Re: universal cosmic radiation
- From: The TimeLord <mathnphysics-not@xxxxxxxxxxxxx>
- Date: Wed, 04 Jul 2007 01:17:39 -0500
wolfgang wrote:
what guaranty do we have that that we call
cosmic background radiation comes from
a big bang long time ago?
The reasoning goes something like this:
In the beginning of the 20th century Edwin Hubble and others observed
that more distant galaxies seemed to be moving away from Earth as
evidenced by the red-shift in their spectral lines. Many other
explanations have been presented to explain the red-shift. However,
the likeliest explanation is that the galaxies are actually moving
away from Earth. The fact that the Earth seems to be the center of
this motion, is just due to the fact that the motion seems to be
connected to four-dimensional space-time, which in turn creates the
illusion that Earth is in the center.
Given this evidence, astronomers naturally assumed that in the past
the galaxies were closer to the same common point than they are now.
In fact, the Hubble relation, describing how the galaxies are moving,
led the astronomers to assume that the whole universe was at a single
point at one time in the distant past. Thus the universe had a
definite beginning.
However, there is a problem with the whole universe being at a single
point. It turns out that a large part of the universe is made up of
particles called fermions (class of particles including electrons,
neutrinos, quarks, etc). Fermions can not share the same space at the
same time unless they have different quantum numbers (because of the
Pauli Exclusion Principle). Now there are definitely more fermions in
the universe than there are quantum numbers for fermions. Thus if all
the fermions were at the same point at the same time, there would be
such pressure as to blow them all apart: thus the Big Bang. So
whatever created fermions, created a possible condition for the Big
Bang to occur. Whatever that is, is still a matter of research.
At any rate, there is a possibility that if all the particles were
bosons (class of particles including mesons, photons, etc), then you
could have the whole universe share a single point, since bosons don't
obey the Pauli Exclusion Principle. However, that would mean that the
whole universe was essentially energy before the Big Bang.
So now we have the picture of the whole universe at a single point
being essentially all energy. Then something causes at least some of
the bosons to convert to fermions and KABOOM!. However, some of the
original energy still remains and bounces around the universe to
create the background radiation we see today.
I know this is a very much oversimplified version of Cosmology, but I
didn't really want to resort to math.
[...]
why is that radiation not much more red shifted
than it is now, still high frequency, becus if it is
now red shifted, then at tha time of the big bang
it was near infinitely high frequency
Well, the reason why it is not more red-shifted is a matter of luck.
As it turns out, had the universe expanded faster (more red-shift),
then the galaxies would have ended up too thin to form a lot of stars.
It would have then been less likely that we would have ended up on a
human-friendly planet orbit a good star. Likewise had the universe
expanded slower (less red-shift), then the galaxies would have formed
too clumpy and thus ended up with too many black holes to form
long-lived stars.
why is this radiation not already absorbed by
dust and cosmic objects?
Well, some of the radiation is absorbed by dust. However, the evidence
is that not too much is. Otherwise you would see a significant
difference between the intensity in H-alpha and H-beta lines coming
from distant galaxies. The two lines appear pretty much equal
intensity for just about all galaxies, thus indicating low levels of
intergalactic dust.
what about tha 90% dark mater, do they not
absorbs radiation
It's pretty clear that whatever dark matter turns out to be, it
doesn't interact too much with the cosmic background radiation. The
reason is that the only evidence for the existence of dark matter is
in the galaxies. Between the galaxies (in free space) there is no
evidence for dark matter.
what about antiparticle mater? doesnt they
also absorbs cosmic background radiation?
Antimatter is just matter that behaves like it's left-handed. An
example is that positrons are anti-electrons. As far as the matter
aspect goes, positrons act just like electrons: both have the same
mass. They do have opposite charge though, so they act opposite in
electrical situations.
--
// The TimeLord says:
// Pogo 2.0 = We have met the aliens, and they are us!
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