282 research outputs found
Il volto di Flora
No full textOpera sconosciuta di A. Spallicci, intellettuale mazziniano e organizzatore di cultura. Un saggio del curatore ricostruisce la genesi d'una coscienza ecologica nella "provincia" romagnola, ai primi anni '60, cui seguirà la cura del Parco del Delta del Po, del reimpianto della Pineta di Ravenna, e di altre iniziative intese a sollecitare una legislazione governativa sulla protezione dei "beni ambientali"
Saggio introduttivo. Aldo Spallicci, Scritti e discorsi politici
No full textIl saggio pone in primo piano la cultura politica, l'intreccio fra morale e politica in un socialista mussoliniano passato poi al mazzinianesimo e infine alla piena accettazione delle istituzioni democratiche. Il regionalismo riassume, in questo quadro, il tentativo di adattare le idee politiche facendole penetrare nei costumi popolari mediante originali iniziative, che andavano dalla promozione dell'artigianato ai musei degli strumenti di lavoro rurale ai cibi e agli oggetti di uso quotidiano
Aldo Spallicci. Scritti e discorsi politici
No full textVolume 7 dell'Opera omnia coordinata dal curatore e diretta da L. Bedeschi. Il volume raccoglie il percorso politico d'un mazziniano emblematico, promotore di riviste letterarie, agitatore politico repubblicano, che da volontario nella Grande guerra, poi antifascista e costituente, approda al seggio di senatore della Repubblica. Un lungo saggio introduttivo ricostruisce il quadro storico, il percorso delle idee politiche, dal socialismo mussoliniano al repubblicanesimo e infine all'adesione alle idee di Pacciardi
Perturbation method in the assessment of radiation reaction in the capture of stars by black holes
No full text10 pages, no figures. Email: [email protected] To appear on Classical and Quantum Gravity March 2004This work deals with the motion of a radially falling star in Schwarzschild geometry and correctly identifies radiation reaction terms by the perturbative method. The results are: i) identification of all terms up to first order in perturbations, second in trajectory deviation, and mixed terms including lowest order radiation reaction terms; ii) renormalisation of all divergent terms by the Riemann and Hurwitz functions. The work implements a method previously identified by one of the authors and corrects some current misconceptions and results
Free fall and self-force: an historical perspective
No full text43 pages; to appear in final form on "Mass and Motion in General Relativity" by Springer (L. Blanchet, A. Spallicci, B. Whiting Eds.) based on the lectures given at the CNRS School on Mass held the 23-25 June 2008 in Orl\'eans. http://www.springer.com/astronomy/cosmology/book/978-90-481-3014-6International audienceFree fall has signed the greatest markings in the history of physics through the leaning Pisa tower, the Cambridge apple tree and the Einstein lift. The perspectives offered by the capture of stars by supermassive black holes are to be cherished, because the study of the motion of falling stars will constitute a giant step forward in the understanding of gravitation in the regime of strong field. After an account on the perception of free fall in ancient times and on the behaviour of a gravitating mass in Newtonian physics, this chapter deals with last century debate on the repulsion for a Schwarzschild black hole and mentions the issue of an infalling particle velocity at the horizon. Further, black hole perturbations and numerical methods are presented, paving the way to the introduction of the self-force and other back-action related methods. The impact of the perturbations on the motion of the falling particle is computed via the tail, the back-scattered part of the perturbations, or via a radiative Green function. In the former approach, the self-force acts upon the background geodesic; in the latter, the geodesic is conceived in the total (background plus perturbations) field. Regularisation techniques (mode-sum and Riemann-Hurwitz function) intervene to cancel divergencies coming from the infinitesimal size of the particle. An account is given on the state of the art, including the last results obtained in this most classical problem, together with a perspective encompassing future space gravitational wave interferometry and head-on particle physics experiments. As free fall is patently non-adiabatic, it requires the most sophisticated techniques for studying the evolution of the motion. In this scenario, the potential of the self-consistent approach, by means of which the background geodesic is continuously corrected by the self-force contribution, is examined
Cosmology and the massive photon frequency shift in the Standard-Model Extension
No full textThe total red shift z might be recast as a combination of the expansion red shift and a static shift due to the energy–momentum tensor non-conservation of a photon propagating through Electro-Magnetic (EM) fields. If massive, the photon may be described by the de Broglie–Proca (dBP) theory which satisfies the Lorentz(-Poincaré) Symmetry (LoSy) but not gauge-invariance. The latter is regained in the Standard-Model Extension (SME), associated with LoSy Violation (LSV) that naturally dresses photons of a mass. The non-conservation stems from the vacuum expectation value of the vector and tensor LSV fields. The final colour (red or blue) and size of the static shift depend on the orientations and strength of the LSV and EM multiple fields encountered along the path of the photon. Turning to cosmology, for a zero Ω Λ energy density, the discrepancy between luminosity and red shift distances of SNeIa disappears thanks to the recasting of z. Massive photons induce an effective dark energy acting ‘optically’ but not dynamically
Newtonian free fall with an Einsteinian view
No full textFree fall is revisited through the legendary Pisa tower experiment. We suppose the absence of air friction and neglect the Earth non-spherical shape, its inhomogeneities and rotation. Asking whether 1kg stone falls like one of 2kg, young pupils may reply negatively, possibly supposing a difference of a factor two. Instead, teachers may say "exactly yes". The right reply is multi-faceted. It is "exactly yes" only in the Earth fixed frame, that by construction is unaffected by any falling mass, whereas in all other frames the answer is "approximately yes". We start considering each mass being released separately and keep the Earth-stone initial distance as fixed throughout the work.
If the observer is at a fixed distance from the Earth centre, e.g., on the Earth surface, he will measure the sum of the acceleration of the stone towards the Earth and of the Earth towards the stone: the larger the stone, the larger the sum perceived by the observer. If the observer is at a fixed distance from the system (Earth and stone) centre of mass (or else imagine that the stone is that heavy to shift the system centre of mass outside the Earth), he will observe the Earth and the stone falling toward him and reaching the system centre of mass at the same instant. Keeping the initial distance Earth-stone constant, by increasing the mass of the stone, the system centre of mass will shift towards the stone and this latter will undergo a smaller acceleration having to cover a smaller distance: the larger the stone, the smaller the acceleration.
In these two last frames, the difference in fall is minuscule, being of the order of the stone/Earth mass ratio, thus not yet measurable by state-of-the-art technology. For the Commander Scott of Apollo 15, the difference in fall between the plume and the hammer was in the order of 6x10-24 s. Nevertheless, this ratio may take large values and be of considerable impact in astronomy. But most stimulating, the heavier stone falls faster or slower than the lighter one depending on the observer. The physics dependency on the observer rises to feature of paramount significance in Einstein's general relativity and thus Newtonian radial fall may be used to introduce gauge dependence. Dealing with two masses released simultaneously, the answer to the three body-problem is numerical, knowing that the system centre of mass will not be equidistant to the two small, but different, masses. The preceding doesn’t violate in any manner the equivalence principle of inertial and gravitational mass.
We briefly deal with radial fall in general relativity where the motion of the falling mass is influenced by the mass ratio as in Newtonian gravity but also by the radiation emitted. In the context of the Pisa tower, the energy-time Heisenberg indetermination impedes measuring the gravitational radiation. Instead, the capture of small black holes falling into supermassive ones is the source targeted by LISA to explore general relativity in the strong field. Finally, the analysis of falling observers in black holes during emission of Hawking radiation is of interest for combining quantum mechanics and general relativity.
FURTHER READING
Barausse E. et al. (2020). Prospects for fundamental physics with LISA. General Relativity and Gravitation, 52, 81. https://doi.org/10.1007/s10714-020-02691-1
Ritter P., Aoudia S., Spallicci A.D.A.M., Cordier S. (2016). Indirect (source-free) integration method. II. Self-force consistent radial fall, Int. J. Geom. Meth. Mod. Phys., 13, 1650019. https://doi.org/10.1142/S0219887816500195
Spallicci A., (2011). Self-force and free fall: an historical perspective, Springer Series on Fundamental Theory of Physics Vol. 162, L. Blanchet, A. Spallicci, B. Whiting, Eds., p. 561. https://link.springer.com/book/10.1007%2F978-90-481-3015-3
Spallicci A.D.A.M., van Putten M.H.P.M., (2016). Gauge dependence and self-force in Galilean and Einsteinian free falls, Pisa tower and evaporating black holes at general relativity centennial. International Journal of Geometric Methods in Modern Physics, 13(8), 1630014. https://doi.org/10.1142/S021988781630014
Fast and Accurate Computational Tools for Gravitational Waveforms from Binary Stars with any Eccentricity
No full textQuestioning the tension via the look-back time
No full textThe Hubble tension is investigated taking into account the cosmological
look-back time. Specifically, considering a single equation, widely used in
standard cosmology, it is possible to recover both values of the Hubble
constant reported by the SH0ES and Planck collaborations: the former is
obtained through cosmological ladder methods (e.g. Cepheids, Supernovae Type
IA) and the latter through measurements of the Cosmic Microwave Background.
Also, other values obtained in the literature are achieved with the same
approach. We conclude that the Hubble tension can be removed if the look-back
time is correctly referred to the redshift where the measurement is performed.Comment: 8 pages, 1 figure, accepted for publication in Physics of the Dark
Univers
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