1,001 research outputs found

### The Reality and Measurement of the Wavefunction

Using a simple version of the model for the quantum measurement of a two
level system, the contention of Aharonov, Anandan, and Vaidman that one must in
certain circumstances give the wavefunction an ontological as well as an
epistemological significance is examined. I decide that their argument that the
wave function of a system can be measured on a single system fails to establish
the key point and that what they demonstrate is the ontological significance of
certain operators in the theory, with the wave function playing its usual
epistemological role.Comment: 10p

### Trans-Planckian Tail in a Theory with a Cutoff

Trans-planckian frequencies can be mimicked outside a black-hole horizon as a
tail of an exponentially large amplitude wave that is mostly hidden behind the
horizon. The present proposal requires implementing a final state condition.
This condition involves only frequencies below the cutoff scale. It may be
interpreted as a condition on the singularity. Despite the introduction of the
cutoff, the Hawking radiation is restored for static observers. Freely falling
observers see empty space outside the horizon, but are "heated" as they cross
the horizon.Comment: 17 pages, RevTe

### A comparison of measured and simulated solar network contrast

Long-term trends in the solar spectral irradiance are important to determine
the impact on Earth's climate. These long-term changes are thought to be caused
mainly by changes in the surface area covered by small-scale magnetic elements.
The direct measurement of the contrast to determine the impact of these
small-scale magnetic elements is, however, limited to a few wavelengths, and
is, even for space instruments, affected by scattered light and instrument
defocus. In this work we calculate emergent intensities from 3-D simulations of
solar magneto-convection and validate the outcome by comparing with
observations from Hinode/SOT. In this manner we aim to construct the contrast
at wavelengths ranging from the NUV to the FIR.Comment: Proceedings paper, IAU XXVII, Symposium 264, 3 page

### On a Time Symmetric Formulation of Quantum Mechanics

We explore further the suggestion to describe a pre- and post-selected system
by a two-state, which is determined by two conditions. Starting with a formal
definition of a two-state Hilbert space and basic operations, we systematically
recast the basics of quantum mechanics - dynamics, observables, and measurement
theory - in terms of two-states as the elementary quantities. We find a simple
and suggestive formulation, that ``unifies'' two complementary observables:
probabilistic observables and non-probabilistic `weak' observables.
Probabilities are relevant for measurements in the `strong coupling regime'.
They are given by the absolute square of a two-amplitude (a projection of a
two-state). Non-probabilistic observables are observed in sufficiently `weak'
measurements, and are given by linear combinations of the two-amplitude. As a
sub-class they include the `weak values' of hermitian operators. We show that
in the intermediate regime, one may observe a mixing of probabilities and weak
values. A consequence of the suggested formalism and measurement theory, is
that the problem of non-locality and Lorentz non-covariance, of the usual
prescription with a `reduction', may be eliminated. We exemplify this point for
the EPR experiment and for a system under successive observations.Comment: LaTex, 44 pages, 4 figures included. Figure captions and related text
in sections 3.1, 4.2 are revised. A paragraph in pages 9-10 about non-generic
two-states is clarified. Footnotes adde

### Analog model for an expanding universe

Over the last few years numerous papers concerning analog models for gravity
have been published. It was shown that the dynamical equation of several
systems (e.g. Bose-Einstein condensates with a sink or a vortex) have the same
wave equation as light in a curved-space (e.g. black holes). In the last few
months several papers were released which deal with simulations of the
universe.
In this article the de-Sitter universe will be compared with a freely
expanding three-dimensional spherical Bose-Einstein condensate. Initially the
condensate is in a harmonic trap, which suddenly will be switched off. At the
same time a small perturbation will be injected in the center of the condensate
cloud.
The motion of the perturbation in the expanding condensate will be discussed,
and after some transformations the similarity to an expanding universe will be
shown.Comment: Presented at the 4th Australasian conference on General Relativity
and Cosmology, Monash U, Melbourne, 7-9 January 200

### Quantum field and uniformly accelerated oscillator

We present an exact treatment of the influences on a quantum scalar field in
its Minkowski vacuum state induced by coupling of the field to a uniformly
accelerated harmonic oscillator. We show that there are no radiation from the
oscillator in the point of view of a uniformly accelerating observer. On the
other hand, there are radiations in the point of view of an inertial observer.
It is shown that Einstein-Podolsky-Rosen (EPR) like correlations of Rindler
particles in Minkowski vacuum states are modified by a phase factor in front of
the momentum-symmetric Rindler operators. The exact quantization of a
time-dependent oscillator coupled to a massless scalar field was given.Comment: 28 pages, LaTe

### Effect of stellar flares on the upper atmospheres of HD 189733b and HD 209458b

Stellar flares are a frequent occurrence on young low-mass stars around which
many detected exoplanets orbit. Flares are energetic, impulsive events, and
their impact on exoplanetary atmospheres needs to be taken into account when
interpreting transit observations. We have developed a model to describe the
upper atmosphere of Extrasolar Giant Planets (EGPs) orbiting flaring stars. The
model simulates thermal escape from the upper atmospheres of close-in EGPs.
Ionisation by solar radiation and electron impact is included and photochemical
and diffusive transport processes are simulated. This model is used to study
the effect of stellar flares from the solar-like G star HD209458 and the young
K star HD189733 on their respective planets. A hypothetical HD209458b-like
planet orbiting the active M star AU Mic is also simulated. We find that the
neutral upper atmosphere of EGPs is not significantly affected by typical
flares. Therefore, stellar flares alone would not cause large enough changes in
planetary mass loss to explain the variations in HD189733b transit depth seen
in previous studies, although we show that it may be possible that an extreme
stellar proton event could result in the required mass loss. Our simulations do
however reveal an enhancement in electron number density in the ionosphere of
these planets, the peak of which is located in the layer where stellar X-rays
are absorbed. Electron densities are found to reach 2.2 to 3.5 times pre-flare
levels and enhanced electron densities last from about 3 to 10 hours after the
onset of the flare. The strength of the flare and the width of its spectral
energy distribution affect the range of altitudes that see enhancements in
ionisation. A large broadband continuum component in the XUV portion of the
flaring spectrum in very young flare stars, such as AU Mic, results in a broad
range of altitudes affected in planets orbiting this star.Comment: accepted for publication in A&

### How to protect the interpretation of the wave function against protective measurements

A new type of procedures, called protective measurements, has been proposed
by Aharonov, Anandan and Vaidman. These authors argue that a protective
measurement allows the determination of arbitrary observables of a single
quantum system and claim that this favors a realistic interpretation of the
quantum state. This paper proves that only observables that commute with the
system's Hamiltonian can be measured protectively. It is argued that this
restriction saves the coherence of alternative interpretations.Comment: 13 pages, 1 figur

### Relativistic Quantum Measurements, Unruh effect and Black Holes

It is shown how the technique of restricted path integrals (RPI) or quantum
corridors (QC) may be applied for the analysis of relativistic measurements.
Then this technique is used to clarify the physical nature of thermal effects
as seen by an accelerated observer in Minkowski space-time (Unruh effect) and
by a far observer in the field of a black hole (Hawking effect). The physical
nature of the "thermal atmosphere" around the observer is analysed in three
cases: a) the Unruh effect, b) an eternal (Kruskal) black hole and c) a black
hole forming in the process of collapse. It is shown that thermal particles are
real only in the case (c). In the case (b) they cannot be distinguished from
real particles but they do not carry away mass of the black hole until some of
these particles are absorbed by the far observer. In the case (a) thermal
particles are virtual.Comment: 24 pages (Latex), 8 EPS figures The text was edited for the new
versio

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