Preferred reference frame

[J.C.MacSwell]

To what extent do the CMB and the Hubble expansion define a preffered reference frame?

[timo]

What´s CMB ?

[swansont]

Cosmic Microwave Background, aka CBR, Cosmic Background Radiation.

[Martin]

To what extent do the CMB and the Hubble expansion define a preffered reference frame?

 

they define an idea of being at rest with respect to the Hubble flow

 

and of being at rest with respect to the CMB

 

after that, orientation of spatial coordinates is arbitrary

 

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so there is no preferred x, y, z directions

 

but professional astronomers do write papers where they say that our galaxy, or our local group of galaxies, is moving at a certain speed w.r.t. the CMB in a certain direction w.r.t. CMB

 

I can tell you what the direction is, and the speed, if you want to know. It is probably in some journal article in the astronomy links sticky thread.

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the Sun and Earth are presumed to be moving at a speed of roughly 0.001 c with respect to the Hubble flow, or the CMB, and in the direction of the constellation Leo.

 

so when they analyze the CMB data, like from WMAP, they factor this "dipole" out of the data because it is presumed just an artifact of the Earth's own motion and not a real feature of the CMB.

 

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if you dont allow for the earth's motion then both the CMB and the expansion of the universe look lopsided. the CMB looks hotter towards Leo and colder away from Leo

 

and the distant galaxies are fleeing faster and more redshifted if you look 180 degrees from Leo, and are fleeing slower and are less redshifted if you look in Leo direction.

 

so if you DONT adjust for the earth and sun moving in absolute terms relative to space then you will have screwed up data.

 

so it is standard procedure for working mainstream astronomers to use a preferred frame, or at least a concept of being at rest. (this doesnt actually contradict Special Relativity, which is about the symmetry of local flat coordinates, not global curved ones, but it SOUNDS like it contradicts it :smile:)

 

this can be cause for some chuckles because of course the standard physics doctrine received from Special Relativity is that you cant have a concept of being at rest (General Relativity is a bit more permissive about what you can have at large scale)

 

IIRC the speed in the Leo direction is 0.0012 c, but all I remember for sure is that it is on the order of a thousandth

[Johnny5]

...the standard physics doctrine received from Special Relativity is that you cant have a concept of being at rest (General Relativity is a bit more permissive about what you can have at large scale)

 

 

Why is that Martin?

 

How do you infer from the postulates of SR, that you cannot have concept of being at rest. I know how to infer this from QM, but not SR.

 

Thank you

[swansont]

How do you infer from the postulates of SR' date=' that you cannot have concept of being at rest. I know how to infer this from QM, but not SR.

[/quote']

 

Both postulates point to there being no preferred rest frame. c is the same and the laws of physics work for all inertial observers.

[Martin]

Both postulates point to there being no preferred rest frame. c is the same and the laws of physics work for all inertial observers.

 

swansont said it more clearly. i did not mean that something cant be at rest relative to you, i meant that in SR there is no preferred observer, no preferred idea of being at rest. equality among inertial POVs

[J.C.MacSwell]

How about in terms of a time frame. Is the CMB/Hubble the "oldest" relative to the big bang? I realize that can vary from body to body depending on it's history (or multiple histories of component parts) but would a particle that has been at rest the longest in this CMB/Hubble frame be the "oldest"? Would a particle that has been at rest "forever" in this CMB/Hubble frame be assumed to be at the age of the Universe (15 billion,say)? I realize a particle that deviated from this "Hubble path" without returning may consider itself "older" (14.9, say, but still considers itself older than the "constant Hubble particle" which it considers to be 14.8,say) .

 

 

Hope this makes some sense.

[Martin]

How about in terms of a time frame....

 

as a non-expert physicswatcher I will hazard a guess here. I think that scientists of all kinds are constantly doing stuff pragmatically that they would have problems doing in a much more rigorous precise way

 

I think (this is personal opinion) that it is logically impossible to define a universal preferred time coordinate with perfect precision

 

I think time is always realistically going to be branched and observerdependent and fuzzy, and if you look closely with a magnifying glass it is going to always be a mess.

 

But the astronomers are doing great. they measure the CMB temperature dipole and they say our earth coordinates are moving towards the hotspot in Leo and they factor that out and everything is wonderful. Because they dont need more than like a few ppm accuracy!

 

but if you were trying to set the clock for the Great Dictator of the Virgo Cluster, or for the High Potentate of the Great Attractor (which the Virgo cluster is surmised to be falling towards) then your life would be miserable because there is no way to determine really which clock is right, I mean down to the "last" decimal place.

 

For reasons, in fact, which you suggest in your post MacSwell. So I have to tip my imaginary hat your way and say I like the way you think.

 

Also remember time goes slower when you are deeper in a gravity well so do we use a clock that is like, halfway between us and Andromeda? or should it be halfway between us and the Virgo Cluster? or at the heart of the Great Attractor? and all these clocks disagree slightly about the age of the universe because of, among other things, the gravity effect on time.

 

there was a neat paper by a Montevideo Uruguay man named Gambini that was about time and how accurately a realistic clock could measure it. I will get the link. it wasnt hard mathematically and it was kind of intriguing

[Johnny5]

 

I think (this is personal opinion) that it is logically impossible to define a universal preferred time coordinate with perfect precision

 

I think time is always realistically going to be branched and observerdependent and fuzzy' date=' and if you look closely with a magnifying glass it is going to always be a mess.

[/quote']

 

Martin, when you get a chance I want to talk to you about this.

 

Regards