This afternoon cosmologist Scott Dodelson, Fermilab, gave a fun talk at the Fermilab Users' meeting. Dodelson, who is the acting head of the Fermilab Center for Particle Astrophysics, spoke about the evolution of the universe and how mapping the universe will provide the answers to many questions that scientists have.
To make the case, he compared maps of celestial objects in the universe to maps of the population of the United States. He first showed a map of the US population as of 1790 (see image right). At that time, immigrants from Europe had only settled in areas along the east coast and lived in small villages. But a map of the US population today shows that the population has spread across the entire continent, with clusters of large cities and traces of the "primordial" population areas.
"I claim that the story of the evolution from the early map to today's map is the history of the United States," said Dodelson. To reconstruct the entire history, researchers would have to obtain maps of the population distribution between 1790 and today, and examine them in finer and finer details. Examining them as a function of time, these maps would reveal the impact of civil wars and many other events, down to the social structure of society. "If we look at this evolution, we can understand the evolution of the people and the sociological, economic, and political forces," he said.
Similarly, maps of the distribution of celestial objects will reveal the fundamental forces behind the evolution of the universe and its constituents. Dodelson looked around the auditorium and pointed out that the universe started out smooth, but now "the density of the universe in the room is 30 orders of magnitude larger than the average density of the universe." The universe started smooth and evolved to be clumpy because of gravitational instability, he said.
Dodelson went on to talk about the Sloan Digital Sky Survey, which has recorded two- and three-dimensional maps of the universe. (The online database, managed by Fermilab, receives a million queries a month.) Together with other observations and future maps, the SDSS results will help to solve the mysteries of the universe such as dark energy. But more work is needed.
"The SDSS covers only 10-to-the-minus-4 of the available cosmic volume," Dodelson said. "With regard to [the map of the] United States, this corresponds to Birmingham, Alabama."
A new project, the Dark Energy Survey, will provide better maps of the universe. The DES collaboration plans to build its digital camera by the end of 2010 and mount it on the 4-meter Blanco telescope in northern Chile. Data taking would begin in September 2011. The DES camera would map a volume ten times larger than SDSS. The data could reveal information on dark energy, neutrino mass, and even test gravity.
"It's all about volume," said Dodelson. "These maps will help us to fill in the details of the cosmic evolution... Going way beyond Birmingham will help us do extraordinary science."
A PowerPoint file of Dodelson's talk is available online (PPT).
See all reports from the Fermilab Users' Meeting 2008 here.
