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- Path: sparky!uunet!think.com!ames!agate!dog.ee.lbl.gov!csa1.lbl.gov!sichase
- From: sichase@csa1.lbl.gov (SCOTT I CHASE)
- Newsgroups: sci.physics
- Subject: Re: No big crunch?
- Date: 6 Nov 1992 11:43 PST
- Organization: Lawrence Berkeley Laboratory - Berkeley, CA, USA
- Lines: 94
- Distribution: world
- Message-ID: <6NOV199211432074@csa1.lbl.gov>
- References: <1992Nov4.203930.20410@murdoch.acc.Virginia.EDU> <1d9lptINN94@agate.berkeley.edu> <5NOV199210450757@csa2.lbl.gov> <1992Nov5.211058.25220@murdoch.acc.Virginia.EDU>
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- In article <1992Nov5.211058.25220@murdoch.acc.Virginia.EDU>, crb7q@kelvin.seas.Virginia.EDU (Cameron Randale Bass) writes...
- >
- > Though I am a bit surprised by this statement since I believe you have,
- > in the past, posited that there was very little fundamental left
- > to discover, I do agree. However, basing one's cosmology on the
- > *requirement* that new, unknown matter actually comprises most
- > of the known universe seems extremely speculative.
-
- I believe that we have built a solid foundation of fundamental physics
- which is well understood and highly unlikely to change. We have a much
- better quantitative understanding of the precise limits of our knowledge
- than we used to. Perhaps, in this context, I should have said "qualitatively
- new" rather than fundamentally new, so as to avoid confusion. The existence
- of dark matter, per se, would not do any damage to the fundamentals of
- physics as we know them. Of course, we might discover some new fundamentals
- by studying dark matter in detail, assuming that it's non-baryonic.
-
- > 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.
-
- (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.
-
- > 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?
-
- > 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.
-
- > I agree. How about making $400 million a year available, and
- > we'll let y'all have $40 million for cosmic ray research? I suspect
- > the concrete requirements (pun intented) for cosmic ray research
- > are somewhat lower than SSC.
-
- Progress in HEP has often depended upon our ability to take initial
- discoveries of particles in the cosmic rays and then to automate the production
- and detection of such particles in accelerators for high precision studies.
- I think it quite likely that, if someone detects dark matter particles,
- as soon as enough is understood about the basic characteristics of the stuff
- an accerator-based production method will be devised to study it in more detail.
-
- 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.
-
- -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
-