Sloan Digital Sky Survey: Mapping the Universe

The Big Questions

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Michael Turner: "If you have big questions, but you don't have the technology to answer them, you're not going to make progress."

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Jason Lelchuk for AMNH

Scientists use the term “Big Bang” to describe the beginning of everything—time, space, and matter—13.7 billion years ago. Theorists suggest that at that first instant, all the fundamental particles of the Universe were squeezed into a space so small that it had no inherent size at all. There were no quasars yet, no galaxies, no structure—just the potential for it all, brewing a hot soup of particles. So by mapping quasars and galaxies as they appeared close to the time of the Big Bang—and by close scientists mean within 900 million years—they get nearer to understanding how that original moment developed into the Universe as it is today.

The In-Between

If the Big Bang is the most important theoretical idea in cosmology, inflation is the second. “It’s a deceptively simple idea,” explains Turner, a cosmologist at the University of Chicago and the Assistant Director for Mathematical and Physical Sciences at the National Science Foundation. “Inflation says that when the Universe was very young it went through a terrific growth spurt.” At .000000000000000000000000000000000001 of a second after that original moment of no size, the Universe rapidly expanded to have breadth and depth. Scientists speculate that the structure of the current-day Universe was likely laid down at this key fraction of a second, and that it was overall smooth and uniform. Still, small fluctuations—“lumps in the pudding”—were present. During the growth spurt, these lumps blew up to enormous sizes. Today, the Universe continues to expand, although not at a rate that even comes close to that of inflation. All the blowup has resulted in the current far-flung arrangement of galaxies and clusters. “The distribution of galaxies today are relics of inflation,” explains Turner.

Sloan’s data has the power to address at least three of the Big Questions (and quite a few more that can’t fit into one essay): the structure of the early Universe, the structure of the current Universe, and the journey in between. When Sloan eyes the farthest quasars, it gets an idea of the Universe near the time of its origin. When it views nearer galaxies and the stars of the Milky Way, it maps the expansive, structured arrangement now. By mapping the positions of space objects in between, time-wise and space-wise, Sloan can help explain how and where objects have clustered as the Universe evolved. This directly tests the idea of inflation.

Scientists have already started wading through Sloan’s voluminous data to further tease apart the Big Questions. What about the events of that first moment, the Big Bang? Or the events that preceded it? “If you had asked that question 10 years ago, people would say, ‘Oh, that's not science, we can't address that,’” says Turner. “Now, we're starting to. It’s one of the big challenges for the next generation of scientists.” In the next 5 to 10 years, expect a battery of large-scale, large-survey telescopes, inspired by Sloan, to arrive on the scene. They’ll employ even more sensitive detectors, shoot an even wider field of view, cover even more sky. They’ll be able to find older, more distant quasars and understand Universe-wide patterns with more precision. As science progresses, they may also be able to answer more Big Questions—maybe even ones we have not yet thought to ask.