Is Cosmology Broken? This Map May Be a Crucial Puzzle Piece

For centuries, cartographers have sought to map Earth’s land masses and seas to better understand the world and their place in it. Now, astrophysicists have taken a major step toward doing the same with the cosmos itself. They have just completed the largest and most detailed map yet of the universe’s early and middle years.

The map sheds new light on a pair of cosmological crises: the debate over the universe’s expansion rate, and a second one about how evenly matter is spread throughout the universe. By showing how light dating back to the Big Bang has been distorted, it provides the clearest picture so far of how fast our universe has been expanding and how quickly gravity has brought together massive structures, like clusters of galaxies and invisible webs of dark matter. Together, these seem to confirm the standard cosmology model of the universe’s growth as well as Einstein’s relativity theory, which describes how cosmic structures grow and how their gravity bends the light from distant objects. At least, the map upholds the model for the universe’s first 8 billion years. After that, strange things seem to happen.

“There’s a lot of excitement about this result. We made a high-resolution dark-matter map of a quarter of the sky,” says Mathew Madhavacheril, a University of Pennsylvania scientist who presented the vast map at a conference in Kyoto, Japan, in April. He is a member of the National Science Foundation-funded Atacama Cosmology Telescope collaboration, an international group of more than 160 members who developed the map. Madhavacheril is the lead author of the team’s new study, which is in peer review at the Astrophysical Journal. They’ll release the map when they complete that process.

The team has been peering through the heavens with a 39-foot-tall millimeter-wave telescope perched on the side of Cerro Toco, a stratovolcano in the Atacama Desert in northern Chile. That’s one of the driest places in the world, and it’s not the easiest spot for researchers to reach, but its unique location makes it easier to discern light from cosmic microwave background radiation, also known as the CMB.

About 380,000 years after the Big Bang, after the universe’s ultrafast expansion known as inflation, it cooled enough to release this embedded radiation. Those photons permeated the universe and are visible today at very long wavelengths. As a result, the CMB provides the earliest snapshot of the structure of the cosmos—a view of the baby universe. 

But the gravitational pull of galaxy clusters and dark matter—the metropolises of the universe—tweak, twist, and wiggle that relic radiation. This phenomenon is called gravitational lensing, and for anyone looking through a telescope, it creates a distorted picture of the cosmos. Yet it presents a boon for astrophysicists, because those distortions are actually clues about how the universe developed after its infant years.

Astrophysicists have been keen to test the standard cosmological model, which uses as its starting point slight temperature fluctuations in the CMB. The model describes the universe’s evolution from there, calculating how the universe has ballooned since its infancy and how clumps of dark matter and galaxies have become more massive over time. It assumes the consensus view on the behavior of dark energy, which permeates the cosmos and somehow accelerates the universe’s expansion, as well as the properties of dark matter, the mysteriously abundant and invisible particles that cluster together, forming the cosmic scaffolding in which galaxies assemble.