Last year, astronomers announced a bit of a curveball age for the universe, a few hundred million years younger than previous predictions, which fueled an ongoing debate within the community. However, new observations of the oldest light in the universe taken by the Atacama Cosmology Telescope (ACT), Chile, have brought the discourse back to the more familiar figure of around 13.8 billion years, proposed by ESA’s Planck Satellite team in 2013 and in line with the standard cosmological model.

“I didn’t have a particular preference for any specific value – it was going to be interesting one way or another,” postdoctoral fellow Steve Choi of Cornell University, said in a statement. “We find an expansion rate that is right on the estimate by the Planck satellite team. This gives us more confidence in measurements of the universe’s oldest light.”

To calculate the age of the universe, astronomers peered at the cosmic microwave background (CMB), the radiation left over from the Big Bang, which existed when the universe was only 380,000 years old. By estimating the distance this first light had traveled to reach Earth, an age could be determined – a task easier said than done. The researchers had to use temperature and polarization variations within the CMB, caused by quantum fluctuations in the early universe, to aid their cosmic geometry.

Luckily, the new improved image of the universe’s first light helped them on the way. “The Planck satellite measured the same light, but by measuring its polarization in higher fidelity, the new picture from ACT reveals more of the oldest patterns we’ve ever seen,” Suzanne Staggs, ACT’s principal investigator, said.

Staggs and colleagues’ exact universe age was 13.77 billion years old, give or take 40 million years, with a corresponding universe expansion rate (Hubble constant) of 67.6 kilometers (42 miles) per megaparsec (i.e. an object 1 megaparsec, or 3.26 million light-years, from Earth is moving away from us at 67.6 kilometers per second due to the expansion of the universe). This is in close agreement with the Planck satellite team, but a lot slower than the calculated figure made by astronomers last year.

Their method differed, though, to that of the Planck and ACT teams. Instead of looking at the CMB, they measured the movement of galaxies, and calculated a Hubble constant of 74 kilometers per second per megaparsec, correlating to a much younger age of the universe. At the time it was suggested that new physics may have caused this discrepancy, which authors of the two new studies, available on preprint server arXiv, do not rule out.

“The disagreement with the 2019 study of the motions of galaxies maintains the possibility that unknown physics may be at play,” cosmologist Simone Aiola said.

For now, the ACT will continue to provide illuminating observations of the age of the cosmos and even perhaps some strange physics. “We’re continuing to observe half the sky from Chile with our telescope,” Mark Devlin, ACT’s deputy director said. “As the precision of both techniques increases, the pressure to resolve the conflict will only grow.”