modularity. Next, we discuss a modified version of the model for which it is even impossible to define an orthocomplementation
on the set of properties. Another interesting feature for the intermediate situations of this model is that the probability
of a state transition in general not only depends on the two states involved, but also on the measurement context which induces
the state transition. 相似文献