From a high mountain in the Atacama Desert in Chile, astronomers at the National Science Foundation's Atacama Cosmology Telescope (ACT) have re-examined the oldest light in the universe. [otherwise known as the cosmic microwave background]. His new observations plus a bit of cosmic geometry suggest that the universe is 13.77 billion years old, roughly 40 million years old.
The new estimate coincides with that provided by the standard model of the universe and measurements of the same light made by the Planck satellite. 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 arXiv.org.
In 2019, a research team that measured the movements of galaxies calculated that the universe is hundreds of millions of years younger than Planck's team predicted. That discrepancy suggested that a new model for the universe might be necessary and raised concerns that one of the sets of measurements might be incorrect. Aiola, a researcher at the Flatiron Institute Center for Computational Astrophysics in New York City, commented:
Now we have found an answer where Planck and ACT agree. It speaks to the fact that these difficult measurements are reliable.
The age of the universe also reveals how fast the cosmos is expanding, a number quantified by the Hubble constant. New measurements from the Atacama Cosmology Telescope suggest a Hubble constant of 67.6 kilometers per second per megaparsec. That means that an object 1 megaparsec (about 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 result almost exactly matches the previous estimate of 67.4 kilometers per second per megaparsec by the Planck satellite team, but it is slower than the 74 kilometers per second per megaparsec inferred from galaxy measurements.
The Atacama cosmology telescope. Using new measurements from this microwave cosmic background telescope, scientists have refined the age calculations of the universe. Image via Debra Kellner / Simons Foundation.
Steve Choi of Cornell University, first author of the other article posted on arXiv.org, said:
He had no particular preference for any specific value. It would be interesting in one way or another. We found an expansion rate that is in Planck's satellite equipment estimate. This gives us more confidence in measurements of the oldest light in the universe.
The close agreement between the ACT and Planck results and the standard cosmological model is bittersweet, Aiola said:
It's nice 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, ACT observes the afterglow of the Big Bang. This light, known as the cosmic microwave background, 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 cosmic microwave background 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 cosmic microwave background offer 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 cosmic microwave background should be spaced every billion light years for temperature and half for polarization. (For scale, our galaxy, the Milky Way, is approximately 200,000 light-years across.)
ACT measured fluctuations in the cosmic microwave background with unprecedented resolution, taking a closer look at the polarization of light. Suzanne Staggs, ACT principal investigator and professor of physics Henry deWolf Smyth at Princeton University, said:
The Planck satellite measured the same light, but by measuring its polarization more faithfully, the new ACT image reveals more of the older patterns we've seen.
As ACT continues to make observations, astronomers will have an even clearer picture of the cosmic microwave background and a more accurate idea of how long ago the cosmos began. The ACT team will also look for signs of physics in these observations that do not fit the standard cosmological model. Such bizarre physics could solve the disagreement between predictions of the age and rate of expansion of the universe derived from measurements of the cosmic microwave background and the movements of galaxies. Mark Devlin, ACT deputy director and professor of astronomy and astrophysics at Reese W. Flower at the University of Pennsylvania, said:
We continue to observe half of the sky from Chile with our telescope. As the precision of both techniques increases, the pressure to resolve the conflict will only increase.
Bottom line: Astronomers have again seen the oldest light in the universe, also known as the cosmic microwave background. Their new observations suggest that the universe is 13.77 billion years old, roughly 40 million years old.
Source: Atacama Cosmology Telescope: DR4 Maps and Cosmological Parameters
Source: The Atacama Cosmology Telescope: A Measurement of 98 and 150 GHz Cosmic Microwave Background Power Spectra
Through the Simons Foundation
