Elveto <zo…@zipzap.ch> wrote in message <news:mt2.0-647-1056716301@sshserv.aei.mpg.de>…
> Rob Oldershaw wrote:
> > Some authors have used the term "metagalaxy" in place of the
> > expression "observable universe". [...]

> > I like the term because it leads one away from the anthropocentric
> > "what we see is all there is" viewpoint to the more likely possibility
> > that "what we see is a bubble in an ocean".

> But isn’t this implying some kind of anthropomorphic metaobserver
> capable of seeing the ocean ? fwiw, I percieve the term of "metagalaxy"
> as an allusion to the equation of the order of magnitude of the number
> of galaxies observable in the universe, with that of the number of stars
> in our own galaxy.

No.  That is not implied, far less required.  "Percieve"(sic) away,
but the concept of a metagalaxy is simply the idea that galaxies are
building blocks of a vastly larger system, of which we view only a

In article <mt2.0-32226-1056655…@sshserv.aei.mpg.de>,
Bill Jefferys  <b…@warthog.as.utexas.edu> wrote:

>In
>Bayesian hypothesis testing where the dimensionalities of the parameter
>spaces under Ho and ~Ho are *different*, it is essential that all priors be
>proper, and furthermore not too spread out, or else the posterior
>probability on the alternative hypothesis can be made as small as you wish
>(just think of the integral up there…the likelihood P(D|u,Ho) has a peak
>somewhere, and most of the value of the integral comes from near that peak.
>The more you spread out the prior, the less the contribution from the peak,
>and the smaller the integral).

There’s an introductory discussion of this — and the slightly more
general problem of comparing multiple hypotheses which have different-
-dimensionality parameter spaces — in chapter 4 of

   D. S. Sivia
   "Data Analysis: A Bayesian Tutorial"
   Oxford U.P., 1996
   paperback ISBN 0-19-851889-7

In general, I highly recommend this book as a nice introduction to
Bayesian methods.  It’s a good "next step" if you’ve had your appetite
whetted by Bill Press’s article (astro-ph/9604126).

–
— "Jonathan Thornburg (remove -animal to reply)" <jth…@aei.mpg-zebra.de>
   Max-Planck-Institut fuer Gravitationsphysik (Albert-Einstein-Institut),
   Golm, Germany, "Old Europe"     http://www.aei.mpg.de/~jthorn/home.html
   "I paid money for this car, I pay taxes for vehicle registration and a
    driver’s license, so I can drive in any lane I want, and no innocent
    victim gets to call the cops just ’cause the lane’s not goin’ the same

sean <jaymose…@hotmail.com> writes:
> Craig Markwardt <craigm…@cow.physics.wisc.edu> wrote in message <news:mt2.0-25632-1056376051@sshserv.aei.mpg.de>…
> > Since you apparently admit that the IPN can work, your subsequent
> > statistical analysis of GCN circulars from 2000, 2002 and 2003,
> > basically addresses the question of multi-wavelength detection
> > *efficiency*, as opposed to functionality.  You have then entered a
> > realm of complex interplay between many observing constraints and
> > sensitivities.
…
> >I`ll Try to cover the above points. I didnt count the fractions
…
> I have to say that to do all the above numbers properly I would need
> a research grant for  about couple of months full time work …

My original point was that efficiency calculations for these sorts of
systems are extremely difficult.  As you admit, you haven’t really
made a numerical case.  I think even for the "insiders" who have a lot
of experience it would be a difficult task.

> Surely though it is the success rate between attempted and
> successful that is important. For instance if lets say only 10 per
> cent of IPN`s were followed up and 90 per cent of HETE etc`s. What
> difference would that make ?

The problem is the definitions of "success" and "attempt."  What if
follow-up observations were made, but only covered a portion of the
error box.  Is that an attempt?  In your example above, if only 10% of
IPN locations were followed up, then by construction no more than 10%
could be localized by that technique.  Some other biases to consider
include: HETE is only sensitive to GRBs on the night side of the
earth, so it will preferentially detect bursts which are observable,
and hence attemptable, by optical telescopes.  Or, IPN single-annulus
solutions and "large error box" solutions are too big to be
successfully covered by narrow-field observers.  These factors, and
others, will most certainly skew the measures of "attempt" and
"success."

> > Analyzing any real life data is complex.  If you are seeking to apply
> > your "own methods," as you claimed in a previous posting, then you are
> > surely aware of this.  You did not mention the data cited in either of
> > the Laros et al papers; why were they not suitable?

> I tried out the paper above and they both seem to be about sn/grb
> relationships and statistics regarding coincidences between the two.
> Its not exactly what I need . What I would need to do is create a 3-d
> model with x,y and z axis .

Neither of the Laros papers that I cited proposes a SN/GRB connection.
In fact, both of the papers provide 3D positions of the spacecraft
involved, as well as the times of arrival.  These should suit your needs.

Laros, J., et al. 1997, Ap. J. Supp. Ser. 110, 157
  Gamma-Ray Burst Arrival Time Localizations: Simultaneous
  Observations by Mars Observer, Compton Gamma-Ray Observatory, and
  Ulysses, (9 bursts, 1992-1993) – coincident GRO + IPN boxes

Laros, J., et al. 1998, Ap. J. Supp. Ser. 118, 391
  Gamma-Ray Burst Arrival Time Localizations: Simultaneous
  Observations by Pioneer Venus Orbiter, Compton Gamma-Ray
  Observatory, and Ulysses (arrival times given) (37 bursts, 1991-1992)

> > No.  X-ray and gamma-ray localizations by imaging satellites like
> > INTEGRAL/IBIS/SPI or HETE, and soon Swift, do not rely on the IPN
> > triangularization technique.  Also, consider GRB 021125, which has a
> > smaller IPN localization than its associated IBIS position.

> I think you misunderstand me here. I realize that the "X-ray and
> gamma-ray localizations by imaging satellites like INTEGRAL/IBIS/SPI
> or HETE, and soon Swift"  do not rely on IPN. What I was saying was
> that these localizations you mention above are the error boxes which
> IPN then uses to refine the annuli.

You are mistaken.  The IPN solution is found by time of arrival
analysis alone, independent of other positions.  It is also true that
if another error box is available, the authors of a GCN circular may
provide the overlap region, but this is quite distinct from the IPN
solution.

> Also regarding 021125 yes as with most IPN the refined overlap
> position is smaller then the error boxes but there were no OT`s
> observed there so we have no proof that that particular refined IPN
> localization is correct. And I believe that it isnt.

There is no need to prefer just optical and radio.  As you point out,
the gamma- and X-ray imagers can provide quite precise positions.  If
the IPN and imaged positions coincide, that should be considered a
"success."  It is too narrowminded to say that the IPN serves only
optical and/or radio.

> AS I mentioned at the beginning of this post I believe that the annuli
> were derived not by pure time of arrival but actually by changing the
> time of arrival data to suit an annuli that does overlap the error
> boxes. I believe that the data must come in to the network with  many
> unexplained inconsistencies that IPN finds impossible to compute
> without admitting c is not constant and therefore they actually make
> or alter existing data until they can come up with an annuli that does
> match the known error boxes.

Your claim is just silly.  The point of the IPN is to enable follow-up
observations (at *all* wavelengths), not to prove that the speed of
light is constant.  You are basically accusing the IPN contributors of
fraudulently altering the data to suit some ulterior motive.  I am
personally acquainted with some of those involved, and they have an
honest interest in localizing GRBs as best as can be done.  They are
using the best tools available for the data hand, which happens to be
time of arrival reconstruction, and it is extremely simple, involving
minimal assumptions.

There are plenty of cases which show that the IPN produces reliable
position constraints, as have been cited in my previous messages.
And, more importantly, you have not provided a single case where the
IPN solution was found to be incorrect.  I have cited a case where an
IPN-only solution was used to localize both a radio and optical
transient, with no other gamma-ray positioning.

When multiple position GCN circulars come out, it is usually because
new data is incorporated into the solution, for example when more
telemetry becomes available, and of course this is always stated in
the circular.

I think enough has been said in this thread.

[[Mod. note -- I am inclined to agree with this last sentiment!  -- jt]]

CM

In article <mt2.0-22949-1055317…@star.bris.ac.uk>,
 rlolders…@amherst.edu (Rob Oldershaw) writes:

> Actually I am saying that the concept of magenetic monopoles is a
> silly one, as those who study nature, rather than just squiggles on
> paper, would be most likely to conclude.

Aren’t you the one urging us to be open-minded?  What makes you think
magnetic monopoles cannot exist?  There certainly used to be lots of
smart people who thought they were a reasonable bet.

Questions for the experts:
1. Is there sound reason for ruling out the existence of magnetic
monopoles?  I know of some upper limits on their abundance, but could
there be any at all?

2. Has there ever been a satisfactory explanation of the "Valentine’s
Day Event?"  Could it have been a genuine (but _very_ lucky!)
monopole detection?

[[Mod. note -- If it was a monopole detection, then we need to
somehow explain why/how none of the other monopole-detection
experiments have seen anything.  I am not up to date with current
work in this area, but I had thought that other experiments now
have cumulative detection cross-sections that are much larger than
Cabrerra's up to the Valentine's-day event.
-- jt]]

–
Steve Willner            Phone 617-495-7123     swill…@cfa.harvard.edu
Cambridge, MA 02138 USA                
(Please email your reply if you want to be sure I see it; include a
valid Reply-To address to receive an acknowledgement.  Commercial
email may be sent to your ISP.)

In article <mt2.0-13665-1052392…@sshserv.aei.mpg.de>, Hieronymous707 wrote:
>>From: Ashok Prasad seekas…@yahoo.com

>>Hi. I am looking for summaries of the current state of the
>>observational evidence for black holes, especially stellar mass black
>>holes where I believe the evidence is of better resolution.

>hth:

>http://www-int.stsci.edu/~marel/m15release.html

I don’t think this one does help — the authors had to more or less
retract their claim of detecting a black hole in the center of M15, I believe.

[[Mod.note -- Looking at the STSCI press release, I was pleased to see
that they actually have a prominent section "Alternative Scientific
Interpretations of the data:" with links to 3 astro-ph preprints
(alas their link for the 2nd one mistakenly gives the 1st's number):
astro-ph/0210158 (Gerssen, van der Marel, et al.)
astro-ph/0210588 (Dull et al.)
astro-ph/0210133 (Baumgardt et al.)
-- jt]]

In article <mt2.0-13665-1052393…@sshserv.aei.mpg.de>,
Gene Partlow  <starg…@earthlink.net> wrote:

>However, in a net search including the Harvard ADS site, I can’t
>find any actual reference to it!  Was I dreaming?  Can somebody
>help me and point me to actual papers which support this?

In addition to the resources the moderator has pointed out, it might
help for you to know that the Mbh – Mbulge relation is often known as
the `Magorrian relation’ (after an early paper by John Magorrian) so that
a Google search for that might be helpful.

Martin
—
Martin Hardcastle             Department of Physics, University of Bristol
    A little learning is a dangerous thing; / Drink deep, or taste not the

[[Mod. note -- It seems the news server to/from which I post moderated
articles no insists on having a valid domain name for the From: line,
so I had to edit the author's spam-proofing.  My apologies for any spam
which gets through now which might have been blocked by the original!
-- jt]]

In article <mt2.0-9640-1050410…@sshserv.aei.mpg.de>, Kent Betts

<kent_be…@hotmail.com> writes:
> This article about very old supernovae states that in the early few
> billions of years that the expansion of the Universe was slowing down.

> http://www.spaceflightnow.com/news/n0304/10supernova/

> It has now been observed that the expansion of the Universe is accelerating.

> I was wondering whether any sort of masking effect on gravity has been
> proposed.  Has it been suggested that perhaps the mutual attraction might
> eventually diminish over great distances?

People have suggested all kinds of things as alternatives to "standard"
cosmology.  Almost always, such suggestions create more problems than
they solve.

Cosmology has been transformed, in just the last few years, from an
armchair pursuit to a data-driven science.  Classical cosmology can be
defined as working out the dependence of some observational quantity,
such as the brightness of a standard candle, on redshift for a given set
of cosmological parameters.  By comparing theory to observation, one
fits for the cosmological parameters.  At the moment, many different
types of cosmological tests result in the same values for the
cosmological parameters.  This lends a lot of credibility to the basic
picture.  Any alternative suggestion, in order to be taken seriously at
all, would have to make equally quantitative predictions AND have those
agree with observations AND show that the predictions could be obtained
without knowing the observations in advance.

> If gravitation were somehow masked, or less efficient, over great distances,
> wouldn’t the observed effect be an increase in the rate of expansion?  I ask
> this because it is usually ascribed to mysterious repulsive forces.

It seems to me that masking gravitation would be much more mysterious
than repulsive forces.  I’m sure some GR experts will point out why it
is very improbably that gravity can be masked.  (H.G. Wells, IIRC, wrote
a story in which a material called Cavorite was used to mask gravity.  
But that is (old) science fiction.)

At the moment, all the observations are consistent with the repulsive
force being a "traditional" cosmological constant ($\omega = -1$ for the
experts).  In some sense, we don’t know "what that is", but in more or
less the same sense we don’t know WHY gravity exists.

> Thx for info.  (I did not find a cosmology newsgroup on my server, BTW.)

Sci.astro.research and sci.physics.research are probably the most
appropriate.

——————————————————————————-
CALIFORNIA magazine, in an article on "The Man Who Invented Time Travel", even
ran a photograph of me doing physics in the nude on Palomar Mountain.  I was
mortified—not by the photo, but by the totally outrageous claims that I had
invented time machines and time travel.

                                                                  —Kip Thorne

I just calculated the density of our own sun:

Radius of sun = 696265 km = 696265000 metres
Volume = (4/3)*pi*(r^3) = 1.41e27 m3
Mass of sun = 1.9891e30 kg
Density of sun = 1406 kg/m3 (close enough to the official value)

That sounds about right.

Then I tried to figure out the density of Proxima Centauri (our most
famous friendly neighbourhood red dwarf), which according to
http://www.solstation.com/stars/alp-cent3.htm has a radius of 14.5%
that of Sol and 12.3% of its mass.

So… for Proxima we’d have

Radius = 696265000*0.145 = 100958425 metres
Volume = 4.31e24 m3
Mass of Proxima = 1.9891e30 * 0.123 = 2.45e29 kg
so Proxima density = 56760 kg/m3.

56,760 kg/m3?!! I can’t see anything I’m doing wrong here. Are red
dwarfs really that dense?! It sounds like they’d actually have a solid
surface that one could land on!

Am I doing something wrong here, that’s so obvious I can’t see it? Or
am I missing something obvious? Or, dare I say it, am I right?

Constantine Thomas                       constantine.tho…@shaw.ca
Mad (Planetary) Scientist, Space Artist, Horseman of the Apocalypse
http://members.shaw.ca/evildrganymede/home.htm
——————————————————————-

I recently stumbled on an interview with cyberneticist
Heinz von Foerster–
 http://www.stanford.edu/group/SHR/4-2/text/interviewvonf.html
–where he described a _logarithmic_ timeline of history
that he constructed, on the theory that the farther back
you go the sparser the ‘events’ become.

I decided to try implementing this using my own theory
of hypertext-timelines, aiming for a 100k page packed
with links to Web resources on every topic from the Big
Bang to the dotcom bubble:
 http://www.robotwisdom.com/science/logarithmic.html

But this design works best only if I can dig up _some_
newsworthy entry for every line… and cosmology seems
to be empty-handed for the ~40 lines between 12Byo and
5Byo: (the line-number is the exponent, eg 10^10.14 years)

10.14 = 13,700,000,000 years BC = Big Bang
10.13: release of Cosmic Microwave Background
10.12: first galaxies, of iron-free stars
10.11: quasars with (unexpected) iron
10.10 = 12,500,000,000 yrs BC
10.09
10.08: Iron Epoch (supernovae creating iron)
10.07
[...] no ‘news’ for seven billion years!?
9.71
9.70 = 5,000,000,000 years BC
9.69: birth of Sun

So is there any useful way to fill this gap?  Some
ideas:

- declining rates of new-star formation?
– increasing percentage of heavier elements?
– declining _size_of newly-formed stars?
– generalisations about stellar lifecycles

Ideally, the entries should suggest increasing
likelihood of life’s emerging, but if worse
comes to worse I may have to settle for random
observations like quasars or supernovae at 10B
lightyears’ distance.

Here is another concern I have with current practices in the field of
cosmology.

A crucial distinction that is increasingly being blurred in
astrophysics is the distinction between true predictions and
retrodictions.  A true prediction of a result or phenomenon must be
made before the relevant experimental results are known, while a
retrodiction only demonstrates a theory’s ability to reproduce known
results.

For example, Einstein’s General Theory of Relativity predicted that
mass "warps" spacetime (which was previously unknown) and retrodicted
the advance in the perihelion of Mercury (which was known but
unexplained for over a century).

  If a theory can make multiple retrodictions, it increases our
confidence in the theory’s internal consistency, scope and potential
correspondence with natural phenomena.

A definitive prediction, on the other hand, is identified prior to
testing and cannot be arbitrarily adjusted afterwards.  These
requirements are much more stringent, and successful predictions
demonstrate what appears to be a unique correspondence between theory
and nature.  No theory can be proven absolutely, but two or three
verified predictions mean that a theory almost certainly represents an
advance in our understanding of how nature actually works.

Molding an adjustable model so that it can retrodict observational
results is a common and useful technique in science, but true
predictions are not involved in this process, and the health of
theoretical science depends on carefully maintaining this distinction.

If retrodictions are elevated to the status of true predictions, then
the integrity of science is compromised.

If anyone is interested in this topic I would like to use the Big Bang
paradigm as a case in point for studying this issue.

Rob O.