Apparent violation of the principle of equivalence and killing horizons

By means of the principle of equivalence we deduce the qualitative behavior of the Schwarzschild horizon about a uniformly accelerating particle. This result is confirmed for an exact solution of a uniformly accelerating object in the limit of small accelerations. For large accelerations the Schwarzschild horizon appears to violate the qualitative behavior established via the principle of equivalence. When similar arguments are extended to an observable such as the red shift between two observers, there is no departure from the results expected from the principle of equivalence. The resolution of the paradox is brought about by a compensating effect due to the Rindler horizon.Work supported in part by the National Aeronautics and Space Administration under Grant No. NSG-7639.     

“Galileo Galilei-GG”: design,requirements, error budget and significance of the ground prototype

“Galileo Galilei-GG” is a proposed experiment in low orbit around the Earth aiming to test the equivalence principle to the level of 1 part in 10¹⁷ at room temperature. A unique feature of GG, which is pivotal to achieve high accuracy at room temperature, is fast rotation in supercritical regime around the symmetry axis of the test cylinders, with very weak coupling in the plane perpendicular to it. Another unique feature of GG is the possibility to fly 2 concentric pairs of test cylinders, the outer pair being made of the same material for detection of spurious effects. GG was originally designed for an equatorial orbit. The much lower launching cost for higher inclinations has made it worth redesigning the experiment for a sun-synchronous orbit. We report the main conclusions of this study, which confirms the feasibility of the original goal of the mission also at high inclination, and conclude by stressing the significance of the ground based prototype of the apparatus proposed for space.     

MICROSCOPE,testing the equivalence principle in space

The test of the equivalence principle can be performed in space with orders of magnitude better resolution than in the laboratory, because of the outstanding steady and soft environment of the in-orbit experiment. The expected new experimental results will contribute to the unification of the four interactions, demonstrate the existence of extra scalar interaction or participate in the research for a quantum gravity theory. The MICROSCOPE space mission is being developed within the framework of the Cnes scientific program with the objective of testing the universality of free fall with a 10⁻¹⁵ accuracy. The concept and the design of the experiment are discussed and the major performance drivers of the room temperature instrument are pointed out. The launch of the drag-free satellite is scheduled for late 2004. By its specific technology demonstration, the mission will open the way to even more accurate acceleration measurements for other space missions in fundamental physics.     

基于原子干涉仪的微观粒子弱等效原理检验

等效原理是广义相对论的两个基本假设之一,也是爱因斯坦对弱等效原理的推广.目前,大量实验证明弱等效原理在一定的实验精度内是成立的.将引力与标准模型统一起来的新理论都要求弱等效原理破缺,因此更高精度的弱等效原理检验具有重要的科学意义.本文介绍了原子干涉仪的原理,回顾了利用原子干涉仪开展微观粒子弱等效原理检验实验研究的历史和现状,介绍了双组分原子干涉仪检验弱等效原理实验涉及的振动噪声抑制、拉曼光移频与相位噪声抑制、四波双衍射拉曼跃迁原子干涉、信号探测与数据处理等关键问题及研究进展,分析了高精度微观粒子弱等效原理检验研究的发展趋势,介绍了长基线原子干涉仪、空间原子干涉仪、超冷原子源以及纠缠原子源制备等方面的研究动态,展望了微观粒子弱等效原理检验研究的发展前景.     

等效原理空间实验检验

等效原理地面实验检验已经达到了10-13,为了进一步提高实验精度,寻找新的相互作用和检验引力理论,人们提出了一系列更高精度等效原理检验的卫星计划.文章主要概述了等效原理空间检验的原理、发展历史和发展现状,并对进一步空间等效原理检验进行了简要展望.     

The confrontation between general relativity and experiment

We review the experimental evidence for Einstein’s general relativity. Tests of the Einstein equivalence principle support the postulates of curved space-time and bound variations of fundamental constants in space and time, while solar system experiments strongly confirm weak-field general relativity. The binary pulsar provides tests of gravitational wave damping and of strong-field general relativity. Future experiments, such as the gravity probe B gyroscope experiment, a satellite test of the equivalence principle, and tests of gravity at short distance to look for extra spatial dimensions could further constrain alternatives to general relativity. Laser Interferometric Gravitational Wave Observatories on Earth and in space may provide new tests of scalar-tensor gravity and graviton-mass theories via the properties of gravitational waves.     

A monte carlo method for approximating critical cluster size in the nucleation of model systems

A formalism is presented for estimating critical cluster size as defined in classical models for nucleation phenomena. The method combines Bennett's Monte Carlo technique for determining free-energy differences for clusters containingn andn- 1 atoms with the steady state nucleation rate formalism. A simple form for the free energy of formation of then cluster [including a termA (n)n ^2/3] is used to predict critical cluster size and critical supersaturation ratio, S^*. This approach is applied to Lennard-Jones vapor clusters at 60 K. Results for free-energy differences for the 13, 18, 24, and 43 clusters predict a critical cluster size of 70 ± 5 atoms at a critical supersaturation ratio given bylnS ^*=2,45 0.15. This method is intended to provide estimates of critical cluster size for more ambitious attempts to calculate cluster free energies or for initializing conditions in microscopic simulations of nucleating systems.This material is based upon work supported by the National Science Foundation under Grant No. ATM80 15790 and the National Aeronautics and Space Administration under Grant No. NAS8-31150.     

ISLAND—Inverse Square Law Acceleration Measurement Using iNertial Drift

By using a novel free-flying, rotating, optical bench aboard the International Space Station (ISS) as the basis for a measurement of differential acceleration between two gravitating bodies, in principle the Newtonian inverse-square law and the constant of gravitation, G, can be determined at the parts in 10⁶ level.     

Equivalence Principle Measurements

Over the centuries there have been many experimental tests of the universality of free-fall. To date, these measurements have established the equivalence between inertial and gravitational mass to high precision, justifying its use as a foundation stone of general relativity by Einstein. There is a surprising richness in the variety of techniques and choice of test bodies which have been used so far, and a brief review is presented. However, future space experiments promise much better precision in this measurement and STEP is presented in some detail as one of a number of such missions. Using pairs of concentric free-falling proof-masses, STEP will be able to test the Equivalence Principle (EP) to a sensitivity at least five orders of magnitude better than currently achievable on ground. The EP is a founding principle of general relativity and STEP is the most sensitive experiment of this type planned so far, aiming at 1 part in 10¹⁸.     

A test of the equivalence principle using a space-borne clock

An experimental verification of Einstein's equivalence principle has been made using an atomic hydrogen maser in a space probe attaining an altitude of 10,000 km above the earth's surface. At the present stage of the data reduction, confirmation is at the 2×10^–4 level of accuracy. The experiment and the resulting data are described including a comment on the limits to the anisotropy of the velocity of light. We believe that this is the first direct, high-accuracy test of the symmetry of the propagation of light and a beginning in the use of high-accuracy clocks in space to measure relativistic phenomena.This essay was awarded the fourth prize for 1978 by the Gravity Research Foundation. (Ed.)     

空间光学的发展与波前传感技术

进入21世纪,国际上一些发达国家和有关部门都已制定了空间发展战略规划,如美国航空航天局(NASA)、欧洲空间局(ESA)和俄罗斯政府相关部门等都提出空间发展战略规划,这些规划提出了今后一段时间内空间科学要解决的问题和发展的方向,而解决这些问题并推进空间技术的发展很大程度上依赖于先进的光学和无线电望远镜及仪器设备。因此,本文介绍本世纪初国际上空间科学应用的大型天文望远镜的发展情况,重点描述了大口径光学望远镜的光学系统以及实现这类天文望远镜的关键技术之一—波前传感技术。     

Equivalence principles exotica

This is a short review of the different principles of equivalence stated and used in the context of the gravitational interaction. We emphasize the need for precision in stating and differentiating these different equivalence principles, especially in the context of prevalent confusion regarding the applicability of the weak equivalence principle in quantum mechanics. We discuss several empirical results pertaining to the validity of the equivalence principle in exotic physical sitautions not directly amenable to experimental tests. We conclude with a section on the physical basis of the universal validity of the equivalence principle, as manifest in the universality of free fall, and discuss its link to cosmic gravity.      

空间光学的发展与波前传感技术

摘要：进入21世纪，国际上一些发达国家和有关部门都已制定了空间发展战略规划，如美国航空航天局（NASA）、欧洲空间局（ESA）和俄罗斯政府相关部门等都提出空间发展战略规划，这些规划提出了今后一段时间内空间科学要解决的问题和发展的方向，而解决这些问题并推进空间技术的发展很大程度上依赖于先进的光学和无线电望远镜及仪器设备。因此，本文介绍本世纪初国际上空间科学应用的大型天文望远镜的发展情况，重点描述了大口径光学望远镜的光学系统以及实现这类天文望远镜的关键技术之一一波前传感技术。     

Raman spectra of nitrogen‐containing organic compounds obtained using a portable instrument at −15 °C at 2860 m above sea level

Well‐resolved Raman spectra of samples of nitrogen‐containing compounds were detected using a portable Raman instrument (Ahura First Defender XL) outdoors at a low ambient temperature of −15 °C and at an altitude of 2860 m (Pitztall, Austria). The portable Raman spectrometer tested here is equipped with a 785‐nm diode laser and a fixed frontal probe. Solid form of formamide, urea, 3‐methylpyridine, aniline, indene, 1‐(2‐aminoethyl)piperazine, indoline and benzofuran were detected unambiguously under high‐mountain field conditions. The main Raman features (strong, medium and partially weak bands) were observed at the correct wavenumber positions (with a spectral resolution 7–10 cm⁻¹) in the wavenumber range 200–1600 cm⁻¹. The results obtained demonstrate the possibility of employing a miniaturised Raman spectrometer as a key instrument for investigating the presence of nitrogen‐containing organic compounds and biomolecules outdoors under low temperature conditions. Within the payload designed by European Space Agency (ESA) and National Aeronautics and Space Administration (NASA) for future missions, focussing not only on Mars, Raman spectroscopy represents an important instrumentation for the detection of organic nitrogen‐containing compounds relevant to life detection on planetary surfaces or near sub‐surfaces. Copyright © 2009 John Wiley & Sons, Ltd.     

Evaluation of a PbTe detector for infrared imaging purposes

Summary An infra-red detector produced by the Elettronica SPA Company for the European Space Agency to be used in the Earth surface mapping from aircraft has been tested in our laboratory. We present the characteristics of the detector working in the spectral range (1÷2.5) μm. The acquisition system and the electronics are discussed and a detailed study of all the noise sources is presented; the measured NEP is 3.2·10⁻¹⁴W Hz^−1/2 at a temperature of 108 K. Paper presented at the V Cosmic Physics National Conference, S. Miniato, November 27–30, 1990.     

The nEDM experiment at the SNS

The nEDM collaboration proposes to measure the neutron electric dipole moment at the Spallation Neutron Source (Oak Ridge National Laboratory). The nEDM is a clear signature of CP violation. According to the Standard Model the nEDM is very small (～10^?31 e cm), but many theories predict much higher values. In the proposed experiment polarized cold neutrons from the SNS would be trapped in liquid helium at a temperature of about 400 mK. The neutron spin would precess in a very uniform magnetic field (H ～ 30 mG), and the experiment would measure the change in the precession frequency when a very strong electric field (E ～ 50 kV/cm) is applied. Polarized ³He atoms serve as a co-magnetometer. The goal of the experiment is to measure the nEDM with an accuracy of ～9 × 10^?28 e cm, which is more than an order of magnitude better than existing results.     

How particular is the physics of the free energy principle?

The free energy principle (FEP) states that any dynamical system can be interpreted as performing Bayesian inference upon its surrounding environment. Although, in theory, the FEP applies to a wide variety of systems, there has been almost no direct exploration or demonstration of the principle in concrete systems. In this work, we examine in depth the assumptions required to derive the FEP in the simplest possible set of systems – weakly-coupled non-equilibrium linear stochastic systems. Specifically, we explore (i) how general the requirements imposed on the statistical structure of a system are and (ii) how informative the FEP is about the behaviour of such systems. We discover that two requirements of the FEP – the Markov blanket condition (i.e. a statistical boundary precluding direct coupling between internal and external states) and stringent restrictions on its solenoidal flows (i.e. tendencies driving a system out of equilibrium) – are only valid for a very narrow space of parameters. Suitable systems require an absence of perception-action asymmetries that is highly unusual for living systems interacting with an environment. More importantly, we observe that a mathematically central step in the argument, connecting the behaviour of a system to variational inference, relies on an implicit equivalence between the dynamics of the average states of a system with the average of the dynamics of those states. This equivalence does not hold in general even for linear stochastic systems, since it requires an effective decoupling from the system's history of interactions. These observations are critical for evaluating the generality and applicability of the FEP and indicate the existence of significant problems of the theory in its current form. These issues make the FEP, as it stands, not straightforwardly applicable to the simple linear systems studied here and suggest that more development is needed before the theory could be applied to the kind of complex systems that describe living and cognitive processes.     

Quantum statistical monte carlo methods and applications to spin systems

A short review is given concerning the quantum statistical Monte Carlo method based on the equivalence theorem⁽¹⁾ thatd-dimensional quantum systems are mapped onto (d+1)-dimensional classical systems. The convergence property of this approximate tansformation is discussed in detail. Some applications of this geneal appoach to quantum spin systems are reviewed. A new Monte Carlo method, “thermo field Monte Carlo method,” is presented, which is an extension of the projection Monte Carlo method at zero temperature to that at finite temperatures. Invited talk presented at “Frontiers of Quantum Monte Carlo,” Los Alamos National Laboratory, September 3–6, 1985.     

Blue luminescence in Tm-doped KGd(WO4)2 single crystals

Up-conversion blue emissions of trivalent thulium ions in monoclinic KGd(WO₄)₂ single crystals at 454 and 479 nm are reported for a single pump laser source at 688 nm. We grew thulium-doped KGd(WO₄)₂ single crystals at several concentrations from 0.1% to 10%. We recorded a polarized optical absorption spectrum for the ³F₂+³F₃ energy levels of thulium at room temperature and low temperature (6 K). From the low temperature emission spectra we determined the splitting of the ³H₆ ground state. The blue emissions are characterized as a function of the dopant concentration and temperature from 10 K to room temperature. To our knowledge, this is the first time that sequential two-photon excitation process (STEP) generated blue emissions in thulium-doped single crystals with a single excitation wavelength.     

Space communications: Practical application of a visible Nd: YAG laser

Space laser communications with the frequency doubled Nd-YAG laser offers the most efficient means for transferring wideband data from one satellite to another. A space test in 1981 of the Nd-YAG laser system operating at a rate of 1 000 Mbit s^-1 will establish the basis for future systems. The system offers growth capability beyond conventional systems and is a major step forward in the application of a low power laser. The Nd-YAG laser design as well as its principles of operation are constrained by the space application. The laser is now conductively cooled, mode-locked, and frequency-doubled, and will be so operated in space. The space system will use both solar and lamp pumped lasers to allow alternate modes of operation.