# Tagged Questions

A theory that describes how matter interacts dynamically with the geometry of space and time. It was first published by Einstein in 1915 and is currently used to study the structure and evolution of the universe, as well as having practical applications like GPS.

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### Two places having same gravitational acceleration - Do they also have same curvature of space time?

If there are two places (possibly on/above two different planets) having same gravitational acceleration (g), would it imply that the two places have same extent of space time curvature and will have ...
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### Is there a parametrization for the shape of space?

I was thinking about how the space is curved. And how do we know that the shape of space arround a singularity is something like that: So I was trying to make a similar parametrization of this kind ...
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### Is there a path to go from GR, to Gravitational Waves, to Gravitational Particles (Gravitons), to Quantum Gravity?

The articles on the subject often say : a part of the mass of the 2 celestial bodies became energy for gravitational waves after merging : E(gravity waves) = (M1 + M2 - M_merged).c^2 Intuitively I ...
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### Is the correspondence between our universe and cellular automata in the presence of time travel just co-incidence? [closed]

I've written a paper discussing a modification to the game of life. Essentially, the traditional game is modified so that a cell is alive if there are 5 or 6 alive neighbours in total across the ...
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### Dirac equation from a vierbein operator?

Klein-Gordon equation can be derived straightforwardly by getting the mass-energy relation from special relativity in tensorial form, $$\eta^{\mu\nu}p_{\mu}p_{\nu} = m^2c^2$$ and promoting the ...
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### About the LIGO result and Abhas Mitra [closed]

Well I read this article https://en.wikipedia.org/wiki/Abhas_Mitra and he has claimed that "The so-called massive Black Hole Candidates (BHCs) must be quasi-black holes rather than exact black holes" ...
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### Is Time Dilation in GR Simply a Consequence of Curved Space?

My understanding of time dilation in General Relativity is that it is the consequence of particles traveling at the speed of causality following longer, curved paths. Since it takes longer for two ...
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### Gravitational wave detection and electromagnetic counterpart

Background Referring to this article on Fermi EM signal, 0.4 s after the gravitational wave detection by LIGO, FERMI detected an electromagnetic signal (poorly localized) with a false alarm ...
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### Einstein's relativity of simultaneity train/embankment thought experiment

Einstein's thought experiment I'm referring to is this one: http://www.bartleby.com/173/9.html briefly: train/embankment experiment is where lightning strikes at either ends of the running train (...
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### Can nonconserved energy in GR be thought of as going into gravitational field energy?

One of the most striking features of GR is that energy is not conserved. Carroll's GR text has an interesting statement about this: Clearly, in an expanding universe... the background is changing ...
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### Is it possible to travel faster than the speed of light under extreme warping of spacetime?

The event horizon of a black-hole is defined as the point at which light itself cannot escape, supposedly due to a black-hole's immense gravity and effect on spacetime. However, would this not require ...
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### Theoretical Possibility of “Opposite” Gravitational Mass? [duplicate]

This is an unusual idea that I have been entertaining for some time, and I can't find anything about it online. However, it is so simple that someone must have conceived it before. First, I will ...
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### The equivalence principle and identifying free-fall as a locally inertial frame

As far as I understand it the equivalence principle in general relativity is the statement that a frame at rest in a uniform gravitational field is equivalent (indistinguishable) to an accelerated (...
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### GR Tetrads & ZAMO example

I am self-learning GR. Intro: Tetrads are a way of representing general relativity in a coordinate-independent fashion. I am having trouble understanding tetrad notations. Basically, I know that I ...
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### Difference between local inertial frame and coordinate chart

In the most cases the local inertial frame is definied "physically" but I'm searching for a mathematically meaningful definition of the local inertial frame to solve my problem: Is the local ...
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### Can we make any implications about the internal structure of black holes from the 'chirp' that LIGO observed?

Are there any implications about a black hole's internal structure we can make based on the chirp issued? For example that a black hole does in fact contain or does not contain a singularity rather ...
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### How does some of the black hole (BH) mass escape the event horizon (EH) of either BH, or the merged EH of two merged BHs?

BH mass is a conserved quantity and cannot escape the horizon of a BH. Yet in mergers some percent (in GW150914 it was about 5 percent, or 3 solar masses) of the binary's mass escaped either before (...
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### Vibrating black holes

From http://ligo.org/science/Publication-S5S6RD/index.php "Every star in the universe vibrates or oscillates in some manner. Turbulence on the surface of the Sun causes well-known solar oscillations ...
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### Can a micro black hole hover above a regular black hole?

So let's say you have a black hole $A$, that is small enough for its gravity to be very small, but has strong hawking radiation, and larger black hole, $B$, with very small hawking radiation, but ...
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### Why does LIGO have an arm length of few kilometers? Is the distance dependent on Gravitational Wave wavelength?

Antennas for capturing radio waves need to have $\frac{\lambda}{2}$ length for optimum reception of signal. Does it imply LIGO arm length is $\frac{\lambda}{2}$ of Gravitational Wave it is trying to ...
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### How is a black hole formed? [duplicate]

As far as I know, whenever we talk about a black hole, we refer to a static or stationary solution to Einstein field equations. I know the formation of a black hole can be discussed by the numerical ...
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### When we spin and feel our arms fly, is it the effect of gravity?

If accelerating reference frames can be treated as normal inertial reference frames but with gravity, then for a rotating reference frame, is the centrifugal force = gravity? More specifically, I was ...
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### Could the September 2015 LIGO gravity wave “detection” from “merging black holes” be fake? [closed]

The following Physical Review D article gives reasonable bounds for gravitational wave detection for Supernova core collapse. These bounds cannot be overwhelmingly different from the bounds on GW ...
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### Physical and non-physical solutions to Einstein's field equations

Einstein predicted gravitational waves in 1916 as a solution to his field equations. Apart from doing experiments, is it possible to tell which solutions exist in the real world and which don't? Are ...
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### How can a five-dimensional black hole 'break' general relativity? [closed]

By the laws of general relativity and the existence of black holes, what makes our universe to be just 4 dimensional but not 5 or more because a 5-d black hole can violate theory of relativity? ...
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### How can geometrized units have more than one constant equal to 1?

I can understand how you could manipulate units to make a certain constant equal to $1$, like $c$ or $G$, et cetera. But how can you make it so two constants (in this case $c$ and $G$) are equal to $1$...
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### Practical time travel: time dilation above the event horizon

Imagine there is a huge black hole with very small gravity gradient so that one doesn't get killed by spaghettification after even nearing the event horizon. Now imagine a very curious creature ...
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### Are we sure that there are at most x different types of black holes?

If I'm not mistaken, there are a limited different types of black holes. Depending on were I look, the black holes are categorizes according to size, or categorized according to surroundings and ...
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### Is the energy released by gravitional waves kinetic energy or converted rest mass?

It is said that at the binary black hole collision LIGO detected recently, the energy equivalent of 3 solar masses has been released. Since no matter can escape a black hole, the only source I can ...
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### Special relativity - Nokton theory [closed]

Is this theory described in this link Nokton theory respects special relativity conditions.
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### Effect of Gravitational Waves on light?

We all know about the gravitational lensing effect. From the analogy of fabric of space time used to explain this concept to laymen like me, i understand that light follows the curvature of spacetime. ...
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### Can light escape a black hole? [duplicate]

I heard that a black hole is not black because it's escape velocity is greater than or equals to the speed of light. But instead it is black because the light that gets emitted from a black hole gets ...
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### Is this actually how gravity is illustrated? [duplicate]

In general relativity, gravity is said to be caused by the curvature of space time. And there are examples that illustrate gravity such as this video https://www.youtube.com/watch?v=MTY1Kje0yLg, and ...
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### Gravity with more than one metric tensor

As weird as it sounds, yes, there are gravity theories with more than one metric tensor. This is called bimetric gravity. My question to those who have encountered bimetric gravity before: a) ...
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### Trouble in understanding spacetime

I have a problem in understanding spacetime. What i understood from the conversion of time to distance is that the interval between any two events is always the same for any observer. But how is that ...