From: metares@well.sf.ca.us (Tom Van Flandern)
Newsgroups: sci.astro
Subject: Re: grav lensing
Date: 29 Aug 92 23:01:26 GMT
Article-I.D.: well.BtrpAF.K1o
Organization: Whole Earth 'Lectronic Link


mock@space.mit.edu (Patrick C. Mock) writes:

>>> I consider only one multiple imaging candidate as a confirmed lens.
>>> Quasar 0957+561, Lehar et al ApJ 384 p453, has a measured time delay of
>>> 540 +/- 12 days.

More recently he continues:

> The data cover a period of 11 years and there is no evidence for
> periodicity especially with a period of ~1.4 years (540 days).  The time
> delay appears to carefully established by the correlation of two aperiodic
> light curves.  I consider this solid evidence that one object is multiply
> imaged.  Thus this quasar must be behind something that is a lens.

     True, and in that case the light variations are most likely produced in
the "lens" rather than in the source.  This still doesn't tell us if the
"lens" is gravitational or a refracting cloud.

> Furthermore, the lensing galaxy has been carefully observed and it's
> redshift is 0.36 (the quasar is at 1.41).  Your refraction model still
> requires the quasar to be behind the refracting lens.  The refracting lens
> must be at or behind the galaxy because image of the galaxy is not affected
> by the lens.

     I don't agree with this last statement.  Whatever the refracting lens
consists of, it must be associated with the quasar, and both can be anywhere
in front of the galaxy or behind it.  (Note: I have no objection to the
quasar being close behind the galaxy, perhaps ejected from it.  I just don't
see that as required from what little we know about the lensing object.)

     What I suppose is really happening is that by chance we occasionally see
a quasar through the entire length of its own jet when that jet happens to be
directed toward us.  Since the jet is long and irregular, with rapidly-moving
blobs and knots, we see multiple images in a random arrangement, varying in
brightness as the index of refraction in the jet varies.

     You describe 0957+561 as your personal best case for being a true
gravitational lens system.  Yet (besides the objections already raised),
Hubble values derived from this system, 40-50 km/s/Mpc, are described as
"disturbingly low" in Press, Rybicki & Hewitt's paper, Ap.J. 385, 404-420
(1992).  With extreme dark matter assumptions, this can only be stretched to
64 km/s/Mpc.

     But more significantly, the system is so complex and unorthodox that it
is now believed that a cluster of galaxies, and not a single galaxy, must be
doing the lensing.  Your Harvard-MIT colleagues call it "a complicated, messy
system" and suggest applying their time-delay techniques, developed for
0957+561, "to other, cleaner, yet-to-be-discovered systems".  An image in S&T
82, 346 (1991) shows a broad X-ray arc encompassing both quasar images.  Is
this perhaps direct evidence of the cloud which produces the images by
refraction?

> careful VLBI observations have shown that core images are achromatic, as
> they must be, and revealed the source of the chromatic behavior to be to an
> extended source, the quasar's jet.

     Sounds like that observation, with a different interpretation, would fit
in beautifully with the alternative idea I mentioned above.

>> But unless someone constructs some [testable] prediction, the
>> gravitational lens model will remain unfalsifiable.

> What do you mean that by unfalsifiable?  The gravitational lens model is
> consistent with observations to date.

     I refer to the goal of science, to falsify hypotheses.  Remember,
hypotheses can only be falsified, not proved.  A hypothesis which is not
falsifiable (disprovable) is not a scientific hypothesis.

> Most of your objections have been due to your misunderstanding of the
> standard model.

     Most of my objections come from the literature, are shared by others,
and arise from an alternative model which appears to me to work even better
than the standard model.  Couldn't I equally well say back to you, "Most of
your objections have been due to your misunderstanding of the alternative
model"?

> I don't object to your presentation of alternate models.  I do object to
> your claims that the standard model is wrong when it is clear that your
> understanding of the standard model is so weak.  For example your claim
> that gravitational lens are concave.  It took several careful posts by me
> and others to explain one of the most basic properties of a gravitational
> lens.
>
> I also object to your distortion of the scientific literature.  For example
> in the discussion of chromatic effects above, you claimed the observations
> of chromatic effects in a gravitational lens cast serious doubt on the
> standard model.  Yet the paper you referred to gives a careful explanation
> of why the chromatic effects can occur in gravitational lenses.  The
> explanation relied on the standard theory and careful observations and you
> completely ignored it.
>
> While I have enjoyed this discussion.  Your misunderstandings and
> distortions cause me to be extremely skeptical of your work.  I do not make
> these claims lightly.  You may claim that I've mislabeled the examples I
> have given.  Nonetheless, I find these examples deeply troubling.

     One of the many unfair ways in which people in general, and politicians
and lawyers in particular, discredit their opponents is to point to some
error they have made, and argue that casts doubt on everything that person
has said or done.  Your point is dangerously close to that sort of argument.

     I would point out that our field has grown at an incredible pace in the
past ten years.  The amount of material one must keep up with is daunting. In
my opinion, many of today's senior astronomers could not pass many current
Ph.D. qualifying exams.  This is because they have tended to keep up only in
areas of personal interest, or in their specialties; but not in the breadth
of subjects which a fresh graduate student must master, and which have
changed rapidly in the interval since their own degrees.

     You have pointed out two places where I was ignorant before, and am
informed now, thanks to you.  But I do not think it is reasonable to
generalize, even a little, that this lowers my overall credibility.  In fact
I would counter-argue that people who adopt such a position are in large
measure responsible for the high rate at which others will defend a wrong
position long after the facts have made a practical defense untenable.  Part
of credibility is admiting when one is wrong, and learning from one's
mistakes.

     I have enjoyed our discussions because you are a knowledgable individual
with a vast breadth of knowledge, some of which is in areas in which my own
familiarity is weak.  I would respectfully suggest that I might know a thing
or two about, say, dynamics (my original degree specialty) which you might be
embarrassed to admit that you did not know.  But with such a vast and rapidly
changing field, that would not lower my estimation of you one bit -- unless,
of course, you gave a "Calvin's-father-type" explanation of, e.g., why the
moon is a satellite of the earth despite the sun's gravitational force being
twice as strong as the earth's, and then refused to part with it.  -|Tom|-

-- 
Tom Van Flandern / Washington, DC / metares@well.sf.ca.us
Meta Research was founded to foster research into ideas not otherwise
supported because they conflict with mainstream theories in Astronomy.
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