A comment on a proposal to use neutrons to reveal gravitomagnetic effects on Earth
Arguments are presented which show that the recent proposals of using neutrons to test gravitomagnetic effects on Earth are impracticable.
gr-qc↗
arXiv subjects
A. Tartaglia
Publications and source records attributed to A. Tartaglia.
Testing gravitomagnetism on the Earth
The paper contains a proposed experiment for testing the gravitomagnetic effect on the propagation of light around a rotating mass. The idea is to use a rotating spherical laboratory-scale shell, around which two mutually orthogonal lightguides are wound acting as the arms of an interferometer. Numerical estimates show that time of flight differences between the equatorial and polar guides could be in the order of $\sim 10^{-20}$ s, actually detectable with sensitivity perfectly comparable with those expected in gravitational wave detection experiments.
gr-qc↗
Verifying the learning process in Physics
The paper describes an automated evaluation system for the learning of general Physics. The system whose name is Test on Line (ToL) is based on a questions bank from which an appropriate software generates individual multi-issue questionnaires to be submitted through the web. ToL has been extensively experimented during three years and is presently in use for basic Physics courses at the Engineering Faculties of the Turin Politecnico. The results of the experimentation and use are presented and discussed. Cumulating data allows for an optimization of the internal partitions of the questions bank and of the selection criteria for the generation of the questionnaires. The instrument proved to be useful and reliable and could become the core of an agreed common standard for physics education at university level.
physics.ed-ph↗
Gravitomagnetism, clocks and geometry
New techniques to evaluate the clock effect using light are described. These are based on the flatness of the cylindrical surface containing the world lines of the rays constrained to move on circular trajectories about a spinning mass. The effect of the angular momentum of the source is manifested in the fact that inertial observers must be replaced by local non rotating observers. Starting from this an exact formula for circular trajectories is found. Numerical estimates for the Earth environment show that light would be a better probe than actual clocks to evidence the angular momentum influence. The advantages of light in connection with some principle experiments are shortly reviewed.
gr-qc↗
Gravitational Aharonov-Bohm effect and gravitational lensing
Considering the spacetime around a rotating massif body it is seen that the time of flight of a light ray is different whether it travels on one side of the source or on the other. The difference is proportional to the angular momentum of the body. In the case that a compact rapidly rotating object is the source of a gravitational lensing effect, the contribution coming from the above mentioned gravitational Aharonov-Bohm effect should be added to the other causes of phase difference between light rays coming from different images of the same object.
gr-qc↗
Geometric treatment of the gravitomagnetic clock effect
We have developed a general geometric treatment of the GCE valid for any stationary axisymmetric metric. The method is based on the remark that the world lines of objects rotating along spacely circular trajectories are in any case, for those kind of metrics, helices drawn on the flat bidimensional surface of a cylinder. Applying the obtained formulas to the special cases of the Kerr and weak field metric for a spinning body, known results for time delays and synchrony defects are recovered.
gr-qc↗
Detection of the gravitomagnetic clock effect
The essence of the gravitomagnetic clock effect is properly defined showing that its origin is in the topology of world lines with closed space projections. It is shown that, in weak field approximation and for a spherically symmetric central body, the loss of synchrony between two clocks counter-rotating along a circular geodesic is proportional to the angular momentum of the source of the gravitational field. Numerical estimates are presented for objects within the solar system. The less unfavorable situation is found around Jupiter.
gr-qc↗
On local and global measurements of the speed of light on rotating platforms
The paper shows that, conceptually and operationally, the speed of light as measured locally in the inertial comoving frame of a point on the rim of a rotating disk, is different from the one measured globally for a round trip along the rim, obtained dividing the length of the rim (as measured in the ''relative space'' of the disk) by the time of flight of the light beam (as measured by a clock at rest on the disk). As a consequence, contrary to some recent claims, the anisotropy found in the global value, obtained by the above procedure, in no way conflicts with the local isotropy, and the internal consistency of the special relativity theory remains unchallenged.
gr-qc↗
General relativistic corrections to the Sagnac effect
The difference in travel time of corotating and counter-rotating light waves in the field of a central massive and spinning body is studied. The corrections to the special relativistic formula are worked out in a Kerr field. Estimation of numeric values for the Earth and satellites in orbit around it show that a direct measurement is in the order of concrete possibilities.
gr-qc↗
Speed of light on rotating platforms
It is often taken for granted that on board a rotating disk it is possible to operate a \QTR{it}{global}3+1 splitting of space-time, such that both lengths and time intervals are \QTR{it}{uniquely} defined in terms of measurements performed by real rods and real clocks at rest on the platform. This paper shows that this assumption, although widespread and apparently trivial, leads to an anisotropy of the velocity of two light beams travelling in opposite directions along the rim of the disk; which in turn implies some recently pointed out paradoxical consequences undermining the self-consistency of the Special Theory of Relativity (SRT). A correct application of the SRT solves the problem and recovers complete internal consistency for the theory. As an immediate consequence, it is shown that the Sagnac effect only depends on the non homogeneity of time on the platform and has nothing to do with any anisotropy of the speed of light along the rim of the disk, contrary to an incorrect but widely supported idea.
gr-qc↗
Is the EPR paradox really a paradox?
The EPR paradox and the meaning of the Bell inequality are discussed. It is shown that considering the quantum objects as carrying with them ''instruction kits'' telling them what to do when meeting a measurement apparatus any paradox disappears. In this view the quantum state is characterized by the prescribed behaviour rather than by the specific value a parameter assumes as a result of an interaction.
quant-ph↗
Quantum theory of frequency shifts of an electromagnetic wave interacting with a plasma
In the paper we calculate the frequency shift induced on a photon by the interaction with a low density electronic plasma. The technique is the standard perturbation theory of quantum electrodynamics, taking into account the many body character of the plasma. The shift in non relativistic approximation is shown to be blue. Besides the quantum shift also the known classical effects and the correct temperature dependence are obtained. Finally the limits of the approximations used are discussed.
astro-ph↗
Four Dimensional Elasticity and General Relativity
It has been shown that the extension of the elasticity theory in more than three dimensions allows a description of space-time as a properly stressed medium, even recovering the Minkowski metric in the case of uniaxial stress. The fundamental equation for the metric in the theory is shown to be the equilibrium equation for the medium. Examples of spherical and cylindrical symmetries in four dimensions are considered, evidencing convergencies and divergencies with the classical general relativity theory. Finally the possible meaning of the dynamics of the four dimensional elastic medium is discussed.
gr-qc↗