Cosmic Inflation Meeting

by Andreas Albrecht, professor

Last March most of the world’s top cosmologists converged on Davis to participate in the Davis Meeting on Cosmic Inflation. The participants enjoyed an impressive array of exciting talks, and the lively discussion and debate continued late into the night in the local restaurants, bars and coffee shops. Dean Rock, one of the key visionaries behind the buildup of cosmology at UCD, opened the conference on March 23rd. That evening Stephen Hawking presented the first of his two sold-out public lectures at the Mondavi Center and charmed and challenged an enthusiastic audience with the idea that our Universe might be a “brane” in a higher dimensional space. That same evening the originators of cosmic inflation theory gathered over dinner at the Katmandu Kitchen to assess Hawking’s very provocative plenary talk at the conference that morning. Yes, the list of speakers read like a Who’s Who of modern cosmology research, but the real stars of the show were a theory (cosmic inflation) and a brand new dataset, the full-sky microwave map produced by NASA’s WMAP satellite and released just a month before the conference.

What is cosmic inflation theory? Cosmologists study the origins and evolution of the universe. For many years now, the “hot big bang” has provided the basic picture of the Universe as it evolved from a very hot dense plasma at early times, allowing stars, galaxies and planets to condense out as the Universe expands and cools. But cosmologists have always found something very strange about the starting point of the big bang theory. To achieve consistency with the observed state of the Universe today, one needs to assume a starting point for the big bang that is precariously balanced in a state highly disfavored by the cosmological equations: Gravity wants to pull matter together and make it more clumpy (ultimately to form one giant black hole). But the universe starts out extraordinarily smooth. The equations of gravity try to amplify any small “curvature” the universe may have, causing it to rapidly curl up either with negative curvature (like a potato chip) or positive curvature (like a sphere). But the real Universe started out so precisely balanced in a “flat” state (zero curvature), that even today any deviation from flatness is un-measurable even using the most modern technology. It is as if the Universe has been perched like a pencil on its point, and balanced so precisely that it has hardly started to fall, even after 14 Billion years! About twenty years ago, cosmic inflation theory was invented. Its goal is basically to explain how the pencil got so precisely balanced on its point. Inflation posits a new state of matter (a so-called “potential dominated” state) that could exist in the early universe, and which actually reverses the dynamical processes discussed above, so that curvature tends to flatten out on its own, and clumpy matter tends to smooth out into a more homogeneous state. If such a state of matter existed in the early universe, the universe is said to have undergone a “period of inflation” (named after the extremely rapid expansion that goes with this special state). Inflation is the hand (or perhaps high precision robot) that carefully places the pencil in a perfectly balanced upright state.

So what is exciting today about this 20 year old theory? To begin with, to fully understand and test the idea of cosmic inflation, one must probe the deepest unsolved problems in physics and cosmology: What is the fundamental theory of quantum gravity and matter? Is that theory able to accommodate the special inflationary state? Is the Universe infinite, extending forever with more stars and galaxies, just like the ones we see, or is our observed universe merely an island adrift in a chaotic sea of something unimaginably different? Interestingly, much progress has been made on these and related questions over the last 20 years, and our meeting proved to be well-timed to debate the current status of these and related questions.

Probably the most celebrated participant at our meeting was the new data from NASA’s Wilkinson Microwave Anisotropy Probe (WMAP), just announced this February 11th. The WMAP satellite is stationed in the depths of outer space (four times as far from earth as the moon). It is systematically mapping out subtle microwave signals from the very edge of the observable universe, signals that convey information about the very earliest stages of cosmic history. The February release of the first year data has already proven to be a gold mine for many aspects of cosmology, especially for cosmic inflation theory.

Despite the fact that there are still important unanswered theoretical questions about cosmic inflation, the theory is well enough understood to makes a whole host of observable predictions. It turned out that the impressive new WMAP data had the potential to falsify inflation in a number of different ways. But as things turned out, inflation passed with flying colors. This added a sense of celebration to the meeting.

Many participants of Davis Meeting on Cosmic Inflation regarded the meeting as a turning point: the start of the much-heralded era of “precision cosmology.” This was the first conference after the release of the WMAP data, a data set at least an order of magnitude more powerful than any other existing cosmological data set. The whole flavor of the field has changed, now that even subtle theoretical debates can be put before the ultimate judge (namely Nature) for a final ruling. The WMAP data has raised the bar, and much of the discussion looked toward the future, as we discussed and debated which new proposed experiments and facilities would provide the best opportunities supercede the success of WMAP and bring the field into a new era of even higher precision.

We are proud that such a special event in the development of cosmology took place here at Davis. It gave us a chance to thank the many colleagues from around the world who have assisted with our buildup through their advice and support, and to celebrate the formation of our cosmology program here, along with the fantastic advances in our field.

Special thanks: The Davis Meeting on Cosmic Inflation was supported by The UCD Office of Research, the UCD Division of Mathematical and Physical Sciences, and the Physics Department, as well as by DOE, NASA, and NSF.
Further info: You can learn more at the meeting web site http://inflation03.ucdavis.edu/ which includes copies of the speakers’ slides and proceedings contributions. You can learn more about the WMAP results at http://map.gsfc.nasa.gov/