Dear George Dishman:
"George Dishman" wrote in message
...
"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox
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I don't have the applet required to play it. I found another
site that had it in Quicktime.
It used Real Player but as long as you got
the idea, a bulk material can switch from
opaque to transparent.
The "bromate clock" does this too, but the symbolism would invoke
the "constant creation" and "recycling Universe" crowds... ;)
Hydrogen absorbs light.
Hydrogen also emits light. By the laws of
thermodynamics, there must be a precise
relationship between the two.
Yes, I finally got it. Only the "vector part of the momentum"
will be altered, since the momentum of the "intervening" hydrogen
(indicating *its* temperature) will average out to no net
contribution. I think.
We find its signature everywhere we look, when we look at
point sources. But we don't find it with the CMBR. And it
has been exposed longer, assuming the Universe filling
gas didn't coalesce.
If the gas is in equilibrium, the energy
absorbed must be balanced by that emitted.
It is therefore exactly at the crossover
between producing absorption and emission
lines. Given the slight anisotropy, perhaps
it will be possible some time soon to detect
a line redshifted down but it has taken
sensitive space-borne missions just to
measure the anisotropy in broad bands so
looking for individual lines would require
another step up in design.
I'm always up for sharper tools.
At some point the CMBR had redshifted enough so
it could not be absorbed at all by hydrogen, and
since then the universe has been transparent to it
(except for isolated objects we call stars).
Let me ask a related question. The CMBRM has
been described as opaque and isothermal. Presumably
"opaque" could be defined as no emissions detectable
from beyond a certain place (watch my terms).
"a certain place" may give the wrong impression
although obviously we are "here".
We can't see beyond the CMBRM, so it is opaque.
That is correct, it rapidly absorbs any light
that passes through it.
If we were on the inside of an event horizon, we could
not see beyond that
That is not correct. Light does not pass out
across the horizon but it does fall in.
But (outer) space becomes (inner) timelike. So any light that
falls in loses any correlation to frequency, or momentum. Only
energy would be conserved, right?
If
you could hover just inside the event horizon
you would be bombarded by high energy photons
falling in.
I don't agree, and I can't quite tell you why that is.
Ultimately I think it is because you cannot hover just inside the
event horizon, since to do so would be to stop time. So if you
infall at a rate of 1 second per second, the light should be
received at finite energy, since your "motion along the time
axis" is also closely correlated to c.
My question to Tom is would this also achieve the appearance of
being isothermal? The entire history of our container Universe
(up until the point we evaporated) is written on/into the event
horizon. Given what we know/expect of Universal temperature, and
size of the Universe at that temeprature, I think this also would
provide a very nice blackbody curve.
Universe's Big Bang, and see specular images of the container
Universe. The Big Bang (aka. the inside of an event horizon)
is
opaque *without* invoking space-filling hydrogen plasma.
The event horizon is not opaque, light passes
through it without being absorbed.
The classical surface of last emission is not within the Universe
inside the event horizon. The closest "place" in this Universe
is "just inside the event horizon". You can't see beyond it. It
is opaque, if you accept my "abomination" of the word. We won't
get specular images from before the CMBRM... either way.
It is perhaps
better to consider opaque in this case in terms
of the mean free path of a photon being greater
than the time from emission to the time of
complete transparency multiplied by the speed of
light regardless of where the photon is emitted
since the CMBRM was almost homogenous throughout
the universe.
So let me ask this question about the Universe that
contains ours...
There is no "Universe that contains ours" in the
Big Bang model so it is not meaningful to ask the
question.
The Schwarzchild solution to GR for a black hole,
describes another Universe inside the black hole, with
internal time starting where external space leaves off.
I'm not sure about that, it seems to depend on
the coordinate system you use but I know too
little of GR to comment sensibly.
You are no more God than I am. You have tried on the hat more
than once, in an effort to help me (and those that might someday
have these or related questions). For that I thank you. Some
questions are so poorly worded that they cannot be understood,
and some questions just cannot be answered. I'm thinking I've
formulated the former, but you never know. ;)
Since the Big Bang model is commonly dressed in the clothes
of GR, are you sure 'There is no "Universe that contains ours"
in
the Big Bang model so it is not meaningful to ask the
question'?
I am fairly sure that the picture of the event
horizon of a black hole to which you are
referring is related to an isolated mass in a
lower density environment while the big bang
scenario has uniform density throughout. You
can get a similar effect I believe in a uniform
density regime:
http://scienceworld.wolfram.com/phys...ntDensity.html
but in this case it would be more like the
horizon that is expected to be produced by
cosmic acceleration and is a limitation on
visibility _within_ the universe.
However, that needn't mean our universe isn't
embedded in something different. The idea I
find most understandable to illustrate the
possibility is that of Alan Guth where he
talks of multiple universes embedded in
'false vacuum' which is in a permanent state
of inflation. That is not exclusive though,
just indicative of the feasibility.
You say imagine the Landolt reaction in reverse...
Purely to suggest the change from opaque to
transparent could be due to a phase change in
the hydrogen/helium mix (plasma to gas) rather
than requiring the material to coalesce into
structures leaving vacuum between as you were
suggesting. That could come later.
imagine that our Big Bang is the inside of the event horizon
of the (probably really big) black hole that contains our
Universe.
So sure are you?
I am sure that the H/He mix was present because
we see the radiation from it in the form of the
CMBR,
This is not conclusive, but *assumed*. That is the crux of my
problem. It is a perfect blackbody radiator, with some hint of
structure (variable intensity) written in/on it. The Universe
should have been mostly hydrogen and helium. Therefore the CMBRM
must be mostly hydrogen and helium. A logical chain, just not
one I am fond of.
it is predicted by nucleosynthesis and we
can see the mix in primeval stars. I can be sure
it was opaque for over 300k years from lab
experiments and WMAP. I can't be sure what we
would have seen had it not existed, but then we
wouldn't be here to see anything.
I don't agree with "lab experiments" since we cannot generate an
opaque plasma in the lab. I also don't agree with the infalling
light being necessarily fatal. If Joe were to don a spacesuit,
and fall into the BH at the center of the Milky Way, would the
infalling light kill him? No. If other stuff didn't kill him
(with differential orbital velocity) he'd just see infalling
light that became more and more distorted (non-specular).
Beyond that,
I would just point you at the faq entry and say
that I wouldn't presume to be any more sure than
Philip Gibbs, and since it is 8 years old,
perhaps even that might be slightly outdated.
http://math.ucr.edu/home/baez/physic.../universe.html
Thanks George. I hope you have/had a great Sunday.
David A. Smith