Questions tagged [equivalence-principle]

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Motivation for curved spacetime on General Relativity

I'm trying to motivate the theory of general relativity. Concretely, using which arguments is it deduced that spacetime must have the structure of a curved Riemannian manifold? From the strong ...
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3answers
719 views

Why is gravity different from other forces?

Unlike other forces, the "amount of force" gravity applies to different bodies is different. for example, if your hand has the force of 10 N, it could have accelerated a body with the mass ...
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3answers
152 views

Are there 4D spacetime not described by GR? [closed]

I heard the EFE is specifically for 4 spacetime dimensions. Does it mean whenever there are 4 spacetime dimensions, there is automatically GR? In other words, are there 4D worlds or spacetime that ...
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0answers
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Is the accelerating field removed when using the GR equivalence principle?

Suppose I have a charged hollow sphere that is hyperbolically accelerated by a constant electric field E. The Equivalence Principle tells me that this is physically equivalent to placing the charged ...
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2answers
711 views

Can the equivalence principle be safely used in non-relativistic mechanics?

Imagine an ideal pendulum in a train. While the train is in uniform motion, Newton's laws apply within the train, and we can easily write down the equations of motion for the pendulum. Now assume the ...
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0answers
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Doubt in the Equivalence principle [duplicate]

In the equivalence principle, being in an accelerated reference frame is equal to being in a gravitational field. So,now I can consider earth as an accelerating reference frame. But, if that is true, ...
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1answer
51 views

The gravity-acceleration equivalence principle doesn't seem like exact equivalence. Is there something I'm missing?

Suppose I'm trapped in a box, and the box is $3\ \mathrm{m} \times 3\ \mathrm{m} \times 3\ \mathrm{m}$. I designate one vertex to be $(x,y,z)=(0,0,0)$ and the opposite one as $(x,y,z)=(3,3,3)$. I'm ...
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1answer
26 views

What is the extent of Local Inertial coordinate system

My professor's notes say, that according to the Equivalence principle there is Freely Falling coordinate system in which the equations of motion for a free particle is $\frac{d^2 \epsilon^{\mu}}{d\tau^...
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2answers
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Why is the frame attached on the Earth non-inertial in General Relativity? ( neglecting rotations etc..)

The EEP says that freely falling frames are inertial. But suppose the freely falling frame is at some spacetime point. At that point you can by a suitable coordinate transformation reduce the metric ...
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1answer
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Can rotation be distinguished from frame-dragging?

I am trapped inside the usual elevator and experiencing a comfortable gravitational field of about 1 g. Or perhaps it's an acceleration of 1 g. I cannot tell which. However, I notice when I drop an ...
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0answers
27 views

Equivalence Principle on Earth

I've read that, according to the Equivalence Principle, no experiment can distinguish between uniform acceleration and gravity. If one is in the classically-described elevator with a basin full of ...
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1answer
43 views

Einstein's equivalence principle and acceleration due to rotation

Einstein's equivalence principle is often illustrated by pointing out that a person trapped in an elevator has no way of telling whether they are on the surface of the earth or in deep space in a ...
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1answer
39 views

Equivalence Principle and Inclined Plane

During a discussion with a friend on the equivalence principle, the point was made that it only applies to objects in free fall, and therefore wouldn't apply to objects on an inclined plane. In other ...
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2answers
60 views

Equivalence principle and inertial frames [duplicate]

In Ta-Pei Cheng's Relativity, Gravitation and Cosmology book, he stated the equivalence principle as Physics in a frame freely falling in a gravity field is equivalent to physics in an inertial frame ...
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0answers
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Paradox of radiation of charged particles in a gravitational field

"Paradox of radiation of charged particles in a gravitational field" - Wikipedia ( Paper by a guy I forget the same of) On wikipedia (reliable ikr), there is a paradox occuring between ...
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0answers
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Finding the integral equation for the current on a thin solid PEC by using the equivalence principle

There's a thin solid PEC (perfect electric conductor) cylinder of length $L$ and radius $r$ aligned with the z-axis and a plane wave $\vec E$ is illuminated. When neglecting the current on the endcaps,...
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7answers
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Why can’t gravitons distinguish gravity and inertial acceleration?

If gravitons mediate the gravitational force, couldn’t the detection of gravitons by an observer be used to distinguish whether they are experiencing gravitational acceleration vs. inertial ...
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2answers
90 views

Does a stationary charge in a gravitational field radiate?

According to the equivalence principle, a freely falling observer constitutes an inertial frame. Thus, locally, Maxwell's equations apply in their usual form. According to these equations, an ...
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2answers
74 views

Free-falling object: When should we consider General Relativity?

My question is related to a statement: If a pendulum is experiencing free fall, then it will not oscillate. The statement is true in the sense that its acceleration is (approaching to) zero, then ...
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1answer
100 views

Do you experience no centrifugal force when in orbit?

I think that the answer is no, but in some sense it feels counter intuitive so I just wanted to check here. So if I understand it correctly, the General theory of relativity tells us that any ...
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6answers
141 views

If gravity were a “real” force, then how would I be able to tell if I'm falling or accelerating in space or on Earth?

Background: I think it would be helpful for laypersons like myself to understand how, in practice, a "real" force differs from a pseudo-force. Virtually all explanations (eg, on this stack, ...
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0answers
26 views

Rindler metric and equivalance principle [duplicate]

I'm trying to understand the connection between The Equivalence principle and the Rindler space. According to Einstein the inhabitants of the elevator should feel the acceleration. However, for an ...
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1answer
86 views

How much is the universe blueshifted at a black hole event horizon? [duplicate]

If Alice falls into a black hole wearing a wrist-watch, an outside observer Bob sees Alice freeze at the horizon, her watch seems to have stopped. This also means that all light that originates from ...
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1answer
36 views

Equivalence principle and time dilation

I apologize to ask, again and again, a question that seems to come back often, but I believe this is new. I am trying to test the equivalence principle applied to two similar situations: Flat ...
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1answer
43 views

Why is the situation of 'accelerating frame in flat spacetime' not equivalent to 'staying stationary in a constant gravitational field'?

One popular form of the equivalence principle states that the effects of a gravitational field in a small enough region of spacetime are indistinguishable from those of being in a uniformly ...
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1answer
56 views

Confusion about the proper time interval along an arbitrary worldline

Let us consider the worldline $x^\mu(\lambda)$ of an observer moving in an arbitrary manner (i.e. possibly non-inertial). If we want to write down the proper time interval measured by that observer ...
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0answers
27 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
107 views

Does a linearly accelerated charge radiate?

Does a linearly accelerated charge radiate? And if yes, is the electromagnetic waves emitted detectable from both its non-inertial frame and from other observing inertial frame? And If yes, doesn't ...
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4answers
168 views

Why is special relativity unable to describe gravity?

The equivalence principle states that there is no difference between an accelerated frame of reference and the acceleration from a gravitational field. Since special relativity is able to describe ...
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1answer
70 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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2answers
193 views

Is general relativity the simplest possible theory of gravitation?

I can't find this, but i've seen that GR is the only possible theory of gravity if you assume causality and principle of equivalence?
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1answer
28 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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4answers
121 views

Am I understanding the equivalence principle correctly?

So Einstein stated that gravity and acceleration are the same things in a local reference frame (please correct me if I misstated that). Here is what I think I understand and want you to verify if it ...
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1answer
66 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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1answer
50 views

Weightlessness during free fall and in free space, are they same?

Einstein's thought of a person under free-fall and when suspended in free space with no forces acting, will feel the same way. On Walter lewin's lecture on free fall he told free fall is when only ...
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2answers
56 views

Consequences of Einstein's Equivalence Principle [duplicate]

"For a person located inside a hermetically sealed box, there is no difference between being in space with the box accelerating and another person located in a similar box resting in a ...
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2answers
45 views

Equivalence Principle and Gravitational Waves

From my understanding, the equivalence principle says that it is impossible to know if you are moving or are stationary (and everything else is moving around you). Do gravitational waves violate this? ...
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1answer
56 views

Magnitude of relative velocity between two frames in special relativity

It seems to be taken trivially, and it is indeed intuitive, that the relative velocity $v$ of some frame $O$ with respect to $O'$ is the same in magnitude to the relative velocity of $O'$ with respect ...
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2answers
54 views

Strange approach to the line-fed slot antenna analysis

There is a beautiful demonstration, available in the text Robert S. Elliot, Antenna theory and Design, Wiley-IEEE Press, page 17 (Stratton-Chu solution), which shows how the electromagnetic field at ...
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9answers
679 views

Suppose you are in a closed box which is in motion [duplicate]

Suppose you are inside a closed box which is moving with a constant speed with no acceleration whatsoever. You cannot see outside the box. If you are given all the instruments you need, what ...
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3answers
119 views

What is the main reason for the locality of Einstein's equivalence principle?

Einstein's equivalence principle (EEP) states: "Locally, a free-fall frame in a gravitational field is equivalent to an inertial frame in space in the absence of a gravitational field". ...
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1answer
41 views

What happens when there is wobbly motion in General Relativity

I know for a fact that when an object starts spinning, it can be described as an inertial frame. For the sake of this question, let's consider a disc with a person placed on the edges of it. Now, the ...
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1answer
43 views

Do spinning object near a spinning black hole obey the equivalence principle?

According to the equivalence principle the path of an object should not depend on it's composition. But on the other hand a spinning object (e.g. an electron) moving past a rotating Kerr black hole ...
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0answers
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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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4answers
104 views

Coordinates that cancel the 64 affine connection components at a point

Consider an arbitrary connection $\Gamma$, compatible with the metric, in 4 dimensional spacetime: $$\nabla_{\lambda} \, g_{\mu \nu} \equiv \partial_{\lambda} \, g_{\mu \nu} - \Gamma_{\lambda \mu}^{\...
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1answer
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A problem regarding light bending

My professor in his lectures has stated that a consequence of Einstein Equivalence Principle (EEP) alone is that light bends in a gravitational field. The proof went as follow: Imagine to be a free ...
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4answers
537 views

General Relativity: Definition of Locally Inertial Frame

The Einstein Equivalence Principle states that in a sufficiently small frame of reference is impossible to know if we are into a gravitational field or not. Equivalently we cannot say if we are in an ...
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4answers
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Difference between Free Fall and Constant Velocity

We know that astronauts in the ISS feel "weightless" because they are in a perpetual free fall. The earth's gravity is the only force acting upon them, and it is accelerating them towards ...
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3answers
170 views

Why do we fall towards earth and not hover during free fall as per General relativity? [duplicate]

So this is what I understand from General Theory of Relativity: A body freely falling towards earth's surface would be in an inertial frame of reference (air removed) with zero net force acting on it. ...
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3answers
109 views

How is 1 g on a planet different from 1 g in a space ship when we look at aging?

This question has been asked before in the form of the 'Twin paradox' , and there are 42 pages of questions on this site alone when I search for 'twin paradox'. For example Does the twin paradox ...

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