3,331 research outputs found
Time in Quantum Gravity
The Wheeler-DeWitt equation in quantum gravity is timeless in character. In
order to discuss quantum to classical transition of the universe, one uses a
time prescription in quantum gravity to obtain a time contained description
starting from Wheeler-DeWitt equation and WKB ansatz for the WD wavefunction.
The approach has some drawbacks. In this work, we obtain the time-contained
Schroedinger-Wheeler-DeWitt equation without using the WD equation and the WKB
ansatz for the wavefunction. We further show that a Gaussian ansatz for SWD
wavefunction is consistent with the Hartle-Hawking or wormhole dominance
proposal boundary condition. We thus find an answer to the small scale boundary
conditions.Comment: 12 Pages, LaTeX, no figur
Thermal conductive connection and method of making same Patent
Thermal conductive, electrically insulated cleavable adhesive connection between electronic module and heat sin
Semiclassical approximation to supersymmetric quantum gravity
We develop a semiclassical approximation scheme for the constraint equations
of supersymmetric canonical quantum gravity. This is achieved by a
Born-Oppenheimer type of expansion, in analogy to the case of the usual
Wheeler-DeWitt equation. The formalism is only consistent if the states at each
order depend on the gravitino field. We recover at consecutive orders the
Hamilton-Jacobi equation, the functional Schrodinger equation, and quantum
gravitational correction terms to this Schrodinger equation. In particular, the
following consequences are found:
(i) the Hamilton-Jacobi equation and therefore the background spacetime must
involve the gravitino, (ii) a (many fingered) local time parameter has to be
present on (the space of all possible tetrad and gravitino
fields), (iii) quantum supersymmetric gravitational corrections affect the
evolution of the very early universe. The physical meaning of these equations
and results, in particular the similarities to and differences from the pure
bosonic case, are discussed.Comment: 34 pages, clarifications added, typos correcte
The Coherence of Primordial Fluctuations Produced During Inflation
The behaviour of quantum metric perturbations produced during inflation is
considered at the stage after the second Hubble radius crossing. It is shown
that the classical correlation between amplitude and momentum of a perturbation
mode, previously shown to emerge in the course of an effective
quantum-to-classical transition, is maintained for a sufficiently long time,
and we present the explicit form in which it takes place using the Wigner
function. We further show with a simple diffraction experiment that quantum
interference, non-expressible in terms of a classical stochastic description of
the perturbations, is essentially suppressed. Rescattering of the perturbations
leads to a comparatively slow decay of this correlation and to a complete
stochastization of the system.Comment: LaTeX (7 pages
Decoherence in the cosmic background radiation
In this paper we analyze the possibility of detecting nontrivial quantum
phenomena in observations of the temperature anisotropy of the cosmic
background radiation (CBR), for example, if the Universe could be found in a
coherent superposition of two states corresponding to different CBR
temperatures. Such observations are sensitive to scalar primordial fluctuations
but insensitive to tensor fluctuations, which are therefore converted into an
environment for the former. Even for a free inflaton field minimally coupled to
gravity, scalar-tensor interactions induce enough decoherence among histories
of the scalar fluctuations as to render them classical under any realistic
probe of their amplitudes.Comment: 15 pages, accepted to be published in Classical and Quantum Gravit
Quantum-to-classical transition for fluctuations in the early Universe
According to the inflationary scenario for the very early Universe, all
inhomogeneities in the Universe are of genuine quantum origin. On the other
hand, looking at these inhomogeneities and measuring them, clearly no specific
quantum mechanical properties are observed. We show how the transition from
their inherent quantum gravitational nature to classical behaviour comes about
-- a transition whereby none of the successful quantitative predictions of the
inflationary scenario for the present-day universe is changed. This is made
possible by two properties. First, the quantum state for the spacetime metric
perturbations produced by quantum gravitational effects in the early Universe
becomes very special (highly squeezed) as a result of the expansion of the
Universe (as long as the wavelength of the perturbations exceeds the Hubble
radius). Second, decoherence through the environment distinguishes the field
amplitude basis as being the pointer basis. This renders the perturbations
presently indistinguishable from stochastic classical inhomogeneities.Comment: 9 pages, LATE
Topology, Decoherence, and Semiclassical Gravity
We address the issue of recovering the time-dependent Schr\"{o}dinger
equation from quantum gravity in a natural way. To reach this aim it is
necessary to understand the nonoccurrence of certain superpositions in quantum
gravity.
We explore various possible explanations and their relation. These are the
delocalisation of interference terms through interaction with irrelevant
degrees of freedom (decoherence), gravitational anomalies, and the possibility
of states. The discussion is carried out in both the geometrodynamical
and connection representation of canonical quantum gravity.Comment: 18 pages, ZU-TH 3/93, to appear in Phys. Rev.
Emergent Semiclassical Time in Quantum Gravity. Full Geometrodynamics and Minisuperspace Examples
I apply the preceding paper's semiclassical treatment to geometrodynamics.
The analogy between the two papers is quite useful at the level of the
quadratic constraints, while I document the differences between the two due to
the underlying differences in their linear constraints. I provide a specific
minisuperspace example for my emergent semiclassical time scheme and compare it
with the hidden York time scheme. Overall, interesting connections are shown
between Newtonian, Leibniz--Mach--Barbour, WKB and cosmic times, while the
Euler and York hidden dilational times are argued to be somewhat different from
these.Comment: References Update
On time and the quantum-to-classical transition in Jordan-Brans-Dicke quantum gravity
Any quantum theory of gravity which treats the gravitational constant as a
dynamical variable has to address the issue of superpositions of states
corresponding to different eigenvalues. We show how the unobservability of such
superpositions can be explained through the interaction with other
gravitational degrees of freedom (decoherence). The formal framework is
canonically quantized Jordan-Brans-Dicke theory. We discuss the concepts of
intrinsic time and semiclassical time as well as the possibility of tunneling
into regions corresponding to a negative gravitational constant. We calculate
the reduced density matrix of the Jordan-Brans-Dicke field and show that the
off-diagonal elements can be sufficiently suppressed to be consistent with
experiments. The possible relevance of this mechanism for structure formation
in extended inflation is briefly discussed.Comment: 10 pages, Latex, ZU-TH 15/93, BUTP-93/1
Probing the Evaporation Dynamics of Ethanol/Gasoline Biofuel Blends Using Single Droplet Manipulation Techniques
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