# 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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### Shouldn't time pass slower and slower for an object under gravity according to the equivalence principle? [duplicate]

According to the theory of special relativity time is relative and passes slower the faster you move. According to the equivalence principle gravitational and inertial forces are of a similar nature ...
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My question is very simple. Is energy is the CAUSE for bending of spacetime ? If yes how energy/mass is interacting/effecting the space time? If yes is it possible curvature of space time without ...
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### Under the equivalence principle, does a bullet experience gravitational time dilation during acceleration?

Does the equivalence principle include gravitational time dilation for an accelerating object? A bullet accelerates in the barrel of a gun at 10^6 m/s^2. If this acceleration was the gravity of a ...
1 vote
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### Enquiry about the gravitational redshift in "The young center of the Earth" by U.I. Uggerhøj et al

I was reading "The young center of the Earth" by U.I. Uggerhøj et al., lately, and the standard gravitational redshift equation given in the paper is: The link to the paper: https://arxiv....
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### Physical significance of metric compatibility

When we try to construct a covariant derivative, we impose several conditions on it so that the resulting derivative is unique. However, I can't make sense of the condition of metric compatibility. I ...
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### Speed of light and the equivalence principle

In 1913 Albert Einstein wrote: "I arrived at the result that the speed of light is not to to be regarded as independent of the gravitational potential. Thus the principle of the constancy of the ...
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### How is a locally inertial frame possible in Principle of Equivalence of General Relativity?

The principle of equivalence states that it is possible to choose a locally "inertial" coordinate at every space-time point, in presence of an arbitrary gravitational field, where the ...
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### EINSTEIN THEORY OF SPACETIME [closed]

CAN SOMEBODY HELP ME ANSWERING THIS QUESTION. HOW WOULD YOU EXPLAIN SPACETIME TO AN UNSCHOOLED PERSON? I AM STILL A STUDENT AND THINKING AN EXACT EXAMPLE IS QUITE HARD FOR ME.
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### Is there a way to know if you accelerate in empty space or in a uniform gravitational field?

If I'm in a room that accelerates through empty space uniformly I won't measure tidal forces. The situation is the same as standing on an infinite massive plane. So I could think, while looking ...
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### Tidal force in equivalence principle

The inertial frame of reference in a gravitational field is defined locally, but couldn't a sufficiently sensitive instrument detect tidal forces in the gravitational field and thus make the frame in ...
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### Principle of Equivalence for non-uniformly accelerated system

Consider a frame being accelerated according to the law of gravity, $a=-K/r^2$ where $K$ is some constant and $r$ is measured from some point. Since here the acceleration is exactly the form of ...
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### How to resolve this asymmetry in an example for the weak equivalence principle?

I am trying to unknot an obvious error in my understanding of the following example: Fact 1: An observer on the moon watches a tiny ball of uranium and a tiny ball of iron fall. Both fall fall at the ...
1 vote
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### Speed of the light traversing an accelerated elevator

Consider an upwardly accelerated elevator as in the figure. From outside the elevator, an inertial observer (unseen in the figure) shoots light perpendicular to the moving direction of the elevator. ...
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### The Equivalence Principle necessitates a mixed state description for the exterior of a black hole?

I am going through this review paper on the black hole information paradox. In section 2.2 page 10, the author argues the following: One of the basic tenet of general relativity is the Equivalence ...
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### Equivalence principle, geodesics, and proper acceleration are exclusive to general relativity, or they can be understood in classical mechanics terms?

I have been told that "inertial movements, or distinction between proper and coordinate acceleration don't have meaning out of GR". But now I'm confused, I always though of these concepts in ...
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### Does the equivalence principle hold for rotational motion?

This question made me think about linear vs. rotational motion. The general view expressed in the answers is that rotational motion is not the same as linear motion. It is claimed that in a rotational ...
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### Light deflection due to acceleration vs due to constant velocity

In an intro level college physics class, we were taught about the thought experiment showing how light would be bent in an accelerating reference frame (see this YouTube video for a visual), and by ...
1 vote
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### Worries about the equivalence principle

I have a serious worry about the equivalence principle in general relativity. I have been learning general relativity from different sources (Quantum Gravity by Carlo Rovelli, A First Course in ...
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### Are the laws of physics same in all inertial and non-inertial frames of reference?

I have read in an article on Special relativity that laws of physics are the same in all inertial frames of reference but then while reading a book on GR, I came across the notion that laws of Physics ...
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### Time dilation from the Equivalence Principle

I've read as many questions as I can before asking this question, but most questions involve examples of specific situations with specific spacetime metrics, which is helpful but not really what I'm ...
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### Is there a difference in energy required to make 2 items with the same exact mass but different material travel the same distance whilst in free fall?

is there a difference in energy required to make 2 items with the same exact mass but different material travel the same distance whilst in free fall? Please answer for all cases of free fall: ...
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### Why is Einstein's equivalence principle a statement about inertial mass?

The elevator thought experiment states that one cannot distinguish between an observer inside an accelerating elevator and one inside a stationary elevator within a gravitational field. Why does this ...
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### Is this a disproof to Einstein's equivalence principle? [closed]

Did i found a disproof to the Einstein's equivalence principle? Collisions effects are not the same in equivalence principle scenarios (gravitational field and accelerated frame). Specifically the ...
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### Flywheel half-way through the event horizon of a black hole vs the equivalence principle

Imagine I am inside an isolated rocket of arbitrarily small size, and I have a spinning flywheel right next to me. Now suppose my rocket passes through the event horizon / Schwarzschild radius of a ...
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### How can weight be equal in the equivalence principle?

According to Einstein, weight will be the same as here in earth in a rocket going at 1G far from gravity fields. If we propulse an object here it will feel two forces, F=mg and F=ma of the thrust, but ...
1 vote
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### How does existence of graviton helps explain 2 different objects fall at the same rate?

Actually I want to see how gravitons help to explain why a feather and a bowling ball would fall at the same rate towards the ground assuming no air resistance, I would imagine bowling ball to emit ...
1 vote
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### Has anyone directly observed the equivalence of inertial and gravitational mass for the electromagnetic force?

Before someone tells me to drop a bowling ball and feather off the Leaning Tower of Pisa in a vacuum, let me point out that, in general relativity, you can't deduce anything about either mass of a ...
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### What is common between gravitons and Higgs bozon? [duplicate]

The General Relativity started from the consideration of Einstein that the heavy mass (due to gravitational field and inertial mass (Higgs field) are locally equivalent. What is the connection between ...
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### Violation of Einstein equivalence principle and Galileo Relativity

Two pulleys with one motor with the same force in each one. Between them a half strap or a rope which last sides is glued to each pulley. The force of the motors acts on opposite direction. Each motor ...
1 vote
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### Is every frame in which Newton's third law is verified a non-inertial frame?

In this question How can a person inside from a veiled and free-falling elevator distinguish whether he is in an inertial or non-inertial frame?, Dale answered: Within the frame of the free falling ...
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### How can a person inside from a veiled and free-falling elevator distinguish whether he is in an inertial or non-inertial frame?

From wikipedia: "A non-inertial reference frame is a frame of reference that undergoes acceleration with respect to an inertial frame", according to that statement, I would say that an ...
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### Is there any physical experiment that could tell us which object is moving to the other?

Imagine in empty space there are two objects in where one of them is moving to the other. How we can know which one is moving to the other? If there is an experiment that could tell us, would this ... 1 vote
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### Michelson-Morley interferometer in free fall

We suppose that we have a Michelson-Morley interferometer in free fall, will there be no interference: the round trip time in both arms of the interferometer is the same?
1 vote
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### Can someone explain what Einstein meant by the distinguish in his equivalence principle?

Did he meant that it's impossible to distinguish between an elevator lying on earth and an elevator going at 1G? (As long as there is no tidal force involved and the experiments are inside). I don't ... 412 views

### Isn't the Equivalence Principle technically wrong?

Isn't the Equivalence principle not quite true, technically speaking? A gravitational acceleration and an inertial acceleration are communicated very differently. A gravitational acceleration is ...
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### Unruh radiation "observed" by a particle undergoing Brownian motion

The Unruh effect is a basic result from the theory of quantum fields in curved space-time (a sort of precursor to quantum gravity) which can be thought of as describing how the ground state of ...
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### Would I be able to tell if I was inside a piece of distorted space? Are objects distinct from spacetime?

If one could hypothetically stretch / squash / in some way distort a piece of space, an outside observer could tell by looking at the distorted object/space that it had changed because the difference ...
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### How can an accelerated frame and a gravitational field be equal?

How can two things that are different be equal? In a gravitational field there is actually gravity that push us down, but in the accelerated frame there is nothing that push us down. 106 views

### A silly coincidence: $\frac{c}{\rm year}\approx 9.81 {\rm m/s^2}$ [closed]

Long ago, I sat and wondered about the equivalence of the gravitational pull on my body and upward acceleration. If I am not wrong, there is no way to distinguish between sitting on my chair here on ...
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### Equivalence Principle: Is the earth actually swelling? [duplicate]

This question is related to Weak Equivalence Principle. Is the earth actually expanding at a rate 9.8 ms-2, which is exactly countered by gravitational space expansion (g_rr term in Schwartzchild ...
1 vote
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### On Newton’s laws and inertial reference frames

Why is $\mathbf F = m \, \mathbf a$ only valid in inertial reference frames? Earth is not an inertial reference frame, even if we ignored its rotation. On its surface everything is subjected to a ...
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### Einstein equivalence principle

I know that there are two different formulations of Einstein's equivalence principle: the weak version says that the inertial and gravitational mass are equal. On the other hand the strong version ...
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### Was there an "Equivalence principle" for the energy of the different systems?

The Equivalence principle was the formalism to the assumption of the "the equivalence of gravitational and inertial mass". However, was there an "Equivalence principle" for the ...
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### Lift (elevator) and equivalence principle

A famous example to explain the equivalence principle is a lift (elevator) in the space (no gravity field), moving up with the acceleration of "g". It is said there is no way (experiment) ...
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### Bell's spaceship paradox and equivalence principle

Does Bell's paradox explain why space expands inside a uniformly accelerated rocket - which is locally the same as as a uniform gravitational field as per equivalence principle? Is this why gravity ...
1 vote
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### Equivalence Principle Frame Dragging

Why do metric equations of a rotating body (like Kerr Metric for black holes or EFE solution for rotating bodies) contain a dt dphi term, leading to rotational frame dragging effects? Please don't ...