Astronomers using NSFs Atacama Cosmology Telescope (ACT) have taken a fresh look at the Cosmic Microwave Background (CMB), the oldest light in our Universe. Their new observations suggest that the Universe is 13.77 billion years old, give or take 40 million years. This estimate matches the one provided by the Standard Model of the Universe and measurements of the same light made by ESAs Planck satellite.

This new picture of the Cosmic Microwave Background, the oldest light in the Universe, was taken by the Atacama Cosmology Telescope. This covers a swath of the sky 50 times as wide as the Moon, representing a region of space 20 billion light-years across. The light, emitted just 380,000 years after the Big Bang, varies in polarization (represented here by redder or bluer colors). Image credit: ACT Collaboration.

The Standard Model, the one behind Jim Peebles Nobel Prize, comes through with flying colors, said Professor Lyman Page, an astrophysicist at Princeton University who was the ACTs principal investigator from 2004 to 2014.

This adds a fresh twist to an ongoing debate in the astrophysics community, said Dr. Simone Aiola, a researcher at Flatiron Institute and Princeton University.

In 2019, astronomers measuring the movements of galaxies calculated that the Universe is hundreds of millions of years younger than the Planck team predicted. That discrepancy suggested that a new model for the Universe might be needed and sparked concerns that one of the sets of measurements might be incorrect.

Now weve come up with an answer where Planck and ACT agree. It speaks to the fact that these difficult measurements are reliable, Dr. Aiola said.

The age of the Universe also reveals how fast the cosmos is expanding, a number quantified by the Hubble constant.

The ACT measurements suggest a Hubble constant of 67.6 km per second per megaparsec (km/s/Mpc).

This result agrees almost exactly with the previous estimate of 67.4 km/s/Mpc by the Planck satellite team, but its slower than the 74 km/s/Mpc inferred from the measurements of galaxies.

We dont know if the tension is due to systematic effects or to something new that we have not figured out. Cosmology is as exciting as ever, Professor Page said.

I didnt have a particular preference for any specific value it was going to be interesting one way or another, said Dr. Steve Choi, a scientist at Cornell University and Princeton University.

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 Universes oldest light.

The close agreement between the ACT and Planck results and the Standard Cosmological Model is bittersweet, Dr. Aiola said.

Its good to know that our model right now is robust, but it would have been nice to see a hint of something new.

Still, the disagreement with the 2019 study of the motions of galaxies maintains the possibility that unknown physics may be at play.

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 weve ever seen, said ACT principal investigator Professor Suzanne Staggs, of Princeton University.

The findings were published in a series of papers on the arXiv.org preprint server.

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Simone Aiola et al. 2020. The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters. arXiv: 2007.07288

Steve K. Choi et al. 2020. The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectra at 98 and 150 GHz. arXiv: 2007.07289

Sigurd Naess et al. 2020. The Atacama Cosmology Telescope: arcminute-resolution maps of 18,000 square degrees of the microwave sky from ACT 2008-2018 data combined with Planck. arXiv: 2007.07290

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