Collaborative Research: Using the Lyman Alpha Forest to Probe the Structure of the Universe

University Of California-San Diego, La Jolla CA

Investigators

Abstract

AST 0098731 Tytler In the last few years, astronomers have shown that supernovae (SN), in distant galaxies are fainter than expected. The obvious explanation is that they are farther away than we had thought. If true, this implies that the expansion of the universe is speeding up. This change in expansion is attributed to a so called "vacuum energy" by theoretical physics. This discovery presents both major new opportunities, and a long list of troubling basic new questions. Up to now Gravity has been the hardest part of physics to understand, in part because it has been described by a single number: the Newtonian gravitational constant G which measures its strength. If the universe is speeding up there must be a second number, which should help us understand gravitational physics. In this way, astronomical observations are redefining our understanding of fundamental physics and the universe as a whole. The goals of this project are to provide an independent check of the claim that 70% of the energy density of the universe is some form of mysterious vacuum energy. Astronomical observations are the only way to explore the vacuum energy experimentally, because the effects are significant only over exceedingly large distances. In particular, this project will provide an independent check of the results from supernovae by using angular size as a distance measure. The amount of clumping of the gas between the galaxies will be measured both along the line of sight, and in angle across the sky. The relationship between the two measures gives the distance and hence the acceleration of the universe. The method is insensitive to changes in the state of the universe over long times. The project is urgent, because the vacuum energy remains an unconfirmed, though very plausible, result, and highly significant, because we will have the sensitivity to decisively rule out the amount of vacuum energy suggested by the supernovae, if none were present. In addition to providing an independent check on the SN decelerating universe measurement, this project will also give improved measurements of the clumping of gas between galaxies at early times. This clumping is believed to have arisen from primordial quantum fluctuations when the universe was young.. These fluctuations have been measured at different epochs, and in different ways. However, the methods used in the present project will give the only measurement of the amount of clumping of matter on galaxy sized scales at early times. These new data and simulations will be compared with theoretical predictions, to act as a check on recent investigations which suggest that our present ideas about the growth of small scale structure in the universe are inadequate. Funding for this project was provided by the NSF program for Extragalactic Astronomy & Cosmology (AST/EXC). ***