The Big Bang Theory says that everything came into existence at once during a massive explosion around 13.8 billion years ago. In a fraction of a second, the universe went from being infinitely dense and hot to expanding rapidly, with the explosion releasing energy and the basic building blocks that would later become stars, galaxies, and eventually, planets.
This is the gist of the origin story of the universe, but the fine details are murky and shrouded in mystery. But what if you had a time machine that you could use to wind back the clock to the exact moment the Big Bang happened? For some scientists, this isn't just a hypothetical thought experiment.
More than 150 researchers from dozens of leading universities and research institutes across the world combined data from two major telescope surveys, the Dark Energy Survey and the South Pole Telescope, to plot the most accurate map of the distribution of all the known matter in the universe to date. By getting a better handle on how matter is presently distributed across the universe, scientists can then come to a better understanding of the forces that shaped the evolution of the universe. One day, these efforts could be used to model the expansion of the universe in reverse, all the way back to its point of origin.
While most of the results align with the current best theory of the universe, there are signs of a crack in the existing standard model of the universe. The current universe appears to have slightly less fluctuations than our model predicts, and is less "clumpy" (clustered in certain areas) than expected. If other studies confirm these findings, it may mean that there is something missing in these models.
Where we are now, and where it all began
The Dark Energy Survey (DES) is an international, collaborative effort to map hundreds of millions of galaxies, detect thousands of supernovae, and find patterns of cosmic structure that will reveal the nature of the mysterious dark energy that is accelerating the expansion of the universe. The survey saw first light in 2012, after a decade of planning, and completed observations in 2019 using a newly built 570-megapixel camera installed on the four-meter Blanco telescope at the Cerro Tololo Inter-American Observatory in the Chilean Andes. Previously, this survey yielded an extraordinary 3-D map of over 300 million galaxies and cataloged thousands of supernovae -- the most powerful explosions in the universe, which occur when a massive star dies.
Meanwhile, the South Pole Telescope (SPT) is a submillimeter observatory in Antarctica that performs measurements of the cosmic microwave background (CMB) -- the faint flow of light that permeates the universe and serves as direct evidence of the Big Bang. The SPT is located at the Amundsen–Scott South Pole Station in Antarctica, at an elevation of 2,800 meters (9,300 feet). This high and dry location far from cities provides a clear sky, in addition to the months-long Antarctic winter night. This survey is also involved in measuring the expansion of the universe.
By combining two very different methods for studying the sky, the scientists attempted to enhance the accuracy of their results as much as possible.
“It functions like a cross-check, so it becomes a much more robust measurement than if you just used one or the other,” said University of Chicago astrophysicist Chihway Chang, one of the lead authors of the studies.
In this instance, the analysis centered on a phenomenon known as gravitational lensing, where light passing close to objects with strong gravity, like galaxies, is slightly bent. This method allowed them to capture both regular matter and dark matter as both exert gravity. By analyzing the two sets of data, the scientists could infer where all the matter in the universe ended up, providing a more precise measurement than previous analyses.
All in all, the readings fit almost perfectly with what our best models of the universe predict, except for a couple of anomalies that point to some flaws in scientists' theories.
“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.
However, the authors add that the statistical significance of their results is not exactly 'ironclad', which means there may be some faults in their methods rather than in the standard model itself. But if other research groups reach similar results independently, that might warrant going back to the fabled drawing board in order to rethink how we view the evolution of the universe.
“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.”
The findings appeared in the journal Physical Review D.