# Questions tagged [machs-principle]

Use this tag for Mach's principle. DO NOT USE THIS TAG for the Mach number!

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### Meaning of of inertial frames in special relativity [duplicate]

One of the postulates of special relativity is The laws of physics are the same in all inertial frames There is a mention of inertial frames in the postulate. But the predictions of relativity are ...
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### General relativity, Mach's principle and rotation

During the Gravity Probe B press conference, Kip Thorne gave the following statement: Suppose that the entire universe were rotating rigidly instead of being non-rotating [...]. How would we know? ...
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### Newton's bucket and Mach [closed]

Based on previous q's and a's on this general topic, it seems there is little agreement on whether Mach's analysis is "correct". I am curious about actual experimental tests of a "...
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### Is shape dynamics capable of explaining dark matter?

I recently got introduced to the incredibly fascinating subject of Shape Dynamics: for example see https://arxiv.org/abs/1409.0105 Shape Dynamics uses conformal three-dimensional geometry to build up ...
1 vote
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### Newton's globe experiment with linear acceleration?

Newton's globe experiment: two globes that share all their features are connected with a rope in an otherwise empty universe. Newton introduced this experiment to show that even though the cases where ...
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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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### Mach's principle

The question is about Mach's principle. Suppose ther̥e is a simple pendulum comprising a bob and string suspended inside an accelerating car in space with planets,stars around it(fixed).It will stay ...
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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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### Inertial and non-inertial frame of reference

we know that those frame of references which are in uniform motion relative to an inertial frame of reference are called inertial frame. but the inertial frame we are using for comparing will also be ...
1 vote
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### What would happen if we did a Newton's bucket experiment in the closest accessible approximation to "empty space?"

I will get right to the question; for readers unfamiliar with its genesis, I append a background section below. I want to know how testable the prediction is that the water in a rotating bucket would ...
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### Does Newtonian mechanics define an absolute rotational reference?

I note that there are several question related to absolute rotation so this may be a duplicate but I didn’t see an exact double. In any case, mine is this: In a hypothetical universe made up by only ...
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### Does it actually make sense to talk about "An inertial frame" instead of a collection of frames that are inertial with respect to another?

An inertial frame according to wikipedia "is a frame of reference that is not undergoing any acceleration. It is a frame in which an isolated physical object—an object with zero net force acting ...
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### Acceleration is absolute — is this really true? [closed]

I've looked at the following pages: Is acceleration an absolute quantity? Is acceleration frame dependent or absolute? Is this the reason why acceleration is said absolute? I don't think any of the ...
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### How strong is the inflationary force of the universe's rotational variations?

Let a universe comprise two identical point masses connected by a short massless spring. Suppose somebody reaches in and spins them around their shared centre. Naive mechanics says the spring ...
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### Can we determine if a reference frame is inertial or non-inertial by looking at an accelerating object? [closed]

if we find that in a given frame, an object being acted upon by a force and is accelerating with respect to the frame would that mean that the reference frame in which this object exist is inertial or ...
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### Defining inertial and non-inertial reference frames

This is not the first time I am studying classical mechanics but the idea of reference frames has always confused me, more so after studying a bit of relativity. I'd really like it if you could clear ...
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### Spinning astronauts - can they tell which one is spinning?

If there are two astronauts facing each other along a common axis that goes through both of their centres of gravity, and one is spinning about that axis, which one is stationary and which one is ...
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### If I make the entire universe rotate, will the bucket appear to be rotating?

Newton's bucket experiment is a way to tell if you are in a rotating frame. If you have a bucket of water which is spinning the water surface will form a concave shape. Likewise, if the bucket is not ...
1 vote
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### Does Mach's principle imply that the gravitational field has a non-zero curl?

I would normally visualize the gravitational field as "radial", i.e., one whose curl is zero. However, while thinking about Mach's principle, particularly the notion of frame-dragging (as ...
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### Mach's Principle as an initial value problem?

So in this fascinating interview Abhay Ashtektar claims there is a technical formulation of Mach's principle as an initial value problem. At 1:44:22 and the main point is that the only way to ...
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### How can I know who is accelerating? – Inertial reference frames and relative motion

Suppose I (observer $I$) am standing somewhere in space. I see a region in which my friend ($F$) is accelerating in some direction $\mathrm{\mathbf{\hat{u}}}$. Suppose I see everything in $F$ ...
1 vote
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I am reading Einstein's note about genesis of GR, and I think I did not understand the part below, from the point where he starts talking about time coordinate. In particular, I don't understand this ...
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### Inertial frames and fixed stars

How did newton take fixed stars as inertial frames of reference in his definition of inertial frame? If anyone knows the logic then please help me.
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### What is the origin of the inertia?

Is there any explanation why it is harder to move an object with more mass than an object with lesser mass? What kind of force is opposing our force? Is it finalized currently and well known what the ...
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### Do vacuum solutions of Einstein's field equation violate Mach principle?

The Schwarzschild metric is mainly used to define the gravitational field on exterior region of an isolated, spherically symmetric body, but isolated bodies, according to Mach's Principle, are ...
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### Can I argue that the Earth's surface is an inertial reference to explain why we can't feel it's rotation? [duplicate]

Passengers on a plane cannot feel the plane move when it's at cruise speed. Can the same reasoning be extended to earth's rotation to explain why we cannot feel it rotate even though it's rotating at ...
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### Is there any clear and concrete proof that says the Earth is rotating and orbiting? [duplicate]

As the title states, I am wondering if there exists a clear and concrete proof that proves that the earth is revolving around the sun on an orbit, and proves that the sun is not revolving around the ...
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### Thought experiment in Mach's principle - Can a void universe be considered with special relativity?

Mach's principle is based on a thought experiment in which an astronaut floats in the middle of a space devoid of all matter and all landmarks. No star, no source of energy is present, whatever the ...
1 vote
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### Non-inertial frame and Newton's First and Second laws

The Newton's First law claim that in the absence of forces, a particle moves with constant velocity $v$. The Newton's Second Law claims that for any particle of mass $m$, the net force $F$ on the ...
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### How to affirm whether a frame of reference is Inertial or non-inertial?

As far as I know, inertial frame of reference are the ones where the all the three Newton's laws of motion hold. Having this definition we can then identify all such frames of reference which are ...
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### Will a planet rotate if it is the only being in the universe? [closed]

As a senior student , I have been wondering whatever the word inertia mean . Is inertia lying in the interaction between all the objects , or is it the nature of a space even without anything put into ...
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### Why COM/point frame (Space/Body) is not considered to be rotatory frame as well? Like when asks for angular momentum of a system about a point?

Lets consider this: Imagine the situation where a disc is rolling and also spinning about a point on ground (rolling without slipping) if someone asks to tell whats the angular momentum of disc about ...
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### What is the symmetry group of Mach's spacetime?

Newtonian spacetime can be modeled as a geometric object $M$ (affine space or manifold with connection with an absolute time function etc. etc.) that is symmetric under the action of the Galilean ...
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### What is Shape dynamics?

From Wikipedia: In theoretical physics, shape dynamics is a theory of gravity that implements Mach's principle. In General relativity curvature of Spacetime causes gravity, in String theory it is ...
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### Very strange published papers on Mach's Principle

I have recently come across a set of peer-reviewed conference papers (https://petermarkjansson.com/research/machs-principle/) reporting observations of electromagnetic markers of Mach's Principle. In ...
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### Is General Relativity compatible with Mach's Principle?

Einstein proposed what he called Mach's Principle. For the purposes of this question can we define Mach's Principle as being that e.g. if a bucket suspended by a rope contains water riding up on the ...
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### What makes the inertial reference frames special?

What makes the inertial reference frames (IRFs) special? Specifically: Using inertial reference frames is a matter of computational convenience, but in principle we could build physics without using ...
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### Mach's principle and a reference frame for acceleration

Although there are different statements of Mach's principle, one statement could be that acceleration is meaningless unless it can be defined relative to something. The distance stars provide a fixed ...
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### Isn't Unruh effect against the equivalence principle?

Doesn't the Unruh effect violate EP? Since the temperature of an absolutely accelerating reference frame would be different from an inertial one according to this effect, then one finds a criterion to ...
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### The definition of inertia in Mach's principle

Can anyone please explain me Mach's principle, i.e the definition of inertia he has given? I am really not getting what spin and universe have to do with inertia because what we are taught in our ...
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### Is inertia still considered a mysterious force?

When I first saw, for example, weightless objects in a space capsule, I assumed that pushing them would require no effort because, of course, they did not weigh anything. On Earth, heavy objects are ...
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### How well can we measure how fast are we spinning?

Although absolute translational motion is meaningless and unmeasurable (Michelson and Morley, etc), absolute rotational motion is meaningful (Newton's bucket) and measurable, using Foucault's pendulum....
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### Centrifugal force of static observer at North Pole

This question is somehow related to Newton's bucket and absolute rotation concepts, but applied to a simple, tangible scenario. Let's suppose I could hover over the North Pole, and "detach" ...
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### How do I know if I'm spinning?

Clearly, if I'm spinning, I'll feel my arms lift away from my torso. But what sets the preferred angular momentum? Is there a preferred angular momentum in a vacuum? In Newtonian mechanics, I imagine ...
1 vote
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### Mach's Principle and spin angular momentum

According to Mach's Principle, angular momentum (as in the Newton bucket experiment) is relative to the overall mass distribution of the universe, or perhaps some other characteristic of the universe'...
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### Mach's conjecture and the twin paradox in an empty universe

What would happen if we revisit the twin paradox in an empty universe? Indeed, according to Mach's principle, when a spaceship accelerates in our universe filled with too many stars and other objects, ...
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### What is centrifugal force relative to? [duplicate]

Edit- the answer is mach's principle and mach's principle is sketchy so there is no good answer. So I understand that centrifugal force is really just inertia and stuff but I still have a question. ...
1 vote
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### Would Doubly Special Relativity or Mach's Principle allow faster-than-light travel to occur without violating causality?

Doubly Special Relativity posits that the Planck length is the same in all reference frames. Mach's Principle posits inertia is produced by the combined mass of the universe. From my limited ...
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### Does General Relativity actually satisfy the General Principle of Relativity?

The “General Principle of Relativity” being “All systems of reference are equivalent with respect to the formulation of the fundamental laws of physics”. To my knowledge, this is related historically ...
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