Questions tagged [equivalence-principle]

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Special and general relativity

Is the light postulate in special relativity (that the speed of light is constant in all frames of reference) correct if the equivalence principle shows that light slows down in gravitational field? ...
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Gravity, falling bodies, and the equivalence principle

Why is that bodies in a box accelerating uniformally in space that is sufficiently removed from gravitational fields fall identically to bodies in a box located in a homogeneous gravitational field (e....
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How did Einstein use the conclusions of special relativity to reach the equivalence principle (using the Elevator thought experiment)?

Could someone please explain how Einstein used the Elevator thought experiment and the principles of special relativity to conclude that uniform accelerates creates uniform gravitational field (...
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1answer
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Einstein's Elevator thought experiment and relativity

Einstein's elevator thought experiment contains the following premise: An observer in a box will see free bodies moving identically between when the box is uniformly accelerating in gravitational ...
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Is quantizing acceleration equivalent to quantizing gravity?

It's been said that gravity is locally equivalent to acceleration. It is also been said, that we need to quantize gravity. But doesn't that imply that this would have to be equivalent to quantizing ...
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Is the gravitational field an illusion, a by-product of geometry? [duplicate]

The principle of general covariance from the Equivalence Principle (EEP) tells us that there is no way in principle to locally distinguish between an inertial acceleration and the effects of a ...
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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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Do centrifugal force and gravity differ in their effects on objects?

If the type of object matters, consider the human body. If the situation matters, consider standing on the inside wall of an O'Neill cylinder compared to standing on the surface of Earth. "Differ in ...
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1answer
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Relativity of Jerk

Popular expositions of general relativity start with a thought experiment showing that it is impossible to distinguish a constantly accelerating frame of reference in a free fall from a free floating ...
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2answers
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Reason of no reaction force on a person in a lift falling freely under gravity

a person in a lift falling freely under gravity feels weightlessness because the force of reaction between the person and the plane with which he is in contact vanishes. why force of reaction vanishes?...
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2answers
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Rindler Coordinates and homogeneous Gravity Field

I understood from the equivalence principle that an accelerated observer in free space is equivalent to a stationary observer in a gravitational field. As far as I understood further, this means to ...
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1answer
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How does Rovelli's idea of time and gravity relate to inertia?

In "The Order of Time" (pg 12-13) Rovelli says "If things fall, it is due to this slowing down of time. (near a mass) Where time passes uniformly, in interplanetary space, things do not fall. ...
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Equivalence principle and local inertial reference frames

Local inertial reference frames are defined as follows: Pick a set coordinates for the manifold (assuming the manifold can be described by global coordinates) $\{x^i\}$ such that $g(p) = \eta$ is the ...
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I think I am misunderstanding Einstein's equivalence principle and his elevator

I'm having difficulties understanding why a gravitational acceleration can be guaranteed to be locally equivalent to an accelerating frame. Doesn't it matter on how the force is being applied? If the ...
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4answers
855 views

Did people realize that gravity accelerated things before Einstein's elevator thought experiment?

I'm reading about the (very near) equivalence of gravitational mass and inertial mass in my undergrad GR course, and the text (Lambourne) describes this equivalence as the inspiration for Einstein's ...
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1answer
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Near-relativistic car speeding over a bridge

I have read this problem / exercise (I don't remember the exact numbers, so I put my own) in William Burke's "Applied Differential Geometry" and it has always puzzled me regarding the relation between ...
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Surely space-time Curvature does not explain gravity, it just describe its effects?

In special relativity co-moving objects see the other's 4-velocity as being only temporal. When they move relative to each other they see the other's 4-velocity has rotated so that it points less in ...
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Are mass or inertia the same thing, the same properties?

I think so. But I wold like to know another opinions to confirm.
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Can the origin of mass or inertia depend only of the gravitational field of matter? [closed]

The gravitacional field is directly proportional to mass or inertia. It doesn't have another property or field like this, with this power. I think that when we apply a force to an object, the ...
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1answer
135 views

Can an Observer Distinguish between Unruh Effect and Hawking Radiation by Measuring Temperature?

In Unruh effect, the temperature of background appears to be proportional to acceleration. On the other hand, the temperature of a black hole is inversely proportional to its mass. If the two ...
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Does Bell's Theorem suggest both Nonlocality and “Temporal Nonlocality”? [closed]

Bell's Theorem pretty much rules out any local hidden variable theories, and any hidden variable theory that's nonlocal is just regular quantum mechanics with an extra variable thrown in. But, since ...
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1answer
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Gravitational acceleration in GR

What is the meaning of gravitational acceleration $g$ in the General Theory of Relativity, given that objects in free fall experience weightlessness? Can gravitational acceleration be thought as a ...
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286 views

Why must the worldline for a freely-falling body be straight?

If spacetime were on an xy graph, the x-axis being time and the y-axis being space, an object that is in interstellar space with no noticeable gravitational influences on it will have a worldline that ...
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2answers
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How to infer from Einstein Equivalence Principle that a test particle should follow geodesic?

Einstein Equivalence Principle (EEP) states that A frame linearly accelerated relative to an inertial frame in special relativity is LOCALLY identical to a frame at rest in a gravitational ...
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1answer
107 views

Equivalence principle and bending of a light ray

In some explanations of a phenomena of curved spacetime we have an example of a light ray emitted in a freely falling space ship perpendicular to the direction of a free fall. In this case, for an ...
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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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2answers
484 views

How does acceleration feel compared to gravitational pull?

I was debating a variation of this Phys.SE question with a friend. The original question is: "If you had your eyes closed, could you distinguish between standing still on earth and being in a ...
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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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Can we think of gravity as space itself moving?

So if you move through space with a constant acceleration you experience longer time dilation than when you're at rest, but you also experience the same time dilation when you're under the effect of ...
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1answer
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Riemann tensor and metric tensor second derivatives

I know that in general relativity, unlike in electromagnetism, the field tensor must be dependent on metric tensor second derivatives, since I can always find a reference system in which its first ...
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2answers
249 views

Equivalence principle, is gravity a fictitious force that we feel everyday?

I am currently self studying general relativity. I have a question regarding the equivalence principle. If an observer is in the elevator in deep space (or Minkowski space) where there is no ...
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Equivalence principle and the meaning of the coordinate speed of light

Short version: Does the equivalence principle give us a means to tell if variations in the coordinate speed of light have absolute or only relative significance? Background In general relativity ...
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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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3answers
851 views

Confusion with the equivalence principle and inertial frames

This is an explanation of the equivalence principle. A. says accelerating frames can simulate gravity. Then, I am confused. Are the frames presented in A. inertial frames? Compared to B. I have the ...
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2answers
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Why can't Newton's 1st law be expressed as an autoparallel transportation in space?

I'm following this series of lectures on differential geometry and general relativity. In the linked lecture (Lecture 9), at around 24:24, professor Frederic Schuller made the conclusion that one can ...
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3answers
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If I drop a ball in an accelerating rocket, will it bounce? If so, how?

Einstein's equivalence principle says that you cannot distinguish between an accelerating frame or a gravitational field. However, in an gravitational field, if I drop a tennis ball, it will bounce, ...
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Why model spacetime as a semi-Riemannian manifold?

I'd like to collect arguments for the use of a semi-Riemannian manifold as a mathematical model for spacetime. I think this is closely linked to the equivalence principle, but I can't shape this into ...
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3answers
581 views

Uniform Gravitational Field = No Gravitational Field?

I'm reading Geroch's lecture notes on GR, and in the first chapter he makes the following assertion: People inside an elevator freely falling in a uniform gravitational field cannot distinguish ...
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Active gravitational mass of the electron

In PSE here electrons are added to a sphere and gravitational modifications are expected. My question is: Is there any experiment that show that a negatively charged object is source of a stronger ...
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115 views

Equivalence Principle [closed]

Let’s imagine that the Equivalence Principle did not exist. Let’s assume that gravity works like any other force. That greater masses fell at a faster rate than smaller masses. Under this new ...
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1answer
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Problem with different Equivalence Principle Statements

I'm having trouble understanding the differences between the different forms of the Equivalence Principle. I've search in other questions and I think that this was not previously asked, at least in ...
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4answers
961 views

Why do gravitational mass and inertial mass appear to be indistinguishable? [duplicate]

I have learnt that heavier the object is (the more gravitational mass it has), the more resistance to the change of motion it is (the more inertial mass it has). I can accept this fact but I can't ...
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4answers
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Is there a fundamental reason why gravitational mass is the same as inertial mass?

The principle of equivalence - that, locally, you can't distinguish between a uniform gravitational field and a non-inertial frame accelerating in the sense opposite to the gravitational field - is ...
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Equivalence principle question

I understand the equivalence principle as "The physics in a freely-falling small laboratory is that of special relativity (SR)." But I'm not quite sure why this is equivalent to "One cannot tell ...
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1answer
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Trying to understand the equivalence principle in GRT

Suppose that two observers are on a sphere of radius $r$ with angle $\phi>0$ and distance $d>0$ from each other and they are accelerated from inside to outside perpendicular to the sphere. Then ...
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3answers
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How can one determine if they are not experiencing Earth gravity? [closed]

Suppose you are kidnapped and you don't know who did it. You have no memory of the trip that brought you to the building where you are now being held. You have reason, however, to suspect that you are ...
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Would it help if you jump inside a free falling elevator?

Imagine you're trapped inside a free falling elevator. Would you decrease your impact impulse by jumping during the fall? When?
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2k views

Questions from elevator ride [duplicate]

I like to play inside the lift (elevator). For instance, there are bars attached at the side of the lift, and I like to hold my body up using my two hands on the bar. I realised that I actually feel ...
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1answer
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Electromagnetism and equivalence principle?

The Maxwell equations for the electromagnetic Potential $A_\mu$ are (using Lorenz gauge). $$\nabla_\mu \nabla^\mu A^\nu - R^{\nu \mu} A_\mu = j^\nu$$ However the equivalence principle states: No local ...
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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?

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