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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Can gravitational waves be visualized in the elastic rubber sheet model of gravity?

To visualize the space curvature related to gravity, there is a model or analogy using an elastic sheet and a weight. A rubber sheet is spanned like a very soft trampoline, and a heavy ball on it ...
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Are there good reasons why special relativity should motivate geometrised gravity in a way that Newtonian mechanics does not?

I have studied a bit of Newton Cartan theory recently, the geometrised version of Newtonian gravity in which gravity is due to the curvature of spacetime, but is Newtonian (simultaneity is absolute). ...
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How do we know that Dark Energy has homogeneous energy density? [duplicate]

I’ve read places that the density of Dark Energy is the same throughout the universe. If the expansion density of dark energy were the same throughout the universe, why don’t all galaxies have the ...
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Does static gravity follow spacelike geodesics?

It is well known, albeit a bit counterintuitive, that the Earth is attracted to the "current" location of the Sun. While the concept of "current" involves relativity of simultaneity, of course, the ...
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Time travel / Time machine [on hold]

Basically I’m attempting to design a time machine using a new model of physics which relies on the postulate that gravity is not cause by mass or rather that the weight that is supposedly the cause of ...
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What will happen if a vacuum chamber gets moved with a person inside?

Imagine that a person would be put inside a vacuum sphere, just like the spheres that NASA uses for simulating space's zero gravity. That person would be hovering right in the center of the sphere. ...
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How is the electromagnetic/gravitational force transmitted? [duplicate]

So I was thinking about how a positive and a negative charge (or positive/positive, negative/negative) interact. I have read previously about how photons carry the electromagnetic force. However, how ...
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Is gravity and dark energy really for real? [on hold]

In particle-physics gravity is the unexceptional weakest force. There is proof. Then gravity does not influence the universe nor is there is dark energy except for acceleration. Man does not ...
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How does gravitational potential energy work in Relativity?

According to relativity, the universe is expanding, at an accelerating rate. Far away planets and stars will soon leave our observable universe. But as planets and stars leave our observable universe, ...
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Clock ticks faster with altitude

Suppose there are two identical drones in a weak and uniform gravitational field that are initially at the same place and with synchronized clocks. Assume drone A first rises vertically for 10 ...
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To a distant observer, is the trajectory of an object falling toward a black hole always reversible?

I think (pure intuition) that every object that falls towards a massive center, in the condition of free fall, should always be able to return to the starting point. Even if this massive center is a ...
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Work Done to Separate two contact bodies

can anyone solve for the case when sphere is with a cavity , can we do it by COM method to find potential , then energy ?? So as to find work done ?I want to know by equating self energies , r we able ...
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off shell graviton 3 point vertex

I have a technical doubt regarding the graviton three point vertex from DeWitt's paper of 1967 : https://journals.aps.org/pr/pdf/10.1103/PhysRev.162.1239 Can someone write some of the terms in the ...
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Another theoretical method of defeating gravity? [closed]

So, even though it isn't actually, let's say the force of gravity is -5. (Now, I know someone else has probably already thought of this and tried to put it to some use, but...) What if the answer was ...
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Feynman diagrams for gravity

Feynman rules is the basic tool to compute amplitudes in perturbation theory for a QFT. Here, I am trying to understand perturbation theory in GR around the flat space metric, in terms of Feynman ...
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Ricci scalar in terms of vierbein and spin connection

I have been trying to derive the following form for the Ricci scalar in terms of vierbein and spin connection $$R=(e^{\mu a}e^{\nu b}-e^{\mu b}e^{\nu a})(\partial_\mu \omega_{\nu ab}+\omega_{\mu a}^{\...
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What does the effect of “permanently” altered spacetime, between two objects after suffering a gravity wave, have to do with Einstein's relativity? [on hold]

Is it a contradiction, an irrelevancy, or a conclusion of Einstein's relativity principles? I was thinking either the latter, as an object being relatively deccelerated/accelerated by suffering an ...
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The sign of $d\mathbf{r}$ when integrating the universal gravitational force in order to define gravitational potential energy [duplicate]

I am trying to find gravitational potential energy by integrating the gravitational force: $$\mathbf{F}(\mathbf{r}) = - \ G \frac{Mm}{|\mathbf{r}|^2} \ \hat{\mathbf{r}}$$ where $\mathbf{r}$ is the ...
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Scalar coupled to Gauss-Bonnet invariant vs Horndeski theory

So here it is a somewhat tormenting question. The first statement will be a little specific but then I will make clear what the jargon indicates. How can we show that a Lagrangian made of a scalar ...
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Variable acceleration kinematics [closed]

Two massive planets originally separated at displacement x away from each other. The plants have the same mass m. By considering the non-changing acceleration, calculate the time taken by the two ...
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Does light travelling tangent x distance away from a star fall at the same rate as a mass that is same distance away from the star? If not why not? [closed]

For example if you have a star who's gravity causes a mass to fall at 100m/s^2 at a distance of 1 million kilometers, will a beam of light travelling tangent to the direction of the star at 1 million ...
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Definition of “specific gravity”

I've learnt that a specific quantity is an extensive quantity divided by the mass. How does the definition of specific gravity fit into this scheme?
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Gravitino Equation of motion in second-order formalism

In Freedman and Proeyen's text on supergravity they derive the equation of motion for the gravitino using the second order formalism. However, I'm not exactly clear as to how they use partial ...
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How is spacetime warped by a massive object?

I was going through this question (Why don't planets have Circular orbits?) related to planetary orbits. In the accepted answer it is stated that orbits are actually conic sections. Given this ...
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What is the difference between Einstein aether theory and general relativity?

I'm currently doing some research on the various aether theories and I stumbled upon Einstein aether theory. It appears to be much different from Luminiferous aether and be more closely related to ...
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Can we feel gravity while free falling?

I watched some video saying that there is still gravity in space station and almost same strong as it on Earth, the reason they feel no gravity is because the centrifugal force of the orbit is same as ...
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What are the characteristics of space-time? [duplicate]

How does distortions in space-time caused by earth make us attracted towards the earth?
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If time slows in the presents of gravity, how does the conclusion that the universe’s expansion is accelerating account for this?

I am sure there is a simple explanation for this and I’m not a physicist so hoping someone here can help answer this for me. Time is retarded by gravitational field. Expansion in all directions ...
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Is it possible that the acceleration of the growth of our universe is driven by the overall gravitational pull of neighboring universes [closed]

I am painfully unequipped when I think about my my knowledge of physics. Still, I am enthralled, as many of us are, by the mysteries and complexity of the universe, both known and unknown. I was ...
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How would classical physics explain the sorting of objects according to density in a gravitational field?

I'm wondering how classical physics (i.e., using Newtonian Gravity) would explain why it is that objects are sorted by density in the presence of a gravitational field?
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Finding suitable element to perform integration upon [closed]

Is there any precise (proper) method or technique to specify the element on which integration will be performed. Is it the same for all properties like moment of inertia, gravitational potential, ...
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Negative masses [duplicate]

If there existed negative masses how would one use Newton's law of gravitation (since it doesn't spit out the direction of the gravitational force but only the magnitude like Coulomb's law)? Would ...
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Why are the surfaces of liquids always perpendicular to the gravitational force?

I am not a physicist nor do I have a good knowledge of the topic. Pardon me if I use terms erroneously. I observed that when I put some water in a bottle, without regards to how the bottle is placed,...
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Is it correct to say that 1 meter of water weighs as much as 1000 meters of air?

Pressure $1$ meter under water is approx $1.1$ atm ($1$ atm due to air, $0.1$ atm due to water), and pressure $1000$ meters above water is approx $0.9$ atm. So, roughly speaking, is it correct to say ...
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Graviton propagator, and Gauss-Bonnet gravity

Let's say we consider Einstein's Lagrangian from GR. In linearized gravity, we would expand the Ricci scalar to quadratic order in the perturbation parameter to find the propagator. My question is as ...
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Possible Beginnings of New Universes? [duplicate]

Black holes pull anything and everything that enters past the event horizon into the singularity. What if the current unknown output where all of this infinitely condensed matter goes to is the ...
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How much motion in fluids is random motion?

Say that the only pressure differences in the atmosphere was due to the gravitational pull of the earth. That is, say pressure only changed as a function of height. So we're assuming there's no wind, ...
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Curvature of a two-dimensional hyperboloid

I have a question about an exercise in Misner, Thorne, and Wheeler's Gravitation. On page 334, exercise 14.1. "Curvature of a two-dimensional manifold hyperboloid" says: Compute the curvature of ...
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How do we determine that an object is neutral?

This has been bothering me for a while. Imagine that you are an experimentalist who does not have any known mass or charge to compare against. Imagine also that you do not have any idea about the ...
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Wouldn't gravitons themselves theoretically be affected by gravity? [duplicate]

(I wrote this using the assumption that the graviton exists, which I know is not necessarily true; this is asked from a theoretical standpoint) It is my understanding that General Relativity states ...
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Equation of Motion for a Test Particle

I have a question regarding Misner, Charles W.; Thorne, Kip S.; Wheeler, John Archibald (1973), Gravitation ISBN 978-0-7167-0344-0. It is a book about Einstein's theory of gravitation. At the page ...
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What quantum effects that involve gravity can be studied without stuff like QFT or string theory?

So there is no a full quantum theory of gravitation. However, there are instances where quantum effects due to gravitation have been studied. Like Gravitational neutron interferometry https://arxiv....
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What shape of gravity and EM fields would a hollow sphere produce, with what resulting effects upon said structure?

The Earth generates a gravity field based on local mass, but which mostly appears to act as a point source, though local fluctuations in the crust density and mass affect the gravity in a given region ...
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Does water have a minimal thickness because of van der waals force?

I have read this question: The thickness of a puddled sheet of water https://en.wikipedia.org/wiki/Surface_tension#Puddles_on_a_surface The liquid mass flattens out because that brings as ...
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Torque and angular acceleration in elliptical orbit

I am stuck in a supposedly simple aspect. Consider the Sun-Earth system. The torque is zero and angular momentum is conserved. $L = I\omega$ is constant, but since $I$ changes, $\omega$ should change ...
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General theory of relativity questions [duplicate]

I do not understand how this theory (the theory of general relativity) would work because gravity is what makes things heavy and weight is what bends things. All of the proof makes it hard to question ...
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Feynman Lectures vol.1 Chapter 4 Topic 4-2GravitationalPotentialEnergy

Could anyone explain me in simple words what is being said in topic "4-2 Gravitational potential energy" from "The Feynman Lectures on Physics, Volume I" (great book and author btw)... i don't ...
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Time dilation : Hourclock on Jupiter

Time slows down on Jupiter because of higher gravity, but Hourclock(sand clock) run faster due to higher g. If I am correct than how?
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What is the reason behind black hole making objects near him dissappear? [closed]

If a black hole is formed by the death of a star, why does it suck things with its gravity going inside it? Does it not have a surface or anything? Is it just a hole in the space which keeps on ...
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what Mass would be required to create measurable resistance in this circuit?

sorry I'm not a physicist or student in this is not homework I was just thinking about this. say you have a spherical Mass of a certain density I'm thinking say planet-sized and then tangent to the ...