Preferred Frames not in SR are used in Astrophysics

[RandallB]

I’m extracting here a side discussion on the application of Preferred Reference Frames from a thread on the twins paradox, so that thread does not seem to get “hijacked” by this discussion since the connection may seem thin to some. IMO the preferred frame interpretations as used in Astrophysics in just as accurate with a universally uniform observed physics in all reference frames for solving the twins paradox as is SR alone.

The fact that SR defines a Preferred Frame as indefinable only applies to within the use of SR. Astrophysics is much more than SR and more than just the addition of GR with a wealth of observations to apply to the theories to establish the modern science of Astrophysics.

I am aware that astrophysisists use preferred frames to solve certain problems. I believe this is done for convenience in most cases, although sometimes I think it's used to explore new ideas as well. I don't think it's ever been stated that preferred frames in this context actually represent physical reality though. For example, I haven't read anything coming from the astrophysical community claiming there IS some form of absolute motion; at least in the sense that two simultaneous events in the absolute frame would be simutaneous in all other inertial frames. Please correct me if I'm wrong in this?

But the astrophysical community would never expect two simultaneous events would appear simultaneous in other inertial frames. The point of an absolute (local) frame of reference is to resolve the difference between reference frames as to which one is correct, or at least nearest to correct, as having the fastest relative rate of time and longest relative length of distance, while all other reference frames are slower and shorter in those respects.

The way they maintain a uniform physics between all reference frames is from the ability of each reference frame to establish just how far off the local preferred their own frame of reference is (while maintaining a local physics that does behave and look same from as in any other frame). Astrophysics does this with our own frame of reference by identifying our Earth and Solar system frame as being in motion against the local preferred frame as measured by CMBR observations. Likewise even with our motion against the local preferred frame, through careful observation of light from distant space we to know that light from a Mega Parsec away was generated simultaneous with specific time in our past. That info combined with being able to see that the local preferred frame at a Mega Parsec distance is in motion wrt our own local preferred frame by about 70 km/sec is how Hubble established the Hubble Expansion of space.

Any scientists that claims no theories can establish or use a preferred reference frame must by definition reject the Hubble expansion of space conclusions made by Astrophysics. And you don’t find many physicists of any type anywhere that reject Hubble Expansion. It is just that SR standing alone cannot establish preferred frames.

 

[paw]

Astrophysics does this with our own frame of reference by identifying our Earth and Solar system frame as being in motion against the local preferred frame as measured by CMBR observations.

Hi RandallB. I assumed that might be what you meant and I am familiar with this convention. I completely accept your statement. However, I respectfully submit that this isn't the same as an absolute, or preferred, frame in the sense I meant in the other post.

I can accept that the CMBR gives some kind of absolute motion within the observable universe. But it doesn't give us absolute motion wrt the vacuum or background or spacetime, however we want to label it.

For example, the CMBR is roughly homogenous in all directions. It doesn't establish any two points that all inertial observers will agree are separated by the same distance.

The absolute frame I'm referring to would do exactly that. I think it is clear that such a frame cannot exist unless SR (and I believe GR) would fail.

To be completely clear, I accept the notion of an absolute frame in the sense you are using the term. I see how it is useful. I see it does not violate SR or GR. But it isn't the same as 'absolute' in the sense I've been using the term. 'Absolute' in the sense I been using it means there is some form of absolute motion wrt spacetime.

 

[RandallB]

Hi RandallB. I assumed that might be what you meant and I am familiar with this convention. I completely accept your statement. However, I respectfully submit that this isn't the same as an absolute, or preferred, frame in the sense I meant in the other post.
….
For example, the CMBR is roughly homogenous in all directions. It doesn't establish any two points that all inertial observers will agree are separated by the same distance.
….
I accept the notion of an absolute frame in the sense you are using the term. I see how it is useful. I see it does not violate SR or GR. But it isn't the same as 'absolute' in the sense I've been using the term. 'Absolute' in the sense I been using it means there is some form of absolute motion wrt spacetime.

But the SR version of preferred frame is violated because SR is not a complete theory and was recognized as so almost from the start – at least by Einstein it did take some time for many to catch up at the time as Astrophysics and GR developed beyond SR.
Plus “space-time” is not the issue or standard to use for a reference, again Einstein recognized from the start that it was not a useful way to look at real physics, just a clumsy crutch for understanding SR (not GR). True he did allow that it was good for the way it involved the pubic imagination, I’m not so sure it has been a positive to that imagination.

And when you say the Astrophysics use of Preferred Reference Frames “doesn't establish any two points that all inertial observers will agree are separated by the same distance” you are again exporting a SR standard to formulation beyond the scope of SR alone. In Astrophysics all reference frames in a local area can determine a common Preferred Frame as they have a relatively common view of the same CMBR. Including being able to calculate their own and others motion wrt to that Preferred Local Frame. More than enough info to sort out a common standard of measure for all by translating (using the inverse of the Lorentz factors) to the Preferred Frame of measure; as the common measure by which they will all see the same length.
That is actually easier than working out Hubble Expansion – the tricky part there was figuring out the need to define the preferred frame in a local space is not the same as in distant local space in order to understand or even discover Hubble Expansion.

It is impressive the Hubble Expansion theory was discovered so long before CMBR information was available. I guess from my perspective the reason most don’t recognize the significance of Local Preferred Reference Frames in Astrophysics is a misplaced focus “space-time”. I never did see the point in “space-time” as it doesn’t help derive GR nor add anything really new to SR.

 

[paw]

First off, I have to say I have been using the term 'absolute frame' in the SR sense all along. I hope that was clear. I really tried to make it so.

But the SR version of preferred frame is violated because SR is not a complete theory

Sure SR is not a complete theory. But GR certainly reduces to SR in flat spacetime. A clear violation of SR would be very bad for GR as well. Therefor it's acceptable, I would think, to use SR in the realm where it's valid.

Plus “space-time” is not the issue or standard to use for a reference

I think this is the crux of the matter. I used the terms spacetime/vacuum/background in an attempt to make clear that an 'absolute' frame would be at rest with some background that can be taken to be fixed for all time. To the current state of the art I don't think anyone claims to have found such a thing.

An ether is the best example. If the ether existed then motion could be measured against it and all other inertial frames would have to agree. This is clearly not the case in SR (and by extension GR in the same regime). Note: This doesn't conflict in any way with the use of a preferred frame the way you are using it.

And when you say the Astrophysics use of Preferred Reference Frames “doesn't establish any two points that all inertial observers will agree are separated by the same distance” you are again exporting a SR standard to formulation beyond the scope of SR alone.

Rather than 'exporting a SR standard to formulation beyond the scope of SR alone' I would say instead that I'm using SR for a completely different purpose. That is to show that there is no 'absolute motion' wrt some 'fixed for all time' background. The CMBR doesn't count here because it exists within that very background, whatever that background might be.

 

[yuiop]

The apparent velocity of the Earth with respect to the CMBR is not too great at it would not be too difficult for an observer in a spacecraft to position themselves so that they are at rest with the CMBR locally say within the Solar system or the Milky Way. From that vantage point they could observe a distant galaxy billions of light years away that appears to have a recessional velocity of 1.5c calculated from its red shift. Another observer at rest with that distant galaxy could quite possibly also observe themselves to be at rest with CMBR. Now if two spatially separated observers both appear to be at rest with the CMBR while having motion relative to each other, then the CMBR is not a good candidate for an absolute reference frame for anything other than local measurements.

 

[paw]

Now if two spatially separated observers both appear to be at rest with the CMBR while having motion relative to each other, then the CMBR is not a good candidate for an absolute reference frame for anything other than local measurements.

Exactly my point. The CMBR as a preferred frame is fine for certain types of calculations but isn't the same as a preferred, or absolute, frame in SR. It's a subtle difference but crucial none the less.

 

[RandallB]

... distant galaxy billions of light years away that appears to have a recessional velocity of 1.5c calculated from its red shift. Another observer at rest with that distant galaxy could quite possibly also observe themselves to be at rest with CMBR. Now if two spatially separated observers both appear to be at rest with the CMBR while having motion relative to each other, then the CMBR is not a good candidate for an absolute reference frame for anything other than local measurements.

All your describing here is how Astrophysics most certainly does recognize and use preferred frames not possible in the limited SPECIAL view of SR. Including the concept that measureable frames (local preferred frames included) can move wrt each other at FTL speeds, provided they are separated by enough distance.

Exactly my point. The CMBR as a preferred frame is fine for certain types of calculations but isn't the same as a preferred, or absolute, frame in SR. It's a subtle difference but crucial none the less.

Exactly what is that point?
IMO you seem to be repeating the popular line that “there is no such thing as a ‘Preferred Frame’ in reality“ with no scientific justification. Of course if you limit your comments to what can be shown by SR your statements are irrefutable, but that is NOT what you or proponents of “No Possible Preferred Frame of Reference” are doing, your positing the assertion as a fact of reality.

The real “subtle difference but crucial” point is that it is SR that is limited to SPECIAL “certain types of calculations” making it inadequate to judge reality in this respect, not the application for CMBR observations of Astrophysics.
If SR was to be so complete it should be able to address the above referenced “recessional velocity of 1.5c calculated from its red shift”, without the use of preferred frames. But without local preferred frames SR falls apart as a tool to address observations that show FTL recessional velocities. That ability falls to a more complete description like Astrophysics that does recognize preferred frames, giving us Hubble Expansion, a result SR without preferred frames cannot achieve.

Can Astrophysics define a universal “Absolute Reference Frame” upon which Local Preferred Frames of reference can be measured against? Doubtful, that would require finding something like a reference or reference signal anchored somewhere beyond the source of the CMBR. If such a think may or may not exist, SR certainly is inadequate verify or falsify such a possibility; since SR alone would predict something like Hubble Expansion as impossible.

 

[paw]

Of course if you limit your comments to what can be shown by SR your statements are irrefutable

That's all I've been saying. Limited to SR only. Somehow we're talking at cross purposes.

 

[RandallB]

That's all I've been saying. Limited to SR only. Somehow we're talking at cross purposes.

No I do not believe that to be true.
You were still representing Astrophysics and preferred frames as a special case that can use preferred frames regardless of “facts” indicated by SR.
That is not the same as recognizing SR as the special case; limited, incomplete and unable to judge the real existence of usable Local Preferred Frames of Reference.

 

[Ich]

That is not the same as recognizing SR as the special case; limited, incomplete and unable to judge the real existence of usable Local Preferred Frames of Reference.

SR includes the principle of relativity, which states that the laws of physics have the same form in every inertial frame - including the CMB-frame. What's wrong with that?
Also, our peculiar motion has nothing to do with Hubble's discovery of an expanding universe.

 

[Dale]

Hi RandallB,

When people talk about a "prefered frame" they usually mean that the laws of physics are different in that frame than in others. This is not the sense in which the CMB frame is prefered! If it were the case then, e.g. orbits that were stable in the CMB frame would not be stable in another frame. If an astrophysicist wants to analyze the motion of a system or galaxy or cluster that is moving wrt the CMB they will most likely perform the calculation in the center of momentum frame rather than the CMB frame. This can be done precisely because the CMB frame is not a preferred frame in the usual sense.

The only way that the CMB could be considered "prefered" is that it simplifies the formulation or calculation of certain problems. The GPS system also uses a "prefered frame" in this sense, it uses the earth-centered-inertial frame, simply because calculating locations on the surface of the Earth in this frame is easy. Rotating reference frames can also be "prefered" in this sense. This kind of "prefered" is not physical, it is simply convenience and convention.

 

[RandallB]

When people talk about a "prefered frame" they usually mean that the laws of physics are different in that frame than in others.

This kind of "prefered" is not physical, it is simply convenience and convention.

“People” may think that but nothing in physics says that.
Nothing in identifying the preferred frame requires the physics or experiments in other frames appear different or follow different rules.
If "preferred" is not a real physical thing then the entire concept of Hubble Expansion is just a convenient convention and not something that should be considered a real part of reality.
Unless of course you or Ich can provide a SR explanation for Hubble without the use of Local Preferred Frames of Reference. I don’t think anyone can do you?

Your welcome to your opinion but based on what you say I can only deduce that you prefer Particle Physics and generally reject Astrophysics. They are after all competing branches of science with some fundamental differences which is why GR & QM have not been and some think cannot be unified. I don’t reject Astrophysics and just because there are more Particle Physicists than Astrophysicists doesn’t make Astrophysics the wrong one.

IMO your are jumping to a broad conclusion not justified by the limited scope and ability of SR on its own, just as many that do not really understand Astrophysics do.

 

[Dale]

Nothing in identifying the preferred frame requires the physics or experiments in other frames appear different or follow different rules.

Then to me it seems like your idea of "prefered" frame is the same as in "Coke is preferred over Pepsi".

 

[paw]

RandallB, do you agree that GR predicts the Hubble expansion via the cosmological constant? Do you agree that GR is essential to astrophysics?

Do you agree that in local, flat, spacetime GR reduces to SR?

If you do then you must agree that if SR were somehow falsified that would be a tremendous blow to GR as well?

If GR was found to be on shakey theoretical grounds then surely you agree that Astrophysics would also be on shakey ground?

So the claim made in SR that 'there is no form of absolute motion' or 'there is no 'universal, absolute, frame of reference' must hold for GR and Astrophysics as well. Surely this is clear? In fact in post #7 you said.

Can Astrophysics define a universal “Absolute Reference Frame” upon which Local Preferred Frames of reference can be measured against? Doubtful, that would require finding something like a reference or reference signal anchored somewhere beyond the source of the CMBR.

which to me looks like you agree with me.

My claim that 'there is no 'universal, absolute, frame of reference' in SR is just exactly that. A claim restricted to SR only. The repercussions of that claim certainly do echo through all branches of physics but the initial claim is still restricted to SR.

Again, I stress, we don't appear to disagree in any fundamental way. You do not appear to be claiming any 'absolute' frame exists in SR. Any disagreement I see seems restricted to the use of the word 'prefered'.

 

[RandallB]

RandallB, do you agree that GR predicts the Hubble expansion via the cosmological constant? Do you agree that GR is essential to astrophysics?

Do you agree that in local, flat, spacetime GR reduces to SR?

If you do then you must agree that if SR were somehow falsified that would be a tremendous blow to GR as well?

If GR was found to be on shakey theoretical grounds then surely you agree that Astrophysics would also be on shakey ground?

So the claim made in SR that 'there is no form of absolute motion' or 'there is no 'universal, absolute, frame of reference' must hold for GR and Astrophysics as well. Surely this is clear?

What is that some kind of regressive logic? – it makes no sense at all.
You know that before there was math with negative numbers and “Zero” there was an old math where there were no negative numbers or “Zero”. Certainly within the context of the old math the idea that negative numbers and the concept of “Zero” do not exist is still valid within the context of that old math. Would you then conclude that the idea of negative numbers and Zero are therefore invalid for modern math just some imaginary convention of convenience – that’s nonsense.

And GR deals with gravity, any reduction other than ignoring GR cannot be SR because SR does not deal with Gravity.

And do not put your words in my mouth; I did not say a “Absolute Preferred Reference Frame” could not exist I said if “such a thing may or may not exist, SR certainly is inadequate” to judge it.

My claim that 'there is no 'universal, absolute, frame of reference' in SR is just exactly that. A claim restricted to SR only. The repercussions of that claim certainly do echo through all branches of physics but the initial claim is still restricted to SR.

Again, I stress, we don't appear to disagree in any fundamental way. You do not appear to be claiming any 'absolute' frame exists in SR. Any disagreement I see seems restricted to the use of the word 'prefered'.

Of course we disagree in a very fundamental way.
It’s not like the word ‘preferred’ comes in two flavors like Old Coke vs New Coke.
You claim the conclusion made by SR about ‘preferred’ are still valid and echo through all branches of physics. I claim that SR is too incomplete to pass any meaningful judgment on the issue, and more advanced science is required and has been applied.

If SR were that complete one of you would have addressed, rather than ignore, my previous question:
Can Ich DaleSpam[\b] or you “provide a SR explanation for Hubble without the use of Local Preferred Frames of Reference. I don’t think anyone can do you?”

Care to respond to it?

 

[Dale]

It’s not like the word ‘preferred’ comes in two flavors like Old Coke vs New Coke.

The word "preferred", like most words in the English language, certainly comes in a wide variety of flavors/connotations/definitions/useages.

Can Ich DaleSpam[\b] or you “provide a SR explanation for Hubble without the use of Local Preferred Frames of Reference. I don’t think anyone can do you?”

In GR frames are not preferred (physics meaning) either. Hubble is easily explained using GR.

 

[paw]

Were clearly not on the same page and I won't attempt to respond further.

If SR were that complete one of you would have addressed, rather than ignore, my previous question:
Can Ich DaleSpam[\b] or you “provide a SR explanation for Hubble without the use of Local Preferred Frames of Reference. I don’t think anyone can do you?”

Care to respond to it?

Sure. SR doesn't predict the Hubble expansion. Nor should we expect it to.

 

[Ich]

IMO your are jumping to a broad conclusion not justified by the limited scope and ability of SR on its own, just as many that do not really understand Astrophysics do.

I urge you to refrain from such statements. From your previous comments, it is clear that you lack a fundamental unterstanding of the discussed concepts, and are not in a position to judge the competence of others.

If SR were that complete one of you would have addressed, rather than ignore, my previous question:
Can Ich DaleSpam[\b] or you “provide a SR explanation for Hubble without the use of Local Preferred Frames of Reference. I don’t think anyone can do you?”

SR is definitely incomplete, as it does not include gravitation. GR is needed for cosmology, and from the stipulation that the universe be homogeneous and isotropic, it follows that the average velocity of matter at any point in the universe follows simple laws, like Hubble's.
But this has nothing to with our peculiar motion wrt the CMB (which is the best measure for said averaged velocity at any point), and it does not invalidate SR more that the introduction of GR itself.

 

[RandallB]

I urge you to refrain from such statements. From your previous comments, it is clear that you lack a fundamental unterstanding of the discussed concepts, and are not in a position to judge the competence of others.

That is not a statement as I was clearly stating an opinion.
And in your STATEMENT it is clear you are in no position to judge what I understand.

And IMO (in my opinion) you are intentionally avoiding answering my question.
Do you or do you not believe establishing Local Preferred Reference Frames is required for defining Hubble expansion or not? Yes or No

If yes, then you agree with what I understand.

If no, then outline the method by which Hubble Expansion can be defined without it, because that would be something I do not know.

But if you don’t have anything substantive to offer, other than to yell you know and others do not, that will not advance the discussion and you should excuse yourself from it.

 

[Ich]

Do you or do you not believe establishing Local Preferred Reference Frames is required for defining Hubble expansion or not? Yes or No

No. You take
$$ds^2 = c^2 dt^2-a(t)^2[dr^2+\bar{r}^2 d\Omega^2]$$
and boost it, you get a valid and highly unusable chart of the universe.
There is a frame that is much more convenient, but the physics is the same.

 

[JesseM]

When people talk about a "prefered frame" they usually mean that the laws of physics are different in that frame than in others.

This kind of "prefered" is not physical, it is simply convenience and convention.

“People” may think that but nothing in physics says that.
Nothing in identifying the preferred frame requires the physics or experiments in other frames appear different or follow different rules.

What do you mean by "nothing in physics"? Obviously the laws of physics themselves don't select what meanings should be assigned to particular words--if you wanted to use the word "energy" rather than "momentum" for the quantity mass times velocity, the laws of physics wouldn't strike you down. But human physicists have adopted conventions for what particular terms are supposed to mean in the context of a discussion of physics, and any physicist will understand the term "preferred frame" to mean a frame where the laws of physics are different in that frame, just like any physicist will understand the term "momentum" to mean mass times velocity (or mass times velocity times gamma, in a relativistic context). If you want to communicate clearly, you should use terminology the same way physicists use it.

 

[RandallB]

No. You take
$$ds^2 = c^2 dt^2-a(t)^2[dr^2+\bar{r}^2 d\Omega^2]$$
and boost it, you get a valid and highly unusable chart of the universe.
There is a frame that is much more convenient, but the physics is the same.

Oh what’s the point, why not just say Hubble Expansion = 70 (km/s)/Mpc
I was asking for the method, not a some looked up some formula.

The question was how do you establish and derive the Expansion is real, and the formulas used quantify it value and shape, without establishing some form of description of Local Preferred Frames for the separate regions of space being compared.

The formulas were built presuming Local Preferred Frames in the first place.
Some Local Frame is used compare with some frame at a distance; how are they selected?
They certainly cannot be selected randomly. If they are not determined to be locally “preferred” frames, exactly how are they selected and how are they described or named?

 

[Ich]

The formulas were built presuming Local Preferred Frames in the first place.
Some Local Frame is used compare with some frame at a distance; how are they selected?
They certainly cannot be selected randomly. If they are not determined to be locally “preferred” frames, exactly how are they selected and how are they described or named?

As I said before, some stipulated properties of the universe imply that the average motion of matter at every point in the universe - averaged over a large enough area - follows simple law, e.g. Hubble's law. The frame where this motion vanishes is called comoving frame. Cosmology becomes simplest if you use a coordinate system which is comoving in every point. Those frames are preferred for simplicity.
Now what's your point?

 

[RandallB]

Looks like thread is accepting posts today – I update this one with my reply.

As I said before, some stipulated properties of the universe imply that the average motion of matter at every point in the universe - averaged over a large enough area - follows simple law, e.g. Hubble's law. The frame where this motion vanishes is called comoving frame. Cosmology becomes simplest if you use a coordinate system which is comoving in every point. Those frames are preferred for simplicity.
Now what's your point?

My point is as in the title of this Thread.
Although many like to think of “no absolute frames” as some immutable law of physics based on a SR “proof”.
Many inaccurately extend the idea into all of physics which is clearly incorrect as I described in the title and OP. In a closed lab; such as if our solar system were surrounded by an impenetrable nebulous cloud preventing us from even seeing anything of the Milky Way, it would make finding a preferred frame impossible and there would be Hubble etc. But our real world physics is not limited to such a incomplete SR view. That is the simple point the it seems to me so many not only miss but for some reason it is a significant point many for some reason intentional obscure from others and I guess even from themselves. (Maybe it is just a misplaced effort to pay respect to Einstein and his first work.)

Our ability to define a Local Preferred Frame including being able to measure our own peculiar motion wrt it, and is a vital part of modern physics (like Astrophysics) such as comparing our LPF with distant LPF to define and measure Hubble Expansion.

 

[RandallB]

for some reason the system wil not let me correct complete or repost my prior post

I'll have to fix later.

 

[JesseM]

My point is as in the title of this Thread.
Although many like to think of “no absolute frames” as some immutable law of physics based on a SR “proof”.
Many inaccurately extend the idea into all of physics which is clearly incorrect as I described in the title and OP.

As I said in post #21, it's not incorrect if you define the term "preferred frame" in the way that physicists always do, namely a frame where the laws of physics take a different form than in other frames. Your argument is based on using a nonstandard definition of "preferred frame" or "absolute frame"; it's a bit like saying "energy is not conserved in classical mechanics" and then revealing that you're using the word "energy" exclusively to mean what physicists normally call "kinetic energy".

If you disagree that it is understood among physicists that the term "preferred frame" means a frame where the laws of physics are different, I suggest doing a search for "preferred frame" on google (or on google scholar or google books) to see if you can find examples of physicists using it a different way. And in any case, if you use "preferred frame" to mean a frame which is more convenient to use based on the physical arrangement of matter/energy rather than a frame where the laws of physics are different, then even in special relativity you could imagine arrangements of matter which might pick out a "preferred frame" in this sense (for example, imagine trying to figure out the motion of a charged particle in a universe containing an infinite charged plane; wouldn't it be easiest to analyze this problem in the rest frame of the plane?)

 

[paw]

As I said in post #21, it's not incorrect if you define the term "preferred frame" in the way that physicists always do, namely a frame where the laws of physics take a different form than in other frames. Your argument is based on using a nonstandard definition of "preferred frame" or "absolute frame"; it's a bit like saying "energy is not conserved in classical mechanics" and then revealing that you're using the word "energy" exclusively to mean what physicists normally call "kinetic energy".

Thank you JesseM. I glad to see others understand what I've been trying to say in this post and a previous one. Your explanation is clear and consise. To me it really points out how flawed our everyday language is when applied to problems of physics. If we don't rigorously stick to accepted definitions all that results is confusion and argument.

 

[Dale]

If we don't rigorously stick to accepted definitions all that results is confusion and argument.

I agree! Frankly, as used in this thread, the fact that astrophysicists prefer a certain coordinate system is no more surprising or important than if they prefer Frito-Lay over Doritos.