Re: Cosmic Background Radiation
- From: "George Dishman" <george@xxxxxxxxxxxxxxxxx>
- Date: 5 Jun 2006 03:25:58 -0700
Spoonfed wrote:
George Dishman wrote:
"jmetolius" <jmetolius@xxxxxxxxx> wrote in message
news:1148761125.216761.251840@xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx
It is generally accepted that the uniformity of the cosmic background
radiation provides a ready made test of whether the observer is
actually moving with the cosmic flow of space.
In our case, the background radiation shows a slight blue shift in one
direction that is explained by our 600km/sec relative motion withn that
cosmic flow...(our Earth's motion around the Sun, the Sun's motion
around the galactic center and the entire Milky Way has velocity, in
excess of the cosmic expansion, in the direction of the constellation
Hydra).
Now, could someone please help me understand the following thought
experiment......
If we imagine a planet in a particular far away galaxy, where this
galaxy has a considerable relative recession to ourselves, and where
this relative velocity is almost entirely attributable to the cosmic
expansion ( let's say 20,000 km/sec). The inhabitants of this planet
will, of course, see themselves as almost 'at rest' relative to the
cosmic background radiation. They are almost entirely just moving with
the cosmic flow.
If we then imagine an intrepid astronaut from Earth accelerating off in
the direction of this galaxy, eventually catching it up and landing on
the planet in question. That astronaut now has a 20,000 km/sec
relative motion with their mother Earth's background radiation, and
therefore must see that background radiation as considerably blue
shifted in their direction of travel.
The astronaut may then have tea with an alien on that planet, who views
their backgrond radiation as (almost) not shfted at all. How can this
be? If the astronaut mates with the alien, how will their son see the
cosmic background shifted?
Obviously, I am missing something.....Please help. Thanks
What you are missing is that the material which produced
the CMBR is itself expanding. The radiation seen on the
distant planet was produced in a different location to
the radiation seen by the observer from Earth so it has
a different mean motion. Suppose we currently see CMBR
which was produced 13 billion years ago. In one sense
(ignoring the change of scale in between) you could say
that radiation was produced 13 billion light years away
in all directions, hence in a sphere round us. If I just
represent a line passing through Earth 'E' and your
distant planet 'P', it intersects the material that
produced the radiation we see at W and X like this:
--W----E----X--P-------
Similarly the radiation seen at the same time on P was
produced by plasma at locations Y and Z:
--W----E--Y-X--P----Z--
As you go from point E to point P, then, you will pass through the
Plasma layer Y which is moving toward E from P.
The plasma existed 13.7 billion years ago. You will pass
through the clusters of galaxies which condensed out of
the plsma in that time.
Then you will pass
through the plasma layer X which is the layer we are watching from
Earth. Then you'll land on planet P and no longer be able to see the
near layer X but you'll see the far layer Y.
Do these layers of frozen plasma disappear and reappear as we go
through them, or can you give an explanation of what happens them
during the journey?
They are the galaxies we see all around us. For observers
on some very distant shell, the hydrogen and helium of the
present Milky Way galaxy emitted the CMBR that they are
seeing now.
Now that whole line was expanding at the time the
radiation was produced so W and X were separating from
E to give the red shift we see, and Y and Z were
separating from P. If astronomers could have viewed it
when the redshift was just a factor of 2 (z=1) then the
line would be like this:
----W---------E-----Y---X-----P---------Z----
Now here's the mistake, you said:
If we then imagine an intrepid astronaut from Earth accelerating off in^^^^
the direction of this galaxy, eventually catching it up and landing on
the planet in question. That astronaut now has a 20,000 km/sec
relative motion with their mother Earth's background radiation, and
therefore must see that background radiation ...
Now, you mentioned that this planet, P, was matching the Hubble Flow
exactly, whereas Earth is faster than Hubble Flow by 300km/sec, so
assuming Hubble Constant is 50km/s/MPc and planet P is directly in line
with with the hot dipole of the CBR, it means the relative velocity
between E, and P is 19700 km/second, and P lies right around 400MPc
distance.
Is any of this accurate, or do I need to take into account the
curvature of spacetime somehow?
I haven't checked your numbers bu the idea is right,
the curvature produces the 20000km/s.
By the time he gets to the planet, he isn't seeing "that"
background radiation, meaning the radiation from the same
source material that he saw from Earth, he is seeing
radiation produced at Y and Z, both of which were
apparently moving from left to right when it was emitted,
and if P seems to be moving at 20000 km/s relative to
Earth, the average motion of Y and Z was also 20000 km/s
in Earth coordinates.
HTH
George
The motion of Y (Plasma seen toward E from P), and Z (Plasma seen
opposite E from P) and P (Planet P) are all moving together at 20,000
km/second relative to Earth, and they are all stationary in P's frame.
No, Y would be moving at about 8000km/s relative to
Earth and 12000km/s relative to P. Remember P sees
both Y and Z as red shifted.
So If I understand correctly, you're saying that every planet has it's
own plasma haze that travels along with it.
No, the unverse was filled with plasma which was
everywhere expanding.
Planet P has a CBR
background coming from a sphere moving right along with it while Planet
E is moving 300 km/sec with respect to its plasma haze.
I understand you have the backing of NASA and the WMAP team on this
one, but it still seems a bit farfetched.
It isn't quite as you picked up from my inadequate
description.
George
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