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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Detection of gravitons in gravitatonal wave detectors: what is the expected value of the squeezing parameter for astrophysical sources?

The recent progress regarding the detectability of gravitons is quite interesting, and has been theoretically controversial. A series of papers involving F. Wilczek (the full-glory paper is titled ...
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Einstein strong equivalence principle disproven

I have an easy idea of an experiment that disproves or violates Einstein's strong EP. Where can i post it officialy?
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If kinetic and potential energy are relative, how do they exert a gravitational force? [duplicate]

I am imagining two bodies flying through empty space near the speed of light relative to their (distant) surroundings. Let’s say they are a bowling ball and a tennis ball. They are not moving with ...
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Combination of time dilation due to motion and gravitational time 'contraction' due to negative mass

Consider a system with a moving spaceship of mass $m$ and a huge, fixed negative mass $M$ (with $- M \gg m$). The negative mass will accelerate the spaceship. The astronauts will experience time ...
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How can an observer establish a coordinate system in curved spacetime only with GR?

Consider the theory only posseses GR. If an observer lives in a curved spacetime, how can he measure the metric of the spacetime without knowing the matter distribution? Suppose he can establish a ...
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What are $δ$ and $ε$ in the list of Dirac's five 'fundamental constants', concerning his 'Large number hypothesis'?

From Jean-Philippe Uzan's Varying Constants, Gravitation and Cosmology: Dirac formed five dimensionless ratios among which1 δ ≡ H0ħ/mpc2 ∼ 2h × 10−42 and equation M1 and asked the question of which of ...
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Kruskal coordinates from GR field equations

The "usual" way (as I've seen in most text books) of dealing with Schwarzschild spacetime is to start with Schwarzschild coordinates, then explore the nature of coordinate singularity at $r=...
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About the gravity field around a lightbeam [duplicate]

Imagine there is an infinitely long beam of light. It has impulse and energy. How it affects the spacetime surrounding it? Will masses be pulled towards it perpendiculary and pulled in the parallel ...
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Secondary vs. primary gravitation

Modified Newton dynamics (MOND) works surprisingly well to fit the rotation curves of galaxies. On the other hand, in the solar system, Newtonian gravitational law (which can be derived from general ...
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How would affect a Gravity of 10 in Earth [closed]

My teacher asked me about it in class and I don´t knew what to respond.
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How does a static electric field behave in curved spacetime?

Imagine a simple capacitor of two parallel plates with a static electric field between them. This capacitor is oriented in a gravitational field such that the space between the plates is parallel to ...
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Question about time dilation and what an observer sees

This is a soft question I was discussing with a friend. Suppose a portal opens up (I know this is fiction) but for the sake of argument, let's suppose something like that happens. And the observer can ...
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Is it possible to make a magnetic box that will compensate Earth gravity allowing magnetic objects inside to fly on orbits like in space? [closed]

Is it possible to simulate solar system using magnetic spheres and some kind of box that will compensate the Earth gravity by magnetic force?
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Do electric fields in a capacitor add to its weight?

So this article got me thinking: https://www.scientificamerican.com/article/do-electric-charges-and-m/ It states that according to GR, the energy in an electric field should curve spacetime and ...
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How does spacetime curvature "CREATE" gravity? [closed]

See, I am having a hard time understanding that how spacetime curvature works. Well, I am a beginner in astrophysics so kindly add full details in the answer and a figure too if possible. Also how ...
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A satellite moves in parabolic or straight line path when it escapes and when its total mechanical energy is zero.How can ang. momentum cons. be used?

When a satellite escapes from the orbit of a planet it can have Mechanical energy equal to or greater than 0 but when it is equal to zero it can have a parabolic or straight-line path. When velocity ...
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Would I be able to tell if I was inside a piece of distorted space? Are objects distinct from spacetime?

If one could hypothetically stretch / squash / in some way distort a piece of space, an outside observer could tell by looking at the distorted object/space that it had changed because the difference ...
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How can an accelerated frame and a gravitational field be equal?

How can two things that are different be equal? In a gravitational field there is actually gravity that push us down, but in the accelerated frame there is nothing that push us down.
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What is the current status of the convergence of the post-Newtonian approximation?

In the very well written article by C. Will, On the Unreasonable Effectiveness of the post-Newtonian Approximation in Gravitational Physics, he states: The one question that remains open is the ...
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Increasing the speed of satellite to raise an orbit

Suppose we have a satellite orbiting the Earth in an elliptical-closed orbit. When the satellite reaches the perigee, its velocity is increased in the cross-radial direction. According to all the ...
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A silly coincidence: $\frac{c}{\rm year}\approx 9.81 {\rm m/s^2}$ [closed]

Long ago, I sat and wondered about the equivalence of the gravitational pull on my body and upward acceleration. If I am not wrong, there is no way to distinguish between sitting on my chair here on ...
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Conceptual Question: What would happen to satellites orbiting the earth if mass of earth suddenly increases? [closed]

Would the satellite crash onto the earth? If so, why, and in what kind of motion? A spiral motion sounds intuitive, but why? Or there is another possibility: will the satellite continue to execute ...
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There is a way of making a Balloon lighter than Helium/Hydrogen (or vacuum)? [duplicate]

I don't know much about physics, but I wonder if there is a way of making something like a Balloon to float more than Hydrogen, Helium or Balloon with Vacuum. I say "Vacuum Balloon" because, ...
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What evidence suggests that light exerts a force of gravitational attraction? [duplicate]

I'm aware of other posts outlining the theory of how light generates a force of gravitational attraction, cf. e.g. this Phys.SE post. I'm not so interested in this. I'm interested in what evidence ...
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Is the non-technical definition of weight same as mass or is it also affected by gravity?

Technically, weight is the force which an object applies in downward direction, with Newton as its SI unit. However in non-technical usage, weight is a measure of heaviness or lightness of an object, ...
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Is decrease in gravitational entropy made up for by gravitational waves?

If we look at objects in the universe, they form orderly structures like spheres, planetary systems, galactic spirals, etc. Is this decrease in entropy balanced by a decrease due to gravitational ...
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Does General Relativity provide a value for $G$? [duplicate]

It only recently was specifically pointed out to me that Einstein was right, and Newton was wrong. Newton wasn't wholly wrong. He theorized that gravity was a force that acted between bodies, and came ...
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Could we move a spaceship by moving a Black Hole?

What if a spacecraft were dragged by a black hole, and the black hole were pushed by continuously firing lasers into it? Would this allow the ship to be accelerated faster than laser propulsion, which ...
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Necessarily of gravitons in gravitational thought experiment

The following is strictly a thought experiment, so please forgive the implausability of the scenario. I've read that if an object in space is moving in a relatively straight line, it will begin to ...
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Inertia of an elevator

Imagine a situation where we have a relatively light empty elevator moving up at a pretty high constant velocity say something above $10\ m/s$, just so that it has a considerable amount of momentum ...
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How is time dilated in a gravitational field?

I picture a box that contains a particle that travels back and forth at the speed of light. One round trip is a unit of time. We place this box on the surface of a large planet. The particles run ...
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Hawking Temperature for a Given Metric

I want to calculate the Hawking temperature of the metric $$\mathrm ds^{2}=-\left(1-\frac{r^{2}}{l^{2}}\right)\mathrm dt^{2}\ +\frac{\mathrm dr^{2}}{\left(1-\frac{r^{2}}{l^{2}}\right)}+\ r^{2}\mathrm ...
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Why does the aglet of laces in my jacket hood swing like a pendulum when I walk?

I have observed that the aglet in the laces of my jacket hood swing like a pendulum when I walk. I cannot think of any forces which are the cause of its movement in this way. So why is it like this.
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Outlandish theory; could gravity just be time drag? [closed]

Summary: Instead of large bodies of mass creating gravity, what if the resulting disparity in time dilation creates a time drag and it’s that drag that creates the inward pulling force, not gravity. ...
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Acceleration of the Moon due to the Earth's gravitational pull [closed]

If the Moon has an acceleration of 0.0027 m/s^2 with respect to the earth when in orbit, and it is stopped for an instant and then released, will the acceleration towards the earth now be different? ...
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Replacing $U(1)$ covariant derivative with $GL(4,\mathbb{R})$ covariant derivative... does it give quantum gravity?

I realize that many questions about deriving quantum gravity have been asked multiple times before on this forum, but it hasn't been asked exactly like I am doing here. I would like to know what ...
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What is the physical interpretation of negative Unruh temperature?

Actually the Unruh temperature is vectorial since it is proportional to acceleration but derived for only one space dimension so at least positive and negative. What can negative Unruh temperature ...
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What would the Newtonian-esque approximation for gravity be in other numbers of dimensions, according to relativity?

In 3 dimensions, gravity can usually be approximated using Newton's equation for gravity, $g=G\frac{m}{r^2}$. There have been answers here saying the acceleration of gravity in $n$ dimensions would be,...
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Why would spacetime curvature cause gravity given that the value of gravitational time dilation is so small?

In this question, mpv provides the clearest explanation of the operation of gravity in his answer: The apple moving first only in the time direction (i.e. at rest in space) starts accelerating in ...
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Does an accelerated frame of reference have the same effect as that of mass in space time

According to the equivalence principle, gravity and inertial forces are similar. And according to general Relativity, If there’s a large object in space-time, it warps the space time’s geometry and ...
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When the Earth suddenly stops pulling [closed]

Let's say the Earth stops attracting objects to itself all of a sudden. So, I was wondering what would happen to a person standing on the surface of the Earth? (Neglect the effect of the rotation of ...
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Center of gravity if $g$ varies for discrete particles (2D)

I understand that $$x_{cog}=\frac{\sum{}^{}x_{i}m_{i}g_{i}}{\sum{}^{}m_{i}g_{i}}$$ but why does that holds for $y_{cog}$ $$y_{cog}=\frac{\sum{}^{}y_{i}m_{i}g_{i}}{\sum{}^{}m_{i}g_{i}}$$ if given $g$ ...
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Does a uniform gravitational field exist? Is there any acceleration in a uniform gravity field?

This question arose in the Space Exploration forum, by non-physicists, so it likely sounds naïve. The question involved the plausibility of using a very strong gravitational field to accelerate an ...
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Stephen Wolfram Computational Model and the hypergraphs structure

I just discovered Stephen Wolfram`s project and model and I am fascinated especially since i had a similar ideea a few years ago without ever reading about it. I have a question regarding the ...
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Could quantum gravity be explained via the use of a "gravitational charge"?

Could gravity be explained as the existence of a "gravitational charge", acting similarly to an electromagnetic charge but where like charges attract and opposite charges repel? A graviton ...
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How does gravitational time dilation affect matter?

Einstein successfully melded together space and time into one entity called spacetime in his General relativity theory and gave us further insight into how matter affects spacetime. John Wheeler said “...
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Acceptability of Linearized General Relativity with Exact Linear Metrics

Linearized general relativity is typically employed when gravity is weak, and the metric can be approximated as a perturbation of a (usually flat) background metric. However, for some classes of ...
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Doubt regarding Space-time Grids [duplicate]

I had a doubt regarding space-time grids... I just don't understand, if the universe is three-dimensional (excluding the time dimension) why do we represent the universe as a single 2D fabric of grids ...
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Did gravity exist before the Big Bang?

Gravity is one of the biggest mysteries. It is the weakest of the 4 fundamental forces but we have no clue how it works. Einstein never was able to figure it out in his lifetime. There is evidence ...
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How would water pool on a disc-shaped planet of Earth mass?

All this flat-earthism stuff is best ignored (although that is sometimes difficult) but it did get me wondering about the physics behind the pooling of water on a disc-shaped planet. Not for the sake ...

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