JFernandoPascualS

I just learned that George Smoot passed away at the age of 80.

The discovery of cosmic background anisotropies by the COBE in 1992, allowed scientists to determine the magnitude of primordial cosmological perturbations.
For this discovery, he received the Nobel Prize in 2006.

Gravitational wave cosmology : an introduction This chapter introduces gravitational wave cosmology, focusing on the use of gravitational waves as standard sirens to probe the expansion history of the Universe. It presents and explains the methodo...

Gravitational waves are standard sirens and provide a direct measurement of the luminosity distance through the amplitude of the signal.
But the redshift remains inaccessible.

Gravitational Wave Cosmology : an introduction
G. Pierra, S. Mastrogiovanni

arxiv.org/abs/2507.10597

Addressing the $H_0$ tension through matter with pressure and no early dark energy We propose that the Hubble tension arises due to an unaccounted additional component, that behaves as \emph{matter with pressure}. We demonstrate that this fluid remains subdominant compared to both dust and radiation throughout nearly the entire universe expansion history. Specifically, the additional fluid satisfies the Zel'dovic limit with a constant equation of state, $ω_s > 0$, and a quite small normalized energy density, $Ω_s$. Accordingly, this component modifies both the sound horizon and the background expansion rate, \emph{acting quite differently from early dark energy models}, without significantly affecting the other cosmological parameters. To show this, we perform a Monte Carlo Markov chain analysis of our model, hereafter dubbed $Λ_{ω_s}$CDM paradigm, using the publicly available \texttt{CLASS} Boltzmann code. Our results confirm the presence of this fluid, with properties that closely resemble those of radiation. We find best-fit values that satisfy $ω_s \lesssim ω_γ$ and a relative energy density $Ω_s / Ω_γ= 0.45$, with $ω_r$ and $Ω_r$ the equation of state and density of photons, respectively. The effective fluid may be associated with generalized K-essence models or, alternatively, with Proca-type vector fields, albeit we do not exclude \emph{a priori} more exotic possibilities, i.e., dark radiation, axions, and so on. Physical implications of our results are analyzed in detail, indicating a statistical preference for the $Λ_{ω_s}$CDM scenario over the conventional $Λ$CDM background.

'Addressing the Hubble tension through matter with pressure and no early dark energy'
by Y Carloni, O. Luongo, M. Muccino

The new component modifies both the sound horizon and the expansion rate, acting very differently from early dark energy models.

arxiv.org/abs/2506.11531

The CosmoVerse White Paper: Addressing observational tensions in cosmology with systematics and fundamental physics The standard model of cosmology has provided a good phenomenological description of a wide range of observations both at astrophysical and cosmological scales for several decades. This concordance mod...

'The CosmoVerse White Paper'

A concordant article on COSMOLOGY of about 500 authors, 420 pages and 4300 references.

But, the mounting observational discrepancies suggest that a new concordance model
may ultimately be required to resolve these tensions.

arxiv.org/abs/2504.01669

Colloquium: The Cosmic Dipole Anomaly The Cosmological Principle, which states that the Universe is homogeneous and isotropic (when averaged on large scales), is the foundational assumption of Friedmann-Lemaitre-Robertson-Walker (FLRW) co...

Cosmic Dipole Anomaly poses a serious challenge to LCDM Universe model which assumes the Cosmological Principle.

The matter dipole is anomalously larger compared with the CMB dipole, so either the rest frames are DIFFERENT or that there is an intrinsic anisotropy in one.

arxiv.org/abs/2505.23526

Cosmological Tests of Everpresent $Λ$ Everpresent $Λ$ is a cosmological scenario in which the observed cosmological "constant" $Λ$ fluctuates between positive and negative values with a vanishing mean, and with a magnitude comparable to t...

A radical way out of last DESI results.

The (discrete) causal set programme for quantum gravity gave rise to the prediction that dark energy Λ(t,x) is a function of (space&) time but thus the Einstein’s field equations for General Relativity do not hold.

arxiv.org/abs/1703.06265

YouTube video by wocomoDOCS How humanity has measured time: From prehistory to the digital age

I just rewatched this great YouTube documentary about the measurement of time throughout the ages. It's worth watching!

The part of Relativity was given to Pacôme Delva, a good choice.

It's worth watching!

www.youtube.com/watch?v=rxkJ...

Global hyperbolicity and manifold topology from the Lorentzian distance In this work, we seek characterizations of global hyperbolicity in smooth Lorentzian manifolds that do not rely on the manifold topology and that are inspired by metric geometry. In particular, strong...

Great paper on Lorentzian Differential Topology by a living genius, my friend Ettore Minguzzi.

'Global hyperbolicity and manifold topology from the Lorentzian distance'
by A. Bykov, E. Minguzzi

arxiv.org/abs/2503.04382

Evolution of human cognition required Einstein's gravitational waves We describe an unexpected anthropic fine-tuning of gravity: human cognition arose on Earth only because the laws of gravity included gravitational waves. Their link is the heat from decays of the radi...

A holistic paper.

Three of Nature's four interactions (EM, weak and strong) seek equilibrium, yet it is gravity's persistence in destroying the equilibrium (including gravitational waves predicted by Einstein's theory) that allows life to emerge on Earth.

arxiv.org/abs/2503.03604

As the world turns—irregularly The length of the day varies by milliseconds over the course of weeks, years, and centuries. Conservation of angular momentum explains why.

"As the world turns—irregularly"

The length of the day varies by milliseconds over the course of weeks, years, and centuries. Conservation of angular momentum explains why.

A magnificent and synthetic article of dissemination.

pubs.aip.org/physicstoday...

Observation of the quantum equivalence principle for matter-waves Einstein's general theory of relativity is based on the principle of equivalence - in essence, dating back to Galileo - which asserts that, locally, the effect of a gravitational field is equivalent t...

Confirming the Einstein's Equivalence principle (of local gravity and inertia) in the Quantum domain.

This is done with a novel cold-atom interferometer in which one wave packet stays static in the lab frame while the other is in free-fall.

arxiv.org/abs/2502.14535

Violation of Bell inequalities from Cosmic Microwave Background data In a recent paper [R. Dale. R. Lapiedra, and J. A. Morales-Lladosa, Phys. Rev. D {\bf 107}, 023506 (2023)] a cosmic-like Clauser-Horne-Shimony-Holt (CHSH) inequality was proved for the temperature flu...

Can the “correct” interpretation of quantum mechanics be demonstrated using measurements of background radiation temperatures from WMAP and Planck?

See: Violation of Bell inequalities from Cosmic Microwave Background data

by Roberto Dale et al

arxiv.org/abs/2502.13846

Steven Weinberg: A Scientific Life Steven Weinberg was a giant of late 20th Century physics on whose shoulders we stand while groping for the science of the 21st Century. This article provides a too-brief summary of a selection of his ...

All about Steven Weinberg
Nobel in 1979 for the unification of the electromagnetic and weak interactions between elementary particles, using Yang-Mills gauge theory and predicting the existence of the Higgs boson.

He was very influential in the growth of scientific culture

arxiv.org/abs/2502.10979

How Noether’s Theorem Revolutionized Physics | Quanta Magazine Emmy Noether showed that fundamental physical laws are just a consequence of simple symmetries. A century later, her insights continue to shape physics.

Nöther Revolutionized Physics.

Actually, Nöther conceived TWO ths. In the 1st, if an action (energy times time) is invariant under a finite group of transformations then physical quantities are conserved
The 2nd concerns the invariance under an infinite set

www.quantamagazine.org/how-noethers...

Towards a Non-singular Paradigm of Black Hole Physics The study of regular black holes and black hole mimickers as alternatives to standard black holes has recently gained significant attention, driven both by the need to extend general relativity to des...

Regular black holes and black hole mimickers as alternatives to standard black holes

Towards the evasion (by changing the sufficient conditions) of the Hawking-Penrose singularity theorems of Einstein's theory of gravity in collapse models of astrophysical objects.

arxiv.org/abs/2501.05505

Unveiling the largest structures in the nearby Universe: Discovery of the Quipu superstructure For a precise determination of cosmological parameters we need to understand the effects of the local large-scale structure of the Universe on the measurements. They include modifications of the cosmi...

'Quipu and the Cosmological Principle'

They provide an assessment of the largest five structures at distances between 130 and 250 Mpc.

The largest has a length longer than 400 Mpc, named Quipu, is the largest cosmic structure discovered to date.

arxiv.org/abs/2501.19236

"Por haberse movido, el tiempo transcurrido para usted y su reloj es ligeramente más corto que para el que dejó en casa."
Esto es incorrecto.

Ese tiempo es más corto medido por alguien en la casa, ya que los relojes en movimiento atrasan. Pero es recíproco y usted 'verá' atrasado el reloj de casa.

"Por haberse movido, el tiempo transcurrido para usted y su reloj es ligeramente más corto que para el que dejó en casa."
Esto es incorrecto.

Ese tiempo es más corto medido por alguien en la casa, ya que los relojes en movimiento atrasan. Pero es recíproco y usted 'verá' atrasado el reloj de casa.

Farewell Gaia!

Welcome BepiColombo!

Thanks, Gaia telescope!

I always have in mind this drawing about what can be observed Geometrically in Cosmology.

Thomas--Wigner rotation as a holonomy for spin-$1/2$ particles The Thomas--Wigner rotation (TWR) results from the fact that a combination of boosts leads to a non-trivial rotation of a physical system. Its origin lies in the structure of the Lorentz group. In thi...

Two non-collinear boosts give rise to a boost and a Thomas rotation.

While the space of Newtonian velocities is flat Euclidean (Galilean group), the space of relativistic velocities is negatively curved (Lorentz group) i.e., hyperbolic.

See:
arxiv.org/abs/2310.08121

Cosmic deceptions due to peculiar motions Relative motions have long been known to mislead the unsuspecting observers to false interpretations of reality. The deceptions are usually brief and unimportant, though relative motions have also led...

"Tilted cosmology"

The possibility that the accelerated expansion of the Universe and, hence the so-called dark energy or cosmological constant, is a mere illusion triggered by our peculiar motion relative to the absolute CMB frame.

Look the recent paper by Tsagas:

arxiv.org/abs/2501.04680