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 78712
nather@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