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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Space time expansion near galaxies

I understand that on galactic scales, the expansion of space time has no appreciable effect, gravity being dominant and thus distance between stars remains fixed despite universal expansion. Can ...
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56 views

Gravitational Lensing Diffrence between Big and Small Black Holes

Would you see more of the back holes iris in smaller black holes compared to larger ones and if so can one be big enough the photon sphere would completely cover it and it would look like distorted ...
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25 views

Why does individual N2 molecule rise when heated?

I get that hot air is less dense so it rises due to floatation and all, but what happens to one individual diatomic Nitrogen that it increases it's distance from ground? And why is it that the air is ...
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21 views

Calculating satellites orbits [duplicate]

Do Newton's and Einstein's theory of Gravity differ very much when calculating satellites orbits. If they don't, in what areas do they actually differ?
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1answer
103 views

Gravitation - Is going beyond a model possible? [closed]

I can not really understand why two bodies attract each other, what happens between? One points out the gravitational field to explain this phenomenon and one say that it is because of the general ...
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2answers
48 views

Are parts of objects part of that object's mass?

Disclosure: I'm not a physicist or a scientist, so there is a chance that this will seem like a silly question for some of you. But I'm really curious about this and I want to know the answer. ...
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35 views

How exactly are the relative strengths of gravity and electromagnetism quantified? [duplicate]

I've often heard it said that gravity is much weaker than electromagnetism, and after looking at several questions on SE, I feel that I've got at least a qualitative handle on the concept -- gravity ...
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1answer
34 views

Can the helium from a gas bottle lift the bottle?

Does a gas bottle full of helium contain so much helium that, if the helium can expand into a baloon, can lift the empty gas bottle? And input on this question highly appreciated...
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46 views

Acceleration in a space capsule which is falling to the earth [closed]

At first I apologize for asking such a career killing question in such an elite platform. Today I tried to prove something to four graduated engineers which I will mention below. The argument ...
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3answers
206 views

Time Dilation Equals Red Shift looking in or blue shift looking out

We can see the center of our galaxy. With more density near the center of our galaxy is red shifting observed from our perspective? From the center of the galaxy looking at us would a blue shift be ...
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1answer
39 views

What is the property which flows as described by the stress energy tensor in GR?

I found the following definitions: The stress–energy tensor (sometimes stress–energy–momentum tensor or energy–momentum tensor) is a tensor quantity in physics that describes the density and flux of ...
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2answers
91 views

How is it possible that Thermosphere can maintain so much heat? [closed]

Thermosphere is the Layer of Atmosphere in approx 100-1000 km altitude. Particles in thermosphere are typically at 1400 K temperature. But the sun activity can raise the temperature up to 2300 K. ...
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34 views

Gravitons, photons and conservation of momentum

How can gravitons be emitted from a mass to cause an attractive force to another mass? The same question could be asked of attractive e-m forces as well. Don't these violate the conservation of ...
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2answers
100 views

If gravity dropped off with the cube of distance

If gravity, for instance, dropped off with the cube instead of the square of distance from the Sun, would the planets still follow elliptical paths?
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3answers
97 views

How does a mass create the gravitational field of GR? [closed]

As far as I understand, and please correct me if I am wrong, but the basic idea of general relativity is that spacetime is curved by matter. What we call gravity is then not a force as per Newton but ...
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52 views

Where does gravity get's its energy from? [duplicate]

So I have read this post and I have another question about it. The first answer says that if we lift an object up that is the energy we "give" to gravity and then gravity uses that energy to pull the ...
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2answers
84 views

When sitting on a chair is it the chair actually pushing against me?

I was listening to The Infinite Monkey Cage on the BBC and they were talking about general relativity and gravity. They were saying that gravity is not a force as Newtonian laws describe and is at ...
5
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1answer
167 views

What is gravitational energy in general relativity?

In GR the curvature of spacetime "is gravity". This curvature is expressed via the Riemann tensor (or the Ricci tensor + Ricci scalar). The curvature is connected via the Einstein Field Equations with ...
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1answer
45 views

Why do the satellites revolves on a circular path around a planet at orbital velocity? [duplicate]

We know that there is a particular velocity with which a satellite will move in a circular orbit ( orbital velocity ) but if its velocity is more than the orbital velocity but less than the escape ...
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1answer
30 views

Gasses and Gravity

I have two questions. First question. When gas is placed inside a container it fills the container evenly with constant pressure. If the container size varies the gas expands or is compressed but the ...
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1answer
49 views

Effects of gravity on light on the surface of the Earth [closed]

I read over the question and answers on the effects of gravity on light. I would like to ask a more specific question about gravity and light. What is the effect of gravity on light on the surface ...
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176 views

Why does electromagnetism have torsion, whereas gravity does not?

Why don't we use torsion-free covariant derivatives for QM, even though we already do so in the case of GR? In general relativity, we use the Levi-civita connection, a torsion-free connection ...
2
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2answers
75 views

Gravity spacetime visualization [duplicate]

When gravity spacetime is visualized, it's a sag with the lowest point in the middle of the planet/star as you can see here: For all planets and stars, there is zero G in the core due to that the ...
3
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1answer
40 views

Detection limits on 'd' if gravity force was proportional to $1 / (R+d)^2$

Assume the force of gravity is proportional to $1/(R+d)^2$ where $d$ is sufficiently small, then, how small would $d$ have to be to evade detection by modern experiments? My thinking is that if $d$ ...
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2answers
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Gravitational lensing and perspective

When looking at a black hole the ability to see ourselves is compromised by the small window for the light trajectory to come back to us. The light from the Earth that is bent by (almost) 180° and ...
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1answer
107 views

does my gravity theory sound logical? [closed]

hypothesis: space has the four forces built into it like a density that allows for the atoms and the EMR to move within confined limits i.e. the speed of light, fusion, etc.. Each change in dimension ...
5
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1answer
107 views

Simple metric of stellar collapse

Is there a simple metric (Lorentzian manifold) known which exhibits the formation of a black hole while not having any white hole counterpart and which moreover satisfies the strong and dominant ...
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16 views

if a meteorite is moving in space fast enough to generate a lot of mass shouldn't it generate gravity because its moving? [duplicate]

is it how planets form when is happens to have alot of mass to generate a little bit of gravity, oh and bullets for example they generate mass when moving and causes it generate mass?
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24 views

Atmospheric pressure

Whats the significanc of Atmospheric pressure being refereed as 100kPa ? Does that really mean 10000 kg/m2 acting upon us ? If we are measuring only collision force on the surface and not the weight ...
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3answers
91 views

If photon can bend spacetime how does it exchange graviton?

Say two photons moving beside each other through space at speed of light, since it carries energy it can bend spacetime. So both photons will exert gravitational force on each other at speed of light ...
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2answers
100 views

Why can't gravitational force have repulsive counter part?

The valleys in the space-time curvature signifies the existence of an attractive body which causes the curvature. So why can't we say that the hills in the fabric of space-time is a source of ...
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4answers
217 views

Can there be acceleration without velocity?

If I was in a spaceship continually accelerating at $9.81m/s^2 =1g$ in a straight line, I would reach near light speed within a year. On Earth, we are in a gravitational field of $1g$, which ...
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3answers
384 views

Zero $g$ in a black hole?

At the very centre of the Earth, masses cancel each other out, creating an effective zero-$g$ environment. Would the same happen in a black hole?
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1answer
50 views

3D donuts and the centre of a black hole [closed]

I have been trying to imagine ways to visualise the gravitational field of the earth... It's near zero at the outer edges of the atmosphere, strong at sea level, strongest at the quarter point, then ...
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2answers
51 views

Time dilation and freefall (follow up and simplification) [closed]

A person is four miles up in the atmosphere, and freefalls towards earth. Another person is standing on earth, watching them come down. During this period of freefall, which person experiences more ...
3
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1answer
61 views

When is a circle not a circle?

Imagine a 2D uniform circular motion of constant magnitude but changing direction in an area of zero g. The forces will be equal all the way round - it will be a perfect circle. Now imagine the same ...
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43 views

How can escape velocity be independent of the direction of projection of a body?

I read that the escape velocity of a body is independent of the direction of projection. For example, I could throw a ball at $11.2$ km/s velocity horizontally, and it would still leave earth. I am ...
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0answers
16 views

Observed gravity of a fast moving particle relative to observer [duplicate]

Special relativity tells us that a fast-moving object with sufficient speed will appear more massive that it would at rest relative to an observer. Since the strength of an object's gravitational ...
2
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0answers
51 views

Are gravitational waves constrained by special relativity (speed of light)? [duplicate]

In Lawrence Krauss's excellent book "Universe from Nothing" and his related lectures, he cites findings of the BOOMERANG-instrument observations in Anarctica as used to measure the diameter of ...
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38 views

How does gravity affect entanglement?

Hypothetically an entangled pair of atoms are placed inside two similar satellites orbiting at the same altitude, one of the satellite will then slow its speed and descend towards the surface of ...
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52 views

What sorts of problems does asymptotically safe gravity face as a potential quantum gravity solution?

I've recently read an article by Ethan Siegel over at Forbes (he also blogs at Starts with a Bang) on asymptotically safe gravity as a possible alternative to string theory. I read the author's blog ...
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1answer
46 views

Do zero gravitational-force points produce Naked singularities?

In between two singularities, does a particle experience gravity? If a particle is exactly at the midpoint between two singularities, will its net experience of the gravitational force (ignoring the ...
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66 views

How does bending in space-time caused by mass energy translate into acceleration of object? [duplicate]

Let say we have 2 similar apples separated by a distance apart, just their mass energy alone is sufficient to cause bending in the space-time. I think it is this bending in the space-time that cause ...
4
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40 views

Theoretical limit to gravity detection?

Is there a calculable limit to how sensitive a gravity detector can be (in principle) imposed by the Heisenberg uncertainty principal? To detect gravity something has to move or experience some ...
4
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3answers
74 views

Can gravitational effects create a plane of the ecliptic?

Lots of questions about the why of the plane of the ecliptic, and good answers, but I was wondering about gravitational effects. If we picture for example, Saturn as being a few degrees above the ...
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19 views

how much helium would you need to pick up one kilogram on mars [duplicate]

how much helium would you need to pick up one kilogram on mars? is there an equaison that can be used? thnx alot!
3
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94 views

Dark matter “hair” flowing through the earth

Gary Prézeau of NASA's JPL has done some calculations of how dark matter might be focussed by the Earth's gravitational field (publication preprint), and the results show some remarkable hairy ...
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24 views

Are there any like masses that repel each other analogous to like charges in electromagnetism?

Just thought why the fundamental property of electromagnetism, electric charge, comes in two flavors i.e. positive and negative causing the electric force to be either attractive or repulsive while in ...
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1answer
81 views

Why doesn't gravity have charges?

All other forces have some kind of charge system, electromagnetism has positive and negative, weak force has hypercharges, and strong force has colors. Why doesn't gravity have anything like these?
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1answer
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A question about gravity [duplicate]

Some time ago I encouraged by 11 year old son to watch Cosmos: A Spacetime Odyssey with Neil DeGrasse Tyson, and subsequently Cosmos: A personal Voyage with Carl Sagan, as well as other astronomy ...