1,001 research outputs found

    The Reality and Measurement of the Wavefunction

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    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

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    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

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    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

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    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

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    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

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    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

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    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

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    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

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    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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