NetNews Usenet Archive 1992 #16/NN_1992_16.iso/spool/sci/astro/8179

Text File | 1992-07-21 | 3.6 KB | 74 lines

Newsgroups: sci.astro
Path: sparky!uunet!cs.utexas.edu!usc!zaphod.mps.ohio-state.edu!sdd.hp.com!mips!pacbell.com!well!metares
From: [e-mail] (Tom Van Flandern)
Subject: Re: grav lensing
Message-ID: <[e-mail]>
Sender: [e-mail]
Organization: Whole Earth 'Lectronic Link
References: <[e-mail]> <[e-mail]>
Date: Tue, 21 Jul 1992 16:00:37 GMT
Lines: 62


Earlier, I wrote:

>> More to the point, this complex ad hoc model does not contradict my
>> sentence which led us here.  There are still no lensed *quasar* images
>> which are rings or ring-arcs.  Images possibly produced by invisible,
>> hypothetical quasar jets do not count.  But there ought to be quasar
>> ring-arc images if quasars are truly being lensed.  Where are they?

and [e-mail] (Ralf Stephan) replied:

> First, I observe in all this threads the massive use of the term "ad hoc"
> and, not surprisingly, mostly by Tom. But to me the quoted paragraph above
> itself contains some ad hoc thoughts.
>
> From my reading about QSOs I understand that radio lobes are a common
> feature of QSOs and this beyond doubt, means, lobes and QSOs are connected.
> So what if there is a clear lensing case not for a quasar but for a lobe?
> That makes a strong evidence for cosmological distance for the quasar, too.
>
> And even if the lobes are not associated with the quasar, it at least
> points to cosmological distances of lobes, thus an argument against a local
> interpretation. Of course the lobes have redshifts comparable with the ones
> of the quasar (WRT to the 'hypothetical' angle they are directed WRT our
> line of sight and their speed)?
>
> If there are no major errors in these thoughts one now must question which
> view is more "ad hoc".

     I certainly agree that such an interpretation would be ad hoc and
therefore very likely wrong.  But that is not the interpretation that I was
arguing for.  I agree that the lobes are associated with the quasar.  What I
think I have argued convincingly (though by no means proved) is that the ring
is *not* a gravitational lens.  While admitting that I don't know what it
*is*, I argued in an earlier message that the ring must be the visible part
of a spherical shell, perhaps produced by immersion in the quasar lobe.

> And, Tom, do you sometimes reflect upon your model and try to look for "ad
> hoc"s in it, too?  You should, if you want to use this term as an argument
> in the future to which I object.

     I most definitely do look for such things.  I have insisted at every
step that the models I accept be as free as possible of ad hoc assumptions,
since I see every one of them as a model weakness.  That is why my own model
is derived from first principles, because anything less would be, to some
extent, ad hoc.

     I am sorry to hear that you object to this comparison, because clever
theorists can explain almost any model contradiction with ad hoc helper
hypotheses.  The only way I know of to tell if a widely-accepted model is
right or wrong is to examine the degree to which it is ad hoc.  The only way
I know of to tell a good alternative from among the countless bad ones is to
make the "ad hoc" versus "a priori" comparison of its predictions (assuming
it gets past the first steps of contradicting nothing and adding insight).

     If you aren't willing to make such comparisons, you risk spending your
whole career supporting a bad model.  -|Tom|-

--
Tom Van Flandern / Washington, DC / [e-mail]
Meta Research was founded to foster research into ideas not otherwise
supported because they conflict with mainstream theories in Astronomy.