Eye on the Past
South Pole Telescope is the newest tool for figuring out the origins of the universe
Posted January 21, 2007
John Carlstrom has taken some pleasure from stirring up things around the South Pole this summer during construction of the South Pole Telescope.
“This thing’s sitting out there and it’s erupting; it’s growing,” he said in December. “It’s going to be the largest thing out there. Everyone is [excited about it].”
The principal investigator for the project, Carlstrom said the excitement started with the first flights that brought in summer workers who flew down “with this part of it or that part of it.” Meanwhile, they have been able to watch it grow on the horizon about a kilometer from the elevated station.
People at Amundsen-Scott South Pole Station are no strangers to astronomical research. Conditions there make it an ideal location for staring deep into space. However, the South Pole Telescope (SPT) has raised some eyebrows as the towering structure has raised the skyline at this desolate, isolated place.
“It’s really exciting to see 600,000 pounds-plus of steel arrive and be assembled and have a telescope that dwarfs large buildings that were landmarks on the horizon,” said Jerry Marty, National Science Foundation representative at the South Pole. “People are always excited about seeing the telescope.”
Within the next few weeks, the telescope with the 10-meter dish will move, turn and go to work seeking out secrets of the universe.
The goal“Everyone questions where we’re coming from and how did this happen and what’s out there,” Carlstrom said in explaining interest in the SPT and exploring the universe in general. “I think they, like me, just like to be a part of this.”
And answering questions is what science is all about, even if the answer is wrong. Carlstrom explained what astronomers will look for with the SPT by telling the tale of Albert Einstein’s cosmological constant.
Early in the 20th century, it was thought that the universe was stable, neither expanding nor contracting. However, when Einstein solved his famous general relativity field equations and applied them to the universe, they indicated that a static universe was not possible. If it had matter in it and was static, then it would eventually collapse on itself.
By the time he worked out the math, Einstein had derived a constant of integration that would explain the discrepancy. Its application seemed to resolve the conflict between his theory and a static universe.
“So, basically, his constant of integration, his cosmological constant, acted like a repulsive force at large distances,” explained Carlstrom. “It was like a property of space, an energy of the vacuum, if you will. And that would act like a counter, negative gravitation, to basically balance the mass.”
Edwin Hubble’s observations of redshift showed that distant galaxies are indeed moving away from us and that the universe is expanding. Einstein has been quoted as claiming the cosmological constant was his greatest blunder because it kept him from predicting that the universe was expanding.
Keep that “blunder” in mind, Carlstrom advised, because it would play a later role in the evolution of the SPT’s story. That is something else that is apparent: The pursuit of answers is not necessarily a hasty one.
“It’s a very conservative, cautious process, science is,” said Steve Padin, project manager for the SPT construction, “where you come up with a new idea, you make predictions, you test them. So there’s a tremendous amount of inertia built into that process, and that’s not a bad thing. It means that new ideas have to have credibility, but occasionally it means that we get it spectacularly wrong and we miss a good idea. And I think that’s OK, as long as you keep picking away, asking questions.”
Soon after Hubble discovered that many of the fuzzy spots in the night skies were distant galaxies, astronomers computed that there was not enough visible matter present to justify the movements of those galaxies. What evolved was the opinion that there was a substantial amount of unseen material throughout the universe, which was called dark matter.
“People’s beliefs have changed,” Carlstrom said, “but astronomers have known about dark matter at least 50 years, if not longer.”
As we began to get better looks at those distant galaxies, it was determined that some were bunched together. These galaxy clusters, as they are known, are the largest objects in the universe, he said. Analyses of their movements showed that far more mass than what was visible had to be present.
“So we know where [dark matter] is,” Carlstrom said. “We know that it clumps up. We know it is the source of the gravitational force that keeps galaxy clusters together, that keeps our galaxy together, and we know from this that there is about 10 times more mass in that component than there is in the stars and stuff that we see.
“We don’t know what it is.”
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