ethan@utastro.UUCP (Ethan Vishniac) (05/08/84)
[In the name of Yag-Soggoth begone bug!!!!!]
This newsgroup has been awfully quiet. In an attempt to liven
things up I'm posting a summary of some of the highlights of
the last conference on cosmology I've been to. I'm also posting
it to net.physics since the material is probably of equal relevance
to that newsgroup. The meeting was the
Inner Space/Outer Space conference at Fermilab May 2 - 5.
The conference included various notables in particle physics
and cosmology and a large number of active researchers in these
fields. Talks were about evenly divided between particle theories
and their effects on cosmology and extragalactic astronomy and its
implications for the initial conditions for the universe (and therefore
for cosmology). What I've listed below is by no means a complete
(or even fair) listing of the talks. These are just the points that
struck me as particularly interesting.
1) G. Steigman and B. Pagel both gave talks on the primordial
element abundance. The bottom line is that the standard model
fits quite well if the present baryon density (as a fraction of
the density required to produce a marginally bound universe)
lies between
0.01 h^-2 and 0.035 h^-2 . (Pagel favored a narrower range
with an upper limit of about 0.02). The upper limit
comes from primordial lithium 7. The lower limit comes from
primordial Deuterium plus primordial He3. "h" is, as usual,
Hubble's constant in units of 100 km/sec/Mpc. The primordial
Helium 4 abundance appears to be consistent with the this
picture. However, the range of reported values is large enough
to include anomalously low values. In the numbers quoted above
I have assumed that the present blackbody background temperature
is 2.7 degrees. More on this later.
2) There are still no reported instances of baryon decay. This
probably rules out the minimal SU(5) models of grand unification
(theories which unify strong, weak, and electromagnetic forces).
3) B. Cabrera's reported possible detection of a magnetic monopole
has not been repeated. Various experiments are underway to improve
the upper limits on the local monopole flux. Various astrophysical
constraints are probably much more sensitive than any experiment
now in the cards if monopoles catalyse nucleon decay.
4) Particle physicists are now working on various ways to
a) cause the universe to expand exponentially at some
early epoch
b) cause the "inflationary" epoch to end gracefully
and quietly
c) produce (during the exponential expansion) just enough
cosmological perturbations to explain the large scale
structure of our universe without disturbing its overall
homogeneity.
d) reheat at the end of exponential expansion just enough to
create the matter-antimatter asymmetry in the universe.
e) avoid various monsters whose energy density in the present
universe would be prohibitive large (monopoles, gravitinos etc).
Not much progress was evident in the sense that there exists no
"natural" unification theory which would accomplish these things
or anything else. Nevertheless many ideas were presented.
The expectation remains quite firm that if these schemes are correct
than the present universe is "flat" (i.e. the average energy density
at present is just what is required to produce a critically bound
universe. Compare this to item # 1 to see an obvious problem.
5) Polite (and otherwise) disagreement continues on the subject
of the value of Hubble's constant (which determines the rate of
expansion of the universe).
6) The microwave background spectrum was discussed by P. Richards
The results are now consistent with a blackbody spectrum whose
temperature is about 2.75 degrees (plus or minus somewhat less
than a degree). Other speakers reported that the microwave
background continues to show no anisotropies. The lowest limit
quoted was a fractional temperature variation of less than
5.6x10^-5 on scales of a few arc minutes. (There is a dipole
moment due to our own motion).
7) The Russian measurement of a neutrino mass stands alone and unconfirmed.
New experiments are coming on line to test this result. The latest
fit to the Russian data looks bad for any neutrino mass. The Russians
are suggesting at least two massive neutrinos. Other people are
somewhat (or entirely) skeptical.
8) Preferred models for the formation of structure in the universe
now rely on some massive, collisionless particle to dominate the
structure of the universe. It must be very massive (probably at
least a Kev). Dynamical measurements of the mass density of the
universe give a density which is only about 20% (at most) of the
critical density. There was considerable discussion of having
galaxies form only at unusual density peaks so that galaxies do not
trace the mass density of the universe well. This has problems of
its own.
9) S. Weinberg gave a synopsis of his own hopes for the unification of
all forces in nature. He wants to use a graded Lie algebra in an
N-dimensional space (where N is large). To create a universe
in which space is locally Euclidean in 3+1 dimensions (our familiar
universe) but in which other directions exist in which we have
almost no freedom of motion. These other directions possess
different symmetries than those we normally associate with space.
Distortions of space-time in all these dimensions then generate
the sets of particles and forces we observe.
"Just another Cosmic Cowboy"
Ethan Vishniac
{ut-sally,ut-ngp,kpno}!utastro!ethan
Department of Astronomy
University of Texas
Austin, Texas 78712nather@utastro.UUCP (Ed Nather) (05/08/84)
[zot]
4) Particle physicists are now working on various ways to
a) cause the universe to expand exponentially at some
early epoch
b) cause the "inflationary" epoch to end gracefully
and quietly
c) produce (during the exponential expansion) just enough
cosmological perturbations to explain the large scale
structure of our universe without disturbing its overall
homogeneity.
d) reheat at the end of exponential expansion just enough to
create the matter-antimatter asymmetry in the universe.
e) avoid various monsters whose energy density in the present
universe would be prohibitive large (monopoles, gravitinos
etc).
Dammit, I wish you guys would leave my Universe alone. You're always
screwing around with it. I don't *want* the Universe to expand exponentially,
now or ever. Leave it as is.
Grumble. Snarl.
--
Ed Nather
ihnp4!{ut-sally,kpno}!utastro!nather
Astronomy Dept., U. of Texas, Austin