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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60 views

Where are the L3, L4, and L5 points of a hyperbolic orbit?

Do the L3, L4, L5 points exist in hyperbolic orbits? If yes, then where do they lie?
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151 views

How could they be hit twice by debris?

In the movie Gravity the two astronauts (Bullock and Clooney) are hit twice by the fast moving debris that bring havoc to their locations. I think this is a bad scientific mistake in the movie plot. ...
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Is a “supercritical charge” in graphene similar to Hawking Radiation?

These papers describe a phenomenon referred to as "atomic collapse" and "supercritical charge" in graphene: Wang et al., Pereira et al. "Atomic collapse" appears when you have a large enough Coulomb ...
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87 views

The gravitational random walk

When we shoot a single photon out into space, the chance that it will eventually return to our vicinity from a different direction is vanishingly small, even though spatial curvature exists due to the ...
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89 views

When spacetime expands to the point where galaxy clusters are not observable, will there by any interaction?

It's my understanding that in a few billion years, clusters of galaxies won't be able to directly observe one another due to the expansion of spacetime overcoming gravity between those clusters. ...
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78 views

Dirichlet's work on gravity in non-Euclidean space?

In the book The Norton History of Astronomy and Cosmology by the late John North I have found the following statement (page 514): "The German mathematician Lejeune Dirichlet studied the law of ...
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402 views

include the stretch of the spring own weight in potential energy for spring pendulum?

we are given a problem with spring with its own mass $m$. I am confused how to set up the PE term in the Lagrangian. Assume the spring has length of $L_{0}$ when it is laying on a table horizontally. ...
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162 views

What results from particle collision would ensure the existence of the graviton?

I understand that particles are smashed together to try to enable us to detect some sort of graviton presence but we can't actually detect a graviton due to the fact that it 'exists' in some extra ...
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681 views

Why does a coin falls faster when it's flipping as well?

From my experiments with measuring how fast a coin falls, I have consistently measured a faster falling rate for a coin that flips as it falls. As an example, a coin dropping on its edge from height ...
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31 views

Centripetal force at the pole is different from the equator

why is the centripetal acceleration in the poles and equator if different? I know that it's related to Equatorial budge. But what I don't get it is that the centripetal force is zero at the poles. ...
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51 views

What happens when one uses a blender in zero gravity?

I was recently told by a friend that using a blender type apparatus in a zero gravity environment will act like a centrifuge instead mixing properly. Is this the case? Furthermore, can anyone provide ...
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34 views

Low kenitic Energy and High Kinetic Energy Atoms Attract

Will atoms of 2 difrent energy levels electron and/or Kinetic attract more than 2 Atoms at he same energy level? Do 2 high energy level atoms attract more than 2 low energy atoms?
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103 views

If gravity is due to curvature, how does gravity work in situations with no curvature?

The strength of the gravitational field falls off as the inverse square of the distance from a spherical source. It only falls off as the inverse of the distance from an extended cylindrical or line ...
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48 views

How gravitational waves are exactly produced?

I was thinking about gravitational waves, and I found out that I may have a doubt about their production. Assuming the whole calculations find a wave-like solution to be understood, I was wondering ...
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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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25 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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45 views

What would happen, gravitationally, to ships passing by each other at high speeds vs high accelerations?

Consider this scenario: Two identical space ships, the SS Observer and the SS Accelerator. In scenario A, the SS Accelerator is accelerated up to near C, stops accelerating, then flies past the SS ...
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34 views

Neck size of wormholes in shape dynamics

As far as a dilettante like me knows, in shape dynamics, black holes are really wormholes. What it the expected diameter of the necks of such wormholes (both for regular holes resulting from the ...
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37 views

Non-zero gravitational anomaly

Analogous to the Adler-Jackiw-Bell anomaly of QCD, we have an anomaly in gravity when we consider gravity to be coupled to chiral fermions: \begin{equation} \partial_\nu J^\nu_5\propto R\tilde{R}, ...
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38 views

Boundary condition for holographic Green's function

I understand that to obtain retarded Green's function using AdS/CFT one needs to put ingoing wave boundary condition at the horizon, when one is considering a finite temperature system. For system ...
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34 views

Thermal AdS3 in Chern Simons

I am currently working with (2+1) gravity in Chern-Simons formulation and I have a question about thermal AdS. The way I understand that one retrieves thermal AdS is by Wick rotation and ...
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44 views

Naked Singularity and AdS/CFT

I am a bit confused about the status of naked singularities that appear in black hole physics and more so in the context of AdS/CFT. Here is what I know about this in brief. For a charged ...
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68 views

Mass, density and gravity for 2D SPH

Having previously only worked with 3D sph, the 2d case is confusing me. The concept of mass and density as well as gravity is not easily converted, as I see it. As an example in 3D I take 1000 ...
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30 views

Fields with source property != influenced property?

As far as I know, a field (gravitational, electric, magnetic) is created by something (mass, charge, moving charge) and can exert a force on something (a mass, charge, moving charge). Is there a ...
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62 views

Does this phrase in “Knocking On Heaven's Door”, refer to gravitons?

This is an extract from Knocking On Heaven's Door, by Randall (2011) The suprising fact is that if you have a stable particle whose mass corresponds to the weak energy scale that the LHC will ...
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58 views

Gravity dual of N free scalars in 2D

I have a very basic (and might be very naive) question. What should be the dual gravity description of $N$ (with $N>>1$) free scalars in two dimensions? I was wondering whether it would be ...
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79 views

Any textbook about non-renormalizability of gravity?

I have learned general relativity in a graduate-level. My knowledge about QFT is very rudimentary. But, I need to learn about non-renormalizability of gravity. I have these questions. Is there any ...
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40 views

Quantum corrections to holographic entanglement entropy

I was looking at this paper by Faulkner-Lewkowycz-Maldacena. They give a very interesting proposal of calculating one loop (i.e, 1/N) correction to EE from computing the EE between the bulk regions. ...
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37 views

Would a very long massive rod exhibit a large deviation from Newtonian gravity (specifically a deficit angle rather than 1/r force)?

In General Relativity the metric corresponding to an infinitely long massive rod is flat but with a deficit angle. It exhibits a very large deviation from Newtonian gravity in all regions of space in ...
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88 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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54 views

the torsion balance of the Cavendish experiment

I need to perform the Cavendish experiment and build a torsion balance but I can't find metallic spheres with enought mass so I was thinking about using a pair of dumbbells instead. My question is if ...
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40 views

Measuring Hawking radiation after the coordinate transformation

If an observer can measure the Hawking radiation or surface gravity in his co-moving/rest frame, what happens when we make a coordinate transformation to a moving frame of reference? Can we make such ...
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141 views

Geodetic effect and Frame dragging

Two gyroscopes pointing perpendicular to each other were housed inside Gravity Probe B which performed polar orbit around Earth to test Einstein's theory of relativity. As the probe is orbiting ...
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28 views

Poincare patch of $AdS_2$

I know that a metric for global $AdS_{2}$ can be witten as $ds^2=\frac{1}{\cos^{2}\theta}\left(-dt^2+d\theta ^2\right)$, where $\theta \in [-\pi/2; \pi/2]$. So one can draw Penrose diagram for it as ...
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44 views

Principle behind Atom Interferometry?

In Laser Interferometry, you propagate a laser beam, split it into two different paths, reflect once, combine it back and deduce the phase difference accumulated from the path difference, from the ...
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57 views

Ricci tensor of Metric black holes with nils and solv geometries of Horizon

The metric of black holes with nils and solv geometries of the horizon is generically represented by $$\mathrm{d}s^2=-r^{2z}\mathrm{d}t^2+\frac{\mathrm{d}r^2}{r^2}+\sum_{I=1}^3 r^{2q_I}(w^I)^2$$ How ...
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69 views

Are there experimentally verified differences between general relativity and Lorentz invariant “newtonian” gravity?

I used to have (I lost it) a historical article about how Eintein's general relativity theory "won" over a Lorentz invariant generalization of Newton's gravity (I cannot remember the author). This is ...
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168 views

Marvin the Martian vs. the Death Star: how much energy will they actually need to disintegrate the Earth?

According to a detailed analysis by Dave Typinski, Marvin the Martian’s Illudium Q-36 Explosive Space Modulator will require $1.711 \cdot 10^{32}~\text{J}$ to shatter the Earth into a gravitationally ...
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55 views

Does graviton loops affect the seperately covariant conservation of energy momentum of two noninteracting sectors of matter

Consider the action $$\int \sqrt{-g}\left[R[g]+\mathcal{L}_{m1}(g,\psi_1)+\mathcal{L}_{m2}(g,\psi_2)\right]$$ Classically we have $$\nabla^\mu T^1{}_{\mu\nu}=0,\,\,\,\,\nabla^\mu T^2{}_{\mu\nu}=0$$ ...
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123 views

Relation between $f(R)$ gravity and Tensor–vector–scalar (TeVeS) gravity

We know that there is a relation between f(R) gravity and scalar-tensor gravity. By applying the Legendre-Weyl transform, we can receive brans-dicke gravity from $f(R)$ gravity. If we start with the ...
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103 views

Generalization of Feynman's derivation of the formula for gravitational potential energy in FLP volume I

In the Feynman Lectures on Physics, Feynman derives the formula for gravitational potential energy by applying a line of reasoning he borrowed from Carnot on reversible weight lifting machines (FLP I, ...
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115 views

Conditions for a diagonal induced metric?

Let $M$ be a manifold of dimension $n$ with a (say Lorentzian) metric $g$, that is diagonal in some choice of local coordinates. Let $S$ be manifold of dimension $k<n$ , embedded in $M$ by some ...
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73 views

Geometrised Units

I am curious as to how to express a area units in geometrised ones. I was reading on wikipedia and saw that when angular momentum is converted into geometrised units, it is expressed as a dimension of ...
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391 views

Gravitational potential energy and Center of Mass

I've been reading about the Nordtvedt effect, and how Gravitational Binding Energy (GBE) affects total mass. According to the WP article, experimental evidence rules out the existence of this effect. ...
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100 views

Trebuchet launch into space

I was reading some questions on your site about using a Trebuchet to launch a payload into space. Would it be possible to use the same sort of principle, but to have, say a 100 mile steel cable ...
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273 views

Is inertia actually a property of the force rather than the mass?

I ask this because it occurred to me that the inertial property of mass only actually arises in the context of forces (such as the EM force) as a resistance to their accelerating effect. Inertia plays ...
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129 views

Position vs Time Function for a Falling Object Without Assumption of Constant Acceleration

If you have an asteroid for example and a planet, isolated from all other gravitational influence and initially at rest with respect to each other, how would you find a position vs time function for ...
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43 views

About parametrizing quadratic fluctuations in the metric about $AdS_2 \times S^2$

I am referring to the contents of page 20-23 of the paper, http://arxiv.org/abs/1108.3842.pdf Equation 4.5 seems to suggest that one wants to restrict the metric fluctuations $h$ to a subset such ...
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22 views

Instabilities in the CDMT

Could anyone explain or refer to references on why the CDMT f(R) gravity model suffers from Instabilities any why the sign of ${\mu}^{4}$ matters.
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78 views

What if UV behaviour of gravity was perturbative?

I understand that the UV behaviour of gravity ought to be dominated by black hole production and that graviton-graviton scattering ought to blow up above the Planck scale. Suppose, however, that ...