Perfect Frame of Reference ?

[ajb]

If you know of an official definition of frame of reference please share it with us and cite the source.

This is strange wording as there is no official definition of anything in physics, just agreed upon definitions used by the community within some mathematical framework. The most general definition would really be a choice of local coordinates on space-time.

 

The definition you are working with, and this is on Wikipedia is much weaker and sounds more like a space-time cut into space and time. Locally you can always do this, but in a well defined global manner it is much more tricky; you need to think about global hyperbolic space-times. Anyway, this does not give you coordinates but classes of coordinates adapted to the cut.

[Fred Champion]

So then, how much more "official" could a consensus - community - definition get than to be written down for all to see? And if it is not written down and presented in a source which can be cited are we left with each individual or local group remembering some slightly different version? But wait, isn't that exactly what my definition is, just a slightly different version?

 

 

I will hit this one more time and then (probably) give up. We live in an actual, or real, or physical, frame of reference. The universe is the volume we exist within. Our coordinate origin, our zero point, is the eye of the observer. Our orientation, our zero angle, is the direction we look in when we pick an object to use as a reference for specifying the positions of other objects. Gravity determins the "up" and "down" and "horizontal" of our orientation. Our perception of "near" and "far" provide our metrics. We inhabit one and only one actual universe and have one and only one actual coordinate system for each actual individual. The combination of the volume we inhabit and the way we experience it is not just our "preferred" frame of reference, it is our only actual frame of reference. We do not construct it, we have discovered it.

 

Any other frame of reference we may construct, the combination of a volume and a coordinate system imposed upon that volume, will be imaginary. A coordinate system not imposed upon a volume is a concept only. It provides no means for describing actual nor imaginary observations. A coordinate system without some volume combined provides no "where". Without a volume there is no place for the objects that would be observed or described.

[swansont]

So then, how much more "official" could a consensus - community - definition get than to be written down for all to see? And if it is not written down and presented in a source which can be cited are we left with each individual or local group remembering some slightly different version? But wait, isn't that exactly what my definition is, just a slightly different version?

 

 

I will hit this one more time and then (probably) give up. We live in an actual, or real, or physical, frame of reference. The universe is the volume we exist within. Our coordinate origin, our zero point, is the eye of the observer. Our orientation, our zero angle, is the direction we look in when we pick an object to use as a reference for specifying the positions of other objects. Gravity determins the "up" and "down" and "horizontal" of our orientation. Our perception of "near" and "far" provide our metrics. We inhabit one and only one actual universe and have one and only one actual coordinate system for each actual individual. The combination of the volume we inhabit and the way we experience it is not just our "preferred" frame of reference, it is our only actual frame of reference. We do not construct it, we have discovered it.

 

Any other frame of reference we may construct, the combination of a volume and a coordinate system imposed upon that volume, will be imaginary. A coordinate system not imposed upon a volume is a concept only. It provides no means for describing actual nor imaginary observations. A coordinate system without some volume combined provides no "where". Without a volume there is no place for the objects that would be observed or described.

 

"We"? "Our"? My eye is not co-located with your eye, and I may be moving with respect to you. On what basis do you deem your frame of reference real and my frame of reference imaginary?

[Fred Champion]

 

"We"? "Our"? My eye is not co-located with your eye, and I may be moving with respect to you. On what basis do you deem your frame of reference real and my frame of reference imaginary?

I think you take the meaning of my statement wrong. Of course yours is as real as mine.

 

The origin of every frame of reference, actual or imaginary, is presented as the viewing point of a single observer; it has to be, there can be only one viewing point per observer.

 

Translation from one observer's origin to another's is, as you point out, in terms of displacement within the frame of reference. If one observer recognizes a second, then both observers share that frame of reference. Observations from each observer are made and must be presented from each observer's viewing point (literally, each observer's point of view).

[studiot]

Fred, I find your idea of a frame of reference far to limited and constraining.

 

Why should it be constrained to someone's eye?

 

What if I wished to consider the mechanics inside a solid body?

Where would I place my eye?

 

I say this because there are 'preferred frames of reference' in such circumstances (ajb has already referred to these).

 

The OP has perfect, I agree with ajb preferred is a better word - nothing is perfect.

 

In the example I just gave we call these preferred axes 'Principal Axes', and the (preferred) frame of reference is defined by these.

[swansont]

I think you take the meaning of my statement wrong. Of course yours is as real as mine.

 

The origin of every frame of reference, actual or imaginary, is presented as the viewing point of a single observer; it has to be, there can be only one viewing point per observer.

 

Translation from one observer's origin to another's is, as you point out, in terms of displacement within the frame of reference. If one observer recognizes a second, then both observers share that frame of reference. Observations from each observer are made and must be presented from each observer's viewing point (literally, each observer's point of view).

 

So why can't I just pretend to be in the center of mass of a system in order to figure something out? What is invalid about that approach? Why would I have to physically be there?

[Mordred]

This reminds me of the idea of conformal time or cosmic time in cosmology. Both can be useful ideas of a global time in an expanding Universe, but this should not be confused with the notion of a preferred frame of reference. There maybe frames that are suited to the particular physics at hand, but this does not mean that the theory really singles them out, we do that.

 

 

The CMB is particularly useful in the comoving frame. A proper frame, or comoving frame, is a frame of reference that is attached to an object. The object in this frame is stationary within the frame. The CMB is often used for observers that see the universe as isotropic. However an observer moving at relative velocities would not percieve the universe as isotropic.

 

Proper distance roughly corresponds to where a distant object would be at a specific moment of cosmological time

Comoving distance factors out the expansion of the universe, giving a distance that does not change in time due to the expansion of space

conformal time is similar to having a watch that slows down as the universe expands.

 

You don't see conformal frame used to often nowadays, most articles etc use the comoving or proper frame

 

however this does not qualify the CMB as a perfect frame or an absolute frame, as convenient as it is lol, as you've already pointed out

Edited May 9, 2014 by Mordred

[ajb]

however this does not qualify the CMB as a perfect frame or an absolute frame, as convenient as it is lol, as you've already pointed out

Exactly, "special" frames are usually due to the high amount of symmetry of a specified situation and should not be seen to really define preferred frames. Using the CMBR is a good example: it gives us a nice frame for cosmology but it is nothing special from the point of view of general relativity.

[Fred Champion]

 

So why can't I just pretend to be in the center of mass of a system in order to figure something out? What is invalid about that approach? Why would I have to physically be there?

You may set up any imaginary volume and impose upon it any imaginary coordinate system you can imagine. I expect you will recognize that in that situation you will not be making observations; you may be describing observations or you may be making predictions, or you may be just doing geometry or math. What you figure out may be as valid as the conditions you set up and the methods you apply. My experience is that the problems, if there are any, will come when you try to carry some conclusion from an imaginary environment into our actual environment.

Fred, I find your idea of a frame of reference far to limited and constraining.

 

Why should it be constrained to someone's eye?

 

What if I wished to consider the mechanics inside a solid body?

Where would I place my eye?

 

I say this because there are 'preferred frames of reference' in such circumstances (ajb has already referred to these).

 

The OP has perfect, I agree with ajb preferred is a better word - nothing is perfect.

 

In the example I just gave we call these preferred axes 'Principal Axes', and the (preferred) frame of reference is defined by these.

The individual's "eye" Is just a shortcut way of saying his/her point of viewing, or perhaps more properly his/her point of "experiencing". We will make observations and describe them from a single point of viewing.

 

You may set up any imaginary frame of reference you can imagine. I expect you would base the conditions for your imaginary frame of reference on some set of actual observations. My response to you is the same as my response to Swansot above.

[ajb]

My experience is that the problems, if there are any, will come when you try to carry some conclusion from an imaginary environment into our actual environment.

In the context of mainstream physics this sounds like the usual problem of being careful in deciding what are artifacts of the coordinate system employed and what is the "true physics". This is why tensors and tensor-like objects play a huge role in physics.

[studiot]

Since you have invoked the dreaded 007, to quote him

 

Swansont:

The issue here is that you are not just asking - you have been insisting one answer is correct, and it's not.

 

 

 

Fred Champion

The individual's "eye" Is just a shortcut way of saying his/her point of viewing, or perhaps more properly his/her point of "experiencing". We will make observations and describe them from a single point of viewing.

 

You may set up any imaginary frame of reference you can imagine. I expect you would base the conditions for your imaginary frame of reference on some set of actual observations. My response to you is the same as my response to Swansot above.

 

 

And yet in another thread you were adamant that your eye was the only true origin and continued quite a lively discussion about this assertion.

 

You cannot have it both ways.

 

I doubt that you have any idea what I was alluding to when you made the above response,

 

Yet you did not ask

 

But in IMHO the real issue is as 007 says, you do not listen to any one else.

 

A discussion involves exchange of ideas: I have acknowledged your good ones, but you have steadfastly refused to listen to any of mine or from anyone else.

 

If you could do this there is a real danger that you might learn something new and of possible value.

Edited May 9, 2014 by studiot

[swansont]

My experience is that the problems, if there are any, will come when you try to carry some conclusion from an imaginary environment into our actual environment.

 

Issues arising from improper application of physics and mathematics is universal and not limited to this scenario. Not choosing the simplest frame for the problem has been known to cause problems, too, because that makes one more prone to make math errors.

[Fred Champion]

Since you have invoked the dreaded 007, to quote him

 

 

 

And yet in another thread you were adamant that your eye was the only true origin and continued quite a lively discussion about this assertion.

 

You cannot have it both ways.

 

I doubt that you have any idea what I was alluding to when you made the above response,

 

Yet you did not ask

 

But in IMHO the real issue is as 007 says, you do not listen to any one else.

 

A discussion involves exchange of ideas: I have acknowledged your good ones, but you have steadfastly refused to listen to any of mine or from anyone else.

 

If you could do this there is a real danger that you might learn something new and of possible value.

I believe you are correct. I had no idea you were attempting allusions to illusions.