Dear George Dishman:

"George Dishman" wrote in message
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Dear George Dishman:

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Dear George Dishman:

"George Dishman" wrote in message
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Dear George Dishman:

"George Dishman" wrote in
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... going to attempt some deft trimming ...


More trimmed throughout.


Think of a pool table. It would be easy to define x
and y axes and calculate the motion of the balls
using Newtonian mechanics - no problems. We could
also use polar coordinates (r, theta) with the
origin at the centre of the table. Now every time a
ball passes through the origin, theta becomes
undefined. That is a coordinate problem only though,
the actual motion of the balls must be the same
whichever choice of coordinate system we make.

Right. Now is spacetime, or the underlying reality that has
the features we recognize as spacetime, the billiard table,
the coordinates, or some mixture of both?

Good question, this is perhaps where differing
understanding of the terminology can cause
problems. By "spacetime" I mean the underlying
reality, the billiard table. We have invented a
number of ways of labelling that mathematically
in the form of coordinates such as Schwarzschild,
Eddington-Finkelstein and Kruskal but the are
only coordinates, ways of quantifying locations
and times.

OK.

Space and time are irretrievably bound, which is the strong
suite of GR. "That which works" out here, doesn't at/near
an event horizon. It isn't just mathematics, it is a
requirement of the model.

No, that's not true. The failure at the horizon is
purely mathematical as for the pool table example,
the failure at the singularity is physical.

Consider that the sources that are the most active
astrophysically, are black holes (with companions).

Indeed, but the radiation and jets are produced
in the accretion disk outside the horizon.

So it isn't quite "mathematical", then is it? Physically, the
Universe (and the BH) are attempting to solve the "immovable
object/irresistable force" problem.

Now consider the definition of "singularity". The event
horizon
*is* a singularity. No?

No. The singularity is at the centre, there
is nothing unusual physically at the horizon.

It *is* a singularity in Schwarzchild coordinates. I quote from
Wikipedia
a.. mathematical singularity - a point where a mathematical
function goes to infinity or is in certain other ways
ill-behaved. It is also a point where all functions meet.
a.. gravitational singularity - an infinity occurring in an
astrophysical model, involving infinite curvature (a mathematical
singularity) in the space/time continuum, namely a black hole.

What is unusual at the horizon is that light cannot ever
propagate away from it. In all coordinate choices, this is true.

...
No, from what I have seen, some coordinate systems
stop at the horizon while other don't, but there
is no physical effect there in the GR model.

Look again. A very large number of sources cite how
you never actually get to see anything fall into the event
horizon. GR very much says that what you measure,
does not include the inside of the event horizon. Ever.

Yes, that's true but if you look at a spacetime
diagram showing light cones, it is obvious why
that occurs and it doesn't involve a singularity.

It does involve a singularity, George. As defined by the English
language. A "singularity" is not always just a "point".

...
He made assumptions, assumptions not evident
without mining his pages.

Ah now that's different and very interesting.
Can you give me a pointer to what you found?

... adding the link back in for posterity ...
URL:http://casa.colorado.edu/~ajsh/schw.shtml

It isn't what I found, George. Read my sentence again.
It is that I didn't find "what assumptions the pretty
pictures are based on", in the infinte variations of how
that can be expressed in the English language.

I still read it as saying that you _did_ find
assumptions but that you had to 'mine his pages'
to do so.

I could only have been clearer had I added the sentence:
"Which I did not do."

There is window dressing, but he construction details of the
manequins,
might be there somewhere, but I did not find it. Likely it was
numerical
simulation of the equations of GR direct.

Exactly, the only 'assumptions' were the other
stars he included in the hypothetical system.
The ray tracing I believe is pure GR without
any simplifications at all.

I don't know how he did a "Schwarzchild" solution across the
event horizon. Yet that is the suggestion.

Only the choices of "simplifying assumptions" are (perhaps)
omitted, so
only Andrew knows.

Even he
URL:http://casa.colorado.edu/~ajsh/home.html
... I don't see a path to the answer.

Neither did I which is why I asked where in the
pages you had found them.

I think I'd rather kill my hypothesis with logic
(integrating
over the surface) rather than use someone else's
assumptions to try and do it. I am very uncomfortable
with his assumption that we could fall at c... for
example.

Relative to what? Relative to an observer at
infinity, that's not an assumption but derived
from the theory.

Really? Is that c at the infinite observer's location, or c
at
the local curvature to the faller?

'c' is just a number, a universal constant. AIUI
the speed is greater than c relative to the infinite
observer but it is zero relative to the falling
observer of course (you did say "we could fall at c").

I got my b*tt chewed too.

Light would pass the falling observer at exactly c.

The "infinite observer" sees that over a path that passes
through an area of space with "high curvature", the "flight
time" is longer than if there were less curvature. So
c_nonlocal (better: c_path_average)

No, it would be better to say "speed_path_average" since
c is just a constant, 299792458m/s.

Yes, sloppy talk does no one any good.

would appear to decrease, as observed by an infinite
observer. "Shapiro time delay" is an observation fully in
agreement with GR. So what does it mean to say that
we "infinite observers" can say stuff about physics
beyond the *singularity* that is the event horizon?

David, the event horizon is *not* a singularity,
only certain coordinate system have an *artificial*
singularity on that surface. That is the root of
all our disagreements I think.

It is how the word is defined, George. You (and most other
mainstreamers) place the singularity "at the center", even though
this is not physically meaningful in *this* Universe. Yet in my
hypothesis, the only singularity is the severance of one
spacetime, adjoint to another (essentially identical?) spacetime.
The mass/energy only "reports to a different boss, on a different
form". What the external Universe calls "an infintely dense
central singularity", the insiders call "an approaching
infinitely-diffuse, cold future". We will evaporate before that
will complete, of course.

This is why the r axis is referred to as "timelike".

So time has a different letter in that region,
it is still time.

It *is* still time, but it is not outer-time. It is not
related to
external-time, except perhaps to be orthogonal to it. Again,
this is just the model, I know.

I don't want to sound as though I'm laying down
the law but I think you need to stop and make
some enquiries. AIUI, it isn't the model, it is
the coordinates. Physically time outside the
horizon and time inside are the same, it is only
when you get to the singularity at the centre
that the physics fails.

Then we can agree to disagree. I'll stop offering it, and do
some studying. If no one champions this, in 10 or 20 years
(when/if I can go back to school), maybe I'll take up the
gauntlet again.

I have been trying to find something on this
and this is the best I have found so far:

http://math.ucr.edu/home/baez/RelWWW/wrong.html#holes

Note the bullet list below the Penrose diagram

"The Schwarzschild solution 'changes signature'
at the event horizon. This is incorrect---
this is a common student misconception which
arises from misunderstanding the nature of the
coordinate singularity in the Schwarzschild
chart for the external region at r = 2m."

Note that his comment applies "for the external region"...

No, his comment is that the existence of a change
of signature is incorrect. He explains that this
"arises from misunderstanding the nature of the
coordinate singularity ... for the external region"

The entire bullet point applies to the external region.

I disagree, it seems clear it to me it refers to a
signature change at the boundary between the regions.

Are you familar with German, George?

No, but it isn't written in German. The structure
of English is not the same.

But it is close... NOT! ;)

Are you aware of the importance of the "sequence" of the
word "nicht" in a sentence, and how it applies to the
meaning of the sentence? At the end of that "sentence"
is the phrase:

Schwarzschild chart for the external region at r = 2m.

He says two things, first;

"The Schwarzschild solution 'changes
signature' at the event horizon. This
is incorrect --- this is a common
student misconception ..."

That seems quite clear.

Then he gives the explanation for the source
of the misunderstanding:

"... which arises from misunderstanding
the nature of the coordinate singularity
in the Schwarzschild chart for the
external region at r = 2m."

To rephrase it, 'People incorrectly think there
is a change between inside and outside because
they fail to understand the problem with the
coordinate system used outside.'

Note he specifically says it is a *coordinate*
singularity.

Understood. Disagree. Move on.

It is, as you point out, a modelling problem, with
a model *that* cannot be applied to r = 2m, just
as you cannot apply Lorentz contraction/dilation
to any object (massive or not) travelling at c.

No, I think it is a coordinate problem, not
a model problem. The balls don't fall off the
table.

They start a new table, since the table only exists because there
are balls on it. As I say though, I'll let it go. I can't prove
it.

They are still just coordinates, nothing more.

Tell that to strong X-ray sources. Tell that to objects that
evaporate by quantum mechanical means. They are
coordinates that work really well here in "mostly flatland".
The model says that "something might happen if"...
Have you no curiosity?

This isn't about curiosity or the lack thereof,
I think you are building your views on a trivial
misunderstanding of the GR model.

I hear your words, but mine have been labelled. Mine is an
interpretation based on GR models/coordinate choices. One that
is potentially falsifiable. If the inside of the BH forms a
separate Universe, the we can look around/back and know what that
internal Universe might look like.

I don't hold that this Universe is unique, or at least
self-sufficient.

snip quoted text

The same objects, will provide multiple specular images.
And this is still outside the event horizon.

Interesting but as you say those were for an
external observer and external sources.

Do you think they get *more* pure, or make more "sense"
on the inside?

I think the form of the distortion will vary but
that's all, you still get a distorted view of
sources lying on your past light cone.

Our past lightcone stops at the Big Bang. Some MODELS
of the Universe suggest that the same might be true of
someone infalling across an event horizon. Isn't it worth a
look? (Geez, I'm sounding like Uncle Al, only not as smart.)

Yes, it is worth looking but we need to correctly
understand what the models say.

We understand what the models say. Internal time is NOT directly
correlated to external time, by all metrics than we can yet apply
to BHs. So see how far that can take us to understanding "The
Beginning".

... Kruskal has his name on his choice of coordinates. He
chose them because he wanted to make a prediction (or
solve) to the inside of the event horizon. Predictions are
*enabled* by models, and mathematics.

Exactly, and a method of defining coordinates
that doesn't suffer from the pool table effect
is something that enable predictions to be made
over a greater range, but the predictions themselves
come from the physical model.

And predictions are to be...
- experimentally verified. Right?

Not in this case, we cannot observe the inside
as much as we would like to.

.... unless, the Big Bang *is* inside.

You have misunderstood Chris' page, I believe. All the
pages I have seen refer to the "radius" as "timelike"
inside the BH, regardless of coordinate system. Are
there two times?

No, I think the latter 'r' referes to past versus
future, that's all, but see Tom's reply.

"We can't know." is not very satisfying to me. It seems
that "we can look" is far superior.

Tough. Either we can or we can't, that is
determined by reality, not our preference.
Understanding whether we can or not is the
best we can do.

So why do you have a preference for one model over another? I am
not offering "new physics", I am offering that our Universe is
not unique in the scheme of things. And my hypothesis is
potentially falsifiable.

What is raising the question of a non-closed Universe?

Without dark energy, GR gives some simple
solutions for an expanding universe:

1) Density greater than the critical value
means spatially and temporally finite so
we have a closed universe and a big crunch.
Expansion slows and reverses. A photon
created at t=0 gets exactly half way across
the universe when the crunch arrives.

Which doesn't work too well, since we have photons
arriving in all directions from even ~300,000 y after
the Big Bang.

Why is that relevant, there wasn't a centre as
you know.

Let's see. We can determine the temperature of the CMBR
a "billion years ago" by observing processes in distant stars.
You have arrived at 4300

6300 LY actually but never mind.

I hope to hold that number.

light years for the thickness of the CMBR. Seems to me like
we are still receiving light that has travelled more than once
around the size of that early Universe,

Age now is 13.7 billion years. Hypothetically, if
we were in a closed universe currently at maximum
volume, the crunch would be at 27.4 billion years.
In that case GR said it would take a photon
precisely 54.8 billion years to get back to where
it was created after going "once round". The
cosmological constant changes all that though.

even though it may no longer be able to make it
around the size of the Universe now. So the stated
condition "A photon created at t=0 gets exactly
half way across the universe when the crunch
arrives." is obviously not met in this Universe.

Currently a closed universe seems highly unlikely
as we have discussed.

Agreed. You asked me "why" and I was answering that.

I wonder why they feel that space would contract again
in such a short time?

Why do you think it would be a short time?
http://www.astro.ucla.edu/~wright/flatness.gif
Red is closed, green and black are open.

4300 light years thick. Went opaque "in an instant".

My figure of 6300 LY would suggest it was opaque at
372,700 years and transparent at 379,000 years. "In
an instant" doesn't seem inappropriate in cosmological
terms.

.... but it does to a mechanical engineer! Is the "thickness"
being the same order of magnitude as the global "quench"
meaningful?

The FRW metric has the Universe collapse again, but
after many billions of years.

Exactly.

But it does not "solve" a spacetime that has "chunks" of
mass in it. But then it too is "just a MODEL".

Any solution to the equations is "just a model",
the trick is to find one that matches all we can
observe and then have it tell us about things we
can never see. That's my kind of "what if ...".

But that isn't science, George.

snip
Other than the dark energy contribution, you will
find many argue it is precisely that, the remnant
kinetic motion from t=0. The sum of that kinetic
energy and gravitational potential energy is zero
in many of the GR models.

However, our "expansion velocity" is much higher
than our kinetic motion wrt the Universe at large.

Again you seem to be thinking of expansion as
a motion away from a centre.

No. There is nothing special in "the direction we are
moving away from" kinetically, at 300 km/sec. We
are moving away from the CMBR with a (sort of)
gamma of 1079... which is NOT kinetic motion. I
just don't use the language the way experienced do.

OK, and perhaps I also mis-used it in trying
to understand you. We can measure the dipole
moment of the CMBR anisotropy

.... and the Universe et al...

and call that
a motion relative to locally co-moving
coordinates. I think of that like the proper
motion of a star within our galaxy.

The z of the CMBR can be thought of as produced
by motion of the source away from us but it can
also be considered as similar to gravitational
redshift or a stretching of the wavelength of
the photon while it was travelling through space
that was being stretched.

That sucked when Paul Lutus was feeding it to me. A photon, once
emitted, can be absorbed or scattered. It cannot be "stretched".
The red shift of supernovae duration is similarly red shifted to
its emission spectra. The light emitted is characteristic of the
process that emitted it, the local curvature in which is was
emitted, the global curvature of the Universe that emitted it,
the global curvature of the Universe that detected/absorbed it,
and the local curvature of the detector. Nothing was
"stretched", any more than it is between the Earth's surface and
the GPS satellites, or between the surface of the Sun and here.

Ignoring my 'proper motion' part, the kinetic
motion and the "expansion velocity" are one and
the same.

I think that I will stick with Ned Wright's defintion, wherein
"kinetic motion" is kept separate form expansion. "Let each man
lay his dead according to his own fashion."

When is the last time you asked "what if"?

Frequently, for example in reading Alan Guth's
paper on this subject. That's different to
finding out how to interpret an existing 'what
if'.

http://www.arxiv.org/abs/astro-ph/0301199

OK. Here are mine...

"What if we find structures the same age as the CMBRM?"

Then the observed nature of those structures is
what we should base our hypotheses on if we are
to approach this scientifically.

Good. Do you agree they *could* be observable... to say some
500,000 years after the BB... *IF* they existed?

"What if we find
heavy elements in excess of what can be explained in
standard Big Bang theory, the same age as the CMBRM?"

Then the measured relative abundances are what we
should base our hypotheses on if we are to approach
this scientifically.

I like to be proactive...

I like the scientific method.

I can't reconcile that statement with your disallowing certain
models of GR. But that isn't my problem.

No, "at those temperatures" means at the temperature
necessary to produce the obserevd H/He/Li mix
regardless of whether it happened in our universe
or the container.

This is where I am trying to fabricate some "breathing
room".

But you aren't, you are removing the only mechanism
we know capable of producing what we see.

I *think* I'm trying to offer an alternative, George.

What is your alternative explanation for the ~24%
observed ratio of He/H not involving the conventional
plasma?

As I have said, I cannot disallow such a plasma. I am only
trying to offer an alternative to said plasma, and it (my
hypothesis) will have a spectrum yet-to-be-determined. I
suspect, as you figured out, a time-integrated external-history
will include a good deal of the BH's own "failed evaporation"...
including the bitter end.

And as I've said, I
might by some stretch of the imagination be right, and there
still be a "Universe filling, opaque plasma".

Then if that rips down matter back to protons
then it wouldn't be an alternative.

They keep talking about "recombination", and BHs do tend not to
stay one size... as they ingest matter. It could start out as a
shredder, and end up as a flocculation pond (very slow agitation,
that enables agregation of molecules into skimmable or sinkable
structures)

snip
Our hole could have formed in an early Universe, and
our hole could have consumed its companion(s) early
on too. Or we could have shredded whatever we got
first... somehow I want to believe we are much bigger
than this.

Bigger than infinite? Do you really mean you want
to believe there an "outside" which is older than
this? See Guth.

No, I want to believe in an outside that is disjoint-in-time
from us.

Then that is 'new physics'

No, it isn't. It is a choice of model. And it is potentially
observable/falsifiable.

What I meant by "much bigger than this" is, I think we
have too much mass evident today, to have made a
small BH as a "youth".

Too much??? There is only 4% of the critical density
as baryonic matter and even dark matter only brings
it up to about a third of what is required.

Consider a young Universe, some 6300 ly "across", with mass
sufficient to achieve a "curvature coefficient" of 1079 (compared
to today). That may be a small beginning, but it no less
massive.

But I guess we had
to start somewhere. ;)

I just need spectrum data... the Sun, and some of the full sky
surveys
that mapped the CMBR... which will not do a good job with
individual
spectral lines most likely. Do you have some ideas where I
can look?

The Sun isn't going to be much use, you need spectra
for everything from white dwarfs to red giants and you
need to know the mix visible in the container universe
from our location within it and their ages.

These should be written into spectrum data near the plane of the
Milky Way, in the CMBR data... assuming that is available since
it is "contaminated".

For the CMBR, use this link

http://lambda.gsfc.nasa.gov/product/...prod_table.cfm

Yes. This would be good (as a start) for a free BH, or one near
our position in a "largely spiral" galaxy. Then I need to come
up with a spectrum for a BH consuming a companion, and to somehow
infer the influx to the BH at the center of our own galaxy. If
I'm going to prepare several "broths" best to use many available
spices.

or Google for "firas data products". It should be on
the Lambda site but that seems to be down at the moment.

Thanks George. I seem to be wearing on your nerves. So I will
try not to respond more than once a week. That way the
"potential irritation" level is down. It takes me about an hour
to key this all in, and I hope it doesn't take you nearly this
long to reply. (Although a *lot* of thought goes into your
responses.)

David A. Smith

Dear Geroge Dishman,

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox
wrote in message newsrxMe.57073$E95.48764@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

Just a note, I found some of what we were
discussing.

No, from what I have seen, some coordinate systems
stop at the horizon while other don't, but there
is no physical effect there in the GR model.

I found the relevant part he

http://casa.colorado.edu/~ajsh/schwp.html

"The Schwarzschild spacetime geometry appears
ill-behaved at the horizon, the Schwarzschild
radius (vertical red line). However, the
pathology is an artefact of the Schwarzschild
coordinate system. Spacetime itself is well-
behaved at the Schwarzschild radius, as can be
ascertained by computing the components of the
Riemann curvature tensor, all of whose components
remain finite at the Schwarzschild radius."

I understand what you are saying, George. Now try these:
URL:http://www.aleph.se/Trans/Global/Omega/baby.txt
URL:http://math.ucr.edu/home/baez/PUB/generichole
URL:http://math.ucr.edu/home/baez/gr/oz1.html

There is window dressing, but he construction details of the
manequins, might be there somewhere, but I did not find it.
Likely it was numerical simulation of the equations of GR
direct. Only the choices of "simplifying assumptions" are
(perhaps) omitted, so only Andrew knows.

There is a list on this page under "Caveats"

http://casa.colorado.edu/~ajsh/approach.html

Yes. He supposedly had a Schwarzchild solution that he was able
to map across the event horizon. A nice trick. Then he claims
that we "fall at c". And yet, this seems to be what is at hand.

David A. Smith

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:yUwOe.124442$E95.97537@fed1read01...
Dear Geroge Dishman,

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message newsrxMe.57073$E95.48764@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

Just a note, I found some of what we were
discussing.

No, from what I have seen, some coordinate systems
stop at the horizon while other don't, but there
is no physical effect there in the GR model.

I found the relevant part he

http://casa.colorado.edu/~ajsh/schwp.html

"The Schwarzschild spacetime geometry appears
ill-behaved at the horizon, the Schwarzschild
radius (vertical red line). However, the
pathology is an artefact of the Schwarzschild
coordinate system. Spacetime itself is well-
behaved at the Schwarzschild radius, as can be
ascertained by computing the components of the
Riemann curvature tensor, all of whose components
remain finite at the Schwarzschild radius."

I understand what you are saying, George. Now try these:
URL:http://www.aleph.se/Trans/Global/Omega/baby.txt

David, is there a way to get rid of the "URL:" part,
it breaks the link in Outlook Express because the
text is no longer a URL if you put "URL" in front.

Anyway, from that link I see:

A. The formation of a black hole creates "baby
universe," the final singularity of the black
hole tunnelling right on through to the initial
"big bang" singularity of the new universe
thanks to quantum effects.

The phrase "the final singularity of the black hole"
refers to the point at the centre and confirms what
I have been saying.

Later it says:

"The fact that the entropy of a black hole is (at
least under certain circumstances) proportional
to the area of its event horizon is a curious
relationship between general relativity, quantum
field theory and statistical mechanics that many
people believe to pointing somewhere, but
unfortunately nobody is sure where. Part of the
reason is that the standard derivations are
somewhat indirect, and the event horizon is not
a physical object, so the sense in which it is
the locus of entropy is difficult to understand."

Again "the event horizon is not a physical object"
agrees with my view.

URL:http://math.ucr.edu/home/baez/PUB/generichole
URL:http://math.ucr.edu/home/baez/gr/oz1.html

There is window dressing, but he construction details of the manequins,
might be there somewhere, but I did not find it. Likely it was numerical
simulation of the equations of GR direct. Only the choices of
"simplifying assumptions" are (perhaps) omitted, so only Andrew knows.

There is a list on this page under "Caveats"

http://casa.colorado.edu/~ajsh/approach.html

Yes. He supposedly had a Schwarzchild solution that he was able to map
across the event horizon. A nice trick.

No trick needed, nothing changes at the horizon.

Then he claims that we "fall at c". And yet, this seems to be what is at
hand.

Imagine a duck swimming up river at 5m/s in a
stream that narrows approaching a weir. As the
stream narrows, the water moves faster. If the
duck starts where the water flows at 4m/s it
will escape but if it starts where it is 6m/s
it will move towards the weir ever faster until
it goes over.

A singularity occurs if the width of the stream
gets to zero at the weir as the speed becomes
infinite, but nothing happens to the water (or
the duck) where the flow is 5m/s.

George

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:6twOe.124437$E95.51864@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message newsrxMe.57073$E95.48764@fed1read01...
Dear George Dishman:



Severly trimmed again.

No, that's not true. The failure at the horizon is
purely mathematical as for the pool table example,
the failure at the singularity is physical.

Consider that the sources that are the most active
astrophysically, are black holes (with companions).

Indeed, but the radiation and jets are produced
in the accretion disk outside the horizon.

So it isn't quite "mathematical", then is it?

I don't see your point, the matter in the jets
never gets nearer than r=3m while the horizon
is at r=2m.

Physically, the Universe (and the BH) are attempting to solve the
"immovable object/irresistable force" problem.

No, it's more like the gravitational slingshot
of a probe round a planet, it only passes nearby.

Now consider the definition of "singularity". The event horizon
*is* a singularity. No?

No. The singularity is at the centre, there
is nothing unusual physically at the horizon.

It *is* a singularity in Schwarzchild coordinates. I quote from Wikipedia
a.. mathematical singularity - a point where a mathematical function goes
to infinity or is in certain other ways ill-behaved. It is also a point
where all functions meet.

OK, that says it is "mathematical", i.e. has no
physical significance.

a.. gravitational singularity - an infinity occurring in an astrophysical
model, involving infinite curvature (a mathematical singularity) in the
space/time continuum, namely a black hole.

OK, that could refer to the centre though there is
nothing in the context to differentiate.

What is unusual at the horizon is that light cannot ever propagate away
from it. In all coordinate choices, this is true.

Yep, ask the duck if there is a ripple on the water
at it's point of no return (see my other post).

Yes, that's true but if you look at a spacetime
diagram showing light cones, it is obvious why
that occurs and it doesn't involve a singularity.

It does involve a singularity, George. As defined by the English
language. A "singularity" is not always just a "point".

Sorry, I should have made the distincton between
mathematical and physical.


There is window dressing, but he construction details of the manequins,
might be there somewhere, but I did not find it. Likely it was numerical
simulation of the equations of GR direct.

Exactly, the only 'assumptions' were the other
stars he included in the hypothetical system.
The ray tracing I believe is pure GR without
any simplifications at all.

I don't know how he did a "Schwarzchild" solution across the event
horizon. Yet that is the suggestion.

Indeed, it is possible and retains discrete images
because the GR model does not include any physical
change at the horizon.

No, it would be better to say "speed_path_average" since
c is just a constant, 299792458m/s.

Yes, sloppy talk does no one any good.

Me too, see above.

would appear to decrease, as observed by an infinite
observer. "Shapiro time delay" is an observation fully in
agreement with GR. So what does it mean to say that
we "infinite observers" can say stuff about physics
beyond the *singularity* that is the event horizon?

David, the event horizon is *not* a singularity,
only certain coordinate system have an *artificial*
singularity on that surface. That is the root of
all our disagreements I think.

It is how the word is defined, George.

I'm not sure of the exact technical definition but
"the boundary of the region from which light cannot
escape" is probably close.

You (and most other mainstreamers) place the singularity "at the center",
even though this is not physically meaningful in *this* Universe.

At the centre, many measures become infinite in a
way that is independent of coordinates, the theory
blows up and you have a singularity in the model.
There is no such occurence at the horizon though
some coordiante systems fail.

Yet in my hypothesis, the only singularity is the severance of one
spacetime, adjoint to another (essentially identical?) spacetime.

IMHO, that would be "new physics" since this doesn't
happen in GR.

The mass/energy only "reports to a different boss, on a different form".
What the external Universe calls "an infintely dense central singularity",
the insiders call "an approaching infinitely-diffuse, cold future". We
will evaporate before that will complete, of course.

This is why the r axis is referred to as "timelike".

So time has a different letter in that region,
it is still time.

It *is* still time, but it is not outer-time. It is not related to
external-time, except perhaps to be orthogonal to it. Again,
this is just the model, I know.

I don't want to sound as though I'm laying down
the law but I think you need to stop and make
some enquiries. AIUI, it isn't the model, it is
the coordinates. Physically time outside the
horizon and time inside are the same, it is only
when you get to the singularity at the centre
that the physics fails.

Then we can agree to disagree.

I think that's best, I doubt we will resolve this
here but please note I am not rejecting any aspect
of GR, just your interpretation of it. If it turns
out your version is correct, I will happily
acknowledge being enlightened.

big snip

I don't hold that this Universe is unique, or at least self-sufficient.

Nor am I claiming that (or otherwise), see my
comments on Guth.

Yes, it is worth looking but we need to correctly
understand what the models say.

We understand what the models say. Internal time is NOT directly
correlated to external time, by all metrics than we can yet apply to BHs.

That is where we have agreed to disagree.

"We can't know." is not very satisfying to me. It seems
that "we can look" is far superior.

Tough. Either we can or we can't, that is
determined by reality, not our preference.
Understanding whether we can or not is the
best we can do.

So why do you have a preference for one model over another?

I don't exclude or prefer any model, other than
perhaps being skeptical of "non-trivial topology"
without convincing evidence, I don't like the
idea of the universe being a Klein Bottle!

I am not offering "new physics", I am offering that our Universe is not
unique in the scheme of things. And my hypothesis is potentially
falsifiable.

That isn't contentious, it is only your idea of a
physical singularity at the event horizon that I
consideer to be "new physics" as I believe it is
in contradiction to GR.

What is raising the question of a non-closed Universe?

Without dark energy, GR gives some simple
solutions for an expanding universe:

1) Density greater than the critical value
means spatially and temporally finite so
we have a closed universe and a big crunch.
Expansion slows and reverses. A photon
created at t=0 gets exactly half way across
the universe when the crunch arrives.

Which doesn't work too well, since we have photons
arriving in all directions from even ~300,000 y after
the Big Bang.

Why is that relevant, there wasn't a centre as
you know.

Let's see. We can determine the temperature of the CMBR
a "billion years ago" by observing processes in distant stars.
You have arrived at 4300

6300 LY actually but never mind.

I hope to hold that number.

light years for the thickness of the CMBR. Seems to me like
we are still receiving light that has travelled more than once
around the size of that early Universe,

Age now is 13.7 billion years. Hypothetically, if
we were in a closed universe currently at maximum
volume, the crunch would be at 27.4 billion years.
In that case GR said it would take a photon
precisely 54.8 billion years to get back to where
it was created after going "once round". The
cosmological constant changes all that though.

even though it may no longer be able to make it
around the size of the Universe now. So the stated
condition "A photon created at t=0 gets exactly
half way across the universe when the crunch
arrives." is obviously not met in this Universe.

Currently a closed universe seems highly unlikely
as we have discussed.

Agreed. You asked me "why" and I was answering that.

Then I still don't understand why you said "Which
doesn't work too well, since we have photons
arriving in all directions from even ~300,000 y
after the Big Bang". They were produced everywhere
so would be arriving from all directions even 1s
after the bang.

My figure of 6300 LY would suggest it was opaque at
372,700 years and transparent at 379,000 years. "In
an instant" doesn't seem inappropriate in cosmological
terms.

... but it does to a mechanical engineer! Is the "thickness" being the
same order of magnitude as the global "quench" meaningful?

What do you mean by "global 'quench'"?

The FRW metric has the Universe collapse again, but
after many billions of years.

Exactly.

But it does not "solve" a spacetime that has "chunks" of
mass in it. But then it too is "just a MODEL".

Any solution to the equations is "just a model",
the trick is to find one that matches all we can
observe and then have it tell us about things we
can never see. That's my kind of "what if ...".

But that isn't science, George.

Isn't it? Basing our extrapolations on models derived
from observation instead of philosophy or religion
seems to me to be precisely what science is about.

The z of the CMBR can be thought of as produced
by motion of the source away from us but it can
also be considered as similar to gravitational
redshift or a stretching of the wavelength of
the photon while it was travelling through space
that was being stretched.

That sucked when Paul Lutus was feeding it to me.

It is a standard way of expressing it. I'm not
keen myself but I think the three descriptions
are effectively equivalent while appearing
different in the same sense as wave/particle
duality.

A photon, once emitted, can be absorbed or scattered. It cannot be
"stretched". The red shift of supernovae duration is similarly red shifted
to its emission spectra. The light emitted is characteristic of the
process that emitted it, the local curvature in which is was emitted, the
global curvature of the Universe that emitted it, the global curvature of
the Universe that detected/absorbed it, and the local curvature of the
detector. Nothing was "stretched", any more than it is between the
Earth's surface and the GPS satellites, or between the surface of the Sun
and here.

I hear your assertion.

Ignoring my 'proper motion' part, the kinetic
motion and the "expansion velocity" are one and
the same.

I think that I will stick with Ned Wright's defintion, wherein "kinetic
motion" is kept separate form expansion. "Let each man lay his dead
according to his own fashion."

Can you give me a pointer to this in his tutorial,
I wasn't aware he used the terms. I'll search
later but if you have bookmarked the section it
would save me some time.

"What if we find structures the same age as the CMBRM?"

Then the observed nature of those structures is
what we should base our hypotheses on if we are
to approach this scientifically.

Good. Do you agree they *could* be observable... to say some 500,000
years after the BB... *IF* they existed?

They should be visible after 379,000 years if they
existed then. I am hoping we will see Pop III novae
with the next generation scopes but they are expected
to be around z=20. If super-massive BHs preceded galaxy
formation, we might see quasars even earlier.

"What if we find
heavy elements in excess of what can be explained in
standard Big Bang theory, the same age as the CMBRM?"

Then the measured relative abundances are what we
should base our hypotheses on if we are to approach
this scientifically.

I like to be proactive...

I like the scientific method.

I can't reconcile that statement with your disallowing certain models of
GR.

That's because I don't believe I am, I think you
are inventing "new science" when to suggest a
physical singularity where none exists in GR. If
you want to talk about the Cauchy horizon, that
would be another matter, but I know little of that.

What is your alternative explanation for the ~24%
observed ratio of He/H not involving the conventional
plasma?

As I have said, I cannot disallow such a plasma. I am only trying to
offer an alternative to said plasma,

Yes, I understand that, but how does your alternative
produce that elemental ratio?

and it (my hypothesis) will have a spectrum yet-to-be-determined. I
suspect, as you figured out, a time-integrated external-history will
include a good deal of the BH's own "failed evaporation"... including the
bitter end.

And as I've said, I
might by some stretch of the imagination be right, and there
still be a "Universe filling, opaque plasma".

Then if that rips down matter back to protons
then it wouldn't be an alternative.

They keep talking about "recombination",

It is a misnomer, it should be just "combination",
it's a bit of an in-joke actually.

and BHs do tend not to stay one size... as they ingest matter. It could
start out as a shredder, and end up as a flocculation pond (very slow
agitation, that enables agregation of molecules into skimmable or sinkable
structures)

snip
Our hole could have formed in an early Universe, and
our hole could have consumed its companion(s) early
on too. Or we could have shredded whatever we got
first... somehow I want to believe we are much bigger
than this.

Bigger than infinite? Do you really mean you want
to believe there an "outside" which is older than
this? See Guth.

No, I want to believe in an outside that is disjoint-in-time from us.

Then that is 'new physics'

No, it isn't.

I'll continue to disagree on that.

It is a choice of model. And it is potentially observable/falsifiable.

What I meant by "much bigger than this" is, I think we
have too much mass evident today, to have made a
small BH as a "youth".

Too much??? There is only 4% of the critical density
as baryonic matter and even dark matter only brings
it up to about a third of what is required.

Consider a young Universe, some 6300 ly "across", with mass sufficient to
achieve a "curvature coefficient" of 1079 (compared to today).

Lots of confusion there, the optical thickness
of the period of recombination was 6300 ly but
that happened at 380,000 years so the part of
the universe which is _currently_ observable
might have been 760,000 LY across and the
whole universe would have been billions of
light years across or perhaps infinite.

The universe appears to be flat and would have
been then too. The figure of 1079 is the redshift
compared to today, not the curvature.

That may be a small beginning, but it no less massive.

It still held only 4% of the required matter in
baryonic form.

But I guess we had
to start somewhere. ;)

I just need spectrum data... the Sun, and some of the full sky surveys
that mapped the CMBR... which will not do a good job with individual
spectral lines most likely. Do you have some ideas where I can look?

The Sun isn't going to be much use, you need spectra
for everything from white dwarfs to red giants and you
need to know the mix visible in the container universe
from our location within it and their ages.

These should be written into spectrum data near the plane of the Milky
Way, in the CMBR data... assuming that is available since it is
"contaminated".

For the CMBR, use this link

http://lambda.gsfc.nasa.gov/product/...prod_table.cfm

Yes. This would be good (as a start) for a free BH, or one near our
position in a "largely spiral" galaxy.

I intended that as a good start for the CMBR after
the removal of all stars. You need individual stellar
spectra separately. A free BH has no spectrum since
it is black !

Then I need to come up with a spectrum for a BH consuming a companion,

Try Cyg X1

and to somehow infer the influx to the BH at the center of our own galaxy.

It appears to be in a relatively clear region so
is invisible.

If I'm going to prepare several "broths" best to use many available
spices.

or Google for "firas data products". It should be on
the Lambda site but that seems to be down at the moment.

Thanks George. I seem to be wearing on your nerves.

Not at all, though I think we have done the
singularity thing to death.

So I will try not to respond more than once a week. That way the
"potential irritation" level is down. It takes me about an hour to key
this all in, and I hope it doesn't take you nearly this long to reply.

This one took about the same and I haven't looked up
any new references for you. I spent another half hour
or so reading the John Baez pages but I don't count
that as I learn from them anyway.

(Although a *lot* of thought goes into your responses.)

Thanks, it's nice to know you appreciate it. I could
tell you do the same and while we may disagree I hope
you feel you benefit as much as me from reading the
cited resources.

best regards
George

Dear George Dishman:

"George Dishman" wrote in message
...

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wrote in message news:yUwOe.124442$E95.97537@fed1read01...
Dear Geroge Dishman,

"George Dishman" wrote in message
...

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Dear George Dishman:

"George Dishman" wrote in message
...

Just a note, I found some of what we were
discussing.

No, from what I have seen, some coordinate systems
stop at the horizon while other don't, but there
is no physical effect there in the GR model.

I found the relevant part he

http://casa.colorado.edu/~ajsh/schwp.html

"The Schwarzschild spacetime geometry appears
ill-behaved at the horizon, the Schwarzschild
radius (vertical red line). However, the
pathology is an artefact of the Schwarzschild
coordinate system. Spacetime itself is well-
behaved at the Schwarzschild radius, as can be
ascertained by computing the components of the
Riemann curvature tensor, all of whose components
remain finite at the Schwarzschild radius."

I understand what you are saying, George. Now try these:
URL:http://www.aleph.se/Trans/Global/Omega/baby.txt

David, is there a way to get rid of the "URL:" part,
it breaks the link in Outlook Express because the
text is no longer a URL if you put "URL" in front.

I intentionally add the URL:, so that Outlook Express and other
readers will correctly form long links. Oh well... FWIW the
links work for me.

Anyway, from that link I see:

A. The formation of a black hole creates "baby
universe," the final singularity of the black
hole tunnelling right on through to the initial
"big bang" singularity of the new universe
thanks to quantum effects.

The phrase "the final singularity of the black hole"
refers to the point at the centre and confirms what
I have been saying.

Later it says:

"The fact that the entropy of a black hole is (at
least under certain circumstances) proportional
to the area of its event horizon is a curious
relationship between general relativity, quantum
field theory and statistical mechanics that many
people believe to pointing somewhere, but
unfortunately nobody is sure where. Part of the
reason is that the standard derivations are
somewhat indirect, and the event horizon is not
a physical object, so the sense in which it is
the locus of entropy is difficult to understand."

Again "the event horizon is not a physical object"
agrees with my view.

But nothing else did, nor did it it in any particular talk about
the production of an inner Universe due to a choice of metric.
However, it is not important. I think it is a good question if
the event horizon is even *in* this Universe. You can't measure
it, you can never get information from it, you can only determine
the mass that the BH contains and *infer* its position as the
"asymptote" from which infalling objects might ever get light out
to you. The last stable physical state not involving Steve
Willner's "new physics" is well outside the event horizon. I am
not asking if the event horizon is a physical object, only if it
would appear to be so at the instant of the Big Bang, *from the
inside*.

But you know this...

URL:http://math.ucr.edu/home/baez/PUB/generichole
URL:http://math.ucr.edu/home/baez/gr/oz1.html

There is window dressing, but he construction details of the
manequins, might be there somewhere, but I did not find it.
Likely it was numerical simulation of the equations of GR
direct. Only the choices of "simplifying assumptions" are
(perhaps) omitted, so only Andrew knows.

There is a list on this page under "Caveats"

http://casa.colorado.edu/~ajsh/approach.html

Yes. He supposedly had a Schwarzchild solution that he was
able to map across the event horizon. A nice trick.

No trick needed, nothing changes at the horizon.

Yes, trick needed. Schwarzchild is singular at the event
horizon, as we have covered ad nauseum. Yet he managed to
achieve a continuous presentation... maybe it is well behaved on
either side of the EH.

Then he claims that we "fall at c". And yet, this seems to
be what is at hand.

Imagine a duck swimming up river at 5m/s in a
stream that narrows approaching a weir. As the
stream narrows, the water moves faster. If the
duck starts where the water flows at 4m/s it
will escape but if it starts where it is 6m/s
it will move towards the weir ever faster until
it goes over.

A singularity occurs if the width of the stream
gets to zero at the weir as the speed becomes
infinite, but nothing happens to the water (or
the duck) where the flow is 5m/s.

The analogies are fine George. Unfortunately, *to whom* does the
infalling person appear to fall at c? Presumably a stationary
observer, but there are on possible stationary observers inside
the photon sphere, much less inside the event horizon. So what
use are the words, what meaning can they convey where the context
is not part of this Universe (except though total mass, total
charge, total angular moementum)?

David A. Smith

Dear George Dishman:

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Dear George Dishman:

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Dear George Dishman:



Severly trimmed again.

No, that's not true. The failure at the horizon is
purely mathematical as for the pool table example,
the failure at the singularity is physical.

Consider that the sources that are the most active
astrophysically, are black holes (with companions).

Indeed, but the radiation and jets are produced
in the accretion disk outside the horizon.

So it isn't quite "mathematical", then is it?

I don't see your point, the matter in the jets
never gets nearer than r=3m while the horizon
is at r=2m.

My point is that the first singularity is the event horizon. It
is physically not located *in* this Universe. The fact that any
infalling matter starts boiling away due to collisions, even
though the source of the colliding particles is (most commonly)
the same companion, just adds support to my non-specular arrival
of light to the inside.

Physically, the Universe (and the BH) are attempting to solve
the "immovable object/irresistable force" problem.

No, it's more like the gravitational slingshot
of a probe round a planet, it only passes nearby.

.... and nearby ... and nearby ...

Now consider the definition of "singularity". The event
horizon *is* a singularity. No?

No. The singularity is at the centre, there
is nothing unusual physically at the horizon.

It *is* a singularity in Schwarzchild coordinates. I quote
from Wikipedia
a.. mathematical singularity - a point where a mathematical
function goes to infinity or is in certain other ways
ill-behaved.
It is also a point where all functions meet.

OK, that says it is "mathematical", i.e. has no
physical significance.

As with any English word, it has many meanings. The event
horizon meets this constraint as well.

b.. gravitational singularity - an infinity occurring in an
astrophysical model, involving infinite curvature (a
mathematical singularity) in the space/time continuum,
namely a black hole.

OK, that could refer to the centre though there is
nothing in the context to differentiate.

"a black hole" is really clear George. It doesn't try to
differentiate to "internal structure", only for what we *can* see
(in some sense). It clearly doesn't refer to the center, and I
didn't even write it.

What is unusual at the horizon is that light cannot ever
propagate away from it. In all coordinate choices, this
is true.

Yep, ask the duck if there is a ripple on the water
at it's point of no return (see my other post).

So the event horizon *is* a physical singularity, if not a
physical object.

Yes, that's true but if you look at a spacetime
diagram showing light cones, it is obvious why
that occurs and it doesn't involve a singularity.

It does involve a singularity, George. As defined by the
English language. A "singularity" is not always just a
"point".

Sorry, I should have made the distincton between
mathematical and physical.

There is nothing physical about the inside of BH, George. So the
only flashlight we have to view the caverns where Injun Joe hid,
is via mathematics. Some mathematics indicates that we might see
the inside of an event horizon at the beginning of our
Universe... namely the Big Bang.

There is window dressing, but he construction details of the
manequins,
might be there somewhere, but I did not find it. Likely it
was numerical simulation of the equations of GR direct.

Exactly, the only 'assumptions' were the other
stars he included in the hypothetical system.
The ray tracing I believe is pure GR without
any simplifications at all.

I don't know how he did a "Schwarzchild" solution across the
event horizon. Yet that is the suggestion.

Indeed, it is possible and retains discrete images
because the GR model does not include any physical
change at the horizon.

Not and use "Schwarzchild", unless it is well behaved on either
side of the event horizon. Like as not, he did not use anything
Schwarzchild for the "dive into the BH" animations. So we don't
know what he did use. And it is not important, because it is
"only mathematics", right George?

No, it would be better to say "speed_path_average" since
c is just a constant, 299792458m/s.

Yes, sloppy talk does no one any good.

Me too, see above.

You pretty much kick *ss.

would appear to decrease, as observed by an infinite
observer. "Shapiro time delay" is an observation fully in
agreement with GR. So what does it mean to say that
we "infinite observers" can say stuff about physics
beyond the *singularity* that is the event horizon?

David, the event horizon is *not* a singularity,
only certain coordinate system have an *artificial*
singularity on that surface. That is the root of
all our disagreements I think.

It is how the word is defined, George.

I'm not sure of the exact technical definition but
"the boundary of the region from which light cannot
escape" is probably close.

See both defintions of singularity above, and the various pages
you have shown me that Schwarzchild is singular at the EH. "The
singularity at the center" is a non-sequitur, if you don't agree
that mathematics is our road in-and-out. Some of those roads
describe *our* Universe, and the "singularity at the center" as a
very diffuse, cold future.

You (and most other mainstreamers) place the singularity
"at the center", even though this is not physically
meaningful in *this* Universe.

At the centre, many measures become infinite in a
way that is independent of coordinates, the theory
blows up and you have a singularity in the model.
There is no such occurence at the horizon though
some coordiante systems fail.

They *all* fail, George. You yourself use the word "measure".
How would you measure that which can only reliably return your
signal after the black box has evaporated? The English language
is really slippery, I know. But our grandiose posturings:
- about how this Unvierse must be unique,
- the BH must be some sort of cosmic garbage disposal,
- that our continguous-reality-that-passes-for-spacetime must
have a separate life of its own, and extend "recognizeably" even
down into this garbage disposal,
- and violate all the conservation laws just so that we can be
sure that there is a "singularity at the center",
is simply too much for me to believe.

Yet in my hypothesis, the only singularity is the severance of
one spacetime, adjoint to another (essentially identical?)
spacetime.

IMHO, that would be "new physics" since this doesn't
happen in GR.

GR is a theory, which means it has mathematics associated with
it, and not as some sort of unwarranted "apendage". It has
solutions for BHs. All of the solutions (that I have seen) that
do an adequate job of describing massive structures, do so by
either blending or replacing external space with internal time.

....
This is why the r axis is referred to as "timelike".

So time has a different letter in that region,
it is still time.

It *is* still time, but it is not outer-time. It is not
related to
external-time, except perhaps to be orthogonal to it.
Again,
this is just the model, I know.

I don't want to sound as though I'm laying down
the law but I think you need to stop and make
some enquiries. AIUI, it isn't the model, it is
the coordinates. Physically time outside the
horizon and time inside are the same, it is only
when you get to the singularity at the centre
that the physics fails.

Then we can agree to disagree.

I think that's best, I doubt we will resolve this
here but please note I am not rejecting any aspect
of GR, just your interpretation of it. If it turns
out your version is correct, I will happily
acknowledge being enlightened.

Well, it has been "fun", in some sense. I don't expect to be
right. But I do expect me to ask the question, as clearly as
possible, and defend the right for the question to "exist".

....
Yes, it is worth looking but we need to correctly
understand what the models say.

We understand what the models say. Internal time
is NOT directly correlated to external time, by all
metrics than we can yet apply to BHs.

That is where we have agreed to disagree.

OK.

"We can't know." is not very satisfying to me. It seems
that "we can look" is far superior.

Tough. Either we can or we can't, that is
determined by reality, not our preference.
Understanding whether we can or not is the
best we can do.

So why do you have a preference for one model over another?

I don't exclude or prefer any model, other than
perhaps being skeptical of "non-trivial topology"
without convincing evidence, I don't like the
idea of the universe being a Klein Bottle!

Worse than that. A potentially infinite series of such bottles.
Personally, I think it ends at step two, and "where we came from"
and "where our black holes lead" is to one-and-the-same Universe,
primarily anti-matter, and opposite tendency to chirality. But,
that is for another life...

I am not offering "new physics", I am offering that our
Universe is not unique in the scheme of things. And my
hypothesis is potentially falsifiable.

That isn't contentious, it is only your idea of a
physical singularity at the event horizon that I
consideer to be "new physics" as I believe it is
in contradiction to GR.

Only if you consider spacetime to be "physical" is there a
"physcial singularity" at the event horizon. Since:
- there is no spacetime without matter/energy,
- you cannot interact directly with any matter/energy starting at
(really before) the event horizon,
- any infall is already *NOT* in this Universe... only the
gestalt is evident,
- the population must therefore have its own physics, which I
fully expect to be the Pauli exclusion principle, conservation of
momenergy, and so on. I don't expect "new physics", I only
expect continuation of *known* physics.
And like those that don't want to believe that the
reality-dressed-like-spacetime actually binds time to space, I
see you wanting to believe that all such reality continues
"unbroken" inside the event horizon. And we will agree to
disagree.

What is raising the question of a non-closed Universe?

Without dark energy, GR gives some simple
solutions for an expanding universe:

1) Density greater than the critical value
means spatially and temporally finite so
we have a closed universe and a big crunch.
Expansion slows and reverses. A photon
created at t=0 gets exactly half way across
the universe when the crunch arrives.

Which doesn't work too well, since we have photons
arriving in all directions from even ~300,000 y after
the Big Bang.

Why is that relevant, there wasn't a centre as
you know.

Let's see. We can determine the temperature of the CMBR
a "billion years ago" by observing processes in distant
stars.
You have arrived at 4300

6300 LY actually but never mind.

I hope to hold that number.

light years for the thickness of the CMBR. Seems to me like
we are still receiving light that has travelled more than
once
around the size of that early Universe,

Age now is 13.7 billion years. Hypothetically, if
we were in a closed universe currently at maximum
volume, the crunch would be at 27.4 billion years.
In that case GR said it would take a photon
precisely 54.8 billion years to get back to where
it was created after going "once round". The
cosmological constant changes all that though.

even though it may no longer be able to make it
around the size of the Universe now. So the stated
condition "A photon created at t=0 gets exactly
half way across the universe when the crunch
arrives." is obviously not met in this Universe.

Currently a closed universe seems highly unlikely
as we have discussed.

Agreed. You asked me "why" and I was answering that.

Then I still don't understand why you said "Which
doesn't work too well, since we have photons
arriving in all directions from even ~300,000 y
after the Big Bang". They were produced everywhere
so would be arriving from all directions even 1s
after the bang.

And how they could have NOT been aroud the early Universe *at
least once*, when it took ~300,000 years to get to a size of 6300
ly. Maybe I'm being too Newtonian about it...

My figure of 6300 LY would suggest it was opaque at
372,700 years and transparent at 379,000 years. "In
an instant" doesn't seem inappropriate in cosmological
terms.

... but it does to a mechanical engineer! Is the "thickness"
being the same order of magnitude as the global "quench"
meaningful?

What do you mean by "global 'quench'"?

What was completed by "379,000 years". The plasma was quenched
to a normal matter state. If we were expanding compressed air as
an analogy, it the point at which water vapor (as opposed to
steam) would form.

The FRW metric has the Universe collapse again, but
after many billions of years.

Exactly.

But it does not "solve" a spacetime that has "chunks" of
mass in it. But then it too is "just a MODEL".

Any solution to the equations is "just a model",
the trick is to find one that matches all we can
observe and then have it tell us about things we
can never see. That's my kind of "what if ...".

But that isn't science, George.

Isn't it? Basing our extrapolations on models derived
from observation instead of philosophy or religion
seems to me to be precisely what science is about.

Models involve mathematics, George.

The z of the CMBR can be thought of as produced
by motion of the source away from us but it can
also be considered as similar to gravitational
redshift or a stretching of the wavelength of
the photon while it was travelling through space
that was being stretched.

That sucked when Paul Lutus was feeding it to me.

It is a standard way of expressing it. I'm not
keen myself but I think the three descriptions
are effectively equivalent while appearing
different in the same sense as wave/particle
duality.

But it requires that the photon give up some of its energy, yet
retain the vector portion of its mometum entirely intact. We
don't know how to do that.

A photon, once emitted, can be absorbed or scattered.
It cannot be "stretched". The red shift of supernovae
duration is similarly red shifted to its emission spectra.
The light emitted is characteristic of the process that
emitted it, the local curvature in which is was emitted,
the global curvature of the Universe that emitted it, the
global curvature of the Universe that detected/absorbed
it, and the local curvature of the detector. Nothing was
"stretched", any more than it is between the Earth's
surface and the GPS satellites, or between the surface
of the Sun and here.

I hear your assertion.

It is just a lot longer to say... ;)

Ignoring my 'proper motion' part, the kinetic
motion and the "