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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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Does Matter Cause Curvature or Vice-Versa [closed]

From the way explanations about gravity-acceleration-curvature equivalence are usually phrased here or elsewhere, it would appear many or most think that matter causes space-time curvature. I cannot ...
Prototypist's user avatar
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Doubt about metric tensor definition in Weinberg's Gravitation and Cosmology

In Weinberg's Gravitation and Cosmology, by using the Equivalence Principle, the author defines the metric tensor as (equation 3.2.7) $$ g_{\mu \nu} \equiv \frac{\partial\xi^\alpha}{\partial x^\mu} \...
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Can electrons or protons due to fusion reduce in their individual mass?

It's a ridiculous question, but that's why I am asking it after getting confused over a paragraph about nuclear fusion in my textbook. The total mass of a stable nucleus is slightly less than the ...
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Necessity of equivalence principle

Is the equivalence principle necessary to formulate general relativity or is it possible to formulate general relativity without it?
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Is it possible to know if you're moving or standing still due to the definition of Einsteins equivalence principle?

I have a question regarding Einstein's theory of relativity. Einstein's equivalence principle states that locally it's not possible to tell if you're accelerating or being stationary in a ...
Ethan Brown's user avatar
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Does a charged particle under constant acceleration produce electromagnetic waves? [duplicate]

A charged particle at rest does not emit any electromagnetic waves. It is generally said that an accelerated charged particle does produce electromagnetic waves. But according to Einstein's Principle ...
Rudransh Joshi's user avatar
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5 answers
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Is quantum gravity research implying that gravity is actually a force and not spacetime curvature according to GR?

I am all the time reading that gravity is actually the curvature of spacetime according to general relativity (GR) established theory and not a force, like the known three fundamental forces of nature,...
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Does the equivalence principle only apply for the gravitational field of an infinitely sized body?

From my couch-level understanding of the equivalence principle it seems like unless the source of the gravitational body on that side of the equation was infinitely sized, it would be simple to ...
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Can you reason the equivalence principle from SR?

So for the past few days I've been reading on "why is special relativity incompatible with gravity?". Most answers are something along the lines of "special relativity doesn't have ...
NaiDoeShacks's user avatar
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How is falling into the Earth while orbiting it a geodesic?

So in regular Newtonian mechanics, orbits are generally stable so if there is a metal sphere orbiting the Earth assuming no tidal interactions, they should stay where they are. But then gravitational ...
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Would objects really be at rest relative to each other in orbit?

I am currently reading Gravitation by Misner, Thorne, and Wheeler (MTW). In the very first chapter on weightlessness they make the following claim: “Contemplate the interior of a spaceship and a key, ...
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On the equivalence principle

In its simplest version, it states that the effects of a uniform gravitational field are indistinguishable from those of a uniform linear acceleration of the frame of reference The thing is, you can ...
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Is time period of a pendulum in an accelerating elevator dependent on the weight of the bob?

If a simple pendulum is in an elevator accelerating upwards, Its $T$ decreases. But why is that? The only thing that changes is the apparent weight so does $T$ depend on the weight of the bob but ...
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Strong Equivalence Principle and Milgrom's Law

I am reading this paper by Milgrom(1983) that suggests a modification to Newton's Second Law in order to do away with the requirement of dark matter on astrophysical scales. My question is regarding a ...
Ambica Govind's user avatar
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Einstein equivalence principle and running of couplings

It is known that a spacetime variation of the dimensionless gauge coupling constants of the standard models would lead to a violation of the Einstein equivalence principle (EEP). This point is ...
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Negative Energy and Gravity

Why do many science communicators say that negative masses fall upwards? Is it the same in the physics literature that they say that negative masses fall upwards? In general relativity, things don't ...
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How fast spacecraft should be accelerated that it acts like a black hole?

I am little confused.Please correct me if I am wrong. According to general relativity, there is no way to spot a difference between accelerating frame of reference and gravity. Suppose a spacecraft is ...
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Which version of the equivalence principle affects the coordinate dependency of the Landau–Lifshitz pseudotensor?

We know that the energy-momentum of gravity can be defined by a pseudotensor called the Landau-Lifshitz pseudotensor, which is coordinate dependent. In fact, the gravitational stress–energy will ...
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Global Validity of Locally Inertial Coordinates

Equivalence principle tells us that for a freely falling inertial observer spacetime is locally flat. The coordinate transformation needed to introduce Locally Inertial Coordinates were discusses in ...
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The global metric can't be generated by coordinate transformation. However, the local metric can always be generated from a locally inertial frame

This is my understanding of the equivalence principal, Is it correct? That is, we can always generate the metric $g_{\mu \nu}$ of ANY gravitational field locally via the coordinator transformation of ...
Jack's user avatar
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Einstein equivalence principle conflict

The weak principle of equivalence says that freely falling towards the Earth is the same as being in space far away from any stars. However, imagine that you are freely falling on a planet with $g=9\...
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Equivalence principle: Distinction between sensations of free fall and an inertial system at rest

According to the equivalence principle, it is not possible to distinguish between an inertial system (far from any gravitational interaction) and a system in free fall within a gravitational field. ...
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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 ...
Ahmed Samir's user avatar
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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 ...
More Anonymous's user avatar
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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 ...
Kenneth A's user avatar
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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 ...
Plantation's user avatar
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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?
Hamed Hilal's user avatar
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1 answer
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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-...
Cathartic Encephalopathy's user avatar
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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$...
Il Guercio's user avatar
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3 answers
414 views

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 ...
Il Guercio's user avatar
1 vote
1 answer
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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 ...
Lory's user avatar
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1 answer
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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 ...
Vince Vickler's user avatar
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3 answers
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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 ...
Shirish's user avatar
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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 ...
Just Next to me's user avatar
2 votes
1 answer
185 views

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 ...
VVM's user avatar
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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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