High in Chile’s Atacama Desert, miles from the dull glow of light pollution, the secluded Atacama Cosmology Telescope is in an excellent position to search the sky for answers. The most recent question on his mind? The age of the universe, a cosmic dilemma that can be answered in different ways, depending on how you measure the accelerating expansion of the universe.
Recently a paper published in the Journal of Cosmology and Astroparticle Physics measured the speed of that expansion, called the Hubble constant, using the telescope of the National Science Foundation in Chile.
The team found that the Hubble constant is 42 miles per second per megaparsec – meaning that for every megaparsec, or 3.26 million light years, the speed of the universe’s expansion is increasing at 42 miles per second. The number the international team of astronomers and physicists found, after 730 days of observation from 2013 to 2016, was almost the same as previously reported by the European Space Agency’s Planck satellite in 2013.
“Now we have come up with an answer where Planck and [Atacama Cosmology Telescope] Agree, ”said Simone Aiola, a researcher at the Flatiron Institute’s Center for Computational Astrophysics and a co-author of the paper. in a press release. “It shows that these difficult measurements are reliable.”
There is a pretty big reason why it was worth recalculating the constant: there are a few ways to measure the speed of the universe’s expansion, from which the age of the universe can be deduced. You can measure the speed based on constellations close to us, such as pulsating Cepheid variables. You can also measure the expansion by looking at the polarized light from the cosmic microwave background of the universe, the most distant detectable radiation from the Big Bang, which the Atacama team did here. This dim light has variation in its polarization, allowing scientists to measure how far the light has traveled and how long that journey took. That’s why it’s important to understand the speed of the universe’s expansion: it changes how far light went, and thus the age of everything.
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Here’s the problem: those two ways of calculating Hubble’s constant have yielded quite different speeds:a study from 2019 came in at nearly 46 miles per second per megaparsec, while another from the same year found a number that divided the difference between the other two. While the differences may sound minor, the different estimates represent a range of hundreds of millions of years to determine how old our universe is. (The higher the constant, the younger the universe).
The Atacama team’s findings place the age of the universe at approximately 13.77 billion years. In comparison, our solar system is about 4.57 billion years old, and homo sapiens originated somewhere around 300,000 years ago.
The different numbers so far don’t mean either side is necessarily wrong (although the team behind the new paper, which works with better resolution images of the cosmic microwave background than their predecessors at Planck, confirmed that the earlier team’s maths were solid. used to be) . What it all definitely means is that we are missing something when it comes to how the expansion of the universe works.
The difference between local and distant measurements of the Hubble constant could mean that “there is a problem with one of the types of measurements that we are not interpreting correctly, and therefore there is some kind of systematic problem with one measurement or the other”, said Michael Niemack, an astrophysicist at Cornell University and co-author of the recent paper. “The more exciting possibility is that something is missing from our cosmological model.”
The best is perhaps yet to come for the Atacama telescope, which first received light in 2007 and has the advantage of being on the ground, making it easier to handle than a space telescope.
“We have yet to extract all the information from the data we have already collected with the Atacama Cosmology Telescope,” Steve Choi, an astrophysicist at Cornell University and lead author of the paper, said in an email. “I am hopeful that we will learn even more exciting physics about our universe with upcoming experiments in the Atacama, such as CCAT-prime and Simons Observatory,” referring to two emerging high-altitude observatories in the desert. The CCAT-prime telescope was renamed the Fred Young Submillimeter Telescope in September and it will look at a whole host of cosmological features, while the Simons Observatory will focus its observational capabilities on the cosmic microwave background.
Perhaps a party evaluating the age of the universe is overlooking something in their mathematics – with the many known unknowns of space science and the things completely unknown, it is possible. But according to Niemack, there might as well be something else in the mix that would explain the different numbers.
“This could be an indication that we are just about to discover something new and exciting that we didn’t know about how our universe works,” he said.