Questions tagged [general-relativity]

Questions about relativistic theory of gravity. General relativity describes gravity as a geometrical property of space and time.

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New Object Formation at Stellar Collapse

Assume QM degeneracy pressures exist beyond neutron degeneracy pressure. Under this assumption, what would the sequencing be for new object formation upon the collapse of a massive star whose ...
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Is it “nonsense to even talk about” objects outside the observable universe not having gravitational influence on us? (finite speed of gravity)

In this supplemental answer to Is the zero gravity experienced in ISS the “artificial” kind? in Space Exploration SE I said: Gravity moves at the speed of light so nothing outside out observable ...
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Has gain in mass from accretion onto a black hole been observed?

Have we observed a black hole directly gain mass via accretion? That is, have we observed the black hole to have mass $m_1$ at time $t_1$ and then observed its mass to be $m_2 > m_1$ at a later ...
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Do relativistically measured rotation speeds (Special Relativity) change planetary mass slightly through Lorentz transformation?

Thanks @ConnorGarcia for your Answer. Avoiding 'Tidal Locking' for now - the rotational angular momentum Lrot is 10,000,000 times smaller, so negligible, but could it still be a factor in eccentricity?...
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Time of lunar eclipse relativity

Would there be a change in time in terms of the length of time it take for a lunar eclipse to cross the moon as seen from earth compared to as what would be experienced from the moons surface?
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When will Mercury have rotated an extra round around its axis?

It is well known that Mercury orbits slightly differently from a pure Newtonian orbit. Every year a slight deviation is found. Now if we observe a lot of these orbits then Mercury should at one point ...
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Scalar field displacement from the minimum of the potential gives rise to particles/dark matter, why?

The paper Lyman-alpha Constraints on Ultralight Scalar Dark Matter by Kobayashi et al. says, at the beginning of Section 3.1: A light scalar field stays frozen at its initial field value in the early ...
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Gravitational time dilation

Did clocks run more slowly in the early universe due to gravitational time dilation? Or, alternatively, do they appear to be running more slowly when observed from today, if that is not the same thing?...
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FLWR and curvature

The FLWR metric or model I believe results from Einstein's equations of general relativity if it is assumed the universe is 1. homogeneous and 2. able to expand (or contract). Solutions can have ...
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Do gravitational waves produce a surrounding gravity field?

Massless light beams produce a surrounding gravity field. A massive particle will move towards it and at the same time be dragged along in the direction of the beam's velocity. But what will happen ...
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What would be the electric potential and the energy produced in a cable connecting two electronic devices on the magnetic poles of the earth? [closed]

The earth is a large magnet moving in the magnetic field of another large magnet the sun. And if we connect the two poles of the earth by a cable there would be energy and an electric potential in ...
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Does the sun have a notable frame-dragging effect on the planets?

Frame-dragging is a general relativistic effect that can be imagined as the effect that the momentum of mass-energy has (the stress elements in the stress-energy tensor) on mass-energy in the ...
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About the strange case of Bonnor beams

Bonnor beams are light beams of infinite extent and small thickness. They have an associated spacetime (related to their energy and momentum which shapes the stress-energy tensor) of which Bonnor ...
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Was there a formula-first hypothesis for gravity?

Being a mathematician I wonder, has there been an attempt to blindly approximate a formula for gravitational attraction that would match the data, based on "normal" matter we can see plus ...
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Why is the FLRW universe (general relativity solution(s)) sometimes called the 'FRW universe'?

Why is the letter L for Georges LeMaîtres often, or even usually, left out? Does he, or does he not, deserve some credit for this cosmological solution to Einstein's general relativity?
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Is there anything different about the gravitation around a non-spinning black hole and a neutron star of the same mass?

If we perform a simple experiment by orbiting identical spacecraft around a non-rotating black hole and a non-rotating neutron star of equal mass at a "safe" distance, and ignore differences ...
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Can Newton's gravity equation explain why black holes are so strong?

I was just wondering why black hole's gravitational forces are so powerful. I know it's usually explained by Einstein's relativity which states that when an object becomes infinitely dense (a compact ...
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What exactly is space-time fabric?

I have heard about space-time fabric but I can't understand its definition. Is space-time fabric a physical thing or did Einstein imagine it to assist him with general relativity?
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How fast would an observer have to travel in order to be able to study an entire star's life in one human lifetime?

Humans live for about 80 years. A star, however, lives from 1 million to trillions of years, depending on its mass. If humans want to have a detailed study of the life of a $1 M_\odot$ star, how fast ...
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Would studying massive stars that are experiencing time dilation due to proximity to a black hole be useful?

I saw this question (Could a star closely orbit a black hole long enough for the star to have lost 0.5B+ years to time dilation?) and came up with an interesting thought. Massive stars live for less ...
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Does General Relativity predict anything about the creating of a singularity, once enough matter collapses inward to form an event horizon?

Ignoring quantum gravity, which we don't know much about, current theory (GR) states that an event horizon forms when there is enough matter/energy density to create it, and logically, a singularity I ...
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Is there a closest free-return trajectory to a black hole?

The scenario I am imagining is a test particle falling from infinity with an initial off-center velocity. In Newtonian mechanics the path would be a hyperbola. But I assume that, near a black hole, ...
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Has GAIA learned anything about General Relativity looking near Jupiter? (Gerry Gilmore: “oblate rotating mass moving in a deeper (Solar) potential”)

From Gerry Gilmore (2018) Gaia: 3-dimensional census of the Milky Way Galaxy 4.4 Fundamental physics Relativistic effects are highly significant for Gaia measurement accuracy, with tests of General ...
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Does General Relativity really predict Black Holes?

I'm doing some research on black holes for a science video contest. I want to explain the physics of how they work, but also want to have a little background on how they're formed. As far as I've ...
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How do we know that spacetime is fabric? [closed]

I have started learning about astronomy as it amazes and inspires me. I have a question. What led us to believe that spacetime is fabric? What is the evidence shows this, and is it considered proven? ...
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Does photon capture in a black hole (or any other “very compact” object) reduce the luminosity/photon flux from its self isotropic emission?

I don't know if this is even a feasible question or if I have a point in asking so. Let's say we can model the radiation coming from a very compact object, such as a BH with an accretion disc or any ...
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I need to study space, planets and black holes, how do I study them on my own [closed]

I need to study space, planets and black holes, how do I study them on my own, knowing that I am an Arab and I do not know English. I use translation applications. I speak with you. Can you help me ...
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How to conceptualize the strong equivalence principle (SEP) in the context of stellar motion in an extragalactic galaxy?

In the theory of general relativity, the SEP states all the laws of nature are the same in a uniform static gravitational field and the equivalent accelerated reference frame. I've been reading the ...
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Does a gravitational lens around a body look 3-dimensional?

Suppose we approach a neutron star or a stellar black hole close enough, is the gravitational lens around it 3-dimensional (like a tunnel) or is it 2-dimensional? It's 3-dimensional as if you entered ...
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Confused about rubber sheet analogy!

How to resolve confusions on the rubber sheet analogy of the spacetime curvatures? I am a newbie to spacetime curvature. I have watched several youtube videos on Einsteins GR and spacetime curvature ...
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Does Einstein's theory of gravity say anything about the direction of space [closed]

Why is every representation of Einstein's theory of gravity depicted like this: and not like this: And many other ways it can be depicted. They suggest that the fabric of space-time is a flat plane
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Why does the Hubble flow does not carry photons with it?

I have this naive question. We know that the expansion of the universe "takes" or "carries" the galaxies with it, separating them, but this doesn't apply to photons. My guess is ...
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Does time also pass more slowly for a galaxy that is traveling at relativistic speeds, where the speed difference is due to Hubble expansion?

If time passes more slowly, relative to Earth, for a traveler at relativistic speeds, say at .8c, traveling between stars inside this galaxy, does time also pass more slowly for a distant galaxy that ...
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How String Theory calculates the Entropy of the Black Hole in a Background dependent way?

How does string theory get an agreement to the Hawking-Bekenstein equations to calculate the quantum entropy of a black hole in a background dependent way? Is there any sort of area parameter in ...
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Can Axions escape the Black Holes?

I read about Tachyons and Gravitational Waves and also about Exotic matter, really nothing can escape a Black Hole, can Axions escape for providing a new hope?
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Does gravitational radiation change the eccentricity of binary orbits?

Do the eccentricity of a binary orbit change with change in the semimajor axis due to loss of orbital angular momentum by gravitational radiation?
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Have I nearly found the event horizon of a black hole?

The calculator on the website https://planetcalc.com/1758/ cites Wikipedia's Gravitational acceleration and implements: $$g = G \frac{M}{(R + h)^2}$$ For a black hole with mass $M$ equal to 5 solar ...
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Kinetic energy and galaxy arm rotation rate

The higher than expected rotational velocity of stars and gas clouds in the outskirts of galaxies is explained today by invoking dark mater that supplies not only the additional gravitational mass, ...
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How would you define “space” in GR (General Relativity) and in QFT (Quantum Field Theory)?

Is there a univocal definition of space that can be accepted in GR and in QFT? In GR space is actually "Spacetime", a 4-dimensional entity that includes time. In this case it's impossible to ...
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Can the electromagnetic counterpart of a gravitational be seen by 'small' telescopes?

As follow-up question for my previous question I'm thinking about the search for the electromagnetic (EM) counterpart of a gravitational wave (GW). Is it possible to search for those events with '...
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Does a merging massive binary black hole ‘emits’ more than one gravitational wave?

If we want to use gravitational waves (GW) to determine the Hubble constant, we need to find the source in the electromagnetic spectrum (EMS). However, we need to be lucky to ‘see’ it simultaneously ...
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Does time flow in a Minkowski spacetime?

In a spacetime where the stress-energy tensor is null (no energy, no matter, no entropy), I wonder whether any motion of the variable time in the phase-space is well defined. The arrow of time, meant ...
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If time is not absolute and depends on the gravitational field, then why we keep using our own (particular) time in cosmology?

Sorry if my question is not really clear, but indeed it is not clear in my mind neither. But maybe some of you can help. Time is not absolute and can be affected by the gravitational potential. Now ...
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Has the permittivity or the permeability of space been measured in a gravitational well?

Technically one might say yes since earth is gravitational well. However I am looking for more data points. For example, in deep space where voyager might be at the Lagrange points of massive bodies ...
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How much time passes in the outside universe when falling into a black hole?

If someone were to jump into a black hole, looking back at Earth, how far into the future would they see of Earth? As I understand it, time would dilate approaching infinity as you approach the event ...
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How could we observe a wormhole?

A wormhole is a sort of tunnel that could connect two points in spacetime. These are theoretical objects that have not been observed. What observational evidence could we look for to confirm (or ...
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Why is rotational motion absolute, is the universe spinning? [duplicate]

When considering any object, one can say its translational movement is relative, depending on the point of view or reference frame adopted. If it moves at 1/4c relative to some observer, one might say ...
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At what gravity does a body's gravitational lensing become observable?

I wonder whether we know at how much gravitation a gravitational lensing around a celestial body becomes observable (visible in the sense of that we see stars on the wrong places, stars behind the ...
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Did Einstein supported Big Bang Theory cosmological model?

Einstein made many predictions, including gravitational waves and the possibility of black holes. Relativity is taken into consideration for the Big Bang model, so did Einstein agree with it or did ...
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How was the Messenger spacecraft used to measure Mercury's orbital precession to such accuracy? Could this have been done using radar?

This comment under an answer to Path of Mercury and general relativity mentions that the Messenger spacecraft was used to measure the precession of Mercury's orbit to such accuracy that the tiny ...