Thread: what do spinning reference frames spin against?

I was just wondering why there would be a preferred reference frame in regards to spin.

such as a spinning reference frame is a non-inertial reference frame and so i suppose you could work out what the inertial reference frame was due to measuring a centrifugal force and a coriolis force.

This leads me to believe there is some non spinning grid in the universe.

does this grid stay straight or does it follow gravity lines?

Originally Posted by 514void

I was just wondering why there would be a preferred reference frame in regards to spin.

such as a spinning reference frame is a non-inertial reference frame and so i suppose you could work out what the inertial reference frame was due to measuring a centrifugal force and a coriolis force.

This leads me to believe there is some non spinning grid in the universe.

does this grid stay straight or does it follow gravity lines?

This is an ill-formed question. Anyways, a rotating object is rotating wrt the point located at the intersection of the two perpendiculars onto the velocities at two different points on the trajectory. (they points should not be chosen diametrically opposed).

Originally Posted by xyzt

This is an ill-formed question.

What am I doing wrong?

Originally Posted by xyzt

Anyways, a rotating object is rotating wrt the point located at the intersection of the two perpendiculars onto the velocities at two different points on the trajectory. (they points should not be chosen diametrically opposed).

huh?

what about a rotating reference frame?

I suppose that rotating reference frames are accelerating, so lets talk about an object:

if an object is rotating, then it must be rotating wrt a non rotating reference frame, so this non rotating reference frame would be non rotating in regards to any other non rotating reference frame right?

So therefore there must be a sort of grid system in the universe where to hang these non rotating reference frame.

If something is rotating, then it should have a certain speed of spin wrt the non rotating reference frame, so therefore it should be possible to find out the "grid" in which things are rotating against.

can you repeat the idea of inertial and non-inertial frames?

Originally Posted by ASG141

can you repeat the idea of inertial and non-inertial frames?

umm, i read some wiki page that said that inertial frames are ones that move with a constant velocity and don't accelerate or rotate

Inertial frame of reference - Wikipedia, the free encyclopedia

and that non inertial frames do accelerate or rotate or whatever.

Originally Posted by 514void

Originally Posted by xyzt

This is an ill-formed question.

What am I doing wrong?

Originally Posted by xyzt

Anyways, a rotating object is rotating wrt the point located at the intersection of the two perpendiculars onto the velocities at two different points on the trajectory. (they points should not be chosen diametrically opposed).

huh?

what about a rotating reference frame?

I suppose that rotating reference frames are accelerating, so lets talk about an object:

if an object is rotating, then it must be rotating wrt a non rotating reference frame, so this non rotating reference frame would be non rotating in regards to any other non rotating reference frame right?

So therefore there must be a sort of grid system in the universe where to hang these non rotating reference frame.

If something is rotating, then it should have a certain speed of spin wrt the non rotating reference frame, so therefore it should be possible to find out the "grid" in which things are rotating against.

You don't know what you are talking about.

Originally Posted by xyzt

You don't know what you are talking about.

Ok I'll try again.

Suppose you have a freely spinning body in space, with negligable outside forces acting on it.
how does it know its spinning?
it feels a centrigugal force.
suppose it could change the speed of its rotation somehow, it could speed up its rotation or slow its rotation.
It would know if it speeds up or slows down because of the centrifugal force.
It could find the speed of rotation where it didn't feel the centrifugal force.

from its perspective it could line itself up with the universe.

What is the stuff in the universe called that things can align their spin to?

The universe doesn't really have any property with which something may line up.

There is no speed that something can rotate and not experience a force. The spinning only happens because of a centripetal force (a force towards the centre).

I think it's a pretty good question. See Newton's bucket.
Bucket argument - Wikipedia, the free encyclopedia

Newton discusses a bucket filled with water hung by a cord.^[9] If the cord is twisted up tightly on itself and then the bucket is released, it begins to spin rapidly, not only with respect to the experimenter, but also in relation to the water it contains. (This situation would correspond to diagram B above.)
Although the relative motion at this stage is the greatest, the surface of the water remains flat, indicating that the parts of the water have no tendency to recede from the axis of relative motion, despite proximity to the pail. Eventually, as the cord continues to unwind, the surface of the water assumes a concave shape as it acquires the motion of the bucket spinning relative to the experimenter. This concave shape shows that the water is rotating, despite the fact that the water is at rest relative to the pail. In other words, it is not the relative motion of the pail and water that causes concavity of the water, contrary to the idea that motions can only be relative, and that there is no absolute motion. (This situation would correspond to diagram D.) Possibly the concavity of the water shows rotation relative to something else: say absolute space? Newton says: "One can find out and measure the true and absolute circular motion of the water"

this may be trivial.

a solenoid moved in the vicity of a wire may induce current due to relative velocity measured in the inertial frame of the observer. if the observer now moves keeping the solenoid and the wire stationary to give the impression of relative velocity, there will be no current.

Originally Posted by Harold14370

I think it's a pretty good question.

I agree. It is a good question. Ultimately, the real question is: What is it that defines the inertial frames of reference? My own personal take on this is that if we consider all the possible frames of reference, then some of them must be inertial, and consequently, the others must be non-inertial. Therefore, reality is forced to make a choice as to which ones are the inertial frames of reference. This is known as symmetry breaking. And because reality is forced to make a choice, that choice must manifest itself as some field. That field is known as the connection in general relativity. In the standard theory of general relativity, the connection is determined entirely by the metric tensor field, and the metric tensor field also determines the inertial frames of reference.

why must some be and some not be. an assumption?

sounds way too complicated

Please stop posting asinine nonsense.

Edit: Post this was a response to deleted.

I think the rotating bucket thing is a bit too complicated too, the detailed analysis focuses on the shape of the water which isn't even relevant.
The relevant bit is why the water doesn't stay flat relative to the bucket when it spins.

mach sort of tries to prove/disprove it with a reference frame to the earth and other celestial bodies...
but it doesn't do either.
I looked at mach's principle wiki page where i found that he thought that centrifugal forces only happen when something is spinning relative to everything else in the universe.
That seems a bit far fetched to me....

I read some other wiki page about absolute rotation here:
Sagnac effect - Wikipedia, the free encyclopedia

It sort of proves that there is a sort of spin medium that spin can be measured against.

Originally Posted by 514void

Originally Posted by xyzt

You don't know what you are talking about.

Ok I'll try again.

Suppose you have a freely spinning body in space, with negligable outside forces acting on it.
how does it know its spinning?

....by using an accelerometer.

Originally Posted by 514void

I read some other wiki page about absolute rotation here:
Sagnac effect - Wikipedia, the free encyclopedia

It sort of proves that there is a sort of spin medium that spin can be measured against.

Helicopters use laser gyroscopes (based on the Sagnac effect) to determine the angular speed , no need for any "spin medium".

Originally Posted by ASG141

why must some be and some not be. an assumption?

No. What's the alternative? They can't all be inertial because given any such frame of reference, one can accelerate relative to that frame of reference and therefore construct a non-inertial frame of reference. And they can't all be non-inertial because given any such frame of reference, one can counter-accelerate relative to that frame of reference and therefore construct an inertial frame of reference.

Originally Posted by KJW

In the standard theory of general relativity, the connection is determined entirely by the metric tensor field, and the metric tensor field also determines the inertial frames of reference.

True, but I think we should at least consider the possibility of the presence of torsion also. I just have an intuition that there might be more to geometrodynamics than Levi-Civita.

Originally Posted by Markus Hanke

Originally Posted by KJW

In the standard theory of general relativity, the connection is determined entirely by the metric tensor field, and the metric tensor field also determines the inertial frames of reference.

True, but I think we should at least consider the possibility of the presence of torsion also.

I always do. That's why I referred to the "standard theory of general relativity". Also, my wording in other posts is also suggestive of extensions to the standard theory. I have a particular interest in the torsion tensor as well as the covariant derivative of the metric tensor. However, my main focus is trying to establish the physicality or non-physicality of such fields.

Originally Posted by KJW

I always do. That's why I referred to the "standard theory of general relativity". Also, my wording in other posts is also suggestive of extensions to the standard theory. I have a particular interest in the torsion tensor as well as the covariant derivative of the metric tensor. However, my main focus is trying to establish the physicality or non-physicality of such fields.

I think the main issue here is that the presence of torsion would render the Dirac equation non-linear - unsurprisingly, since we would expect to see some form of spin-spin coupling. However, I am not aware of any empirical data that supports the presence of such interactions. Having said that, I am quite interested in Einstein-Cartan gravity myself, since the choice of the Levi-Civita connection seems entirely arbitrary to me. I am a firm believer in that if Einstein had known about the intricacies of relativistic quantum mechanics, he would likely not have omitted torsion in the first place. But maybe that's just me

What would happen if we have linear particle accelerators in a inertial frame, maybe in space calibarated with sagnac effect detectors.
I bet alot of scientists would love to make that project happen, and also NASA.

I wonder if galaxies would drag the torsion field along with it, that might make the dark matter thing go away?