π Restrictions on initial conditions in cosmological scenarios and implβ¦
Quicklook:
Baumgarte, Thomas W. et al. (2025) Β· Physical Review D
Reads: 9655 Β· Citations: 0
DOI: 10.1103/9nsk-jy7f
π https://ui.adsabs.harvard.edu/abs/2025PhRvD.112l3528B/abstract
#Astronomy #Astrophysics #Cosmology #GeneralRelativityAndQuantumCosmology #CosmologyAndNongalacticAβ¦
π Twins in relativistic spacetimes: dispelling some misconceptions
Quicklook:
da CΓ’mara, T. A. A. et al. (2025) Β· arXiv e-prints
Reads: 2275 Β· Citations: 0
DOI: 10.48550/arXiv.2509.21455
π https://ui.adsabs.harvard.edu/abs/2025arXiv250921455D/abstract
#Astronomy #Astrophysics #BlackHoles #GeneralRelativityAndQuantumCosmology #PhysicsEducation
In contrast to Newtonian physics, there is no absolute time in relativistic (Lorentzian) spacetimes. This immediately implies that two twins may, in general, age at different rates. For this to happen, there must be, of course, some asymmetry between their worldlines, along which the elapsed proper times are evaluated; such asymmetry might not be, however, so intuitively apparent. Our primary objective is to present, in a concise and didactic manner, some lesser-known results and derive novel ones from a modern, geometrical, and covariant standpoint, which aims to clarify the issue and dispel related misconceptions. First, we recall that: (i) the original ``twin paradox'' may be perfectly dealt with in special relativity (physics in a flat spacetime) and does not necessarily involve an accelerated twin. We then explore the issue of differential aging in general relativity (physics in a curved background) in the prototypical case of the vacuum Schwarzschild spacetime, considering several pairs of twins. In this context, we show that: (ii) it is not true that a twin which gets closer to the Schwarzschild horizon, by being subject to a stronger gravitational field, where time sort of slows down, should always get younger than a twin that stays further away, in a region of weaker gravitational field, and (iii) it is also false that an accelerated twin always returns younger than a geodesic one. Finally, we argue that (iv) in a generic spacetime, there is no universal correlation between the phenomena of differential aging and the Doppler effect. Two particularly pedagogical resources provided are a glossary of relevant terms and supplementary Python notebooks in a GitHub repository.
π Visualization and analysis of the curvature invariants in the Alcubieβ¦
Quicklook:
Rodal, JosΓ© et al. (2025) Β· arXiv e-prints
Reads: 0 Β· Citations: 0
DOI: N/A
π https://ui.adsabs.harvard.edu/abs/2025arXiv251220738R/abstract
#Astronomy #Astrophysics #BlackHoles #GeneralRelativityAndQuantumCosmology
In the Alcubierre warp-drive spacetime, we investigate the following scalar curvature invariants: the scalar $I$, derived from a quadratic contraction of the Weyl tensor, the trace $R$ of the Ricci tensor, and the quadratic $r1$ and cubic $r2$ invariants from the trace-adjusted Ricci tensor. In four-dimensional spacetime the trace-adjusted Einstein and Ricci tensors are identical, and their unadjusted traces are oppositely signed yet equal in absolute value. This allows us to express these Ricci invariants using Einstein's curvature tensor, facilitating a direct interpretation of the energy-momentum tensor. We present detailed plots illustrating the distribution of these invariants. Our findings underscore the requirement for four distinct layers of an anisotropic stress-energy tensor to create the warp bubble. Additionally, we delve into the Kretschmann quadratic invariant decomposition. We provide a critical analysis of the work by Mattingly et al., particularly their underrepresentation of curvature invariants in their plots by 8 to 16 orders of magnitude. A comparison is made between the spacetime curvature of the Alcubierre warp-drive and that of a Schwarzschild black hole with a mass equivalent to the planet Saturn. The paper addresses potential misconceptions about the Alcubierre warp-drive due to inaccuracies in representing spacetime curvature changes and clarifies the classification of the Alcubierre spacetime, emphasizing its distinction from class $B$ warped product spacetimes.
π The LIGO Open Science Center
Quicklook:
Vallisneri, Michele et al. (2015) Β· Journal of Physics Conference Series
Reads: 98 Β· Citations: 213
DOI: 10.1088/1742-6596/610/1/012021
π https://ui.adsabs.harvard.edu/abs/2015JPhCS.610a2021V/abstract
#Astronomy #Astrophysics #Galaxies #GeneralRelativityAndQuantumCosmology #AstrophysicsHighEnergyAstβ¦
The LIGO Open Science Center (LOSC) fulfills LIGO's commitment to release, archive, and serve LIGO data in a broadly accessible way to the scientific community and to the public, and to provide the information and tools necessary to understand and use the data. In August 2014, the LOSC published the full dataset from Initial LIGO's βS5β run at design sensitivity, the first such large-scale release and a valuable testbed to explore the use of LIGO data by non-LIGO researchers and by the public, and to help teach gravitational-wave data analysis to students across the world. In addition to serving the S5 data, the LOSC web portal (losc.ligo.org) now offers documentation, data-location and data-quality queries, tutorials and example code, and more. We review the mission and plans of the LOSC, focusing on the S5 data release.
adsdaily