The first step is collecting enormous amounts of data with telescopes.
In this study, scientists combined data from two very different telescope surveys: The Dark Energy Survey, which surveyed the sky over six years from a mountaintop in Chile, and the South Pole Telescope, which looks for the faint traces of radiation that are still traveling across the sky from the first few moments of the universe.
Combining two different methods of looking at the sky reduces the chance that the results are thrown off by an error in one of the forms of measurement. “It functions like a cross-check, so it becomes a much more robust measurement than if you just used one or the other,” said UChicago astrophysicist Chihway Chang, one of the lead authors of the studies.
In both cases, the analysis looked at a phenomenon called gravitational lensing. As light travels across the universe, it can be slightly bent as it passes objects with lots of gravity, like galaxies.
This method catches both regular matter and dark matter—the mysterious form of matter that we have only detected due to its effects on regular matter—because both regular and dark matter exert gravity.
By rigorously analyzing these two sets of data, the scientists could infer where all the matter ended up in the universe. It is more precise than previous measurements—that is, it narrows down the possibilities for where this matter wound up—compared to previous analyses, the authors said.
The majority of the results fit perfectly with the currently accepted best theory of the universe.
But there are also signs of a crack—one that has been suggested in the past by other analyses, too.
“It seems like there are slightly less fluctuations in the current universe, than we would predict assuming our standard cosmological model anchored to the early universe,” said analysis coauthor and University of Hawaii astrophysicist Eric Baxter (UChicago PhD’14).
That is, if you make a model incorporating all the currently accepted physical laws, then take the readings from the beginning of the universe and extrapolate it forward through time, the results look slightly different from what we actually measure around us today.
Specifically, today’s readings find the universe is less “clumpy”—clustering in certain areas rather than evenly spread out—than the model would predict.
If other studies continue to find the same results, scientists say, it may mean there is something missing from our existing model of the universe, but the results are not yet to the statistical level that scientists consider to be ironclad. That will take further study.
However, the analysis is a landmark as it yielded useful information from two very different telescope surveys. This is a much-anticipated strategy for the future of astrophysics, as more large telescopes come online in the next decades, but few had actually been carried out yet.
“I think this exercise showed both the challenges and benefits of doing these kinds of analyses,” Chang said. “There’s a lot of new things you can do when you combine these different angles of looking at the universe.”
University of Chicago Kavli Associate Fellow Yuuki Omori was also a lead co-author for the papers. The full studies and authorships, "Joint analysis of Dark Energy Survey Year 3 data and CMB lensing from SPT and Planck," can be found in three papers selected as the editor's suggestion at Physical Review D.
The South Pole Telescope is primarily funded by the National Science Foundation and the Department of Energy and is operated by a collaboration led by the University of Chicago. The Dark Energy Survey was an international collaboration coordinated through Fermi National Accelerator Laboratory and funded by the Department of Energy, the National Science Foundation, and many institutions around the world.
—Prof. Jacqueline Stewart
