A series of new papers is set to reinvigorate a major debate in cosmology. You see, for a few years now, the field has been dealing with a severe crisis. Different approaches to measuring the expansion rate of the Universe ended up with different values. This has profound consequences on our understanding of the Universe in general. It can also be understood in a more straightforward way: the age of the cosmos is estimated from the measured expansion rate.
So on one hand, we have the measurements from Cosmic Microwave Background (CMB) from the European Space Agency’s Planck mission. This puts the age of the cosmos at 13.78 billion years old. But measurements from the motion of galaxies suggest that the universe is expanding faster, making it hundreds of millions of years younger.
The new work, published in the Journal of Cosmology and Astroparticle Physics, reports on the observations from Atacama Cosmology Telescope (ACT). This instrument also studied the CMB, the afterglow of the Big Bang. The age measurement they made is 13.77 billion years old – plus or minus 40 million years – well in agreement with Planck.
"Now we've come up with an answer where Planck and ACT agree," Simone Aiola, a researcher at the Flatiron Institute's Center for Computational Astrophysics and first author of one of the papers, said in a statement. "It speaks to the fact that these difficult measurements are reliable."
While it was considered very unlikely, there has been discussion that maybe that the tension between the two ways to measure the expansion rate was due to an error somewhere in the Planck observations or data. The result, independently obtained, shows that this is not the case. There must be something new to consider in our cosmology.
“The growing tension between these distant versus local measurements of the Hubble constant suggests that we may be on the verge of a new discovery in cosmology that could change our understanding of how the Universe works. It also highlights the importance of improving our measurements of the CMB with ACT as well as the future Simons Observatory and CCAT-prime projects that we are now building,” said co-author Michael Niemack, associate professor of physics and astronomy.
New measurements of the expansion rate of the universe are expected using upcoming observatories. Researchers have even suggested the use of gravitational waves to probe the universe in a completely different way. While the tension is certainly not ideal, it is also an exciting time for cosmology. A more accurate understanding of the universe could be just around the corner.