Up in the Atacama Desert in Chile, a few kilometers away from the dull glow of light pollution, the retired Atacama Cosmological Telescope is in a prime position to search for answers in the sky. The most recent question in her mind? The age of the universe, a cosmic dilemma that can be answered in different ways, depending on how you measure the accelerated expansion of the universe.
A recent work published in the Journal of Cosmology and Astroparticle Physics measured the rate of this expansion, called the Hubble constant, using the National Science Foundation’s telescope in Chile.
The team found that the Hubble constant is 42 miles per second per megaparsec – that is, for every megaparsec, or 3.26 million light-years, the speed of the universe’s expansion increases by 42 miles per second. The number found by the international team of astronomers and physicists, after 730 days of observations between 2013 and 2016, was almost the same rate as previously reported by the European Space Agency’s Planck satellite in 2013.
“It simply came to our notice then [Atacama Cosmology Telescope] I agree “, said Simone Aiola, researcher at the Center for Computational Astrophysics of the Flatiron Institute and co-author of the paper, in a press release. “There is talk that these difficult measurements are reliable.”
There is a fairly large reason why it was worth recalculating the constant: there are several ways to measure the rate of expansion of the universe, from which the age of the universe can be deduced. You can measure the rate based on stellar things near us, such as pulsating Cepheid stars. You can also measure the expansion by looking at the polarized light of the universe’s microwave cosmic background, the farthest detectable radiation in the Big Bang, which the Atacama team did here. This fuzzy light has variations in its polarization, allowing scientists to measure how far light has traveled and how long the journey has taken. Therefore, understanding the rate of expansion of the universe matters: it changes how far light has gone and thus everyone’s age.
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Here’s the friction: These two ways to calculate Hubble’s constant came at quite different rates –a 2019 study came at almost 46 miles per second per megaparsec, while another from the same year found a number that divided the difference between the other two. Although the differences may seem small, various estimates mean 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 discoveries place the age of the universe at around 13.77 billion years. For comparison, our solar system is about 4.57 billion years old and homo sapiens appeared somewhere about 300,000 years ago.
The different numbers so far do not mean that any party is necessarily wrong (although the team behind the new paper, working with better-resolution images of the microwave cosmic background than their Planck predecessors, said the previous team’s math was solid). What it certainly means is that we are missing something when it comes to how the expansion of the universe works.
The disparity between local and remote measurements of the Hubble constant could mean that “there is a problem with one of the types of measurements that we do not interpret correctly and therefore there is a kind of systematic problem with one measure or another,” said Michael. Niemack, astrophysicist at Cornell University and co-author of the recent paper. “The more interesting possibility is that something is missing from our cosmological model.”
It may still be the best for the Atacama Telescope, which had its first light in 2007 and has the advantage of being on the ground, making it easier to manage than a space telescope.
“We have not yet extracted all the information from the data we have already collected with the Atacama Cosmology Telescope,” said Steve Choi, an astrophysicist at Cornell University and the lead author of the paper, in an e-mail. “I hope we will learn even more interesting physics about our universe with future Atacama experiments, such as CCAT-prime and Simons Observatory,” referring to two future high-altitude observatories in the desert. The CCAT-prime telescope was renamed the Fred Young Submillimeter Telescope in September and will analyze a number of cosmological features, while the Simons Observatory will focus its observation capabilities on the cosmic microwave background.
Perhaps a part that assesses the age of the universe overlooks something of their mathematics – with the many known unknowns of space science and things that are completely unknown, it is possible. But, according to Niemack, just as easily there could be something else in the mix that would explain the different numbers.
“This could be an indication that we are about to discover something new and interesting that we did not know until now about how our universe works,” he said.