#general-relativity — Public Fediverse posts

My #paperOfTheDay was "Galilei invariance, action-reaction principle, and center of mass theorem" from 1983.
This is an article about #generalRelativity , without anything quantum. From daily experience, we know that every object has a mass, but thinking more closely, the parameter we call mass actually appears in different ways in #physics, and it is not a priory clear how they are logically related. Einstein's famous thought experiment was about the "falling elevator", that is, if you are in a box and can't look outside, you can not distinguish whether you fall freely, or you are located far away from a planet where there is no gravitational field. This "weak equivalence principle" asserts the equivalence between "inertial mass", the parameter which determines how hard it is to accelerate something, and "passive gravitational mass", the parameter that determines how strongly a gravitational field acts on an object.
But there is a third type of mass, the "active gravitational mass", which determines how much gravitational field is generated by an object. The "strong equivalence principle" asserts that all three masses are the same.
The present article demonstrates that, as far as classical celestial mechanics is concerned, the strong equivalence principle can not been distinguished from the weak one. That is, the observed motion of celestial bodies can already be explained by the weak equivalence principle, regardless of whether the strong one holds or not.
I don't know what the current state of affairs is in that question, in particular regarding quantum theory.
https://link.springer.com/article/10.1007/BF01889417

Well that takes a load of my mind - I'm glad we got to the bottom of this!

Researchers @ University of Pennsylvania have confirmed that gravity's strength weakens with distance almost exactly as predicted by the equations developed by Newton and later incorporated into Einstein's theory of general relativity. https://phys.org/news/2026-04-gravity-newton-einstein-cosmic-scales.html #Gravity #Newton #Einstein #GeneralRelativity #TheoreticalPhysics #Physics #Astrophysics #Universe #Galaxies #UniversityofPennsylvania

We spent six weeks computationally analyzing the Rodal (2025) warp drive metric, the latest attempt to build a warp bubble without exotic matter. The result is a definitive negative, but the reason why is more interesting than "it doesn't work."

The irrotational construction reduces violations by 37x vs Alcubierre. But observer-robust analysis shows it hides violations across 45% of the domain that comoving observers never see.

1/3 #WarpDrive #Physics #GeneralRelativity

1/n Notes on #UAP Discussions : This particular exploration is a milestone. If we map what they eventually wind up talking about to vexing questions in current #Physics we have a direct confrontation with #GeneralRelativity, #QuantumMechanics, and the applied mass- energy firewall problem that lies at at the heart of several open problems in #Cosmology and the SM. It should be noted that the intuition of #Engineers in this case is capable of beating #Physicists to the punch.
There is a bit…

This is way above my pay grade, and I've only read the article, not the actual technical work underneath it (because my maths is insufficient to know what it's talking about, so there's not a lot of point). But it sounds really interesting.

https://muellerberndt.medium.com/how-observer-path-holography-improves-on-the-standard-model-and-general-relativity-c971c376027e

I've never heard of "observer patch holography" (note typo in slug text), but a theoretical framework which has just a single free variable but lets you derive general relativity and the standard model, correctly predicting a bunch of magic numbers that we input as free variables into the standard model, is interesting as hell.

Maybe someone smarter than me has already looked at this and debunked it. Sabine doesn't seem to have done a video on it (or I missed it). And "one guy with four information theory axioms solves all of physics' problems" is definitely on the Hollywood-script end of the plausibility scale, but who knows? Weirder things have happened.

@cenobyte - thought of you, of course.

#StandardModel #physics #GeneralRelativity #GR #ObserverPatchHolography #OPH #quantum

Today's #paperOfTheDay is "Why there is Nothing rather than something: A theory of the cosmological constant" from 1988. Like yesterday's paper, it deals with the intersection between quantum field theory and #generalRelativity, but the 30 years between them clearly show. Coleman's 1988 paper is an argument in the style of that time (which structurally is quite similar to much of the older #renormalon literature): Heuristic manipulations of formal objects such as the wave function of the universe, or divergent sums over all spacetime geometries. The outcome of this argument is that if #wormholes exist (caused by quantum effects at a scale that is much smaller than observations, but larger than the Planck scale), they can drive the cosmological constant to zero in an Euclidean path integral formulation of general relativity. As always with Coleman, the language is quite funny and frank about the paper's limitations: He writes "Although I find this theory in many ways very attractive, I must honestly stress its speculative character. It rests on wormhole dynamics and the Euclidean formulation of quantum gravity. This is doubly a house built on sand. [...] the Euclideon formulation of gravity is not a subject with firm foundations and clear rules of procedure; indeed, it is more like a trackless swamp". Observations like these have by now, 30 years later, led to a style of theoretical physics that is much more systematic and mathematical than in the 1980s, but also sometimes less intuitive. #dailyPaperChallenge https://doi.org/10.1016%2F0550-3213(88)90097-1

`The Lense-Thirring effect, a prediction of general relativity, implies that massive rotating objects like Earth can slightly "drag" spacetime, which could affect the pendulum's oscillation. This effect, though theoretically significant, is currently too small to measure with a Foucault pendulum.`

https://en.wikipedia.org/wiki/Foucault_pendulum#Absolute_reference_frame_for_pendulum

#physics #Foucault #pendulum #FoucaultPendulum #Earth #rotation #relativity #generalRelativity #Einstein

GR vs MOND - not competing theories, both emerge from 7D geometry.

New paper: Kaluza-Klein reduction splits into GR (metric) + MOND (scalar sector).

7D Einstein-Hilbert → Einstein's equations + AQUAL.

Prediction: lensing = dynamics. Testable.

🔗 https://zenodo.org/records/17922212

@fqxi @Physics

#physics #GeneralRelativity #MOND #cosmology #ModifiedGravity #KaluzaKlein #openscience #preprint

RE: https://mathstodon.xyz/@johncarlosbaez/115725040764787796

#RogerPenrose #GeneralRelativity #BlackHole #BlackHoles #maths #mathematics #physics #astrophysics #cosmology #GR

Another of my videos just hit 1.1k views

https://youtube.com/shorts/HlCvdxvgDwg

📹<^-^7🎨

#art #artist #illustrator #illustrated #quantummechanics #generalrelativity

I guess I'm #writing again, because yesterday I brainstormed a bunch of ideas for #book three, (Moon,) and then I woke up at 2:30 AM, realizing (I think) that I had messed up the #generalrelativity between #books one (Atmosphere,) and two, (Ocean.) This, after I spent a whole lot of time trying to make it work during the writing #process. I have a tenuous grasp on the #theory. Wish I had a #physicist friend I could #brainstorm with. #physics #question

I've come up with an equation that describes the early universe and how it was created. I've described and shown how symmetry breaking occurs due to black hole structure

I'm currently being considered for Mensa here in Australia because of my Quantum Mechanical Diagrams

<O,O>

#art #artist #illustrator #illustrated #quantummechanics #generalrelativity

I'm being considered for Mensa because of my Quantum Mechanical Diagrams

<O,O>

#art #artist #illustrator #illustrated #quantummechanics #generalrelativity

3I/ATLAS might have just proven Einstein's 1915 theory right before unusually deviating near the Sun, which resurfaces the question: Is it really a comet?
https://atlas.whatip.xyz/post.php?slug=3iatlas-might-have-just-proven-einsteins-1915-theory-right-before-unusually-deviating-near-the-sun-which-resurfaces-the-question-is-it-really-a-comet
"Unraveling Celestial Mysteries: Is 3I/ATLAS Really a Comet?" #CosmicEnigma #EinsteinTheoryConfirmed
#space #astronomy #3iatlas #generalrelativity

I learned Einstein's General Relativity in 24 hours

#LookingGlassUniverse

#generalrelativity #physics #einstein

https://www.youtube.com/watch?v=KEce3se9bMI&list=UULFFk__1iexL3T5gvGcMpeHNA&index=1

Twin #blackhole collisions put #Einstein’s #generalrelativity to its most extreme test

https://www.sciencedaily.com/releases/2025/10/251029100139.htm

Macroscopic Theories Of Matter And Fields A Thermodynamic Approach ( Advances in Science and Technology in the USSR)

Advances in Science and Technology in the USSR
Mathematics and Mechanics Series

This is a collection of articles by Soviet scientists on current issues of building macroscopic models of matter and fields. Based on thermodynamics concepts the papers develop general variational techniques of modeling material continuous media and fields allowing for their interactions in reversible and irreversible processes. The book is intended for researchers, engi­neers, graduate and postgraduate students interested in the mechanics of continuous media.

Translated from the Russian by Eugene Yankovsky

You can get the book here and here.

Twitter: @MirTitles
Mastodon: @[email protected]
Mastodon: @[email protected]
Bluesky: mirtitles.bsky.social

Contents
Preface, L. I. Sedov 7
A Thermodynamic Approach to the Basic Variational Equation for Building Models of Continuous Media, L. I. Sedov 19
Applying the Basic Variational Equation for Building Models of Matter and Fields, L. I. Sedov 43

Introduction 43
Definitions 43
Variations of Tensors for Which Scalar Invariants Retain Their Form 46
Special Types of Tensor Components Qlj 48
Defining Variations and Their Interrelationship in the Comoving and the Observer’s Reference Frame 50
Auxiliary Formulas for Variations 55
Given Scalar and Tensor Parameters Characterizing Models of Material Media and Fields 56
The Determining Parameters in the Characteristics of a Continuous Medium as a Whole and the Characteristics of Individual World Lines 60
The Basic Variational Equation and Identities Following from the Scalar Nature of the Lagrangian Density 62
The Euler Equations for the Basic Variational Equation (2.8.1) 66
The Conditions at Strong Discontinuities 71
On Models of Fluids 74
An Elastic-Body Model 79
Constructing Models of Fields 81
A Model of Interacting Material Medium and Electromagnetic Field 83
Examples 90
Transition from Relativistic to Newtonian Mechanics in the Presence of Irreversible Processes, L. T. Chernyi 98
The Basic Vibrational Equation 98
The Euler Equations and Conditions on Discontinuities 102
Transition to Newtonian Mechanics 106
Irreversible Processes 108
Conclusion 114
Models of Ferromagnetic Continuous Media with Magnetic Hysteresis, L. T. Chernyi 116

Introduction 116
The Determining Parameters 118
The Variational Principle and the Main Equations 121
A Phenomenological Theory of Irreversible Processes 126
Some Corollaries of the General Theory 130
Examples of Models of Magnetizable Media 137
Magnetizable and Polarizable Media with Microstructure, V. A. Zhelnorovich 141

The Determining Parameters of Magnetizable and Polarizable Media with Microstructure 141
Relaxation Models of Magnetizable and Polarizable Media Without Microstructure 150
Models of Magnetizable Liquids with Intrinsic Moment of Momentum 156
Couette Flow of an Incompressible Viscous Magnetizable Liquid 156
Poiseuille Flow in Cylindrical Channel 157
Magnetoacoustic Waves in Magnetizable Liquids 160
On Exact Solutions for Interacting Gravitational and Electromagnetic Fields, G. A. Alekseev 168

Introduction 168
The Einstein-Maxwell Equations in Matrix Form 169
Building the Associated Linear System and the Reduction Conditions 172
Soliton Solutions of the Einstein-Maxwell Equations 176
One-Soliton Solutions with Minkowski’s Space-Time as Background 180
Interaction of Solitons with a Uniform Electromagnetic Field 184
Neutrino Fields in General Relativity, N. R. Sibgatullin 187

Introduction 187
Canonical Equations of Neutrino Fields and Waves 188
On the Infinite Dimensional Algebra and the Lie Group of Neutrino Vacuum Equations 199
Exact Solutions of Neutrino Vacuum Equations 208
Rotation of the Polarization Vector of Gravitational Waves in a Burst of Neutrino Radiation 220
Tensor Representation of Spinor Fields, V. A. Zhelnorovich 224

Introduction 224
Dirac Matrices 224
The Spinor Representation of the Lorentz Group 226
Spinors in Four-Dimensional Pseudo-Euclidean Vector Space 231
Conjugate Spinors 233
The Relation Between Even-Rank Spinors and Tensors 234
The Relation Between First-Rank Spinors and Systems of Complex Tensors 234
Real-Valued Tensors Determined by a Spinor 238
Rotations in Four-Dimensional Space and Spinors 240
Invariant Spinor Subspaces 243
Spinors in Three-Dimensional Euclidean Space 244
Tensor Representation of Spinors in Three-Dimensional Euclidean Space 246
Rotations in Three-Dimensional Space and Spinors 248
Tensor Representation of Differential Spinor Equations in the Minkowski Space 250
Some Solutions of Differential Equations for Relativistic Models of Magnetizable Fluids with Intrinsic Angular Momentum in an Electromagnetic Field 254
Index 26

#elementaryParticles #generalRelativity #mirPublishers #physics #quantumMechanics #sovietLiterature #variationalPrinciples

Asked the duckduckgo free versions of AI:

Given the more specific answer for radial and tangential velocity in
https://physics.stackexchange.com/questions/814589/what-is-tangential-and-radial-velocity-of-light-in-schwarzschild-metric-at-dista ,

what is general velocity of light in Schwarzschild metric at distance 𝑟 for observer that is infinitely far away?

Results are as expected: the radial and tangential results are recited and then a train wreck.

#physics #generalRelativity #math #schwarzschild

In 1965, Roger Penrose made a groundbreaking discovery in mathematical physics. He demonstrated that under two simple assumptions, space-time inevitably leads to singularities—points where it ends. This landmark paper has been hailed as the most crucial contribution to general relativity since Einstein. #Physics #GeneralRelativity #RogerPenrose

https://www.quantamagazine.org/singularities-in-space-time-prove-hard-to-kill-20250527/

This is a fun twist:

Though astronauts aboard the International Space Station age more slowly (at a rate of about 0.01 seconds per year or--as I calculated earlier--about 317 picoseconds per second), a computer at the top of a server rack would experience time more quickly than one at the rack's bottom.

That's because the orbital speed of ISS negates gravitational time dilation.

https://en.wikipedia.org/wiki/Gravitational_time_dilation

#science #GeneralRelativity #ScientificComputing

New video by dialect:
Mastering Riemannian Curvature: Parallel Transport & Connections
https://www.youtube.com/watch?v=MRU2D6sLpU0&t=13 #geometry #generalrelativity #physics

Relativity ...

I believe I understand the usual calculations for time dilation and length contraction using the concepts of an inertial frame of reference and watching a "clock" that consists of light bouncing between two mirrors.

I'm pretty sure I've got that.

So ... are there are similarly elegant thought experiments to show:

* why clocks run slower when they are in a gravity well?

* why clocks run slower when accelerating?

What should I be reading?

Assume I know nothing about tensors, but am happy with complex numbers, calculus, and matrices.

#Relativity #GeneralRelativity #ThoughtExperiment

If you want to read all the fun science in its full glory, this way please:

📄 “GW250114: Testing Hawking’s Area Law and the Kerr Nature of Black Holes”, Phys. Rev. Lett. 135, 111403, https://journals.aps.org/prl/abstract/10.1103/kw5g-d732 (Open Access)

📄 “Black Hole Spectroscopy and Tests of General Relativity with GW250114”, arXiv:2509.08099, https://arxiv.org/abs/2509.08099

#GW250114 #10YearsGW #GravitationalWaves #Astrophysics #BlackHoles #GeneralRelativity

✨ Exciting news to celebrate the 10-year anniversary of gravitational-wave astronomy 🎂

A recent gravitational-wave signal, known as GW250114, is the clearest one observed to date.

Its source and intrinsic signal strength are quite similar to those of the first-ever signal, GW150914, which was observed almost exactly 10 years ago.

However, improvements of the detectors, waveform models, and analysis methods over the past decade have resulted in a much clearer detection.

This allows scientists to conduct some of the most stringent tests of general relativity and confirm Hawking's black hole area theorem.

For the first time, researchers have identified or constrained at least three different gravitational-wave tones during the ringdown. This is the phase in which the remaining black hole settles into its final state right after the merger.

➡️ https://www.aei.mpg.de/1286736/ten-years-of-gravitational-wave-astronomy-and-the-clearest-signal-yet

#BlackHoles #GeneralRelativity #GW250114 #GW150914 #10YearsGW
#Astronomy #Astrophysics

Black holes question:

1. As things get to the event horizon, their speed converges to zero, being zero at the event horizon --- according to the distant observer.

2. There is a singularity inside with infinite density where all that mass went to.

How and in particular WHEN can anything get to the singularity if it stops at the event horizon --- when basing WHEN on our normal calendar.🤔

More elaborate: https://miamao.de/blog/2025-08/31.Black_Holes_Singularity_Seriously.html

#astrophysics #gr #generalrelativity #blackhole #physics

What, exactly, is space-time?
#Science #SpaceTime #Physics #Einstein #Relativity #QuantumTheory #Cosmology #Universe #Time #Reality #PhilosophyOfScience #Astrophysics #ScienceExplained #GeneralRelativity #Matter
https://the-14.com/what-exactly-is-space-time/