🚀 go-pugleaf

In article <1d99kkINNqu7@agate.berkeley.edu>, ted@physics.Berkeley.EDU (Emory F. Bunn) writes...

I have one nit to pick in an otherwise excellent explanation of CDM:

>This argument sounds good, but it isn't right.  The dark matter and the
>visible matter can have extremely different distributions.  To explain 
>why, I'll describe one specific cosmological model, the "cold dark 
>matter" model.  According to this theory, most of the mass of the 
>Universe is composed of massive particles that only interact via 
>gravitation and the weak force.  In particular, the dark matter doesn't
>interact electromagnetically.  (That's why it's "dark.")  Now think

Just because WIMPS are "weakly interacting" doesn't mean to imply
that they interact via the weak nuclear force.  In fact, I think that
they are supposed to be *much* more weakly interacting than that, via 
some unknown mechanism, of course.  (If they are not baryonic, they 
can damn well interact however they like!)  

I may be wrong on this point, but I remember being told that if they
interact as strongly(!) as the weak interaction, then the model doesn't
work, presumably because it allows too much interaction to keep the 
CDM from thermalizing when things are hot and the weak interation is 
important.

-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