The Atacama cosmology telescope measures the oldest light in the universe, known as the cosmic microwave background. Using those measurements, scientists can calculate the age of the universe. Credit: Image courtesy of Debra Kellner.
The findings from the Atacama Cosmology Telescope suggest that the universe is 13.8 billion years old.
From a mountain in the Atacama desert in Chile, astronomers from the Atacama Cosmology Telescope of the National Science Foundation have again examined the oldest light in the universe. Their new observations, plus a bit of cosmic geometry, suggest that the universe is 13.77 billion years old, plus or minus 40 million years old.
The new estimate coincides with that provided by the standard model of the universe and measurements of the same light by the Planck satellite, a space observatory that was run between 2009 and 2013.
This adds a new twist to an ongoing debate in the astrophysics community, said Simone Aiola, first author of one of two new articles on the findings published on July 15 at arXiv.org. The problem is that research teams that measure the movements of galaxies have calculated that the universe is hundreds of millions of years younger than Planck’s team predicted. That discrepancy suggested that a new model might be necessary for the universe, and raised concerns that one of the sets of measurements might be incorrect.
“We have now found an answer that Planck and the Atacama Cosmology Telescope agree on,” said Aiola, a researcher at the Flatiron Institute Center for Computational Astrophysics in New York City. “It speaks to the fact that these difficult measurements are reliable.”
A portion of a new image 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 across. Light, emitted only 380,000 years after the Big Bang, varies in polarization (represented here by more red or blue colors). Astrophysicists used the space 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 how fast the cosmos is expanding, a number called the Hubble constant. Atacama measurements suggest a Hubble constant of 67.6 kilometers per second per megaparsec. This result coincides almost exactly with the previous estimate of 67.4 made by Planck’s satellite team, but it is slower than the 74 inferred from the galaxy measurements.
“Taking this independent measurement is really exciting because there is a mystery in the field, and this helps us sharpen our understanding of that mystery,” said Jeff McMahon, associate professor of astronomy and astrophysics at the University of Chicago who directed the design of the detectors and other new technologies used to perform this measurement. This confirms the ongoing discrepancy. And we still have a lot more data to analyze, so this is just the beginning. “
Assoc. Prof. Jeff McMahon
The close agreement between the Atacama Cosmology Telescope and Planck’s results and the standard cosmological model is bittersweet, Aiola said: “It is good to know that our model is robust right now, but it would have been nice to see a hint of something new.” . Still, disagreement with the 2019 study on galaxy motions maintains the possibility that unknown physics may be at stake, he said.
Like the Planck satellite and its terrestrial cousin, the South Pole Telescope, the Atacama Telescope looks out into the glare of the sun. big Bang. This light, known as the cosmic microwave 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 then, the cosmos was opaque to light.
If scientists can estimate how far light from the CMB traveled to reach Earth, they can calculate the age of the universe. However, that is easier said than done. Judging cosmic distances from Earth is difficult. Instead, scientists measure the angle in the sky between two distant objects, with Earth and the two objects forming a cosmic triangle. If scientists also know the physical separation between those objects, they can use high school geometry to estimate the distance of objects from Earth.
Subtle variations in the brightness of the CMB provide anchor points to form the other two vertices of the triangle. Those variations in temperature and polarization resulted from quantum fluctuations in the early universe that were amplified by the expanding universe in regions of varying density. (The denser patches would form galaxy clusters.) Scientists have a strong enough understanding of the early years of the universe to know that these variations in the CMB should generally be spaced every billion light-years for temperature and half for polarization. (For scale, our Milky Way the galaxy is approximately 200,000 light-years across.)
The Atacama Cosmology Telescope measured the 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 more faithfully, the new Atacama image reveals more of the oldest patterns we’ve seen,” said Suzanne Staggs, principal investigator for the telescope and Professor Henry deWolf Smyth. Physics in Princeton university.
This measurement was made possible by new technology designed and built by the McMahon team. “Basically, we figured out how to make detectors measure two colors and pack as many in each chamber as possible,” said McMahon. “Then we develop new lenses from metamaterials.” (Metamaterials they are a type of material designed to produce properties that do not exist naturally.)
From conception to deployment to the telescope and analysis, the process has spanned nearly 10 years, McMahon said. “It has been absolutely fantastic to work with this incredible team to develop this project from conceptual sketches to producing results at the forefront of cosmology.”
Professor Wendy Freedman explains a new method for measuring the expansion of the universe.
Sara Simon, now at the Fermi National Accelerator Laboratory, made significant contributions to the detector design; UChicago graduate student Joey Golec developed methods for fabricating metamaterial optics; and UChicago graduate student Maya Mallaby-Kay is now working to make the data sets public.
As the Atacama Cosmology Telescope continues to make observations, astronomers will have an even clearer picture of the CMB and a more accurate idea of how long ago the cosmos began. The team will also search those observations for signs of physics that do not fit the standard cosmological model. Such strange physics could solve the disagreement between the predictions of the age and the rate of expansion of the universe derived from the measurements of the CMB and the movements of the galaxies.
“We continue to observe half the sky from Chile with our telescope,” said Mark Devlin, deputy director of the telescope and professor of astronomy and astrophysics Reese W. Flower at the University of Pennsylvania. “As the precision of both techniques increases, the pressure to resolve the conflict will only increase.”
“I had no particular preference for any 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 found an expansion rate that is in Planck’s satellite equipment estimate. This gives us more confidence in the measurements of the oldest light in the universe. “
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References
“The Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters” by Simone Aiola, et al., July 14, 2020, Astrophysics> Cosmology and Non-Galactic Astrophysics.
arXiv: 2007.07288
“The Atacama Cosmology Telescope: A Measurement of 98 and 150 GHz Cosmic Microwave Background Power Spectra” by Steve K. Choi, et al., July 14, 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.
