From: sichase@csa2.lbl.gov (SCOTT I CHASE)
Newsgroups: sci.physics
Subject: Re: No big crunch?
Followup-To: sci.physics
Date: 5 Nov 1992 10:45 PST
Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
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In article <1d9lptINN94@agate.berkeley.edu>, ted@physics3 (Emory F. Bunn) writes...
>In article <1992Nov4.203930.20410@murdoch.acc.Virginia.EDU> crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes:
> I prefer pixies.
>(Stuff deleted.) 
>I said:
>>>Dark matter, in contrast, seems qualitatively to explain what's observed
>>>without any completely outrageous new physics.
>>
>To which Dale replied:
>>     Except, of course, for the completely outrageous production of 
>>     unknown matter.

[...Ted's response deleted...]

I would like to support Ted's comments by adding that I can't imagine
any particle physicist who would argue that we have identified the
complete spectrum of fundamental particles.   HEP is a very young science.
It's amazing, IMHO, that we have been able to arrive at any kind of 
synthesis in so short a time.  But having achieved this with the Standard
Model, we should not draw the conclusion that all that's left is dotting
the i's and crossing the t's. 

I think that it is far from "outrageous" to speculate that there are 
vast amounts of "unknown", a.k.a. nonbaryonic matter in the Universe.  In
fact, questions of abundance aside, I regard it as likely that other
forms of matter do exist.  I think it would be both presumptuous and 
a bit naive to think that at this early stage in our understanding of
the high-energy world that nothing fundamentally new will show up.

Having said that, let me add that my personal guess would be that most
of the dark matter is not all that exotic.  I base this upon the same
argument - our poor state of knowledge.  I count it as almost certain
that at least some of the dark matter will be identified with large
lumps of normal matter - brown dwarfs, etc., and some more of it with 
massive (but not necessarily "heavy") neutrinos.  After that, of course,
there may still be something more interesting, but right now it's anybody's
guess.

One reason that the dark matter hypothesis is so popular is that it is
so straightforward to test.  Conversely, long-range modifications to GR
are very messy to study in the lab.  Dark matter searches, now just
starting, are a natural extension of our decades long experience with 
cosmic ray physics - looking up into the sky to search for particles raining
down on us.  Much of what we know about particle physics comes from this
avenue of research.   

The possibility that dark matter dominates the Universe has reminded 
physicists that we have never really studied "cosmic ray" physics with
the kind of completeness that it deserves.  We have almost completely 
ignored the possibility of weakly interacting particles in the cosmic
radiation.  We have been entirely preoccupied with charged particles, which
are easily studied using emulsions and plastics.  Now we have embarked
on a program to search for other types of particles, which if successful
will surely revolutionize particle physics, even if the things that are
found end up having no significance in explaining galactic rotation curves
and other problems with large scale gravitation.

-Scott
--------------------
Scott I. Chase			"It is not a simple life to be a single cell,
SICHASE@CSA2.LBL.GOV		 although I have no right to say so, having
				 been a single cell so long ago myself that I 
				 have no memory at all of that stage of my 
				 life." - Lewis Thomas
Newsgroups: sci.physics