Dear Bill Rowe:

"Bill Rowe" wrote in message
...
In article PYTLe.43692$E95.33607@fed1read01,
"N:dlzc D:aol T:com \(dlzc\)" N: dlzc1 D:cox
wrote:

"Tom Roberts" wrote in message
.. .

N:dlzc D:aol T:com (dlzc) wrote:
"George Dishman" wrote in
message
...

Yet spacetime is a product of mass/energy,

No, it is not. Spacetime is a geometric MODEL of the world.
It is a "product" (in the sense of result, not
multiplication) of
the human imagination.

So you are then saying that there is no need in anyone (even
Idiots) trying to extend the MODEL of the world to make
predictions?

Your question here implies you see Tom's comments as
saying something about the need to extend a model of the
world. How do you arrive at that?

I do not get that from Tom's comment. Science is about
modelling, PREDICTION, and testing. Some solutions to black
holes (using GR) have an entirely new Universe formed inside.
Universes that are expected to have similar (or identical) laws
to ours. In the context of this thread, and my remark above, I
am making a verbal prediction, that we could *perhaps* test this
on our Universe by looking at the CMBR. GR can be made to model
the inside of a black hole, so this is not straight fantasy. It
is not even extending the model, except possibly to a place that
is unphysical.

What I got from Tom's comment is that it wasn't worth the time or
effort, because it is all imaginary anyway.

In the context you used it, product could mean a literal
multiplication of mass and energy to get spacetime. I don't
think this is what you had in mind as it doesn't make sense.

It is not. I intended something along the lines of "to issue
from".
Quoting Einstein "Relativity; The Special and the General
Theory", Appendix Five
QUOTE
On the basis of the general theory of relativity, on the other
hand, space as opposed to "what fills space," which is dependent
on the co-ordinates has no separate existence.
snip one sentence
If we imagine the gravitational field, i.e. the functions g_ik,
to be removed, there does not remain a space of the type (1), but
absolutely italicsnothingend italics, and also no
"topological space".
END QUOTE

But as I have pointed out to others... Einstein is dead. And
others have pointed out that Relativity has advanced much since
Einstein's time.

Alternatively, I could take your comment to mean
spacetime is the result of mass and energy. Tom simply
points out spacetime is the result of human imagination
rather than mass and energy. I believe the point is
spacetime has no existence outside of human thought.

I understand the point. However science is about testing the
"limits of thought", if you really intend to dereference
"reality" in this way. We don't know what the underlying reality
is, but our models allow us to both interpolate (usually to good
effect) and extrapolate (commonly with comical effect).

But I don't see anything in these comments having
anything to do with the need to extend any model of the
world.

Except where I implicity said that was my intent. I intend to
see if the history of light impinging on the surface of a BH is
isothermal *in toto*. It will a least be better than spending
all my brainpower tweaking sewer networks...

David A. Smith

"Tom Roberts" wrote in message
.. .
....

Thanks for clarifying what I was trying to say.


Yet spacetime is a product of mass/energy,

No, it is not. Spacetime is a geometric MODEL of the world. It is a
"product" (in the sense of result, not multiplication) of the human
imagination.

Tom, can I take issue with that in the hope of learning a
bit more. I have seen some posters who are familiar with
GR (not cranks) say that the metric of GR is 'physical'
and my own thoughts suggest that if gravitational energy
can be propagated away from a binary system (Hulse and
Taylor) then it must be more than just a model. True the
equations of GR are just our way of quantifying that, but
is there not something there to be modelled.

Having said that, I could see how quantisation of GR might
lead to a model in which gravitons carry the energy through
some fixed geometry (Minkowski?) but is that not analogous
to saying that energy is carried by photons and an electric
field is just a 'product of the human imagination'?

George

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:7hLLe.36643$E95.9310@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:81xLe.35947$E95.12374@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:YsdLe.25309$E95.8692@fed1read01...

... going to attempt some deft trimming ...

That's cool. A number of replies have superseded
this so I'l chop much too.

When we look at a distant star, we see it at
one particular time in the past related to its
distance. Looking out through an event horizon
would not change that.

I understand your assertion. Kruskal coordinates do not require/allow
this.
....
A change of coordinates cannot change the
appearance, it must be the same in all
though some may be easier to use than
others.

You say "it must be the same in all"?

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.

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.

Models can change, but unlikely they they will get fundamentally simpler,
more easy to understand. I think you are being provincial. I accept that
you do not wish to do the "leg work" required.

I never learned tensors so it would be years of
work. I have bought some textbooks and might get
there eventually but that's of no consequence,
I do know that those books say the problems at
the event horizon are merely mathematical, not
physical.

It is the same as using cartesian
or polar coordinates to calculate the effect
of an inverse square law force, one or the
other might be easier but both must predict
Keplerian orbits.

Yet "time stops" at the event horizon (stationary time, which of course is
non-physical).

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.

Space must therefore stop since c and time define space (again, stationary
space). Yet spacetime is a product of mass/energy, and a BH has that in
plenty. I am proposing that things "must be the same in all". I am
simply toying with *which* things are the same. Einstein (and Mach)
suggested that the the things I think are important/invariant, NOT
spacetime, is mass/energy. The field equations even "fabricate" spacetime
from mass and energy terms, for crying out loud.

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.


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").
Light would pass the falling observer at exactly c.

Look, George, we "fall at c" through time (hackles raise on the backs of
necks of those whom I have now affronted).

No hackles if you are talking of four-velocity.

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

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

Are there two time axes? I think Andrew's verbiage is no less "loose"
than mine above, in his assertion.

...
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.

It says something about the Scwarzchild coordinates at the event horizon.
It says they are not usable on the inside. Kruskal is, and even Eddington
has a *fundamentally different* "time axis" inside.

They are still just coordinates, nothing more.

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.

... 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.

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.

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.

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.

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

Exactly.

2) Density equal to the critical value means
spatially and temporally infinite, no big
crunch. Expansion continues for ever but
is asymptotic to zero speed.

Which doesn't quite appear here, because of "acceleration of expansion"

3) Density less than the critical value also
means spatially and temporally infinite and
expansion continues for ever but never slows
to zero.

Wright addresses this a bit he

http://www.astro.ucla.edu/~wright/cosmo_03.htm

Dark energy throughs a spanner in the works so
different combinations of open/closed and a crunch
become possible.

And the cosmological constant as well/in addition...

Same thing, different names, essentially.

Expansion doesn't involve expanding "into" anything,

Correct.

so how can we verify an extent into which matter is entering "new"
space?

It isn't, old space is stretching.

I guess it is the fabric of the English language that is stretching in my
mind. When I hear "non-closed", I think of "opening into another space"
either "in the beginning" or "in the middle" or "at the end".

No, open in this context means basically
infinite volume while closed is finite volume.

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.

Then you would get an almost flat spectrum.
A black body would require either one constant
temperature throughout the history or a red-shift
from it to us that exactly matched the variation
in temreature over time.

I don't think it would be a flat spectrum, since an expanding Universe
would decrease the intensity on the surface... if the surface were
controlled/limited by the amount of matter/energy inside (ie. Schwarzchild
radius).

The radius of a black hole is r=2m so it would
be a fixed radius on the outside but expanding
(and probably infinite) on the inside (ouch).

The point is, is it worth/possible to check it? Can we use this model to
describe the early Universe, or is it a "band aid" where none is required?

Neither, it is a disagreement about what the
existing model predicts. Checking is another
matter. The surface is hidden from us if
current theories are correct so first you
have to find a way of removing the CMBR
plasma that doesn't break the explanations
for all the other observations that lead us
to believe that is what we are seeing.

It is a valid and accepted way to model a black hole. It has
consequences. *These* consequences are testable. If
Kruskal is a valid method, and describes an internal
Universe with separate spacetime, we should be able to
"look back". Depending on the nature of the CMBRM.

We are defined by our questions.

I commented on coordinates earlier.

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

Notion 3) hasn't really happened yet.

No, more mature galaxies are being found earlier
than expected but at the same time the role of
super-massive black holes is being reconsidered
and simltaneous evolution is looking more
favourable. Given the high density in the early
universe, the existence of super-massive black
holes prior to decoupling would not surprise me,
but the formation of solid objects at those
temperatures would.

"At those temperatures" assumes that you can't see the container.

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.

....
My hypothesis actually cannot "do away with" the plasma, much to my
chagrin. It is possible that our horizon were small enough that the
strong and weak interaction forces would succumb, and external structures
as small as atoms get shredded into protons, neutrons, and electrons.

Typically though that would happen in an acretion
disk so the CMBR should look like the Milky Way,
not uniform over 4 pi steradians.

And it could all still have happened just as the standard theory predicts,
and *still* we be derived from a container.

That our universe might exist within something
else is another matter. See Guth's paper for
example.

So we may be struggling with something that is just like the aether...
completely unverifiable.

Perhaps, or maybe like inflation it could show up
in indirect ways, perhaps in the angular power
spectrum of relic neutrinos if we are ever able
to measure that.

The elemental abundancies
match the nucleosynthesis model very well but require
high density and teperatures around 10^9K. We see
samples of that mix in Pop II stars so losing the
low-metallicity early universe would be an immense
problem.

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.

best regards
George

George Dishman wrote:
"Tom Roberts" wrote in message
.. .
Spacetime is a geometric MODEL of the world.

I have seen some posters who are familiar with
GR (not cranks) say that the metric of GR is 'physical'

That depends in detail on what one means by the word.

I generally find it useful to distinguish geometrical from physical, but
there is no sharp boundary between them. To me, the metric tensor is
geometrical, and the energy-momentum tensor is physical (as are the
related matter fields). But the geometry is inextricably linked to the
physical contents of the world, and the physical contents are
inextricably linked to the geometry.

The basis for my distinction is that the metric describes/models
(infinitesimal) distances, but distances are not things; the physical
fields describe/model things. This distinction is not sharp, as the
matter fields are themselves models of how matter behaves....


and my own thoughts suggest that if gravitational energy
can be propagated away from a binary system (Hulse and
Taylor) then it must be more than just a model.

It is a model of what is happening in the world. You are intermixing
model and world -- energy belongs to the model, not the world. The only
part of the world available here is the observations themselves (and it
requires a model to understand how signals propagate from system to
observer, and how received signals relate to the behavior of the system,
how received signals are observed, etc.).

The model predicts that such binary systems will spin down at
such-and-such a rate, and the observations agree with the prediction of
the model. What more could you want?


True the
equations of GR are just our way of quantifying that, but
is there not something there to be modelled.

I don't know what you mean -- "what is there" to be modeled is the
behavior of those binary systems. And the model agrees well with
observations of those systems. What more could you want?


Having said that, I could see how quantisation of GR might
lead to a model in which gravitons carry the energy through
some fixed geometry (Minkowski?)

I doubt very much that is anything at all close to a description of an
ultimate theory of quantum gravity. In QG I suspect that not even the
local topology is "fixed", and the very notion of "manifold" breaks down
(along with "geometry", of course)....


but is that not analogous
to saying that energy is carried by photons and an electric
field is just a 'product of the human imagination'?

Photons, too, are a product of human imagination. As are electric
fields. Indeed, EVERY component of EVERY model is such a product. And,
of course, EVERY word we use is ultimately related to some MODEL....


Tom Roberts

Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox
wrote in message news:7hLLe.36643$E95.9310@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox
wrote in message news:81xLe.35947$E95.12374@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox
wrote in message
news:YsdLe.25309$E95.8692@fed1read01...

... going to attempt some deft trimming ...

That's cool. A number of replies have superseded
this so I'l chop much too.

When we look at a distant star, we see it at
one particular time in the past related to its
distance. Looking out through an event horizon
would not change that.

I understand your assertion. Kruskal coordinates do not
require/allow this.
...
A change of coordinates cannot change the
appearance, it must be the same in all
though some may be easier to use than
others.

You say "it must be the same in all"?

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?

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). Now consider
the definition of "singularity". The event horizon *is* a
singularity. No? So to impress some external geometry into the
black hole is to go beyond foolishness into madness, it would
seem.

Models can change, but unlikely they they will get
fundamentally simpler, more easy to understand. I
think you are being provincial. I accept that you do not wish
to do the "leg work" required.

I never learned tensors so it would be years of
work. I have bought some textbooks and might get
there eventually but that's of no consequence,
I do know that those books say the problems at
the event horizon are merely mathematical, not
physical.

They are physical too. Witness the extreme amount of energy
released (Oh, but we *know* what causes that!), and the expected
loss of "discreteness" of matter/energy that enters the event
horizon.

It is the same as using cartesian
or polar coordinates to calculate the effect
of an inverse square law force, one or the
other might be easier but both must predict
Keplerian orbits.

Yet "time stops" at the event horizon (stationary time,
which of course is non-physical).

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.

....
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.
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)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? Does it mean that we
are extending the model, or describing what experiment might
determine?

Look, George, we "fall at c" through time (hackles raise on
the
backs of necks of those whom I have now affronted).

No hackles if you are talking of four-velocity.

Tom Roberts didn't like it. Because I don't have that clear
enough in my head yet, we can leave it.

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 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? 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.

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.

It says something about the Scwarzchild coordinates at the
event horizon. It says they are not usable on the inside.
Kruskal is, and even Eddington has a *fundamentally
different*
"time axis" inside.

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?

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.)

... 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?

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.

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 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, 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.

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".

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".

....
3) Density less than the critical value also
means spatially and temporally infinite and
expansion continues for ever but never slows
to zero.

Wright addresses this a bit he

http://www.astro.ucla.edu/~wright/cosmo_03.htm

Dark energy throughs a spanner in the works so
different combinations of open/closed and a crunch
become possible.

And the cosmological constant as well/in addition...

Same thing, different names, essentially.

Accepted for now.

Expansion doesn't involve expanding "into" anything,

Correct.

so how can we verify an extent into which matter is
entering "new" space?

It isn't, old space is stretching.

I guess it is the fabric of the English language that is
stretching in my mind. When I hear "non-closed", I
think of "opening into another space" either "in the
beginning" or "in the middle" or "at the end".

No, open in this context means basically
infinite volume while closed is finite volume.

Ah.

"Those French! Its like they have a different word for
*everything*."
Steve Martin, "The Jerk" (I think.)

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.

Then you would get an almost flat spectrum.
A black body would require either one constant
temperature throughout the history or a red-shift
from it to us that exactly matched the variation
in temreature over time.

I don't think it would be a flat spectrum, since an expanding
Universe would decrease the intensity on the surface... if
the surface were controlled/limited by the amount of
matter/energy inside (ie. Schwarzchild radius).

The radius of a black hole is r=2m so it would
be a fixed radius on the outside but expanding
(and probably infinite) on the inside (ouch).

Agreed. At least such is my delusion, expecting that the
Universe formed inside is "just like" ours.

The point is, is it worth/possible to check it? Can we use
this model to describe the early Universe, or is it a "band
aid" where none is required?

Neither, it is a disagreement about what the
existing model predicts. Checking is another
matter. The surface is hidden from us if
current theories are correct so first you
have to find a way of removing the CMBR
plasma that doesn't break the explanations
for all the other observations that lead us
to believe that is what we are seeing.

Understood.

It is a valid and accepted way to model a black hole. It
has consequences. *These* consequences are testable. If
Kruskal is a valid method, and describes an internal
Universe with separate spacetime, we should be able to
"look back". Depending on the nature of the CMBRM.

We are defined by our questions.

I commented on coordinates earlier.

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

I like to be proactive...

Notion 3) hasn't really happened yet.

No, more mature galaxies are being found earlier
than expected but at the same time the role of
super-massive black holes is being reconsidered
and simltaneous evolution is looking more
favourable. Given the high density in the early
universe, the existence of super-massive black
holes prior to decoupling would not surprise me,
but the formation of solid objects at those
temperatures would.

"At those temperatures" assumes that you can't
see the container.

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

...
My hypothesis actually cannot "do away with" the plasma,
much to my chagrin. It is possible that our horizon were
small enough that the strong and weak interaction forces
would succumb, and external structures as small as atoms
get shredded into protons, neutrons, and electrons.

Typically though that would happen in an acretion
disk so the CMBR should look like the Milky Way,
not uniform over 4 pi steradians.

Only if the infall were from an orbiting point source, or we were
otherwise spinning (ignoring any "integration" by the event
horizon). We are currently surrounded by light sources in all
directions, other than the CMBRM. To say nothing of the
gravitational optical effects you disagree with being
"significant" or "unusual" or "surprising". Keep in mind that
there is *some* hint of structure in the CMBRM, whatver the
cause.

And it could all still have happened just as the standard
theory predicts, and *still* we be derived from a container.

That our universe might exist within something
else is another matter. See Guth's paper for
example.

So we may be struggling with something that is just
like the aether... completely unverifiable.

Perhaps, or maybe like inflation it could show up
in indirect ways, perhaps in the angular power
spectrum of relic neutrinos if we are ever able
to measure that.

OK.

The elemental abundancies
match the nucleosynthesis model very well but require
high density and teperatures around 10^9K. We see
samples of that mix in Pop II stars so losing the
low-metallicity early universe would be an immense
problem.

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. 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". 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?

David A. Smith

In article UgeMe.51736$E95.23797@fed1read01,
"N:dlzc D:aol T:com \(dlzc\)" N: dlzc1 D:cox wrote:

"Bill Rowe" wrote in message
...

Your question here implies you see Tom's comments as
saying something about the need to extend a model of the
world. How do you arrive at that?

I do not get that from Tom's comment. Science is about
modelling, PREDICTION, and testing. Some solutions to black
holes (using GR) have an entirely new Universe formed inside.
Universes that are expected to have similar (or identical) laws
to ours. In the context of this thread, and my remark above, I
am making a verbal prediction, that we could *perhaps* test this
on our Universe by looking at the CMBR. GR can be made to model
the inside of a black hole, so this is not straight fantasy. It
is not even extending the model, except possibly to a place that
is unphysical.

What I got from Tom's comment is that it wasn't worth the time or
effort, because it is all imaginary anyway.

I believe the point is spacetime has no existence outside of human
thought.

I understand the point. However science is about testing the
"limits of thought", if you really intend to dereference
"reality" in this way. We don't know what the underlying reality
is, but our models allow us to both interpolate (usually to good
effect) and extrapolate (commonly with comical effect).

I don't know how you can not "dereference" "reality" in this manner. A
large part of the problem is we don't know what "reality" is. All we
have is our measurements, observations and models.

I see as one of the main goals of science is to test the limits of the
model, i.e., how well it agrees with measurement and observation. And
since the model doesn't exist outside of human thought, I suppose this
is equivalent to your testing the "limits of thought". But I don't see
that saying models don't exist outside of human thought as implying it
isn't worthwhile to pursue science and extend models.

--
To reply via email subtract one hundred nine

Dear Bill Rowe:

"Bill Rowe" wrote in message
...
In article UgeMe.51736$E95.23797@fed1read01,
"N:dlzc D:aol T:com \(dlzc\)" N: dlzc1 D:cox
wrote:
....
What I got from Tom's comment is that it wasn't worth
the time or effort, because it is all imaginary anyway.

... But I don't see
that saying models don't exist outside of human thought
as implying it isn't worthwhile to pursue science and
extend models.

I guess it was the:
[... further nonsense ignored]
that gave me that impression, Bill.

David A. Smith

"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
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:7hLLe.36643$E95.9310@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote in
message news:81xLe.35947$E95.12374@fed1read01...
Dear George Dishman:

"George Dishman" wrote in message
...

"N:dlzc D:aol T:com (dlzc)" N: dlzc1 D:cox wrote
in message news:YsdLe.25309$E95.8692@fed1read01...

... 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.

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.

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.

....
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.

...
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.

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.

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.

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.

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.

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.

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 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.

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.

... 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.

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.

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.

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.

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.

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 ...".

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 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.

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

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.

"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.

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?

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.

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'

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.

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.

For the CMBR, use this link

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

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

George