Questions tagged [equivalence-principle]

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Graviton detector thought experiment

I was recently thinking of a thought experiment: Assumptions Graviton detectors can exist The equivalence principle will hold in the final theory of quantum gravity We can accelerate the graviton ...
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448 views

Auto-parallel Transport or Principle of Extremum Action?

In an affinely connected spacetime with a metric compatible connection, the equation of the curve in which the tangent vector at each point is the result of the parallel transport of every tangent ...
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1answer
96 views

What mathematical constraints does the equivalence principle impose on GR

I'm trying to determine exactly how the equivalence principle affects GR mathematically (rather than conceptually). I found this StackExchange post which more or less says that the equivalence ...
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150 views

Is the equivalence principle Machian?

There is a lot of discussion on the subject of Mach's principle, and whether it has any place in the theory of relativity. But it seems to me that one could argue that Mach's principle is at the heart ...
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370 views

Different versions of Einstein's equivalence principle

As I understand it, there are two versions of Einstein's equivalence principle. The first states that "Locally, a frame in free-fall in a gravitational field is equivalent to an inertial frame in ...
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86 views

Does relativistic glider violate principle of equivalence?

The relativistic glider proposed can slow down the fall of an object in gravitational field. Will this violate the principle of equivalence which says that one cannot distinguish between free falling ...
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199 views

Is the equivalence principle in General Relativity an approximation?

I read in web that Einstein used the principle of equivalence to explain General Relativity but we know the gravitation is approximately equal in all of rested frame in gravitional field. In contrary,...
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1answer
50 views

Is Einstein Equivalence principle a consequence of weak equivalence principle + covariance principle?

I have been doing some thinking about the Einstein Equivalence Principle (EEP) and its formulation, namely: The outcome of any local non-gravitational experiment in a freely falling laboratory ...
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80 views

Equivalence principle: electric charge and coil

The near-range magnetic field $\vec{B}$ of a point charge $q$ at distance $\vec{r}$, moving at a non-relativistic velocity $\vec{v}$, is given by $$\vec{B}=\frac{q}{4\pi\epsilon_0c^2}\frac{\vec{v}\...
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1answer
181 views

How does the Equivalence Principle imply that derivatives of the metric vanish in a freely falling frame?

Why do the first derivatives of $g_{\mu\nu}$ vanish in a freely falling coordinate system? I would like to start from the Equivalence Principle that for any point in spacetime there exists a locally ...
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2answers
168 views

Einstein's Principle of Equivalence - Infinite Acceleration/Energy?

Hello and thank you for your time. I've been wondering about Einstein's Equivalence Principle core idea. That is, from experiment alone, one cannot differentiate between a gravitational field and a ...
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144 views

What is the inertial mass of a black hole?

Or the inertial mass of any spherically symmetric object, can I calculated by measuring very accurately the spacetime distortion this object produces in its surroundings? With 'inertial mass' I mean ...
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122 views

Is there a theory that physically explains the origin equivalence principle / explains gravity via acceleration?

I've been thinking about how gravity could arise from a 4th dimensional spinning cylinder with space-time that has pliability like rubber (which I think is a generally accepted analogy). The ...
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825 views

Free fall coordinates/Fermi (normal) coordinates

It makes sense intuitively given the equivalent principle, and I've seen many times it stated, that for a free fall (geodesic) path in an arbitrary spacetime, we can choose our coordinate system to ...
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805 views

How does one refute a Machian mechanism for inertial emergence?

Introduction: Consider the diagrams representing the duality between the weak and strong principles of equivalence. Now based on how these diagrams were taught to us (at least how they were taught ...
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1answer
110 views

How does the equivalence principle imply that the laws of physics are frame-independent?

Many texts on GR, after introducing the equivalence principle as the equivalence of inertial and gravitational mass, or the equivalence of gravity and acceleration relative to a local inertial frame ...
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1answer
386 views

Why dynamic Casimir effect does not appear in static gravity field?

Dynamic Casimir effect tells us that a constantly-accelerated mirror should emit radiation due to interaction with vacuum. Following principle of equivalence, a similar mirror placed in static ...
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21 views

Equivalence principle and uniqueness theorem

We work with Maxwell's equations in the frequency domain. Let's consider a bounded open domain $ V $ with boundary $ \partial V $. The equivalence theorem tells me that if the field sources in $ V $ ...
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1answer
25 views

In terms of being on an elevator, velocity, acceleration and forces, how are they related?

Before you answer, read this: Say you are on an elevator, and for some reason, when in it and you jump, you have a different velocity from the elevator, say the elevator is at 15 MPH and you are ...
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1answer
58 views

General relativity and absolute rotation

Are both centrifugal force and Coriolis force really fully explained by what is called "frame dragging" in GR? And if that is correct, does this concept "frame dragging" solve the ...
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21 views

Frequency increase due to equivalence principle vs gravitational attraction

In Volume II Chapter 42 (on General Relativity), Feynman uses the equivalence principle to show that clocks etc. higher in a gravitational field run faster, and as a result emit photons with higher ...
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78 views

Effective potential in static spherically symmetric spacetime and equivalence principle

In a static and spherically symmetric space-time, using the standard coordinates $\{t,r,\theta,\phi\}$ the geodesic equations imply that $$ g_{rr}\biggl(\frac{dr}{d\tau}\biggr)^2+\frac{J^2}{r^2}-\frac{...
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1answer
64 views

Falling EM system contradicts equivalence principle?

The following is an improved version of my previous post Falling electric dipole contradicts equivalence principle? Consider the following system comprising a particle on the left with charge $+q$ ...
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39 views

Einstein's equivalence principle applied to a constant accelerated system comprising two mirrors

Let us consider a system comprising two mirrors with an observer placed in between. The distance from the observer to each of the mirrors is $d$. At $t=0$ the observer emits a light signal in both ...
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1answer
41 views

Do gravitational mass equalling inertial mass when object is at rest just a coincidence?

Rest mass can be thought of as the measure of energy that object posses. This mass that appears in Newton law of motion measures inertia and hence called inertial mass. Gravitational mass is like ...
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82 views

Entanglement of Black Holes with the outside universe

Black holes are thermal objects which means the density matrix of the black hole is in a thermal state. This means that the black hole has to be maximally entangled with the rest of the universe to ...
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4answers
270 views

Acceleration in general relativity

Let's say that, from my point of view, another observer is accelerating. Now, from his point of view, he is standing still: all he feels is an overall fictitious force of gravity, which is just a ...
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32 views

Experimental evidences satisfying charged particle emits radiation in gravitational field

Is there any experimental evidence exist that a charged particle at rest in gravitational field emit radiation and charged particle in free fall don't emit radiation ( According to equivalence ...
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152 views

Is Thomas rotation compatible with equivalence principle?

I have designed a thought experiment for which I cannot find a clear solution: An infinitesimal laser gun and a point target both move with a velocity $v$ towards a deep rhomboidal hole dug in the ...
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1answer
136 views

Quick check: relativity, rockets, clocks and the equivalence principle

One common thought experiment that introduces relativity on gravitational fields is the "clocks on an accelerating rocket": Paraphrasing Mr. Feynman: Suppose a rocket, with two clocks, one on each ...
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147 views

Violation of the strong equivalence principle in scalar-tensor theories

As I understand it the strong equivalence principle is the statement that within a infinitesimal neighbourhood of any spacetime point all physical interactions (gravitational and non-gravitational) ...
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86 views

Naked Singularities Out of Extremal Black Holes?

Consider a pair of identical extremal black holes at rest. It is a fact that they exert no net force on each other and remain in static equilibrium. Now, clearly, each of the black holes is in ...
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108 views

Conservation of energy and momentum in SRT

I recently studied SRT and came across a strange thing which I don't really understand (it's from a book, but without the example): Let's consider two charged particles which repell each other such ...
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132 views

Rotating Particle - Violation of Einstein Equivalence Principle

How does adding rotation to a freely falling particle violate the Einstein equivalence principle? I realize there is a similar post here: An example of a theory that respects the Weak Equivalence ...
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159 views

Use of Principle of Equivalence

Let $x^\mu$ be the coordinates of a reference frame, $K$, where all bodies feel the same constant and uniform acceleration $\textbf{a}=\textbf{g}=-\nabla\varphi$; let $\xi^\mu$ be the coordinates of a ...
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1answer
191 views

Does curved spacetime arise from inhomogeneity of gravitational field?

In general relativity textbooks such as Sean Carroll's Spacetime and Geometry, there is often a line of reasoning that goes like this: Strong equivalence principle states that free falling frames are ...
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1answer
241 views

Equivalence principle for test fields

My question is very simple. We all know that, for a test particle(classical) in a gravitational field, the motion is only determined by the geodesic lines(let's forget about the initial conditions for ...
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2answers
175 views

Equivalence Principle holding in Special Relativity? (let alone QFT)

Motivation I am pretty confused of why people are hopeful to find a version of the equivalence principle ("the complete physical equivalence of a gravitational field and a corresponding acceleration ...
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26 views

Gravitational time dilation using accelerating light-clock

I've been trying to understand gravitational time dilation by considering a light-clock of length $l$ undergoing an equivalent acceleration $a$ from rest along the direction of the bouncing light ...
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69 views

Does the Lie derivative of a tensor satisfy the strong Einstein equivalence principle?

The Lie derivative of a tensor is a tensor of the same rank and type. But it is connection independent meaning it can be expressed in terms of covariant or partial derivatives. Since the Strong ...
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1answer
25 views

Screening tensor-scalar mechanics with equivalence principle

Modified gravity with scalar degrees of freedom generally requires some screening mechanism to pass solar system tests, and that generally breaks down the equivalence principle. Question: is there ...
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43 views

Does a vertical light beam violate Einstein's equivelance principle?

Imagine the classic Elevator thought experiement. Einstein said there's no physical experiement that shows the difference between gravity and upwards acceleration. What if we casted a light beam ...
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1answer
80 views

Does gravitational red shift test the equivalence principle or general relativity?

These comments seem to say gravitational redshift experiments would only verify theories that obey the equivalence principle (ep), not specifically general relativity: https://arxiv.org/abs/0806.0528 (...
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Can we apply the equivalence principle in electromagnetics to multiple regions simultaneously?

Note: I posted the same question on the electrical engineering stack exchange with no luck so far, possibly because it's quite theoretical, so I'm posting it here again. I'm not sure if it's ...
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1answer
33 views

Falling bodies in an accelerated elevator

If a sealed elevator were subjected to a massive acceleration in interstellar space and two weights were dropped from ceiling to floor, as far apart as possible on opposite sides of the elevator, ...
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1answer
81 views

Is it true that when you accelerate due to a non-gravitational interaction gravity is pulling you in the direction opposite to the acceleration?

We don't feel acceleration when we are only in a gravitational field due to equivalence principle as I understand it says gravity is simply inertia in spacetime. Is there any other type of force ...
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56 views

Equivalence Principle and Exapansion and Shear Tensor

I read in my class notes that the professor said using equivalence principle, it is always possible to choose around any point $p$, a 2-dimensional space-like neighborhood such that the expansion and ...
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89 views

Electron and gravity- equivalence principle

According to equivalence principle, we cannot distinguish gravity with inertial force. Let's assume that there is space shuttle which contain observer and electron. There is some force that is gravity ...
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129 views

No such thing as density in general relativity?

In this paper from Wang, 2016, it is stated (pg. 3) that a consequence of the equivalence principle is that there is no density for gravitation. Can anyone expand on why this should be so? In the ...
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1answer
161 views

Acceleration in Space

Lets assume a body with a certain mass is in a region of space that has zero $g$ (or pretty close to zero $g$). Would acceleration in a straight line produce $g$-forces? Would that mass acquire ...