Quasar found 13 billion years away

Chalky wrote:

[...] is not rigorous science.

The physics of hydrogen is.

Yes, and whether that physics of hydrogen is
restricted to a thought experiment in a closed
partitioned box, showing that any gas that radiates
where it is also transparent allows for the
construction of a perpetual motion machine, and so
no such gas can exist, or whether that physics is
spread across the width of the universe, where
_still_ NO SUCH GAS CAN EXIST, it is the _same_
physics.

You need to try to read what you are being told with
understanding rather than through the filters of your
preconceived notions and preselected outcomes, and
rather than dismissing all evidence against your
notions as you are doing.

Speculating about hypothetical bricks made from
hypothetical matter, ...

There's also nothing very challenging to comprehend
about the optical depth of "opaque bricks" as
Richard Saam has done the calculations, that you
should be mischaracterizing it so.

That term "bricks" is a "precise-enough"
specification of the size chunks in which the matter
is aggregated, to allow computation of the optical
depth it implies, and yet again you have dismissed
the evidence with a quip rather than realizing that
it conveys physical realities about how the universe
can or cannot be constructed.

This leads to unnecessarily long conversations in
which correspondents must attempt many times to
convey to you understandings which a more careful
reading by you would have had you acquiring on the
first try.

There is no win available to anyone in such
behavior.

Quantum valeat.

xanthian.

In article , Chalky
writes:

writes:
If Richard Saam's figures are correct, this suggests that a universe
with 4% baryonic matter, of which a quarter has still not been
converted into stars, should have an optical depth of 100x200 light
years.

I make that ~ z = 10. Certainly not ~ z = 1000

100*200 = 20 thousand. This is well within the Milky Way.

Maybe I misunderstood and/or some needed context is missing. Can you
explain the step from "100x200 light years" to "~ z = 10"?

Phillip Helbig wrote:

Maybe I misunderstood and/or some
needed context is missing. Can you
explain the step from "100x200 light
years" to "~ z = 10"?

More than that, what the heck does it mean to
have an "optical depth", which is a linear
measure, expressed in terms of square light
years, an areal measure?

Quantum valeat.

xanthian.

On Jul 4, 4:14 pm, (Phillip Helbig---
remove CLOTHES to reply) wrote:
In article , Chalky

writes:
writes:
If Richard Saam's figures are correct, this suggests that a universe
with 4% baryonic matter, of which a quarter has still not been
converted into stars, should have an optical depth of 100x200 light
years.

I make that ~ z = 10. Certainly not ~ z = 1000

100*200 = 20 thousand. This is well within the Milky Way.

Maybe I misunderstood and/or some needed context is missing. Can you
explain the step from "100x200 light years" to "~ z = 10"?

That was not the step. The step is actually from

"4% baryonic matter, of which a quarter has still not been converted
into stars"

to

"~ z = 10"

This was, of course, only a guestimate, but is based on the following
considerations, assuming concordance model:

At z=6 so many galaxies are out there (observationally), that most
gaseous hydrogen must have been converted into stars by that time, to
produce that observed density of galaxies.

So few galaxies are visible towards z=7, that a lot of hydrogen must
have still been in the form of gas, then (because luminosity distance
only increases by 15% from z=6 to z=7, assuming concordance model).

That would suggest more than 25% of hydrogen is gaseous at z=7

Richard Saam's figures suggest however that this much gaseous hydrogen
would reduce visibility to 0.02 glyr, making all galaxies invisible
to anyone outside that galaxy.

This is why I increased the guestimate to ~z=10

If you want to increase it still further, you will have to come up
with a pretty good explanation for how hot plasma can end up as
galaxies in less than half a gigayear, yet fail to end up as
galaxies in three quarters of a gigayear.

On Jul 4, 3:58 pm, Kent Paul Dolan wrote:
Chalky wrote:
[...] is not rigorous science.
The physics of hydrogen is.

Yes, and whether that physics of hydrogen is
restricted to a thought experiment in a closed
partitioned box, showing that any gas that radiates
where it is also transparent allows for the
construction of a perpetual motion machine,

This proof of Kirchhoff's Law violates the First Law of Thermodynamics

Please argue about this in the physics forum.

See 4 July postings at sci.physics.research:
http://groups.google.com/group/sci.p...7dc218ea47e501


More than that, what the heck does it mean to
have an "optical depth", which is a linear
measure, expressed in terms of square light
years, an areal measure?

Oh dear, I did not say square light years, I said 100 times
This is because a quarter of 4% is 1%.

You don't really want to argue about basic arithmetic too, do you?

Chalky

On 3 Jul, 08:53, Chalky wrote:
On Jul 2, 8:28 pm, "
wrote:
On 30 Jun, 09:08, Chalky wrote:
On Jun 29, 7:46 am, Steve Willner wrote:

Chalky wrote:
If these successive shells of gas do not at least help to produce the
observed microwave radiation, why not?

Optical depth. At wavelengths relevant to the microwave background,
the Universe is transparent in nearly all directions.
....
I don't see how transparency to such radiation, once emitted, can
prevent such emissions from happening in the first place.

Take a thermally insulating box with perfectly
reflective walls and divide it with a transparent
window (double glazed). Fill one half with your
transparent but emitting gas. In the centre of
the other half place a black sphere. The sphere
absorbs adiaton and heats up. It emits radiation
which passes through the transparent gas, bounces
round the walls and ends up on the sphere again.

If only the temporal dynamism of the universe could be constrained
that easily!

The gas is always emitting thermal radiation
which is absorbed only by the sphere so the gas
cools while the sphere heats up.

The analogy is hardly appropriate on the scale of the universe.

You misunderstand, the box wasn't meant as an
analogy for the universe. Think of a box say
1m on edge and the 'thought experiment' shows
why it is necessary for the emission and
absorption by the gas to be symetrical. It
explains why any truly transparent material
cannot emit radiation as a result of the laws
of thermodynamics which was the point you were
querying. At the quantum level, just note that
time-reversal of emission looks like absorption
and the statistics are the same - if acceleration
of a charge can emit a photon then a photon
hitting a charge will accelerate it.

George

On Jul 5, 10:33 am, "
wrote:
On 3 Jul, 08:53, Chalky wrote:





On Jul 2, 8:28 pm, "
wrote:
On 30 Jun, 09:08, Chalky wrote:
On Jun 29, 7:46 am, Steve Willner wrote:

Chalky wrote:
If these successive shells of gas do not at least help to produce the
observed microwave radiation, why not?

Optical depth. At wavelengths relevant to the microwave background,
the Universe is transparent in nearly all directions.
....
I don't see how transparency to such radiation, once emitted, can
prevent such emissions from happening in the first place.

Take a thermally insulating box with perfectly
reflective walls and divide it with a transparent
window (double glazed). Fill one half with your
transparent but emitting gas. In the centre of
the other half place a black sphere. The sphere
absorbs adiaton and heats up. It emits radiation
which passes through the transparent gas, bounces
round the walls and ends up on the sphere again.

If only the temporal dynamism of the universe could be constrained
that easily!

The gas is always emitting thermal radiation
which is absorbed only by the sphere so the gas
cools while the sphere heats up.

The analogy is hardly appropriate on the scale of the universe.

You misunderstand, the box wasn't meant as an
analogy for the universe. Think of a box say
1m on edge and the 'thought experiment' shows
why it is necessary for the emission and
absorption by the gas to be symetrical. It
explains why any truly transparent material
cannot emit radiation as a result of the laws
of thermodynamics which was the point you were
querying. At the quantum level, just note that
time-reversal of emission looks like absorption
and the statistics are the same - if acceleration
of a charge can emit a photon then a photon
hitting a charge will accelerate it.

The crux of the issue here, then, is your use of the term "truly
transparent"

Nothing actually is, on a sufficiently large scale, except a perfectly
hard vacuum.

What I am actually interested in is the real behaviour of real matter
in a real universe. What I am being offered though are two
diametrically opposed idealisations at the opposite ends of the
theoretical spectrum, with nothing in between.

a) perfect transparency and no radiation
b) perfect opacity and black body radiation.

Surely you can see that the reality of the situation must be
intermediate, for real gases in the real universe?


Chalky

In article , Chalky
writes:

I make that ~ z = 10. Certainly not ~ z = 1000

100*200 = 20 thousand. This is well within the Milky Way.

Maybe I misunderstood and/or some needed context is missing. Can you
explain the step from "100x200 light years" to "~ z = 10"?

So few galaxies are visible towards z=7, that a lot of hydrogen must
have still been in the form of gas, then (because luminosity distance
only increases by 15% from z=6 to z=7, assuming concordance model).

Surface brightness goes as (1+z)^{-4}. (assuming no K-correction).
That's almost a factor of 2 decrease between z=6 and z=7. Absence of
evidence is not evidence of absence. :-)

On 6 Jul, 09:31, Chalky wrote:
The crux of the issue here, then, is your use of the term "truly
transparent"

Nothing actually is, on a sufficiently large scale, except a perfectly
hard vacuum.

Dark Matter appears to be truly transparent, but
that's another matter ;-)

What I am actually interested in is the real behaviour of real matter
in a real universe. What I am being offered though are two
diametrically opposed idealisations at the opposite ends of the
theoretical spectrum, with nothing in between.

a) perfect transparency and no radiation

You asked: "I don't see how transparency to such
radiation, once emitted, can prevent such emissions
from happening in the first place."

b) perfect opacity and black body radiation.

Surely you can see that the reality of the situation must be
intermediate, for real gases in the real universe?

Of course, so if a particular material emits at
half the black body rate for some temperature and
wavelength, then it should reflect 50% of incident
radiation at that wavelength. There is a direct
link between reflectivity and emissivity hence
transparency implies lack of emission. That was
the original point of your question, wasn't it?

George

[Mod. note: quoted text trimmed. -- mjh]

On Jul 6, 9:32 am, (Phillip Helbig---
remove CLOTHES to reply) wrote:
In article , Chalky

writes:
I make that ~ z = 10. Certainly not ~ z = 1000

100*200 = 20 thousand. This is well within the Milky Way.

Maybe I misunderstood and/or some needed context is missing. Can you
explain the step from "100x200 light years" to "~ z = 10"?
So few galaxies are visible towards z=7, that a lot of hydrogen must
have still been in the form of gas, then (because luminosity distance
only increases by 15% from z=6 to z=7, assuming concordance model).

Surface brightness goes as (1+z)^{-4}. (assuming no K-correction).
That's almost a factor of 2 decrease between z=6 and z=7. Absence of
evidence is not evidence of absence. :-)

Now, perhaps it is my turn to have misunderstood. Luminosity distance
for stars / galaxies is a direct indicator of brightness. In a flat
universe, LD = (1+z)R, by definition. Where do you get this (1+z)^{-4}
factor from?

C