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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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Doesn't gravity collapse superposition?

Correct me if I'm wrong, but if you have a proton that is in superposition, you don't know where exactly it is; it is everywhere but with different probability. Couldn't you measure the gravity field ...
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Can a system be engineered to cause a standing wave resonance with gravity waves

Can a system be engineered to cause a standing wave resonance with gravity waves? It appears that gravity waves can be reflected. Do Mirrors for Gravitational Waves Exist? Stephen J. Minter, Kirk ...
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In the Schwarzschild Metric does $\sin^2\theta{\Delta}\phi^2={\Delta}\phi^2\sin^2\theta$?

In the Schwarzschild Metric as the spacetime interval between two points in spacetime approaches $0$ for any ratio between the length of time and space the spacetime interval between the points in ...
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Difference between coordinate systame and frame of reference in relativity

I have taken a relativity course, and am not quite clear as to whether the notion of a frame of referene is independent of the coordinate system. At the moment, I think that any frame of reference (of ...
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Forces on a railway track with curvature and cant (inclined plane)

I'm trying to work out the forces acting on the left and the right rail if the track has curvature and cant (i.e. is an inclined plane) I've come this far as you see in the picture but I'm struggling ...
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What's the spin rate of an “earth ball”, as far from the sun as it is? [on hold]

I'm a EE (Electrical Engineer), and it's a while since I've had done any mechanics from my years of schooling, also a minor in mechanical engineering, but not using it "on the job." Last night, I had ...
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Science Fiction Question [on hold]

I have been reading some scifi articles where 100 kg weight is surrounded by an "antigravity" shield and accelerated to the speed of light. If the shield was suddenly removed once it was at C, what ...
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Gravitational effects of a single human body on the motion of planets

(This is going to be a strange question.) How big a difference does the existence (or positioning) of a single human body make on the motion of planets in our solar system, millions of years in the ...
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Converting from trace reversed to standard metric perturbation

In linearised gravity, when dealing with gravitational waves it is common to consider just the spatial part of the trace-reversed metric perturbation $\bar{h}_{ij}$. I know that in general the trace-...
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Energy-momentum for gravity [duplicate]

My question is as follows: Why is it problematic to define energy-momentum tensor for the gravitational field? P.S. It is well-known that in GR we get the energy-momentum tensor of "matter" by ...
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Can mass be ejected from a black hole within the Schwarzschild radius?

This goes far beyond my limited knowledge regarding the physics of black holes, but my colleague told me this today: I doubt that if I stand on the surface of a black hole - inside the ...
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Is gravity linked with another force?

Electricity and magnetism are linked. As are space and time. Is gravity linked to anything so far as we know?
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What if interactions such as gravity faded with respect to the cube of distance, rather than square? [duplicate]

It's generally understood that anything that "spreads out" in 3D space dissipates at a rate proportional to the square of distance. Light, sound, gravitational force, etc. I know this is a pretty ...
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Is the gravitational waves velocity also $c$, regardless the adopted inertial frame, and the source movement conditions? [duplicate]

The second postulate of STR was made exclusively for light (electromagnetic waves)? If gravitational waves also travel at velocity $c$, then are they obliged to fulfill this second postulate? Any ...
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Writing the curvature tensor in terms of spin connection

I am trying to know what are the missing steps in deriving the following expression for the Riemann curvature tensor in terms of the spin connection $\omega$ and the triad $e_\mu^j$. Where the ...
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Does the density of an object play a role for it's gravitational effects?

My thought experiment: We repalce our sun with an object of identical mass, rotation, shape, etc. but not the same density, i.e. the object would have a radius of 100km. The "replacement-time" would ...
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Will we be able to experience huge waves one after the other if we were near a strong gravitational field?

I was wondering if we will have huge waves due to the presence of a strong gravitational field nearby earth? If our planet is rotating around the gravitational field, is there a possibility for ...
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Would a puddle of spill milk on the elevator floor float when I cut the cable?

Imagine I pour some milk inside the elevator and then I cut the cable to allow the elevator to free fall, does it immediately float or only when the elevator speed has reached 9.81m/s/s? Oh and assume ...
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Direction of gravitational field given equipotential lines

I've attached the question as an image below as it's a graphical question. It simply states: "The diagram shows equipotential lines near a group of asteroids. Which arrow shows the direction of the ...
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Why do photons get sucked into black holes? [duplicate]

As far as I am concerned photons don't have a mass so how it gets sucked into black holes or is it because of black holes huge mass bends time can some one explain why and what forces or what ever ...
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Gravitation in relativity vs classical physics and the 1919 eclipse experiment

I am trying to understand the issue of light bending in relativity vs classical physics. I will clearly describe my understanding/assumptions in case I am wrong on those. In relativity, unlike ...
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Is a body in passing gravitational wave still in free fall?

I have a simple apparatus: a box and inside it a test particle (small bullet). If the device is in inertial motion or affected only but (static) gravitational field of another massive body (in free ...
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Correction to Newton's law of Gravity for dark energy

Is there any correction to Newtons law of Gravity that takes into account the expansion of the universe?
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Does kinetic energy warp spacetime?

My interpretation of GR leads me to think that energy (namely kinetic) also adds to the curvature of space-time. Which, has raised a thought experiment. If a $10000$ kg ship closely passed a $1$ kg ...
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Does gravity follow law of conservation of energy? [duplicate]

Law of conservation of energy states that energy cant be created nor destroyed.I dont understand how it is applicable for a object moving under influence of gravity.If some force has been applied on ...
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Black hole gravity and light [duplicate]

When an object is squeezed to it’s swartzschild radius it becomes a black hole (made by density) and it’s mass does not change (it’s gravity doesn’t change), but if it’s mass doesn’t change (it’s ...
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Modeling the distance between two point masses in space with gravity as a function of time

Assume that there exist two point masses in space, an isolated system with only gravity acting. I wish to find the distance between the masses as a function of time. I have arrived at the result of $$...
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If gravity turns out to be mediated by exchange particles, would that imply a problem with gravitational fields around a black hole?

In general relativity, gravity is a distortion of spacetime due to mass. Its effects travel (if that's the right word) at the speed of light. In the SM all 3 other known interactions are mediated by ...
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Is there a temporal difference between planets due to the sun's gravitational field?

since the Sun generates a gravitational field it also generates gravitational time dilatation. Hence, time further from the Sun should pass quicker than in its proximity. Can we, therefore, say that ...
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Does liquid have normal velocity when it moves on Inclined plane?

After the ball moves horizontally to Inclined plane, because the direction of motion is not parallel to Inclined plane, the ball will have normal velocity (perpendicular to Inclined plane); after the ...
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Gravitational redshift and mass decrease

If there are two distant gravitationally unbound galaxies and the observer galaxy loses its mass twice faster than the distant galaxy. So gravitational blueshift decreases in the observer galaxy. ...
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Answering simple questions about black holes to someone not knowing GR

In the Newtonian description of a black hole, it is a gravitating astrophysical object for which the escape velocity exceeds the speed of light in vacuum ($c$). But what does this actually mean for a ...
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What would happen to our universe if an object of infinite mass suddenly appeared? [closed]

The scenario is this: randomly, an object of infinite mass but of a limited size appears in our universe. What would happen to the rest of the universe? My intuition is that everything else in the ...
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Can gravity be quantized in a way that doesn't require a particle? [duplicate]

I understand what gravitons are and why they are theorized to exist, but is there any way to quantize gravity without a boson? In other words, possibly geometrically with no particle at all? For ...
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No hair theorem and Killing tensors

I have 2 questions regarding Killing Tensors : A practical question is how to guess whether a spacetime has Killing tensors or not. We can guess some simple Killing vectors by looking at the ...
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Killing tensor and Conserved quantities

The definition of the killing tensor is written above, as taken from Wikipedia. My question here is two-fold: Can all Killing tensors be build from the Killing vectors of that spacetime? Do Killing ...
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What happens if you dump antimatter into a black hole? [duplicate]

Let's say you have a 10 solar mass BH and dump 10 solar masses of antimatter into the BH... What would happen? Would I have a 20 solar mass BH? Would the BH explode Do we even understand what would ...
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Strength of tides induced by the Earth on the Moon to Moon on the Earth calculation [closed]

In my astrophysics problem sheet I have to compare the strength of tides induced by the Earth on the Moon to that induced by the Moon on the Earth. This is my attempt: $$F_\text{grav}=\frac{GM_\text{...
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Could there be observable gravitational warnings of an approaching vacuum decay bubble?

I understand both gravitational waves and a hypothetic vacuum decay bubble travel with the speed of light. Does this mean there won't ever be any observable warnings of vacuum decay before an ...
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A limit to absorption by black holes?

We know that a black hole draws everything nearby into it but is there a limit to which black holes can consume matter into it?
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Do tears come out of eyes in a region with no gravity?

If a human start crying in a zero gravity region, will the tears come out from eyes or not?
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Can we shield against gravity by surrounding ourselves with a sphere of black holes?

The common idea is that gravity can't be shielded against. I highly doubt that. Let us create a sphere: $$s: r^2 = x^2+y^2+z^2$$ which is centred on a point $M$. Now we start putting tiny black ...
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How to calculate the stress energy tensor of a particle of rest mass m?

I was trying to calculate the stress energy tensor of a point particle of rest mass m whose world line is given by $w^\mu(\tau)$ where $\tau$ is proper time. But I am not getting the correct answer. ...
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3answers
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Why do people suspect antimatter falls upward? [duplicate]

Antimatter is similar to ordinary matter except they have the opposite charge, i like to know why this difference in their spin would affect their motion in the curvature of our 4-dimensional ...
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Gravitational field at point just outside the sphere using integration

consider a point P at a distance k*R from a hollow sphere The Gravitational field at point P can obtained by the summation of gravitational fields due to small rings which make up the ring. the ...
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What would happen to the water bodies if gravity ceased to exist on Earth?

If water stopped flowing (it would stop flowing downwards from mountains and all) then, would it start rising upwards? If it floats on the space ( I say space because there'd not be any atmosphere) ...
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Is there a limitation on the values ​that Einstein tensor $G_{\mu\nu}$ can take?

Is there a limitation on the values ​​that Einstein tensor $G_{\mu\nu}$ can take? For example: Is it always bigger than zero? What is the highest amount that can be taken by it? What is the ...
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How spacetime distortion can ever be noticed from inside spacetime itself?

this is a naive question from a non-physicist. It is my understanding that gravitational waves are a deformation of spacetime. However, those are noticeable through, for example, laser interferometry. ...
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What happens to the heavy elements when a gas giant with no core or one with metallic hydrogen is formed?

I have been trying to visualize how a gas giant like Jupiter originally formed. I am assuming that in its early stages it formed by aggregation similar to how the rocky inner planets were with an ...
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Which place in the universe that does not have force at all

Does a place without force exsist, if it so where or how could it be. I mean if we include Gravity and friction as our force in universe.