Questions tagged [equivalence-principle]
In general relativity, the equivalence principle is the equivalence of gravitational and inertial mass, along with the observation that the gravitational "force" experienced on a massive body is the same as the pseudo-force experienced by an observer in a non-inertial (accelerated) frame of reference.
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Equivalence principle(s) and geodesic equation(s)
The equivalence principle (EP) is often stated in many different forms, sometimes leading to different interpretations. To make things easier for beginners to understand, I find it useful to give a ...
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Connection between pseudometric and Einstein elevator
I have a hard time understanding GR. I understand a lot (from a math point) about (pseudo)Riemannian manifolds, and I also learned about Einstein's elevator thought experiment. So let me elaborate:
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Equivalence principle and gravitons
If gravitons exist, are they always detectible in any frame? I'm asking because if I'm in a freely falling frame in a uniform gravitational field, and I detect gravitons, I will no longer be able to ...
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Gravity is not a Force? [duplicate]
I don't know much about this topic, but I read something saying that gravity is not a force using an example of inertial observation. I started thinking about the topic again when I was researching ...
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What will I feel if I experience a force in an accelerating frame of reference?
If I am in an inertial frame of reference, and I experience a force, what will happen is that I will accelerate relative to this inertial frame of reference. Say I am 60 kg and the force is 5 N and ...
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On quantization of gravitational potential?
Imagine I am doing Einstein's famous thought experiment: I'm in a lift and I'm asked to do local experiments to determine if I am accelerating in a non-inertial reference frame or in some ...
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Equivalence Principle in Newtonian Physics vs GR: A Thought Experiment
I have a question regarding the equivalence principle as it applies in Newtonian Physics and General Relativity. Consider a thought experiment involving a free-falling elevator.
Inside the elevator, ...
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What if the linearized gravity equation was the fundamental equation instead of the full Einstein Field Equations?
In Wald's "General Relativity," he discusses two key ideas that motivated Einstein to develop the theory of general relativity:
The Equivalence Principle: All bodies fall the same way in a ...
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How the equivalence principle leads to the idea of curved spacetime? [duplicate]
In wikipedia https://en.wikipedia.org/wiki/Equivalence_principle, there are three forms of equivalence principle ( equivalence of gravitational and inertial mass ) :
Weak version (Galilean) :
The ...
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If gravity is fictitious force why we search for gravitons? [duplicate]
If gravity is fictitious force why we even search for gravitons?
I mean, centrifugal or coriolis force don't have carriers, because these forces dont exist.
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Geodesic equation and inertial reference frame
When your covariant derivative of your 4-velocity is zero, you are in geodesic. Now, what if I measure your 4-velocity from a non-inertial reference frame, and see that it is constant with respect to ...
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Equivalence principle near a black hole
At every spacetime point, there is a locally inertial frame in which the effect of gravitation is absent. Can this point be taken near the center of a black hole?
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Does a metric theory of gravity plus torsion violate the equivalence principle?
I have read that the Einstein-Cartan theory introduces torsion into general relativity in a way that produces coupling between gravity and the spin of particles. Then, the gravitational field is able ...
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Why does general relativity assume that the torsion is equal to zero?
I do not understand why the torsion is set equal to zero in the general theory of relativity. The geodesics would be the same. Is there even a way to test it?
Pg 250 from the 2017 edition of MTW says
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Field of Inertial Forces
Although inertial forces are just our mathematical creation to help apply Newton's law even in non-inertial frames, can we assume or is it (mathematical proof) that inertial forces also create its ...
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Are objects in an uniform field inertial?
It is currently understood that gravity is not actually a force, and a fact that is often used to show this is that an object in free fall doesn't "feel" that it is accelerating and is thus ...
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When doing general relativity in practice, how do we choose the appropriate manifold describing the scenario?
The theory only deals with the local curvatures, not the global topology. Hence any manifold with an allowed metric is allowed. These can be infinitely many, especially for negative curvature space-...
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How is the intensity interpretation of Bohr's correspondence principle equivalent to the frequency interpretation?
The frequency interpretation of Bohr's correspondence principle seems obvious, given that a photon emitted after a dexcitation of an electron has to have the frequency that corresponds to the ...
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Is the equivalence principle violated for photons in the field of an infinite massive plane?
I had a discussion with someone about the motion of a photon in the field of an infinite massive plane. The metric of the spacetime above and below the plate is:
$$ds^2=e^{2g|z|}(-dt^2+dx^2+dy^2)+dz^2$...
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Why does acceleration in special relativity give rise to general relativity (and thus gravity)?
If we include accelerated motion in special relativity, the result is general relativity. But why should that give rise to gravity? Is that only because Einstein introduced the equivalence between ...
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Inertial Mass = Gravitational Mass. Why? [duplicate]
Okay, so the inertial mass of an object is always equal to the gravitational mass of the object. Conceptually, however, they seem different. Then what makes them identical? Is it because they are ...
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Can fictitious forces always be described by gravity fields in General Relativity?
I was debating a geocentrist online who said that Einstein and a bunch of other physicists admitted a geocentric framework is valid. I replied that this was technically correct, but if you wanted to ...
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How are the " free fall" formulation and the " accelerated rocket" formulation of the (Weak) Equivalence Principle related? (General Relativity)
This question pertains to a very basic level of understanding of Einstein's theory; my formulation of the equivalence principle does not aim at technical accuracy (in particular it ignores the problem ...
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Acceleration in an empty universe [closed]
Regarding an acceleration in an empty universe, from the special relativity we feel an acceleration in an empty universe since there is still the presence of an space-time with respect to which an ...
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Confusion on a couple of paragraphs on equivalence principles
I'm reading Carroll's GR book. I'm able to follow it for the most part, but a couple of paragraphs are a bit hard to decipher:
According to the WEP, the gravitational mass of the hydrogen atom is ...
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Is there really no way to know if you are accelerating or you are in gravitational field? [duplicate]
So any gravitational field will have a gradient, no? But an accelerating object does not experience any gradient of force. So you should be able to tell if you are in gravity or accelerating by ...
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Can we infer Hawking radiation assuming the Unruh effect?
An observer near the event horizon of a black hole will experience an extremely strong gravitational field.
Due to the principle of equivalence, this observer cannot locally distinguish between this ...
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Equivalence principle in geometrical terms
I am learning general relativity by myself. I wonder if the equivalence principle is simply equivalent to, in geometrical terms, the statement that a Lorentzian manifold is locally flat, which is a ...
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Validity of source reconstruction method for a partial measurements [closed]
Is it possible to extract equivalent current sources from the partial measurements? I am specifically thinking of a scenario where we have a radiating source inside a closed surface and we measured ...
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A possible way to generate Electric current
What is electric current?
An electric current is a flow of charged particles, such as electrons or ions, moving through an electrical conductor or space. It is defined as the net rate of flow of ...
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Does the path of free fall through a non-uniform gravitational field constitute an inertial reference system?
It's clear to me that when an object is in free fall in a uniform gravitational field ("Einstein's Elevator") it feels no tug of gravity. However if it is in free fall in a nonuniform ...
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Why does gravity-induced quantum interference in quantum mechanics show that gravity is not purely geometric at the quantum level?
I am asking problem from the 'J.J. Sakurai and Jim J. Napolitano' Book Modern Quantum Mechanics 2nd edition. It reads as follows:
"...This experiment also shows that gravity is not purely ...
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Where is the normal force that pushes us up comes from if gravity is not a force according to general relativity?
https://youtu.be/XRr1kaXKBsU?t=530
I was watching this video and at this point he said that since gravity is not a force as per GR, we are left with only these normal forces pushing you up that ...
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Local inertial frame by linear transform?
By equivalence principle, one can find a local inertial frame at every point of spacetime. Then this is usually used to introduce the general spacetime metric, as a back-transform of the Minkowski ...
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Since when did inertial mass and gravitional mass became equal?
If we think about inertial mass and gravitational mass as independent concepts and develop physics then we would know after a while they are only propotional (by precision we have by now). but it seem ...
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When observers moving along different geodesics meet locally, can they detect one another's acceleration?
Consider two free-falling observers in the Earth's gravitational field, A and B, who meet at point C, where A orbits the Earth at a constant radius from the Earth's center, and B falls towards the ...
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Test for inertial frame of reference
In the book Physics by Resnick, Halliday, and Krane, in chapter 3 there was a statement which confused me.
To test whether a particular frame of reference is an inertial frame, we place a test body ...
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What does it mean that a falling mass in space doesn't sense any force?
I heard someone explain that if you were falling in space (i.e, a rooftop) you wouldn't sense gravity as a force acting upon you. But it would accelerate (≈ 9.8 m/s^2)
, which to me suggest that a ...
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The relation between Hamiltonian mechanics and geodesic spacetime
One way to write the action for a particle moving in curved spacetime is to use the proper time as a parameter and the metric tensor as a function of the coordinates. This leads to an action that is ...
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Did Feynman use the equivalence principle to compute spacetime curvature correctly?
Chapter 42 of the Feynman Lectures on Physics claims that a clock "higher up" in a gravitational field will tick more slowly, and that is used to argue that space-time in a constant ...
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Radial Coordinate or Equivalence Principle: What Determines Time Dilation in Free Fall?
I have a question regarding the math of General Relativity. Let's consider an observer with two clocks attached to their head and feet. If the person is in free fall, their feet would have a lower ...
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How can time run differently for different objects in models where the equivalence principle is broken?
In these three papers, the effect of gravity on anti-kaons, antiprotons, and positrons, is tested by how quickly time moves for them in the presence of Earth's (or the Sun's) gravitational field.
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Is gravitational mass always the same with inertia mass?
I read an article.
When an object is travelling near speed of light, it's mass increase.
The article argues while the inertia increased, that is, the object will be harder to speed up, the ...
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Principle of general covariance follows from principle of equivalence?
I am reading the book gravitation from Weinberg. On page 93 he states the principle of covariance. I attach a screenshot below. I think Weinberg is saying (below the enumeration) that the principle of ...
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Question on the value of speed of light, non-inertial frames and equivalence principle
One of the axioms of special relativity concerns on the value of speed of light measuread by a family of inertial observers. They must measure $c$.
Now, the global inertial frame is lost if the ...
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Why don't two accelerated clocks behave like two clocks in a gravitational field?
If we immerse two clocks in a gravitational field at different altitudes (with the approximation that both heights share the same g for equivalence to be true), the falling and Schwarzschild observers ...
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Is the gravitational force a phenomenon or a theoretical invention? [closed]
We use to say that gravitational force is a phenomenon. But since the theory of General Relativity replaced Newtonian gravitational force, how is it possible for a phenomenon to be replaced by a ...
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Reason for differentiation between inertial and gravitational mass
To my knowledge, inertial and gravitational mass are equivalent according to the weak equivalence principle. I believe modern experiments have shown that $\lvert \frac{\mu}{m}-1\rvert\leq 10^{-15}$, ...
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How does one show the equivalence principle is manifest in the EH action? [duplicate]
How does one start from the Einstein Hilbert action and show that in a small neighborhood the metric must be Lorentzian (equivalence principle)?
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Acceleration and gravitation are locally equivalent ? I find not
In a gravitational field, the above and below clocks do not run at the same rate.
The acceleration equivalent means that the simultaneity changes. During acceleration there would be a gravitational ...
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