Re: CMBR's motion wrt the Earth


"Nicolaas Vroom" <nicolaas.vroom@xxxxxxxxxx> schreef in bericht
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"Nicolaas Vroom" <nicolaas.vroom@xxxxxxxxxx> schreef in bericht
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"Tom Roberts" <tjroberts137@xxxxxxxxxxxxx> schreef in bericht
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mluttgens wrote:
Can somebody explain how, physically, an electromagnetic
radiation filling the universe can move relative to the Earth?

Your descriptions are insufficiently precise. There is no such thing as
"The CMBR" -- the cosmic microwave background radiation is comprised of
myriads of photons moving in all directions. This is not a "thing" in
any normal sense, it is a vast collection of photons.

What you are missing is the fact that measurement of "the earth's motion
with respect to the CMBR" is really a measurement of the earth's speed
relative to THE FRAME IN WHICH THE CMBR DIPOLE MOMENT IS ZERO [#]. This
is not in any sense a "rest frame of the CMBR", because the CMBR is
myriads of photons NONE of which are at rest in any frame. This is
purely a statistical property of the collection of all the photons
comprising the CMBR.


There are also people in favour to call it a rest frame:
See: http://arxiv.org/PS_cache/astro-ph/pdf/9601/9601151v2.pdf

The Dipole Observed in the COBE DMR Four-Year Data
C. H. Lineweaver, L. Tenorio, G. F. Smoot, P. Keegstra,
A. J. Banday & P. Lubin

Page 1: " A measurement of this Doppler dipole thus tells us
our velocity with respect to the rest frame of the CMB."

IMO the whole issue is a statistical (average) aspect.

Nicolaas Vroom
http://users.pandora.be/nicvroom/

However I think there is more involved.
If you position an observer at the equator than you can build
a frame of reference in which the inertial observer 1 is at rest
(rest frame observer 1)
You can also consider a second observer positioned
at the other side of the earth with a frame of reference in which
observer 2 is at rest (rest frame obeserver 2)
Both rest frames are in relative motion which each other and each
with the rest frame of the CMBR.
Suppose there is also a third observer with has the speed of
370 km/sec in the direction of the constellation of virgo.
This observer 3 sees a the uniform CMBR directly undisturbed
without the necessity for dipole subtraction.
The two other observers, to see the same, have to perform
dipole subtraction.

See:
http://aether.lbl.gov/www/projects/cobe/COBE_Home/DMR_Images.html

The question is:
is observer 3 in the special situation that only he can actually claim
that based on his observations that from all directions all photons are
having
the same speed (c) ?
At the same time he claims that for the observers 1 and 2
this is not the case.

Observer 3 can even go further:
He can claim from all directions from the same distance.

I do not know the answer.

Nicolaas Vroom
http://users.pandora.be/nicvroom/



There is one more special situation which requires study.
Consider two observers identical like Observer 3.
We will call them Observer 31 and Observer 32.
Both have the same speed 370 km/sec in the direction
of Virgo. Both are a certain distance apart.
In fact, both are "at rest" in the rest frame of the CMBR.
The idea is to synchronise their clocks.
This is a simple exercise.
In fact much simpler than two Observers which both should
be at rest in, for example, the rest frame of Observer 1.
They should have the same speed and direction as Observer 1
and that is without a grid of rods very difficult to establish.

Nicolaas Vroom


.

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