(Photo: KICP/Daniel Luong-Van)
The new South Pole Telescope helps explore dark energy that may be causing the universe to accelerate.
“The number to remember from tonight: 100 billion,” he said. “That’s the rough number of individual stars in each galaxy, and there are, we estimate, about 100 billion galaxies in the known universe. And it’s about 100 billion years old in dog years, which is about 14 billion years old in human years, or the equivalent in Apple’s cash reserves if you’re measuring it in dollars.”
Even astrophysicists can have a sense of humor.
Lots of space, he went on to detail, is wide open. “But telescopes are essentially time machines, and we’re looking back into the past to a time before many galaxies were formed, in some cases 10 billion years ago or more. There might be galaxies there now, but light hasn’t arrived here from them yet, and we can’t see them.”
Starlight, star bright
Starlight, which is visible to the eye, is great, but microwave light is all around and essentially glowing all the time, providing a lit backdrop against which galaxy clusters could be observed and tracked.
That’s where the SPT comes into play. A collaboration of nine U.S. and Canadian institutions, the SPT is a 10-meter telescope at the Amundsen-Scott South Pole research station. (Robert Scott’s original 1912 tent house is still standing and open to visits, if you can make it down there.)
Constructed between November 2006 and February 2007, the SPT is by far the largest telescope ever deployed at the South Pole. This telescope provides astronomers a powerful new tool to explore dark energy, the mysterious phenomena that may be causing the universe to accelerate, rather than slow down its rate of inflation, as has been previously theorized. Back home here in the Eastern Sierra, the Hooker Telescope at Mt. Whitney helped reveal that the universe was expanding.
Taking advantage of the exceptionally clear, dry, and stable atmosphere at the South Pole, the SPT maps large areas of the sky with high sensitivity at millimeter and sub-millimeter wavelengths. “We’ve found new classes of galaxies never before seen,” Carlstrom told the audience.
The 700,000-pound telescope is comprised of 960 detectors, and is so heavy that a foundation for the telescope had to be excavated and reinforced, even though it sits on a snow and ice pack two miles deep. Pieces of the facility had to be flown in by US Air Force planes from New Zealand and assembled on site. The facility has to withstand winter temperatures that can reach -80°F, and uses carbon fiber epoxy structural components, as opposed to conventional materials. (The temperature of dry ice, for reference, is typically about -100°F.)
About 5,000 structural bolts, some measuring 37 inches, hold the telescope together. And, as Carlstrom noted, are too cold to even be touched by bare hands. “When we were raising the main dish assembly up to the platform, the entire staff ran outside, and we asked, ‘What’s going on?’ They said, ‘Well, if you drop it, we don’t want to miss it; we’ll never get to see that again,’” he quipped.
The 208 panels containing the detectors all had to be calibrated within 2 microns of precision tolerance. Of course, the South Pole is actually moving at about 8 meters a year, which has to be accounted for in the calculations.
The SPT project’s “five-year mission” is to explore the nature of dark energy, an unexplained phenomenon responsible for the observed acceleration in the expansion of the universe. The SPT will search for massive clusters of galaxies by looking for spectral distortions in the cosmic microwave background. Dark energy inhibits the growth of galaxy clusters, so studying the population of clusters through cosmic time will influence future models of dark energy.
At the most fundamental level, the universe is made up of gas and sound waves resulting from compression caused by particle interaction. The universe has a specific “tone” and harmonics, not unlike music, and microwave analysis of those harmonics allows mapping to very detailed resolution. Distortions of the CMB spectrum are used to measure the density of the universe, and using the Sunyaev–Zel’dovich (SZ) effect, similar to the Doppler effect associated with sound, and whether waves are coming at you or going away, dense galaxy clusters have been observed.
According to recent estimates, all known matter constitutes only about 5% of the universe, dark matter makes up another 23% and the rest is assumed to be dark energy. The most widely accepted property of dark energy is that it leads to a pervasive force acting everywhere and at all times in the universe. This force could be the manifestation of Albert Einstein’s 1917 cosmological constant, which implies that empty space has energy, even when it is free of matter and radiation.
Einstein added the cosmological constant to his theory of general relativity (remember E=mc2?) to accommodate a stationary universe, the dominant idea of his day. He later considered it to be his greatest blunder, after the discovery of an expanding universe. Physicists now think that Einstein’s constant accounts for all that remaining dark energy, though Carlstrom acknowledged they still don’t know how to calculate it exactly.
“Maybe his theory of relativity was wrong,” Carlstrom posited. Is the universe expanding and accelerating, essentially running away with itself to some climactic, catastrophic end millions or billions of years from now? Carlstrom said science wants to find out, even if some of its hypotheses are proven wrong. “Scientists love to proven wrong,” he quipped. “We’ll be examining relativity and other concepts with this new SPT project, using what we learn about the formations of galaxy clusters to trace a history of dark matter versus dark energy back through time. The vacuum of space contains energy, Carlstrom pointed out. So far, even though he did happen on it via a “blunder,” it appears Einstein was right.
A few things we do know: there is no speed limit to the rate at which the universe can expand. There is only a limit on the speed at which an object can be propagated through it. And science also asserts there is no “center” to the universe, that viewpoint is based on perspective. “What we see looking out in any given direction is basically the same thing you’d see if you were on the other side of the known universe looking back at Earth,” Carlstrom related, adding that cosmological physicists don’t know what else might lie beyond that 14 billion time curtain. For now, that’s as far back as we can see.
Carlstrom said another important goal is to ultimately rule out various competing ideas for the origin of the universe. One thing’s for certain, the new telescope is yielding results much quicker than its predecessors. The SPT is capable of mapping one square degree of the sky every 20 minutes, as opposed to previous equipment, which could take up to one year to map the same space.
Answers to many of man’s scientific and other more philosophical questions are still out there in the cosmos.
It’s at least something for mere mortals to ponder as we gaze up in wonder at the light show we are treated to by the universe, its deepest secrets tucked into cosmic riddles and wrapped in celestial enigmas, waiting for Carlstrom and his colleagues to discover in good time.
The next OVRO lecture will be held Wednesday, Oct. 10, at 7 p.m. at Cerro Coso College in Bishop.