Re: A question about cosmic microwave radiation and special relativity

From: Michael Levin (mlevin77_at_comcast.net)
Date: 03/20/05 

Date: Sun, 20 Mar 2005 17:36:40 -0500

Thank you everyone who replied - lots to think about for me.

Mike

On 3/20/05 4:28 PM, in article
UVl%d.8478$ZB6.664@newssvr19.news.prodigy.com, "Tom Roberts"
<tjroberts@lucent.com> wrote:

> Michael Levin wrote:
>> If space is filled with cosmic microwave radiation, doesn't this pick out
>> a special reference frame,
>
> Certainly, as far as the cosmic background radiation (CMBR) itself goes.
> Just like the earth picks out a special reference frame for the earth.
>
> But there is no wider significance to this frame. For instance, inside a
> sealed room on earth the CMBR is not observable, and neither is its
> frame (numerous claims by cranks notwithstanding).
>
>
>> going against special relativity?
>
> SR says that the laws by which systems change state are the same when
> referenced to any inertial frame. This says nothing at all about the
> acual stuff in the universe, and it should be obvious that any object
> naturally has its own reference frame (i.e. the reference system in
> which it is at rest) -- the CMBR is not different from this. The earth,
> the sun, my left foot, and the CMBR all have their own rest frame; for
> all of these the rest frame depends on the place and time one inquires
> about it....
>
>
>> It seems to me
>> that if I'm moving, then the crests of the radiation will hit my detector
>> more frequently in the direction of my motion, raising its wavelength as
>> perceived by me in the direction of motion. Therefore, couldn't I define a
>> universe-wide unique observer, and thus a standard "Newtonian" frame of
>> reference, as one who is not moving with respect to the microwave background
>
> There are difficulties with this: You describe a method to find the
> locally-inertial frame in which the CMBR dipole is zero -- how do you
> know that this dipole=0 frame extends throughout the universe? Note that
> there are observations of distant galaxies that show the CMBR has a
> different mean temperature far away. This is, of course, wrapt up in
> issues of the time coordinate and its relationship to distance (i.e. we
> are observing distant galaxies a long time ago, when perhaps the
> universe and the CMBR looked different from what they do today).
>
>
>> And a related question, I'm not sure I understand how this cosmic
>> background works relative to universal inflation/expansion. I've read a
>> number of books where they talk about it "permeating all of space".
>
> This last is only approximate -- inside a closed copper cage there is no
> CMBR. Ditto inside stars and planets and....
>
> Basically as the universe expands the mean temperature of the CMBR
> decreases. This happens because the expansion causes a cosmological
> redshift in all radiation (in current cosmological models).
>
>
>> I assume
>> it's like normal microwaves, which spread outwards from a center, at the
>> speed of light.
>
> No. In current cosmological models, the CMBR is a relic from the time
> when atoms first coalesced out of their individual components (mostly
> electrons and protons forming H and then H_2). This happend throughout
> the universe, so this is not a "point source" at all, it is diffuse
> throughout the universe at that time.
>
>
>> It doesn't just sit there, permeating space - it's moving
>> through it from the source, right?
>
> Right, in the sense that each individual portion of the CMBR had a
> definite source long ao and far away. But in different directions the
> individual sources are a different direction, distance, and time (this
> is even so in a given direction at different observation times).
>
>
>> So how come it's still here?
>
> Lots of differnet sources back then.
>
>
>> If it got
>> generated at the time of the big bang,
>
> The CMBR was generated much later than that, in current cosmological models.
>
>
> Tom Roberts tjroberts@lucent.com 

-- 
Mike Levin
mlevin77@comcast.net

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