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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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387 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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142 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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1answer
326 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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84 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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0answers
195 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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2answers
120 views

Does the equivalence principle imply that light must move slower when moving away from a massive object?

Thought experiment: Elevator going up at an extreme acceleration, pulse of light bouncing up, and down between mirrors on the floor, and the ceiling. Won't it take light longer to travel from the ...
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0answers
134 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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110 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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772 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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713 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
102 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 ...
2
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1answer
382 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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1answer
81 views

Why do we know that light must follow a geodesic?

THE CONTEXT: Some context to my question: Einstein once posed the thought experiment of a man falling inside a closed box. Just before the box was dropped, a photon was fired horizontally moving from ...
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76 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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2answers
130 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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1answer
109 views

Equivalence Principle and bending of light

Basically, the equivalence principle (EP) states that if someone is in a rocket in empty space with acceleration $g$ equal to that at the surface of the earth, any experiment he does cannot ...
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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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150 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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0answers
137 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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78 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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100 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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2answers
162 views

Path of light rays in uniform velocity elevator

I have been told that light rays seen from inside an accelerated elevator will seen as following a curved path, parabola. Like the image below. But what happens when a pulse of light entered into a ...
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124 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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1answer
113 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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1answer
169 views

Dark Matter and Equivalence Principle

Dark Matter effects show up in galaxies. Why isn't it considered as a violation of equivalence principle instead of assuming all these extra non-interacting particles as gravitational mass and ...
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0answers
158 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
178 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
235 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
163 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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37 views

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
27 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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40 views

Invariance of forces

In Newtonian mechanics, the inertial forces depend on the reference frame and the other forces are invariant. Are they still invariant when special or general relativistic effect are involved?
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1answer
77 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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1answer
97 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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48 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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85 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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121 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
101 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 ...
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381 views

Bending of light in a gravitational field & the principle of equivalence

I have a few conceptual issues following a standard thought experiment to argue why light bends in a gravitational field and I'm hoping I can clear them up here. Consider an observer in a lift in ...
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1answer
43 views

The equivalence principle and experiments concerning it?

Imagine that we are in a rocket accelerating with some magnitude $a_1 = dx^2/d^2t$, also imagine that we have a stationary rocket ship in close proximity to ours, stationary relative to our reference ...
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1answer
101 views

If a place a spring in a box and drop the box, what happens?

Suppose I a holding a box in my hands, and inside the box a spring with some mass attached hangs from the cieling of the box. Initial the system is at equilibrium, then I let go of the box and it ...
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273 views

Paradox - Laws of physics are the same in all inertial reference frames vs Equivalence Principle (Pictures Added)

According to the equivalence principle, no experiment should exist that one can perform to determine whether one is in an accelerating elevator, or in a gravitational field. I will outline two ...
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1answer
49 views

Equivalence principle and quantum gravity

Do new concepts of gravity negate the validity of the equivalence principal? or do all theories (waves, string, etc) and mathematics apply equally to gravitation and accelerating frames?