From: crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass)
Subject: Re: No big crunch?
Organization: University of Virginia
Date: Fri, 6 Nov 1992 20:07:52 GMT

In article <6NOV199211432074@csa1.lbl.gov> sichase@csa1.lbl.gov (SCOTT I CHASE) writes:
>In article <1992Nov5.211058.25220@murdoch.acc.Virginia.EDU>, crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes...
>
>>     I did not say that such *speculation* was outrageous, it was the
>>     *production* that seems outrageous.  I would be perfectly happy
>>     if all discussions of nonbaryonic dark matter were preceeded by 
>>     the statement that 'this is extremely tenuous speculation'.
>
>Several additional comments are in order here, to supplement the discussion
>of the past few days.
>
>(1) Dark matter does not only explain gravitatinal anomalies.  It also 
>is necessary to get the right primorial nuclear abundances from the Big
>Bang.  Essentially, the more matter in the early Universe, the longer 
>the hot dense phase lasts, and the more He3, for example, gets produced.

     I think that the phrase 'necessary to get the right' is a bit too 
     strong, focusing on the word 'necessary'.

>(2) Tecent HST high-res imaging of a new gravitational lens demonstrates that
>99% of the mass of the lens is not in the luminous part of the galaxy.  I 
>imagine that any alternative to dark matter along the lines of GR modifications
>will be highly constrained by reproducing such a lens.  Perhaps we are not
>too far from ruling out the alternatives to dark matter by such observations.

     Only if it is 'mass' that is the solution.

>>     After all, apparently HEP theorists did not do a very good job
>>     extending the Standard Model to predict the top mass.  Why should
>>     we take as anything but doubtful fancy the tenuous speculative
>>     extentions that predict such things?
>
>I suppose that you are entitled to take that position with regard to any
>unproven scientific speculation.  On the other hand, the people who are
>excited about the possibility of dark matter are not all reckless, off chasing
>wild speculations.  The clues which point to the possibility of dark matter 
>(not *exotic* dark matter) are as good a scientific lead as you will ever
>get, IMHO, pointing towards something completely new.  What do *you* make
>of all the excitement about dark matter searches, given your viewpoint
>on this issue?

     I have no problem with dark matter searches, that certainly seems
     prudent on some level.  However, there are those in this thread
     that would have us believe that the hypotheses are much more
     solid and certain than they are.  Characterization as 'wild speculation'
     is partly a matter of taste.  I prefer 'tenuous speculation'.

>>      However, how easy it is to test is a matter of debate.  I suspect
>>      that I could invent a dark matter distribution of various forms
>>      of dark matter with different interactions that would pass any and
>>      all observational tests.  I would be happy to hear differently,
>>      but I'm not holding my breath.
>
>All of the direct searches for exotic dark matter have the single assumption
>that there is a measureable flux of dark matter particles in our part
>of the galaxy.  If it exists at all, this is a fair assumption.  The
>detectors are designed to be as generic as possible.  They are not dependent
>upon the dark matter particles having any particular interaction, but merely
>that they *have* an interaction with baryonic matter.  The typical apparatus
>is a liquid-helium temp. bolometer which is sensitive to the small 
>temperature fluctuations which result from a dark matter/atomic interaction.

     The problem is that we can always posit that the interactions are
     as small as we need them to be to correspond with the fact that
     we don't see any.   

>However, you surely know that the SSC is dedicated to a completely different
>research task.  The SSC is bread-and-butter high-energy physics, without which
>the field will have a hard time proceeding.  Dark matter searches are a 
>more speculative avenue of research, one of many different approaches trying
>to take a stab beyond the Standard Model, to point to way to whatever
>lies beyond.  It is really a bummer, in a way, that the SM repeatedly 
>manages to give correct answers to our best experimental tests.  It gives
>is more and more confidence that the SM is basically sound, but leaves
>up high and dry when we try to figure out what's next.

     That's funny.  I thought I heard several Senators tell us the SSC
     is about 'jobs'.

                              dale bass
-- 
C. R. Bass                                          crb7q@virginia.edu        
Department of Mechanical, 
     Aerospace and Nuclear Engineering
University of Virginia                              (804) 924-7926
Newsgroups: sci.physics,sci.math