How old are we? Debate over the age of the universe just got a bit more complicated

Another telescope is helping us better understand the age of the universe and its future.

Using the Atacama Cosmology Telescope (ACT) in Chile, a group of astronomers say their observations support an earlier estimate as to the age of the universe: 13.77 billion years, give or take 40 million years. Their paper was released on the pre-print publishing service arXiv.org on Wednesday and submitted to the Journal of Cosmology and Astroparticle Physics.

The estimate supports observations taken by the European Space Agency's Planck space telescope in the early 2010s. 

Over the years, there have been other studies that have disputed that number. For example, in 2019, a study published in the journal Science suggested the universe was 11.2 billion years old.

"For a half dozen years, I'd say even more ... within the past three years, there has been one conference after another all over the world completely focused on this issue where one group comes up and they say, 'Oh, this is what we get,' and the other group comes up and says, 'This is what we get," said Richard Bond, co-author of the paper and director of the Canadian Institute for Theoretical Astrophysics at the University of Toronto.

"We call it the Hubble tension."

Why isn't there a clear-cut answer?

It all comes down to the methods used to calculate the expansion of the universe.

Stars vs. the Big Bang

In 1929, astronomer Edwin Hubble found that the universe is expanding. Ever since, scientists have attempted to calculate just how fast that's occurring. The rate of expansion is called the Hubble Constant.

But the challenge with determining the age of our universe — which in turn helps us better understand not only its past but also its future — is that there are a few methods used to make the calculations.

One involves looking at things that are relatively nearby, cosmologically speaking, such as supernovas (exploding stars) and a particular type of star that varies in brightness, called a Cepheid variable. 

Yet another involves looking far, far back, to a time shortly after the universe came to be — in particular at the cosmic microwave background radiation, or CMB, left over from the rapid birth of the universe, some 380,000 years following the Big Bang.

ACT also used this method, though from a ground-based telescope. But one advantage it had over Planck was the ability to better measure polarization of the CMB, which tells the scientists in what direction the light is moving. This allows it to be more precise.

New physics?

Just how close were their findings to Planck's?

The space telescope put the rate of the expansion of the universe at 67.5 kilometres per second per megaparsec (one megaparsec is 3.26 million light years). The new findings put that at 67.6 kilometres per second per megaparsec.

"What ACT has done is taken away the option that the CMB measurements were just a fluke of some kind," said Mark Halpern, a professor at the University of British Columbia's department of physics and astronomy in Vancouver and co-author of the paper.

This is an important step, the authors say, in trying to determine whether astrophysicists truly understand the universe.

"If we want the universe to be consistent, then what we need to understand is: [Is] it that we have [something] we haven't accounted for in any of the measurements? Or is there some kind of new physics?" said Renee Hlozek, co-author and a professor of astrophysics at the Dunlap Institute at U of T's department of astronomy and astrophysics.

"Because it could be that we're living in a universe that looks a certain age close to us, but then either the expansion rate changes over time or there's exotic physics that means it's a different age."

Wendy Freedman is an astronomy professor at the University of Chicago's department of astronomy and astrophysics who was not involved in the study. She also researches the expansion of the universe and has used a particular type of star — a red giant — as a method of calculating the expansion.

"I think it's a really superb piece of work," she said of the new paper. "It's a major study — and looking through the papers, they have paid a huge amount of attention to details and possible uncertainties and errors and run tests and checked through their data."

Freedman said while the data supports Planck, there's still something fundamental that we don't understand, something that the authors themselves acknowledge. 

But with the new ground-based findings, they hope that this will be another piece in the puzzle in an attempt to understand what's going on in our universe — in particular how it will ultimately cease to be.

"If we understand the age of the universe now, that can actually help us have a better view of how this is going to end," Hlozek said.