Questions tagged [equivalence-principle]

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7answers
193 views

Can we feel gravity while free falling?

I watched some video saying that there is still gravity in space station and almost same strong as it on Earth, the reason they feel no gravity is because the centrifugal force of the orbit is same as ...
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2answers
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On local inertial frame and acceleration in general relativity

[Q1] In the general relativity, a local inertial frame is mentioned. The local inertial frame is a notion, which is related to (or represents) the equivalent principle. Here, I understand that, in ...
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2answers
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Silly doubt about tidal effects and Einstein Field Equations

Suppose I give you the following line element: $$ ds^{2} = -(1+2\phi)dt^{2}+(1-2\phi)(dx^{2}+dy^{2}+dz^{2}) \tag{1}$$ Without saying anything you might think that this is just another line element ...
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3answers
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Equivalence Principle: Why is sitting in space the same as failling in a uniform gravitational field [duplicate]

The equivalence principle states that no experiment can determine whether one is being accelerated or if there is gravity present. This is insightful and intuitive. However, I was sort of surprised. ...
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4answers
151 views

Why gravitational mass and inertial mass being same was a problem before Einstein solved it?

Why is it so that Einstein is credited with telling us the reason for the equivalence of inertial and gravitational mass of an object? Did Newton ever make a distinction between the two masses? What ...
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2answers
175 views

Does semi-classical gravity obey the equivalence principle?

Question I was recently wondering about semi-classical gravity : $$ G_{\mu \nu} = \frac{8 \pi G}{c^4} \langle \hat T_{\mu \nu} \rangle_\psi$$ Does this obey the equivalence principle? My ...
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5answers
8k views

Is floating in space similar to falling under gravity?

In the case there is no air and your eye are closed, then does falling from the sky under gravity have the same feeling as floating in space? Can our body feel that we are accelerating without the ...
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1answer
26 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
46 views

Is a body in passing gravitational wave still in free fall?

I have a simple apparatus: a box and inside it a test particle (small bullet). If the device is in inertial motion or affected only but (static) gravitational field of another massive body (in free ...
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0answers
32 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
36 views

What is proper name for non-inertial forces in GR?

General relativity works in all reference frames, so inertial forces are real in it. And due to the equivalence principle, gravity should be also considered inertial. So what is a good term for the ...
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1answer
62 views

How do we know who is moving? [duplicate]

If I am in a free float environment and there is another object at rest relative to me, and then I start to accelerate towards this object, do I know I am the one who is moving, since I am the one who ...
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3answers
158 views

Does general relativity reduce to special relativity for free falling objects?

The following was stated in a general relativity lecture series: "Full space is needed in GR. Minkowski space is sufficient for SR. However, Minkowski space is sufficient to compute properties of free ...
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2answers
114 views

Different prediction about the motion of a charge as observed by two different observers?

Suppose a charge is at rest in the laboratory frame. Also, say two observers in two vehicles A and B are approaching towards it. Let A be accelerating towards it and B be moving uniformly towards it. ...
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2answers
68 views

Is there “artificial gravity” created by a reference frame on a spinning object? [closed]

Believing the answer is yes, how then is spacetime curved? Will the spacetime uncurve when rotation stops? According to special relativity you can only see things from one's own reference frame. I do ...
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6answers
141 views

Acceleration in free fall [duplicate]

A body in free fall "feels" no gravitational force (equivalence). Why does it continue to accelerate. Why is your program refusing my question?
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1answer
67 views

Will tidal effect make physics laws different?

I was reading Wheeler & Taylor's Spacetime Physics. The authors mentioned about tidal effect, as well as all physics laws are same in free-float frame. I am left wondering if tidal effect will ...
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6answers
458 views

If an object with more mass experiences a greater gravitational force, why don't more massive objects fall faster? [duplicate]

According to Sir Isaac Newton, the gravity equation runs like this: $$ F = \frac{Gm_1m_2}{r^2} $$ where $F$ is the gravitational force, $G$ the gravitational constant, $m_1$ and $m_2$ are the ...
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1answer
53 views

Do “light” and “heavy” objects still accelerate at the same rate at near light speeds?

My (very poor) layman's understanding of physics is that as something approaches c, it has a relativistic mass that is a combination of its actual mass and velocity. Do this affect its acceleration ...
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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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2answers
66 views

Now when we can measure gravitational field, how does the principle of equivalence hold true?

LIGO measured gravitational field waves. The whole thought experiment of Einstein, leading to ‘principle of equivalence’, assumes that there is no way to know inside the rocket that whether its ...
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1answer
70 views

Does general relativity (GR) solve mass-equivalence problem or just renames it?

It is usually said that GR solved problem of equivalence of gravitational and inertial mass. Yet, my objection is: OK, there is no gravitational mass in GR, but Einstein had to introduce mass as "...
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1answer
74 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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1answer
100 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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2answers
62 views

How come planets with different masses can orbit at the same velocity at the same altitudes?

Angular momentum is equal to r × p and angular momentum is also what gives planets with lower orbits a higher speed (because angular momentum is conserved). So as r decreases either m or v (p=mv) has ...
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1answer
51 views

Why acceleration due to gravity is not reliably defined?

In Sean Carroll's Spacetime Geometry, there is the following line on Page No.50 in 2014th edition: "The acceleration of a charged particle in an electromagnetic field is uniquely defined with respect ...
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1answer
92 views

Does a charge in a gravitational field make a magnetic field?

I know that general relativity unifies the electric charge with the magnetic field via relative motion. So if I accelerate a charge then anyone in another inertial frame will see a magnetic field. ...
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1answer
45 views

Detecting external 'forces' in an inertial frame

Disclaimer: Science noob here, I may not use all terms correctly. I've read somewhere of the following situation: An observer is inside a room (elevator) with no ...
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5answers
137 views

Einstein's Elevator - Constant acceleration eventually reaches $c$. Can't that be used to detect gravity vs acceleration?

Objects with mass that continuously accelerate will eventually approach $c$, but cannot exceed it. So if I find myself in an elevator, unable to determine if I'm in a uniform gravitational field or ...
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2answers
127 views

Christoffel symbol

In flat space, it is possible to find a coordinate system in which the Christoffel symbols are equal to zero at every point on the flat manifold. However, I was wondering if it is possible to find a ...
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4answers
504 views

Falling electric dipole contradicts equivalence principle?

Consider an electric dipole, with total mass $M$, consisting of charges $q$ and $-q$, separated by a distance $d$. The total mass $M$ includes the mass defect due to the negative electrostatic energy ...
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1answer
42 views

Equivalence Principle: from falling bodies to all physical processes [duplicate]

Einstein's elevator thought experiment considered that in the Minkowski space-time of special relativity, all bodies fall identically. What grounds did Einstein have to generalise this falling bodies ...
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1answer
91 views

Einstein Elevator thought experiment

Were there any background theories for Einstein's elevator thought experiment which developed the equivalence principle. Can Newton's equivalence principle (the equality of inertial and gravitational ...
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1answer
52 views

How did Einstein generalise the Einstein elevator thought experiment to conclude with the equivalence principle?

Suppose a reference frame S1 is accelerated in the x direction with a constant acceleration g. A second frame S2 is at rest in a homogeneous gravitational field which imparts to all objects an ...
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1answer
69 views

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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0answers
23 views

Why do bodies fall identically in uniform acceleration and uniform gravitational field? [duplicate]

In his reformulation of Einstein’s Elevator thought experiment, James Robert Brown (1993) says that an observer in a uniformly accelerating spaceship in space (free of gravitational effects) will see ...
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4answers
132 views

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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1answer
41 views

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
104 views

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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7answers
4k views

If gravity is a pseudoforce in general relativity, then why is a graviton necessary?

As far as I’m aware, gravity in general relativity arises from the curvature of spacetime and is equivalent to an accelerated reference frame. Objects accelerating in a gravitational field are in fact ...
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1answer
386 views

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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1answer
121 views

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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0answers
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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3answers
86 views

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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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
351 views

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
96 views

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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2answers
128 views

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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1answer
198 views

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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1answer
88 views

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 ...