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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19
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3answers
10k views

Maximum spin rate of a black hole?

I have just been watching a podcast called "Deep Astronomy" and the discussion was about a super fast spinning black hole discovered with the NuSTAR space observatory. This black hole was modeled with ...
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1answer
283 views

Have more recent LIGO/VIRGO gravitational wave measurements narrowed down the speed of gravity further?

This answer to How precise are the observational measurements for the speed of gravity? says: ...in 2013 a Chinese group built a model using Earth's tides that helped them narrow it down. ... [T]he ...
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What is our universe expanding into?

From inflation theory and other theories explaining the birth of the universe, the universe is expanding and recently it's been discovered that the expansion has been accelerating. My question is ...
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2answers
756 views

Spacetime curvature illustration accuracy

When a particle travels through spacetime, this is sometimes illustrated moving in flat grid with various depths. How accurate is this way of imagining gravity? Can the gravity well be infinitely ...
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1answer
432 views

Are wormholes even possible?

While this question could fall under Space Exploration or Physics (I don't have the "best" reputation on THAT forum), I feel that it is very much related to how the universe itself functions, ...
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5answers
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If light has no mass, why is it affected by gravity?

Light doesn’t accelerate in a gravitational field, which things with mass would do, because light has a universally constant velocity. Why is that exception?
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2answers
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Age of the universe and time dilation

Given our knowledge and the standard cosmological model, we estimate that the age of the universe is about 13.7 billion years old. How much sense does it make to talk about the age of the universe as ...
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4answers
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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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4answers
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How could a neutron star collapse into a black hole?

White dwarfs usually do not collapse, as they have electron degeneracy pressure due to the Pauli exclusion principle. However, if one accretes mass beyond the Chandrasekhar limit, it is energetically ...
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2answers
884 views

Is there a better explanation of Hawking radiation?

I'm writing a piece on Hawking radiation, and find I have something of a problem. The "given" explanation which I find on Wikipedia and elsewhere is unsatisfactory: "Physical insight into the ...
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1answer
690 views

Where did this famous Planetary Precession Formula come from?

The following equation (which I shall term the Planetary Precession Formula, PPF for short) famously appeared in a 1915 publication by Einstein where he indicated how it could be derived from his ...
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Gravitational lensing in Newtonian physics

Famously, when Eddington attempted to measure gravitational lensing during the Eclipse, it was the measured magnitude of the lensing that gave gravity [pun, obviously, intended] to General Relativity -...
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2answers
380 views

Can General Relativity indicate phase-dependent variations in planetary orbital acceleration?

In a previous question about differences in Newtonian and GTR gravitional force for the case of star-planet gravitational interactions an approximate relationship was noted between the expressions for ...
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1answer
106 views

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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1answer
248 views

What it would look like to observe people with a different time flows?

As I learned, that the bigger gravity source you are influenced by the more slow time ticks for you, the farther away you are from a gravity source the faster times ticks. So Imagine two different ...
5
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1answer
209 views

How did the Hulse-Taylor Pulsar Provide Confirming Evidence of General Relativity?

What measurements and observations of the Hulse-Taylor Pulsar agreed precisely with the predictions of general relativity, and how did these measurements support the theory?
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1answer
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Relativistic Mercury orbit around the Sun

My question is the following,would the scalar of precession of Mercury orbit be the same if Mercury orbited Sun in the oposit direction?
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1answer
136 views

How far should the source be, for the gravitation waves to be visible on Earth?

If I understand it well enough, gravitational waves cause ripples in the space-time fabric. To our eyes, that would look like those rippling-effects on amateur videos. Where does a source have to be,...
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1answer
747 views

Is a black hole a 5 dimensional vortex?

We know that a black hole behaves like a whirlpool or a tornado or any of the other rotating phenomena we experience on Earth.But the thing is, all these phenomena, except the black hole, are 2-...
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2answers
134 views

Gravitational field released during supernovae

During the collapse of a star at the commencement of supernovae, the intense pressures force fusion and fission to create the heavier elements and release vast amounts of energy. As this energy/mass ...
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1answer
389 views

What can be learned from, or noted in this LIGO Orrery video?

The Ars Technica article Physicists detected gravitational waves from four new black-hole mergers notes that This brings the total number of events detected by LIGO and Virgo to 11. It also has a ...
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1answer
92 views

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 ...
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Can A Black Hole Exist?

In 1939, Robert Oppenheimer and other concluded that a certain neutron stars could collapse to black holes and no known law of physics would intervene. As far as I can tell, there is no observational ...
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1answer
788 views

Latest cosmological parameters

I'm looking for the latest values (with uncertainties) of the four main cosmological density parameters $\Omega_i$ : \begin{align}\tag{1} \Omega_{\text{mat}} &={} ?, &\Omega_{\text{rad}} &=...
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3answers
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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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514 views

Recommendation for introductory cosmology text

I am looking for recommendations for an introductory text (or texts) on cosmology on the advanced undergrad or beginning grad level. I am coming from primarily a physics undergrad background (doing ...
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1answer
219 views

Are there sufficient observational data to measure non-Newtonian perihelion advances of any Asteroid and Comet orbits?

Anomalous (i.e. not predicted from Newtonian theory) advances of the perihelion direction have been observed for many solar system planet orbits and have been accounted for by Einstein's General ...
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0answers
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Is TDB monotonic? Does it or any of its derivatives have yearly discontinuities with respect to an atomic clock?

This in-depth answer mentions that ...TDB is updated every year. As technology improves, these subtle updates change the timing of past events. This makes me wonder... Does this updating result ...
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3answers
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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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1answer
213 views

Are astronomers researching or trying to find signs of worm holes?

In many movies and in the popular culture wormholes are often referenced, as well as "faster than light travel", which seems almost to be the same thing, is possible. Are astronomers seriously ...
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662 views

What can we expect from the first accurate image of a black hole?

From recent news from the Max Planck Institute for Radio Astronomy: The European Research Council (ERC) has awarded 14 Million Euros to a team of European astrophysicists to construct the first ...
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475 views

Can you create a black hole using kinetic energy?

Imagine you have a particle accelerator that you can crank up to arbitrarily high energies. Because of General Relativity, the particles get heavier and heavier as you dump more energy into them. ...
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1answer
169 views

Time dilation on an object circling earth

How would a receiver on Earth hear a radio transmission from an object circling earth at 99% of the speed of light for 24 hours. The transmission from the object circulating would be non-stop. ...
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325 views

Strong force and metric expansion

If the expansion of the universe (the metric) continues (and perhaps is accelerating), in a very large but finite time the expansion of the metric will clash with the effects of the strong nuclear ...
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2answers
2k views

Why does earth not collide with the sun? [duplicate]

Gravity is most accurately described by the general theory of relativity (proposed by Albert Einstein in 1915) which describes gravity not as a force, but as a consequence of the curvature of ...
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1answer
209 views

What you would see in a wormhole?

Science fiction seems to depict the experience of traveling through wormholes (if possible of course) as seeing psychedelic colors or lines of light where stars once were (ie. 2001 or Contact). I ...
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1answer
401 views

How does an absolute horizon form before the apparent horizon?

If I understand it correctly, the apparent horizon is the boundary between where light directed outwards will move outwards, and light directed outwards will move inwards. Even if light is moving away ...
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2answers
109 views

Can the range of the observable universe be extended through an intermediary?

I understand that the so called observable universe has a limit we cannot see through. My question is whether we might get information through an intermediate hypothetical actor located halfway to ...
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1answer
757 views

Is there any significant time dilation on other planets orbiting the sun?

Is there significant time dilation on the other planets orbiting the sun? Would an 'hour' experienced on earth actually be 59 or 61 minutes on other planets, depending on their distance to the sun? ...
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2answers
122 views

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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2answers
338 views

A camera and time dilation?

If I travelled near a black hole, my time would progress slower relative to someone on Earth. This is clear enough. However, what if we sent a probe with a camera to a black hole? When we watch the ...
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1answer
105 views

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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2answers
138 views

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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1answer
61 views

Lunar Eclipse and relativity

I am currently working on A Depth Study for my year 12 Physics class, and am looking at relativity and time dilation of a lunar eclipse experience on the moon compared to as seen from on Earth. From ...
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1answer
50 views

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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3answers
364 views

Why doesn't the vertical light beam get out of a black hole?

I'm asking this question as a follow-up to if light has no mass why is it affected by gravity? Imagine you’re standing on a gedanken planet, shining a laser beam straight up into space. The light ...
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0answers
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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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1answer
121 views

Path of Mercury and general relativity [duplicate]

I have read that many physicists challenge the theory of general relativity, and it has been proved many times that it is correct; my question is on Mercury's orbit. And we know that many of ...