Questions tagged [gravity]
Gravity is an attractive force that affects and is affected by all mass and - in general relativity - energy, pressure, and stress. Prefer newtonian-gravity or general-relativity if sensible.
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Can the Flow of Time be explained as a "force" from a singularity at the end of time? [closed]
I know this is a very contentious topic, with wide range of theories, philosophies, etc. I am also not a physicist or mathematician, so kindly forgive me. My question is very specific about a ...
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Can you directly feel the effect of gravity, or only opposing forces?
I was trying to think through the consequences of Einstein's observation that a freely falling body does not experience its own weight. And, as freely falling (or "inertial") bodies will ...
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How LEptons in Muonium are INteracting with Gravity? (LEMING-Experiment, Soter et al.)
How LEptons in Muonium are INteracting with Gravity? (LEMING experiment, Soter et al.)
I have read an article from the Physical Society Zurich, Switzerland about Prof. Dr. Anna Sótér planned LEMING ...
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If I swirl water in a cup in a zero gravity zone like outer space will the water ever stop spinning?
was just thinking about this in class and it poped into my head while someone was spinning their water in their waterbottle
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Can antimatter create antigravity? [duplicate]
CERN's scientists have discovered that antimatter does not create antigravity, they have dropped , or observed an antimatter particle with the help of a magnetic field and after making this discovery ...
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Why is it that galaxies tend to form large-scale "sheet" and "filament" structures?
I recently picked up a book on physical cosmology, and the first couple of chapters make frequent reference to the development of large-scale "sheet" and "filament" structure. ...
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Questions About Gravitational Waves and Uniform Circular Motion
I recently learned about gravitational waves, and a question came to mind:
Uniform circular motion is an accelerated motion, so it should lose energy. For example, electrons emit light during circular ...
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Why quantum fluctuation during inflation contributes to structure formation and how it sets the initial condition?
I'm trying to understand the role of the inflaton condensate and quantum fluctuations during inflation and how they evolve into the large-scale structure we observe today. Here's where I’m getting ...
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Cosmological constant and gravitational lensing
The cosmological constant, $\Lambda$, leads to a uniform positive energy throughout the universe. It would lead to a more positive Ricci Scalar.
The question is whether it should lead to slowing down ...
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Should density be considered in the role of the strength of a gravitational field?
Ok, here me out. Black holes are usually formed from the compression of the mas released during the death of a supermassive star, however they have the same mass as the star (or even less). Yet when ...
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In GR, what is Gravity? A force or curvature of spacetime?
GR starts with a principle called the Equivalence Principle, which states that gravity is indistinguishable from acceleration locally.
Here, what do we mean by gravity?
Case 1: Do we mean gravity as a ...
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Stretching of space as distance to massive body like black hole decreases, true or false?
This question is about the stretching/elongation/expansion of a measuring rod in a gravitational field according to general relativity. It's not about the spagettification of something falling into ...
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Does gravity cause energy to exist? [closed]
I may be fundamentally misunderstanding Poincare symmetry, but does the curvature of spacetime due to energy generate the topological conditions required to satisfy the translational time symmetry of ...
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Could spacetime curvature change faster than speed of light?
I don't think that this is experimentally testable due to it not being physically possible to recreate anything like the below video. But, you can see that when the Sun disappears the curvature ...
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Does speed affect gravitational force according to special relativity? [duplicate]
According to the special relativity, when the speed of an object increases, its mass also increases. Does it mean that objects moving at speeds close to the speed of light exert higher gravitational ...
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$S$-modular transformation to the torus partition function
My general objective is to obtain the Cardy formula (see this related question) through the saddle-point approximation, nonetheless, I'm confused in how apply the $S$-modular transformation to the ...
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Why can magnetic fields be blocked but gravitational fields can't? [duplicate]
Except for the stuff I know, I don't know anything about physics. I assume a magnetic field can be blocked, because they put Nixon's tapes in a lead box. And I know gravitational fields cannot be ...
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Exploring Non-Rotational Artificial Gravity: Can Geometric Energy Fields Create Gravity-Like Effects?
I’ve been thinking a lot lately about ways to simulate artificial gravity in space without relying on rotational systems (like spinning habitats or stations). I'm curious if it's possible to create ...
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Is having no general closed-form solution (the three-body problem) related to the non-renormalizability (of gravity)?
The three-body problem is nonlinear. Gravity is also nonlinear and blows up at small scales due to higher order interactions. Renormalization of the three-body problem does not make sense since there ...
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Portal Loop in a gravity well [duplicate]
Weirdly, I didn't find an answer or even close to one with a search through the forum. I probably missed it.
Portals! Speed thing go in, speedy thing go out. Lots of sci-fi fun.
I've got a hair-better ...
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Density changes of 3D projections of spacetime in relativity theory?
In relativity theory, the metric tensor $$g_{\mu\nu} $$ describes the gravitational field.
Can one treat the determinant of the metric tensor, normalized by the square of the Jacobian of the ...
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Gravothermal catastrophe in 2+1 and 4+1 dimensions?
Before I go do a week of numerical simulations...
In our 3+1D spacetime, gravitationally-bound systems of large numbers of particles, like stars in globular clusters, can be stable for long periods, ...
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Throwing a clock out of a white hole
If we look at a clock falling into a black hole (Schwarzschild metric), we will see its time slowing down further and further as it approaches the event horizon.
What would we see by looking, from far ...
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Quadrupole radiation formula for gravity
I derived the formula for the quadrupole radiation power emitted by a system of masses:
$$P=\frac{1}{45}\dddot{Q}_{kl}\dddot{Q}_{kl} .\quad\quad (*)$$
Note here that: (1) I am using geometrized units, ...
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Query regarding the popular demonstration of spacetime curvature [duplicate]
These demonstrations usually begins with some guy taking an table covered with some fabric, put a heavy weight in the middle of it, calls them the "Sun", and makes some marbles ("...
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Variation of Chiral Plebanski Action for GR
In the Einstein-Cartan action for GR in the 'first-order' formalism, one has a solder-form $e^a$ together with a connection $A^{ab}$ assuming values in $\mathfrak{so}(1,3)$. The action
\begin{equation}...
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General relativity near an infinite plane
By Newtonian physics if we are above a infinite plane with acceleration of gravity $2$ then falling object reach to plane in $1$ second and this is independent of horizontal speed of falling body. Now ...
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Formulating the dynamics of mass distribution in Newton-Cartan gravity
I am a mathematician following the lectures of Schuller about General Relativity, in particular this lecture. My main motivation is to understand how do we use Einstein field equation to model a ...
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Does acceleration by gravity cause an electric charge to emit photons? [duplicate]
There is a discussion here
Gravity and electric charges
About electric charges and whether they can emit photons in a gravitational field.
The conclusion is that it still isn't known for sure one way ...
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Why can’t acceleration in GR be defined the same way as in EM?
This question stems from page 36 of Misner, Thorne and Wheeler’s Gravitation, where they compare the Lorentz force equation with the equation of geodesic deviation. Specifically, see the second row in ...
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Can objects with mass be influenced by their own gravitational waves from their past, bent around a black hole?
If gravitational waves are influenced by the deformation of spacetime around a very dense object like a black hole, and thus can be "reflected" back to (the future position of) their source, ...
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Self-confinement of $N$-body gravitational systems
Consider $N=2$ point particles (each having unit mass) interacting via Newtonian gravity in the usual 3-dimensional space. There is a simple criterion to assess whether the system is bounded or not: ...
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Question about comoving frame
From what I understand, in an expanding universe given by
$$ds^2=-dt^2+e^{2Ht}dx_{com}^2,$$ where I believe that $dx_{com}$ denotes a comoving spatial line element, the distance between a comoving ...
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What is the cause for the acceleration of Earth?
I've read that spacetime curvature is present wherever initially parallel geodesics converge or diverge, and also that mass causes spacetime to curve. If there is indeed spacetime curvature due to the ...
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Does mass of comet change its orbit? [closed]
Consider a comet that is losing mass as it begins to orbit a planet. Does the mass of the comet affect its path? I have seen answers that say that the path will be affected. However, the change in ...
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Is there any reference where Roger Penrose addresses the "effective size" of the mass density in a neutron star which must be at least 100 fermis?
The background is the following. Roger Penrose has proposed that a spatial quantum superposition collapses because of gravity. To put in a nutshell, the probability of quantum collapse per unit of ...
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Does gravitational acceleration vary when changing Galilean reference frames in special/general relativity?
The Lorentz transformations allow us to deduce how the acceleration of a material body changes when we move from one Galilean reference frame to another. But what if we consider not the acceleration ...
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Can we make field lines for gravity?
I wanted to know if we can draw field lines for the gravitational field
Why I think we should:
Field lines for electrostatics is defined as the path that the positive charge actually undergoes while ...
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Problem understanding the bending of space-time curve as gravitational force! [duplicate]
I got the point of considering gravitational force as curvature on space-time fabric for bigger objects like stars, planets, blackholes. But my doubt is over the objects like us, what keeps us on this ...
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About Relativistic time in different planets and moons [duplicate]
Since the planets and moons in the Solar System has diferent gravitational fields, What happen to the relativistic course of time if we compare it to an absolute Newtonian time or in other words ...
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Why light have gravitational lensing? [closed]
I was reading about light in a book there it was there that light is not a physical quantity, light has no mass as photons are more and more smaller then atoms. Then how does gravity affect the path ...
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Quantum Gravity is non-renormalizable...So what?
It is well known that quantum gravity is non-renormalizable. But why should we care? We successfully use many EFTs, like the Chiral Lagrangian or even Fermi's theory. So, why do we make such a deal in ...
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Can light blueshift from gravity assists?
I'm aware that light can redshift when escaping from a gravity well, and that it can blueshift when entering a gravity well of the observer. But is it also possible for light to blueshift from '...
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If the electrostatic force is so much stronger than the gravitation force, then how do black holes form?
When most discuss black-holes, they refer to the 'singularity' at the centre. A point of theoretically infinite density at an infinitesimal point. However, if the electrostatic force repelling the ...
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Can gravitational attraction be thought of as a cascade of gravitational length contractions? [closed]
We know from the answer to previous questions that gravity contracts length and the length contraction only happens vertically, that is towards the centre of mass.
If we think of an object at a ...
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How to show the ratio (spin angular momentum density)/(energy density) for circularly-polarized gravitational plane wave = $\pm 2/\omega$?
It is well understood that an infinite monochromatic, circularly-polarized electromagnetic plane wave has no angular momentum density. However, a finite monochromatic, circularly-polarized ...
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How to correctly find the "linearly extrapolated" retarded position of gravity
I'm unsure how to interpret the "linearly extrapolated" retarded position of gravity, or electromagnetic field as well. I've read up on as many explanations of this as possible and am still ...
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Under which conditions may gravity superconductivity arise?
The phenomenon of electric current superconductivity is well known and there are even talks about color charge superconductivity.
Is there a context in which gravity superconductivity makes sense? It ...
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Why is a black hole black, according to theory (and observation, and ignoring QM & Hawking radiation)? [duplicate]
I had already edited this question in response to the criticisms of those who closed its first version, as described in my comment below following the first group of others' comments. Perhaps I ...
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Possible reasons concerning decreased suspension height of an copper object in an electric field
I am transcribing an article that discusses electrostatic levitation. A segment of this article pertains to the author describing a charged spherical object composed of copper with its suspending ...
