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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relations opf space-time to gravitation as an evolutionary process [on hold]

just thoughts - 1 -gravity - could it be that it is not a fundamental force after all - could it be that it evolved after the big bang? space time was evolving and things [lets call them string but ...
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62 views

What is wrong with this theory? - This is a unique way to visualize the universe [on hold]

Assuming that particles move in two ways: 1st, conformationally changing relative to itself over time regardless of its location in 3d space (i.e. staying in one place but conformationally changing) ...
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1answer
78 views

Forces that fall under gravitational forces [on hold]

I was explaining the air motion in the atmosphere, so I introduced Gravity, Pressure Gradient and Coriolis Forces. Then one of the Professors asked me this question, which I couldn't answer. He said ...
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131 views

Does gravitational field has gravitational mass?

Other questions closely related to the one of the title (as I will show) are Does speak about work done on photon has sense? Does photon has a gravitational mass? Does exists a modern (and more ...
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2answers
87 views

Is the stress energy tensor continuous at the interface between an object and vacuum?

The stress energy tensor has (as I understand) zero value in the region where there is no matter and non-zero value where there is matter. Suppose there is one matter object in space, now how does the ...
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1answer
59 views

Is gravity weak negative electric charge? [duplicate]

This could be true since the both have infinite range and other common properties. They both have fields.
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27 views

In discrete models of spacetime, what are some implications of the Einstein equation

We have several models of discrete spacetime. Sorkin has a causal growth dynamics, there's spin foams, Panangaden showed a correspondence between interval domains and spacetimes. I am looking for ...
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2answers
111 views

Can anyone explain me how time can bend according to Einstein in simple way? [duplicate]

I am just 16 and curious to learn about Theory of Relativity. Can any one explain it simple enough for me to understand? I read that it is bending of time-space or space-time that causes gravity. How ...
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24 views

Throwing the object around the Earth [on hold]

You have to throw an object to a point diametrically opposite od Earth surface, take that Earth does not rotate and that it is perfect sphere. What angle to the ground and velocity must object have? ...
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1answer
20 views

Is 0.1 bar (hydrostatic pressure) equivalent to 0.1 bar vacuum pressure (absolute pressure)?

Suppose we would like to test the ability of an objec to withstand the pressure under 1 meter of whater. I would like to understand how to simulate this situation using vacuum. Is the 0.1 bar (for 1 ...
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1answer
10 views

Lenghthwise center of gravity of a boat based on flotation angle

I am trying to determine the center of gravity horizontally along the length of a pontoon boat so I can properly position the load on my lift. Approximate will do. It seems like an impossible question ...
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33 views

Is the Universe a 4D elastic shell that is contracting with time, where particles are traveling waves or standing waves of energy density? [closed]

In gravitational red shift, “the phenomenon known as the red shift of a photon is really the blue shift of an atom.” This conclusion also applies to Galactic redshift. According to Hubble’s law, when ...
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50 views

What fills the space between the galaxies, stars and planets? [duplicate]

What fills the space between the galaxies, stars and planets with the exception of gas clouds, dust, atoms, elementary particles and electromagnetic radiation? What the authoritative opinions exist on ...
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55 views

Is electricty matter? [closed]

Electricity is a flow of electrons. I'm right until here, and matter is something that takes up space. (I can't be in the same place as my friend does). And correct me if I'm wrong but an electron ...
2
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1answer
86 views

Can gravity in principle be made to flow through a “wire”?

Electricity can be made to flow preferentially through a conductor such that a potential difference can be exploited and it can be used to do work remotely. In principle could an analogous "gravity ...
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1answer
45 views

“This Side Up” in Zero g?

I know that at a particular altitude above Earth, the effects of its gravitational pull become negligible- thus the feeling of weightlessness by astronauts. In most Sci-Fi movies, including the much ...
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3answers
129 views

I Think I am Misunderstanding Einstein's Equivalence Principle and His Elevator

I'm having difficulties understanding why a gravitational acceleration can be guaranteed to be locally equivalent to an accelerating frame. Doesn't it matter on how the force is being applied? If the ...
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1answer
27 views

Distance of closest approach

When deriving the gravitational bending angle of light, In this paper, the author introduced $R$ (the distance of closest approach), in equation ($7$), to solve the problem. My question: How is $R$ ...
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40 views

About spin 2, graviton, in the context of attractive force.

excerpt from Introduction to Black hole physics, Valeri P. Frolov and Andrei Zelnikov In this textbook, there is comment about spin of gravitons as follows For gravitating bodies the gravitational ...
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2answers
76 views

What is the binding energy in General Relativity?

In general relativity, the potential energy is given by $$V(r)=\frac{h^{2}}{2r^{2}}\left(1-\frac{2M}{r}\right)-\frac{M}{r}.$$ Solving $V^{\prime}(r)=0$, there are two points where circular orbits ...
2
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50 views

Choice of framing in Gravitational Chern-Simons

I was trying to understand formula(2.21) in Witten's paper "Quantum Field Theory and Jones Polynomial"(link: https://projecteuclid.org/euclid.cmp/1104178138) (Page 360). There, it was mentioned, the ...
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3answers
804 views

What is the radius of the event horizon?

I know that the Schwarzschild radius is given by $$r~=~\frac{2GM}{c^{2}}.\tag{1}$$ However, If we had the metric $$ds^2~=~−A(r,t)dt^2+\frac{dr^2}{B(r,t)}+r^2(dθ^2+\sin^2{θ}dϕ^2),\tag{2}$$ where ...
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3answers
134 views

How to derive the Schwarzschild radius? [duplicate]

I know that the Schwarzschild radius is given by $$r=\frac{2GM}{c^{2}}.$$ but I never seen a derivation for this equation. 1- Does anyone know how to derive this equation from general relativity? ...
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1answer
40 views

Can pre-inflationary gravitational attraction affect objects after inflation?

According to inflation theory, the inflation itself took place at some short yet finite time after Big Bang, so there should be some gravitational interactions present before inflation, some objects ...
2
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1answer
64 views

Do gravational effects 'travel' through a wormhole?

Lets say a wormhole exists with point A inside the gravity well of a star and point B in a space where there is no notable nearby mass to create a gravitational force. If one were to approach point B, ...
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1answer
69 views

The age of black holes

I have a very small understanding of space-time however I have been watching some interviews and reading articles featuring theoretical physicist Kip Thorne and I have a few questions that I hope can ...
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72 views

Will a black hole cause scattering of a gravity wave?

In my GR textbook, it states that gravity waves can undergo interference but not scattering. I am just starting the chapter on linearised gravity concepts (weak field approximation) and my apologies ...
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3answers
129 views

Is the Universe being dragged into a singularity rather than expanding?

Recently I've read that the expansion of the Universe as observed is not exactly uniform as proposed by Hubble. Therefore is it possible that instead of space expanding in all directions all matter is ...
16
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3answers
411 views

Swimming in a ball of water in space

What would I feel if I went swimming in a ball of water in space? Would I feel greater pressure as I went deeper into the sphere? What would it be like to swim in something like that? Also, let's say ...
0
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1answer
40 views

Capillary effect to pump water up to cool water

Chinese scientists demonstrated anti-gravity pump, which uses capillary effect and super-hydrophobic screen to flow water upward by 1cm using internal energy of water. How much water will be cooled ...
2
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4answers
798 views

When space bends, what are the lines that are being bent?

In an electric field diagram, the lines represent the electrostatic force vector at the position. These lines are bent when you place a charge into the system. What is the equivalent description ...
5
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1answer
101 views

How is the Lagrangian defined in GR?

Reading about the Schwarzschild metric in general relativity I see that sometimes $$L=g_{\mu\nu}\dot{x}^{\mu}\dot{x}^{\nu}$$ and sometimes $$L=\sqrt{g_{\mu\nu}\dot{x}^{\mu}\dot{x}^{\nu}}.$$ Which is ...
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28 views

Anomalies in weighing a magnet [duplicate]

In weighing a strong magnet there is a difference in weight when the magnet is weighed from different polarization directions. The differences in weight are not due to polarization because ...
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12 views

Integro-Differential Equations [migrated]

I was looking for elementary examples of integro-differential equations, and I wondered would the following equation, $\frac{d^{2}x}{dt^{2}} = \frac{GM}{x^{2}}$ qualify as a valid example? Because it ...
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2answers
37 views

Falling into the sun, a thought experiment for trying to understand reference frames

If someone were transported out into empty space, idk like hundred of thousands of miles straight "up," would they fall into the sun? It would depend on their velocity right? If they were moving at an ...
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1answer
58 views

Weight of magnetic objects and polarization [closed]

I am an Iranian engineer and have a question which no one has answered me yet. In weighing a strong magnet, there is a difference between the weights from different polarization directions, why is ...
-1
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1answer
34 views

modified gravitational model

In the modified gravitational model $ f(R)=R+\lambda{R_{0}}\left(\left(1+\frac{R^{2}}{R_{0}^{2}}\right)^{-n}-1\right) $ what are the units of $\lambda$ and $R_{0}$.
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1answer
52 views

Circular orbits in general relativity(GR)

Reading about Schwarzschild geodesics, I found that circular orbits are possible when the effective force $$ F=-\frac{dV}{dr}=-\frac{\mu{c^{2}}}{2r^{4}}\left(r_{s}r^{2}-2a^{2}r+3r_{s}a^{2}\right)=0 ...
2
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1answer
53 views

Observed gravity of Venus aside from the Magellan probe

I have been searching but cannot seem to find it. I would like to know what the surface gravity of Venus has been observed to be from different missions/probes that were sent to Venus on separate ...
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26 views

Pendulum gyroscope

Is there a gyroscope (a device that enables orientation detection) built with only a pendulum and a gimbal? If I understand the terminology, this device would not use conservation of angular momentum ...
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28 views

Reduced gravity flight's affect on convection based cooling

I came across this question about possible issues a reduced gravity flight might pose for a the operation of a MacBook Pro. This answer claims that reduced gravity could affect the laptops cooling got ...
3
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1answer
36 views

gravitational wave detection using interferometer detectors

I understood that the basic idea of the interferometric detectors is the michelson interferometer experiment, in which the change in the position of the mirrors will cause the interferometer ( ...
2
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2answers
282 views

How can we feel the effects of a Black Hole if all the mass is gone?

This question may help me learn more about the subtleties involved between the notions of gravity, in the Newtonian sense and those of curved spacetime, in the General Relativity sense. I will take ...
2
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1answer
81 views

Gravitational potential in GR

In proving that the metric will play the role of gravitational potential, there is this chain of ideas: ...
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1answer
101 views

How do I graph acceleration?

I have written some java code for the calculation of some various acceleration and etc. type data. I am now trying to graph that data so I can pull specific data over a time line. The values I have ...
2
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0answers
73 views

Is there any physics arguments behind NASA pen joke

I am just wondering are there any reasonable physics arguments behind difficulty making pen for no gravity conditions. My thoughts are that there are many ways to make it working as: Pressurized ...
3
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1answer
65 views

Are moving objects producing stronger gravity fields? [duplicate]

If the strength of gravitational influence exerted by a body is derived from its mass and energy then is it true that a moving object which has some kinetic energy should also produce stronger ...
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4answers
564 views

What happens if gravity of all objects in the universe disappears?

I've been trying to find the answer to this question for a few days and I ended up in having different answers from different sources. A website says: Everything on the universe would move in this ...
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1answer
46 views

Potential for particle rolling down slope of arbitrary shape

I've been thinking about how to calculate the potential $V(x)$ of a particle rolling under the force of gravity down some curve, given by $f(x)$ (suppose nonincreasing). My idea was to simply ...
1
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2answers
1k views

Is Gravity a Problem?

I was watching the movie "Interstellar" recently and in that a character "Romly" mentions that if he could peep into the black hole "Gargantua" he could solve gravity. I have a questions, is that a ...