Vis Lab Brings the Red Carpet to SLAC
The movie begins with a tangled jumble of orange tentacles reaching out in all three dimensions, including straight towards the audience. As time fast-forwards through millions of years in a matter of minutes, bright, circular clumps take shape in seemingly random positions. Engrossing as it is, this 3-dimensional masterpiece of galaxy formation isn't produced in Hollywood. The simulation is calculated, rendered, and displayed right here at SLAC.
The simulation was created in the Kavli Institute for Particle Astrophysics and Cosmology (KIPAC) Computational Physics department led by SLAC and Stanford physics associate professor Tom Abel. It was recently viewed by science professors from San Mateo Community College as part of the lab's educational outreach program. The program encourages instructors to invite speakers from the lab into their classrooms and take their students on similar field trips of the site. Aside from "being amazed at all the different areas of science at SLAC," as one instructor put it, the group was deeply impressed with the movies presented at the Kavli Building.
"They were oohing and ahhhing through the whole presentation," said Education Officer Susan Schultz, who organized the tour. "The 3-D movies are a great tool to spark interest in SLAC science."
The movies are quite impressive but rely on equally impressive equipment for their presentation. On the second floor of the Kavli Building, the Schwob Computing and Information Center houses two projectors mounted in front of a large screen. Each projector's image is shone through separate polarizing filters and is viewed through specially polarized glasses. The system has wowed many visitors with 3-dimensional movies of colliding galaxy clusters and the formation of stars and supermassive black holes.
The movies and simulation models are created using software developed at SLAC that cannot be found anywhere else. Over 70,000 lines of code are responsible for accurately computing how the universe turned some of its initially hot, almost homogeneous soup of hydrogen-helium gas into the first stars, black holes, and galaxies.
Running for months on KIPAC's computers and using over a hundred processors at a time, the software spits out hundreds of gigabytes of data detailing the "soup," including density, gas temperature, rates of motion, and chemical states. Despite this massive amount of analysis, the software can render 3-dimensional representations in a matter of days.
"Some movies are actually quite simple to make," said Abel. "But others take a long time to choose which variable to show [such as density or temperature], colors to use, and camera angles to reveal the physically relevant features in the data."
Ralf Kähler, a visualization expert in Abel’s group, wrote the rendering software from scratch. "It's just fantastic!" said Abel. "Ralf's renderer allows us to create realistic images that reflect our best understanding of the universe during a time when nobody was around to see it!"
In addition to the movies of celestial phenomena, guests can also navigate their way through space, leaving Earth to fly through the Milky Way galaxy. This separate program allows guests to freely explore space, speeding past over 200,000 stars as if captaining a spaceship. The simulation uses real data to construct a factual representation of space complete with the types and names of stars and galaxies passing by.
The movies have been shown to various tour groups ranging from the recent physics instructors to a Department of Energy review board. No matter who the audience is, the results are the same.
"Everyone says they learned something new," said Schultz. "And they love the experience."
Though the system is great for tours, research is the driving force behind the technology. The software allows scientists to view their data in ways not before possible, providing novel and invaluable insights and information.
"Each time we see new data popping out of the screen we learn some new physics.” said Abel. "Being able to look at the whole picture makes otherwise abstract concepts intuitive and some even obvious."
Ken Kingery, SLAC Today, July 19, 2007