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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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What happens to the water on the surface of the Earth if the Earth is not rotating about its axis in the Earth-Moon system?

Suppose the Earth is not rotating. As usual, the Moon follows its normal path around the Earth. Let's assume it's a circular motion and that there are no other gravitational influences. A test ...
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Is this arXiv article from 1999 discussing Gravity as an indirect consequence of the Strong Force been shown as obsolete due to new discoveries? [on hold]

Apologies for asking an ambiguous question like this. Feel free to let me know and I can go into depth with what the article says and post it in this question itself. I realize it will take a lot of ...
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Is Gravity still considered to be part of the “Superforce” which existed at the instant of the “Big Bang”

My limited understanding of the Big Bang is that all the Fundemental Forces (Electromagnetic, Weak Nuclear, Strong Nuclear and Gravity) were originally part of a "Superforce." As the universe cooled ...
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How to calculate the velocity change of a object if it's going past a object

So, I am making a physics engine, for a game, and I need to know how to calculate the acceleration caused by gravity and angular velocity caused by a big objects. In other words: Let's say I've got ...
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1answer
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Does an external perturbing potential appear in the gravitational Poisson equation

We could use any self-gravitating fluid for this question, but let's take a star as an example. Left alone, it's density is the source of it's potential and thus we have the simplest form of Poisson's ...
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Do the inertial mass and gravitational mass of an object depend on the frame of reference?

My understanding is that the "relativistic mass" of an object means any of the following three quantities (which are all identical): The "mass-energy", as defined by the formula $m = E / c^2$. The ...
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1answer
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Physical meaning of curvature in relativity [on hold]

I understand space is not a rigid structure which actually bends (like a metal bar or rubber sheet) so "curvature" due to energy momentum pressure and stress (stress energy tensor) is?? This is were I ...
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What is the second gravitational charge and second strong force charge? [on hold]

I have been watching documentaries and reading up on the 8 charge dimensions of Emergence Theory. In his Ted Talk (liked below) Garrett Lisi mentions 2 gravitational charge directions. Mass is ...
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To quantize or not to quantize? Is less quantization needed or better in physics? [on hold]

This is not a question specifically about quantum gravity, but rather about attempting to bring quantum mechanics and the foundations or principles of physics in general towards more determinism and ...
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Gravity act on the body lie on the center of EARTH? [duplicate]

Gravitational law: "Every body of the universe attract every other body with a force which is directly proportionl to the product of there masses and inversiliy proportional to the square of the ...
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1answer
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Elevator and measuring of $g$

Imaging a person in an elevator accelarating towards earth with accelaration $a$. At some point the person let a ball fall from his hand. Does the time that ball needs to hit floor equal time that ...
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The event horizon of a black hole supposes an absolute zero in some field?

Based on the Schwarzschild black hole theory, if the gravitational pull of the singularity were to equalize the energy that a photon has by approaching the event horizon from a special angle, would it ...
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Two meanings of acceleration in gravitational fields?

Question about General Relativity. Edit: I've gotten some really good input to help me better phrase my confusion. I think the heart of my problem is understanding the difference between geodesic ...
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4answers
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What is the geometric interpretation of the Einstein tensor $R_{\mu \nu} - \frac{1}{2} g_{\mu \nu} R$

The Riemann curvature tensor $R_{\mu \nu \rho \sigma}$ has the geometric interpretation of giving how much parallel transport fails to close around tiny loops. The Ricci tensor $R_{\mu \nu}$ the ...
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173 views

What is a theory of gravity?

Let me introduce this question by noting that my training is in condensed matter physics, and my familiarity with gravity is superficial at best. Hence, this question may be somewhat naive. In ...
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2answers
299 views

Are photons affected by Earth's gravity? [duplicate]

Just wondering if the Earth's gravity affects the photons? We can obviously think about equivalent mass of photons by using de broglie relation and then use it to calculate force of gravitational ...
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1answer
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Is there an Abraham-Lorentz force for Gravity?

The Abraham-Lorentz force in Electromagnetism is the recoil a charge experiences as it accelerates due to own emission of radiation. The Newtonian theory of gravity is identical to that of ...
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1answer
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Can a free electron accelerating in a gravitational field absorb photons? [duplicate]

An 'free' electron accelerated in an electromagnetic field can both absorb and emit a photon. What about an election accelerating in a gravitational field? Edit: Some users have suggested that the ...
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How many types of msc. physics programs are there? [on hold]

I am interested in both elecrodynamics and gravity. Is there any any msc. course which primarily focuses on these subjects.
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What is Gravity made out of? [duplicate]

${}$ What is Gravity made out of?
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1answer
26 views

Struggling with gravitational potential definition

The textbook for my A-Level physics course defines the gravitational potential at a point as: The work done per unit mass to move a small object from infinity to that point. But if Work = Force * ...
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1answer
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Calculating the distance between two masses with respect to gravitational force [duplicate]

Call them $m_1,m_2$. They are compressed to their center of masses, if you wish. If the initial distance at $t=0$ is $d$, is there a formula or an efficient way to calculate the distance between them ...
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1answer
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Pulling of Light by a Black Hole? [duplicate]

We all know that light has no mass at all. Yet we say that the gravitational pull of a Blackhole within Schwarzschild radius doesn't let light to pass. If the light has no mass, how can it experience ...
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At what density and pressure will hydrogen coalesce rather than disperse in the vacuum (or pressure) of space? [closed]

When hydrogen becomes more dense in one area, it becomes less dense in the surrounding areas. How dense would hydrogen have to be in the vacuum of space for it to continue to coalesce?
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Gravity, planetary orbits [closed]

If a planet was slowed down, what effect would it have on it’s orbit around a star. Or adversely if it were speeded up what effect would that have ?
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1answer
51 views

What happens to the gravitational potential energy of the objects at the singularity of a black hole?

As they are 0 distance from the center of the gravitational body, do they have no potential energy? Does this mean that the singularity is at the lowest energy state possible? Sorry if this sounds ...
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1answer
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About gravity and the making of stars [closed]

They say gravity is because mass stretches space time and it makes matter fall to it and can prove it. And that makes sense when there is a lot of mass. But they say stars are made from gas clouds ...
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REAL reason of Gravitational Time Dilation [duplicate]

I might have got everything wrong, but I always treated "time dilation" really skeptically because slowing time in fact means slowing all physical processes and all interactions. First I heard of time ...
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Why do numerical relativity papers show $\ddot{h}_x$ instead of $h_x$ for gravitational waves amplitude?

I am very confused about why numerical relativity papers, when talking about gravitational wave extraction, usually plot the real part of the fourth Weyl scalar, $\Psi_4$, instead of its double ...
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Gravity from algebra

Can someone provide me a reference that describes the gauging of the Poincare algebra to obtain Einstein's relativity? "It is well known that Einstein’s formulation of gravity can be obtained by ...
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5answers
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Why do we say there are four fundamental forces instead of some other number? [duplicate]

In my physics textbook (and in popular science culture) it is stated that there are four fundamental forces: electromagnetism, strong, weak, and gravity. But Wikipedia tells me that there is a ...
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33 views

What are the exact qualities of gravity that are not understood? [duplicate]

I have seen too many theories about gravity to know whats what. To make it easier for me, I'm wondering which aspects of gravity are 100% confirmed, but more importantly, what are the things that are ...
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Why didn't Gravitational waves from neutron star passed into extra dimensions? [duplicate]

String theory is most prominent candidate for theory of everything but it defines our universe correctly through higher dimensions, precisely 11 dimensions. We know that gravity can pass through ...
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2answers
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Speed of light in gravitational field [duplicate]

Why has the speed of light in a gravitational field always the same value $c$ when measured locally? More precise: When you are far away from any masses, that means when the spacetime is flat, and ...
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0answers
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Does “Quantized Inertia Theory” violate conservation of momentum? [closed]

This recent news article reports that DARPA is doing work with "quantized inertia", despite their claim that it's not widely accepted by physicists: The Defense Advanced Research Projects Agency (...
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1answer
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Gravitational refraction

I recently used another venue to ask about the speed of gravity, specifically if the speed of gravity is constant or if it is subject to refraction when passing through media, akin to light. The ...
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1answer
56 views

Attraction of matter in curved spacetime

Is there still going be a force between them (converging space which makes the two bodies meet together at a point)if both of them are absolute rest with respect any frame of reference.
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3answers
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“Dark Matter” vs. “Dark Spin”

I am rephrasing an answer to another PSE question as an new question here. Dark matter is invoked to explain the 'observed space-time geometry that does not match with predictions'. According to the ...
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Acceleration in Theory of General Relativity [duplicate]

I know that in Theory of General Relativity, mass curves the space-time. Then how is a body attracted towards the body of larger mass.
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1answer
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How can a gas produce gravity? [closed]

I’m asking this because, I heard that the gas does produce gravity. So, how does actually works? What’s the phenomenon for gas producing gravity? Because, all what I want is a clear explanation in ...
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Spacetime geometry of black hole formed by the scattering of two gravitons

In the paper "Breakdown of predictability in gravitational collapse" Stephen Hawking mentions the following on section 5: Consider, for example, the scattering of two gravitons. In this case the ...
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1answer
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Simulating trajectory of object in a non-uniform but static gravitational field

This is a physics question, but the motivation for it comes from game design. I want to simulate the motion of an object in 2D space with several point sources of gravity (actually stars). The point ...
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1answer
70 views

What is the interaction of gravitational waves?

Please excuse my lack of knowledge about the subject but, If gravitational waves travel thru the fabric of space time do they interact with each other? Meaning do they create interference patterns ...
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2answers
45 views

Is it possible to survive the destruction of a planet (earth)? [closed]

I recently watched Star Trek VI: The Undiscovered Country again. The main story evolves around the destruction of a moon of the klingon empire which is their main ...
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How to derive the hamiltonian of general relativity (ADM formalism without surface terms)?

given that $ds^{2} =−N^{2}dt^{2} +h_{ij}(dx^{i} +N^{i}dt)(dx^{j}+N^{j}dt)$ $S=\int dt d^{3} x\sqrt{h} N(^{3}R+K_{ij}+K^{ij}-K^{2})$ where $(^{3})R$ is the Ricci scalar of hij, h the determinant of ...
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3answers
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According to general relativity, why are two objects at rest attracted to each other? [duplicate]

I'm trying to understand gravity in General Relativity and I'm having some questions. I can understand that an object in orbit around another more massive object is free falling and simply following a ...
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1answer
31 views

Schwarschild Metric from Kepler law

Can we redrive Schwarschild metric from Kepler's law without assuming General Relativity?
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Gravitational attraction between a particle and a bar

I'm trying to solve this problem from the book "Fundamentals of Applied Dynamics" by R.A.Tenenbaum. I start it by trying to find the resultant gravitational force by the means of integration. $$d\...
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Entropy and equilibrium concepts at astronomic scales

I am always puzzled to read here and there discussions dealing with thermodynamic concepts applied to astronomic scales where gravity matters. To my opinion, there is a certain carelessness to go into ...
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Has the pilot-wave model been used to make cosmological predictions?

In Roman Sverdlov’s paper Incorporation particle creation and annihilation into Bohm's Pilot Wave model1 he says: Finally, we have pointed out that the modification of gravity had a side benefit: ...