Questions tagged [gravity]
Gravity is an attractive force that affects and is effected by all mass and - in general relativity - energy, pressure and stress. Prefer newtonian-gravity or general-relativity if sensible.
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Is the newtonian equation precise for any non trivial situations? [closed]
When you calculate the gravitational force $F_G = G \cdot\frac{m\cdot M}{r^2}$.
Are there any cases where you get a precise result other than $m = 0$ or $M = 0$?
If so which?
It does not matter if the ...
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At Relativistic Speeds, Would the Blue-Shifted Light at the "Front" of the Spacecraft cause Gravitation? [closed]
I was doing a thought experiment about how mass is lost from gravitational waves, which led me to thinking about how a "bow shock" or gravitational shock wave might appear in front of any ...
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What is Dirac talking about here? [duplicate]
https://www.youtube.com/watch?v=xJzrU38pGWc&ab_channel=mehranshargh
"I might say that my recent work has been very much concerned with Einstein's general relativity and I believe that the ...
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Is the gravitational equation accurate for not moving objects? [closed]
When you calculate the gravitational force $F_G = G \cdot\frac{m\cdot M}{r^2}$.
Is this equation precise for relativistic big masses, given that $m$ and $M$ do not and can not move?
If not is there an ...
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Dual water wheel lifting water back with little inclination [closed]
This is meant for mechanical closed system for hydroponics. Two wheels connected by same shaft so the wheel going down lifts the water back with the other interconnected wheel to a slight incline. ...
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Eccentricity with a law of gravity different from the classical one
How can I calculate the eccentricity of the orbit of a planet (with mass equal to that of the Earth) around a star (with mass equal to that of the Sun) assuming that the force of gravity is given by ...
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Why is the holographic encoding from Bekenstein-Hawking entropy remarkable?
The holographic encoding interpretation from the Bekenstein-Hawking entropy is due to it scaling with the area $S_{BH} = A/4$ of the surface, rather than the volume $V$. While I am aware that most ...
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Deriving the equation for a particle in curved spacetime [closed]
When Dirac derived his equation he started from the non relativistic time dependent Schrodinger equation and then treated the partial derivative of time as the partial derivative of position and then ...
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How to create a more accurate gravity simulation? [duplicate]
Goal:
I am interested creating a simple gravity simulation and was wondering if it was possible to describe two objects motions through time with percision. All other parameters are known (...
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Where does it's gravitational force come from to maintain its constant somewhat spherical shape? [duplicate]
How dose a Tidally locked gas giant have a balanced gravitational force to keep it's spherical shape when one side is constantly facing the sun? Where does it's gravitational force come from to ...
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Is the law of the lever equation the same in classical physics as in relativity ? Why?
In classical mechanics the balancing lever equation (law of the lever) is
$$M_1 a = M_2 b$$
Where $M_1$ is the mass at a distance $a$ from the fulcrum and $M_2$ is the mass at a distance $b$ from the ...
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The Relation Between Maxwell's Equations and the Equations of Gravitoelectromagnetism
Under certain conditions, it is possible to approximate the effects of the theory of relativity through equations very similar to those of Maxwell, but for gravity. In these equations, our "...
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Why do we say gravity curves space but the other forces don't?
I'm generally aware that there have been attempts to describe things like magnetism and the other forces geometrically, like with gravity, and that QFTs have essentially supplanted them. But it's also ...
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Why fully does the curvature of Spacetime cause gravity? [duplicate]
I´m already quite familiar with concepts of spacetime curvature and have heard of the metaphor of two men walking north on the Earth appearing to gravitate towards one another as they approach the ...
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Self-coupling of gravity
From the EInstein eqn it is obvious the metric field couples to itself since $R_{\mu\nu}$ is derivative and multiplication of $\Gamma$'s.
Some GR textbooks explained this coupling as necessary from ...
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Weight of magnet depends on its N-S orientation?
I weighed a Neodymium disc magnet and found that it weighs about $1$ mg more when the north pole is upwards than when the south pole is upwards.
Can this be explained by "conventional" ...
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Ramp friction error: Answer seems to depend on coordinate system
I am a junior level mechanical engineering student, and have taken physics, statics, dynamics, etc. so I know how to do this problem, though something seems to be tripping me up.
Given a standard ramp ...
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How to interpret the soft theorem consequence that the gravitational charge of massless particles is $2E$?
In Weinberg's 1964 paper "Photons and Gravitons in S-Matrix Theory: Derivation of Charge Conservation and Equality of Gravitational and Inertial Mass" where he proved the leading soft photon ...
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Understanding calculation in Feynman's Lecture on Theory of Gravitation about age of universe and gravitational constant
I am reading Feynman's Lectures. In the chapter entitled "The Theory of Gravitation", there is the following part
If we take, in some natural units, the repulsion of two electrons
(nature’s ...
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Why must average velocity of a gas be 1/6 times escape velocity of planet for it to escape [closed]
I read this in my class textbook, and learnt the reason of absence of Hydrogen from atmosphere and Maxwell distribution curve from Physics stack exchange. But I am unsure of why should the average ...
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Self-study for quantum foundations and quantum gravitation
I want to study quantum foundations, and also quantum gravitation.
What is a starting point?
(Although I have a ph.D of physics but I don't have sufficient knowledge about those topics.)
good review ...
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Lagrange Points in General Relativity
In the Newtonian formulation of celestial mechanics it makes sense that a Lagrange point is a point where two gravitational forces of two bodies (and the centrifugal force of the rotating reference ...
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Question on the existence of a higher dimensional spacetime metric for a slowly rotating body
There is a spacetime called "Myers-Perry black hole" $[1]$ which postulate the existence of a $5th$ spatial dimension. Its metric is given by:
$$ds^{2} = -dt^2 +\frac{(dt+asin^2\theta d\phi ...
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Distribution of Earth's mass and its role in the nodal precession of satellites?
From what I have read and understood so far, the nodal precession of a satellite in low Earth orbit is caused by the bulge equatorial of the Earth (caused by its rotation on itself) which moves the ...
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Jackiw-Teitelboim (JT) gravity as a matrix integral
I am reading https://arxiv.org/abs/1903.11115 by Saad, Shenker and Stanford. They relate an (averaged) $n$-point function in a random double-scaled matrix model to a path integral genus expansion in ...
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Is Newton-Cartan theory really equivalent to Newton's theory of gravity?
It is often said that Newton-Cartan theory is a reformulation or perhaps a generalization of Newton's theory of gravity, and it is said that (given certain conditions/assumptions) the two theories are ...
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Does a particle which crosses the galaxy straight (not orbiting) suffer MOND's force in MOND theory?
Lets suppose a particle coming from intergalatic space crosses a galaxy. The particle is not rotating the galaxy, so it has no angular velocity or acceleration. The particle is attracted to the galaxy ...
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Solving Poisson equation for galaxy rotation curves
Can someone point me to the numerical methods to solve the Poisson equation for the galaxy rotation curves?
I've heard of some tools like PETSc or OpenFOAM. But I'm not sure if these are the right ...
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Is the wave, as described by Schrödingers equation, itself the cause of the gravitation's curvature of space time?
Considering a one-dimensional inelastic string that is tensioned from its ends, wouldn't both ends of the string have to be pulled inward when it is rippled by a wave? Wouldn't the same be true in a ...
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If I suddenly store a lot of energy in a small space, this induces spacetime curvature. Does that create gravitational potential energy?
Let us presume that I have a capacitor and suddenly charge it. This induces a (miniscule) spacetime curvature. Nearby objects would experience a gravitational attraction and by extension would have ...
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If an object that falls into a black hole takes infinite time to enter the black hole from the perspective of an observer, how does anything enter it? [duplicate]
If I am making any incorrect assumptions please correct them.
I know this is a common question but I've never seen a clear answer to it. Basically if an object can never be observed entering a black ...
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Conjugate variables in gravity?
We know that in the traditional quantum mechanics the conjugate variables are position and momentum, but what is known about the elusive quantum gravity?
It came to my mind that if there is something ...
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What's the geometrical meaning of the Einstein Tensor? [duplicate]
What is the geometrical meaning of the Einstein tensor $G_{\mu \nu}$ ?
I know the field equations and all of that standard stuff.
I know that the tensor $R = g^{\mu \nu}R_{\mu \nu}$ quantifies the ...
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Does rate of expansion of the universe affect perceived strength of gravitational pull?
As I understand expansion of the universe could be viewed as a constant negative pressure. So when we are looking at two bodies like Earth and Sun, from their perspective there should be a force ...
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Does weightlessness make no difference to free fall?
I looked up a lot of articles and questions about free fall motion and weightlessness. And I know there are a lot of similar questions.
In conclusion, I understand that there is no way to distinguish ...
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Does Global Warming play any significant role in increasing velocity of atmospheric gases?
I understand that moon does not have an atmosphere because it's escape velocity is low and atmosphere gases if it had would escaped into vacuum.
I know Earth has a relatively larger value of escape ...
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Calculations with tensors give two different results from seemingly equivalent paths:
$\require{cancel}$
I want to calculate some operators in the context of Metric-Affine-Gravity: specifically spinors. I will work in tangent space, where all greek ($\mu,\nu,..$) indices are cast into ...
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Could Dark Matter be comprised of gravitational waves entrained in the bulk?
The evidence is strong that more massive galaxies have more massive Dark Matter (DM) halos (for example, Qi Guo et al, Monthly Notices of the Royal Astronomical Society, Vol 404 (2010)). Might this ...
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Gravity, orbiting bodies and Newton’s second law of motion [duplicate]
As I understand it an object travelling in a circular motion is undergoing a centripetal ‘force’. As Newton’s second law of motion, put in simple terms states that a moving object will tend to ...
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Why don't two accelerated clocks behave like two clocks in a gravitational field?
If we immerse two clocks in a gravitational field at different altitudes (with the approximation that both heights share the same g for equivalence to be true), the falling and Schwarzschild observers ...
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Why do we call it "Euclidean Quantum Gravity" instead of "Riemannian Quantum Gravity"?
Euclidean quantum gravity is an approach to quantum gravity based on working with Riemannian-signature manifolds and eventually relating the results to our Lorentzian spacetime by means of analytic ...
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Current bounds on the value of $g$ for antimatter
In 2011, the ALPHA experiment showed that the gravitational acceleration for antihydrogen was between -65 and 110 times the normal gravitational acceleration. Has there been any improvement on the ...
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Is the gravitational force a phenomenon or a theoretical invention? [closed]
We use to say that gravitational force is a phenomenon. But since the theory of General Relativity replaced Newtonian gravitational force, how is it possible for a phenomenon to be replaced by a ...
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Is it possible for a black hole singularity to interact gravitationally with other celestial bodies (if we analyze it using the concept of gravitons)? [duplicate]
It is known to all that the travelling speed of gravitons (the propagation speed of gravitational field) is not instant. So for black holes, the gravitons (the gravitational field) generated by the ...
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How do we know the connection associated with general relativity is the Levi-Civita connection, the one compatible with space-time's metric? [duplicate]
In the standard model the other forces of nature are also defined as connections associated to principle bundles of different gauge groups. There is only one connection on a manifold that describes ...
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Can some regions of space (independent of size), be completely devoid of matter?
Before answering the question, keep in mind that I am a second year Biology student, with no experience in studying Physics and a very basic understanding of Mathematics. However, I have some ...
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An excitation of the gravity field
Does the term "excitation of the gravity field" have any meaning ?(or is it just word salad perhaps?)
Other fields seem to have particles associated with them that are described as an ...
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If the reduction in Grav. PE in falling into a large Neutron Star approaches $mc^2$, shouldn't we conclude that a black hole is a large Neutron Star?
If we integrate the potential energy due to surface gravity from the surface to infinite radial distance (deep space), with a bit of basic calculus we should get
$\Delta E = mgr [J]$.
This depends ...
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Duality and corrections to second-order gravity without and with torsion terms
Recently, there appeared a paper by Giacomo Pollari, A Nieh-Yan-like topological invariant in General Relativity, where the action for gravity looks like:
$$S_g=S_{EHP}+S_{HO}+S_{PO}+S_{GB}+S_{NY}+S_{...
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How does gravitational redshift and blueshift work?
In a gravitational field, if a source emits a signal from below (at higher potential) every second, the signal will be received above (at lower potential) with a lower apparent frequency because time ...
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