New turning point to debate the age of the universe from a new vision of the oldest light in the universe


The Atacama Cosmology Telescope measures the oldest light in the universe, known as the cosmic microwave background. Using these measurements, scientists can calculate the age of the universe. Credit: Image courtesy of Debra Kellner

Findings from the Atacama Cosmology Telescope suggest that the universe is 13.8 billion years old.

From a high mountain in Chile’s Atacama Desert, astronomers at the National Science Foundation’s Atacama Cosmology Telescope have taken a fresh look at the oldest light in the universe. Their new observations, plus a bit of cosmic geometry, suggest the universe is 13.77 billion years old, roughly 40 million years old.

The new estimate matches that provided by the Standard Model of the Universe and measurements of the same light made by the Planck satellite, a space observatory that operated from 2009 to 2013.

This adds a new twist to an ongoing debate in the astrophysical community, said Simone Aiola, first author of one of two new results articles published on July 15 on The problem is that research teams measuring the movements of galaxies have calculated that the universe is hundreds of millions of years younger than what Planck’s team predicted. This discrepancy suggested that a new model for the universe might be needed, and raised concerns that one of the measurement sets might be incorrect.

“We have now found an answer where Planck and Atacama’s cosmology telescope agree,” said Aiola, researcher at the Center for Computational Astrophysics at the Flatiron Institute in New York. “It shows that these difficult measures are reliable.”

Part of a new photo of the oldest light in the universe taken by the Atacama Cosmology Telescope. This part covers a section of the sky 50 times the width of the moon, representing a region of space 20 billion light years away. Light, emitted only 380,000 years after the Big Bang, varies in polarization (represented here by redder or bluer colors). Astrophysicists used the spacing between these variations to calculate a new estimate of the age of the universe. Credit: Image courtesy of ACT Collaboration

The age of the universe also reveals the rate at which the cosmos is growing, a number called the Hubble constant. Atacama’s measurements suggest a Hubble constant of 67.6 kilometers per second per megaparsec. This result agrees almost exactly with the previous estimate of 67.4 by the Planck satellite team, but it is slower than the 74 deduced from galaxy measurements.

“Taking this independent measurement is really exciting because there is a mystery in the field, and it helps us to refine our understanding of this mystery,” said Jeff McMahon, associate professor of astronomy and astrophysics at University of Chicago who led the design of the detectors and other new technologies used to perform this measurement. “This confirms the current divergence. And we still have a lot more data to analyze, so this is just the start. “

Jeff McMahon

Assoc. Prof. Jeff McMahon

The close agreement between the results of the Atacama and Planck cosmology telescope and the standard cosmological model is bittersweet, Aiola said: “It is good to know that our model at the moment is robust, but it would have been nice to see a hint of something new. Still, the disagreement with the 2019 study of the movements of galaxies maintains the possibility that unknown physics may be at play, he said.

Like the Planck satellite and its terrestrial cousin, the South Pole telescope, the Atacama telescope looks at the remanence of the Big Bang. This light, known as the microwave cosmic background, or CMB, marks a time 380,000 years after the birth of the universe, when protons and electrons joined together to form the first atoms. Before that time, the cosmos was opaque to light.

If scientists can estimate the distance traveled by light from the CMB to reach Earth, they can calculate the age of the universe. It’s easier said than done. It is difficult to judge cosmic distances from Earth. Instead, scientists measure the angle in the sky between two distant objects, the Earth and the two objects forming a cosmic triangle. If scientists also know the physical separation between these objects, they can use high school geometry to estimate the distance of objects from Earth.

Subtle variations in the glow of the CMB provide anchors to form the other two vertices of the triangle. These variations in temperature and polarization were the result of quantum fluctuations in the early universe which were amplified by the expanding universe in regions of varying density. (The densest patches would continue to form clusters of galaxies.) Scientists have a fairly strong understanding of the early years of the universe to know that these variations in CMB should generally be spaced every billion light years for temperature and half for polarization. (For the scale, our Milky Way galaxy is approximately 200,000 light years in diameter.)

The Atacama Cosmology Telescope measured CMB fluctuations with unprecedented resolution and sky coverage, taking a closer look at the polarization of light. “The Planck satellite measured the same light, but by measuring its polarization with greater fidelity, Atacama’s new image reveals more of the oldest models we’ve ever seen,” said Suzanne Staggs, principal investigator of the telescope and Professor Henry deWolf Smyth of Physics at Princeton University.

This measure was made possible by new technology designed and built by the McMahon team. “Basically, we figured out how to make the detectors measure two colors and package as many as possible in each camera,” said McMahon. “Then we developed new lenses from metamaterials.” ((Metamaterials are a type of material designed to produce properties that do not exist naturally.)

From conception to deployment on the telescope to analysis, the process spanned almost 10 years, McMahon said. “Working with this amazing team to develop this project, from conceptual sketches to producing cutting edge results in cosmology, has been absolutely fantastic.”

Professor Wendy Freedman explains a new method for measuring the expansion of the universe.

Sara Simon, now at Fermi’s National Accelerator Laboratory, made a significant contribution to the design of the detectors; Joey Golec, graduate student from UChicago, developed methods to fabricate metamaterial optics; and UChicago graduate student Maya Mallaby-Kay is now working on making the datasets public.

As the Atacama Cosmological Telescope continues to make observations, astronomers will have an even clearer picture of the CMB and a more accurate idea of ​​when the cosmos began. The team will also examine these observations for signs of physics that do not fit the standard cosmological model. Such strange physics could resolve the disagreement between predictions of the age and rate of expansion of the universe resulting from CMB measurements and the movements of galaxies.

“We continue to observe half the sky from Chile with our telescope,” said Mark Devlin, assistant director of the telescope and Reese W. Flower professor of astronomy and astrophysics at the University of Pennsylvania. “As the accuracy of both techniques increases, the pressure to resolve the conflict will only increase.”

“I didn’t have a particular preference for a specific value – it was going to be interesting in one way or another,” said Steve Choi of Cornell University, first author of the other article published on arXiv. org. “We find a rate of expansion that exactly matches the estimate of the Planck satellite team. This gives us more confidence in the measurements of the oldest light in the universe.



«The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters» par Simone Aiola, et al., 14 juillet 2020, Astrophysics> Cosmology and non-galactic astrophysics.
arXiv: 2007.07288

«The Atacama Cosmology Telescope: A Measurement of the Cosmic Microwave Background Power Spectra at 98 and 150 GHz» par Steve K. Choi, et al., 14 juillet 2020, Astrophysics> Cosmology and non-galactic astrophysics.
arXiv: 2007.07289

The ACT team is an international collaboration, with scientists from 41 institutions in seven countries. The telescope is supported by the National Science Foundation and contributions from member institutions.


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