The Atacama Cosmology Telescope (ACT) has reached the end of its journey, but its nearly 20 years of discoveries are setting the stage for future cosmic exploration. The final data from ACT is a major leap in our understanding of the universe’s evolution, particularly the mystery surrounding the “Hubble constant,” which describes the rate of the universe’s expansion.
So, what’s the big deal? When scientists gauge the Hubble constant using nearby galaxies, they get one number. But when they look at the far-away universe, they come up with a different number. This difference is called “Hubble tension,” and it has puzzled astronomers.
ACT’s findings confirm that this tension is real. By showing that the Hubble constant differs based on distance from Earth, scientists can rule out many alternative theories about how the universe evolved. This means that despite seeming like a setback, ACT’s work narrows the field of possible explanations for our universe’s growth.
ACT made significant strides by measuring the Cosmic Microwave Background (CMB), a remnant light from just after the Big Bang. This light is crucial for understanding the early universe. While the European Space Agency’s Planck mission focused on the CMB’s temperature, ACT’s higher-resolution polarization maps fill in many gaps left behind, similar to putting on a clearer pair of glasses, as noted by Erminia Calabrese, a cosmologist from Cardiff University.
“For the first time, a new experiment has matched Planck’s observational capabilities,” said Thibaut Louis from the Université Paris-Saclay. Despite being Earth-based at an altitude of 16,400 feet in Chile, ACT’s results hold up against those from the space-based Planck mission.
Colin Hill, a cosmologist at Columbia University, emphasized that ACT’s data aligns with Planck’s findings, pointing to an even stronger Hubble tension. This strong agreement signals to researchers that something crucial is missing in the Lambda Cold Dark Matter (LCDM) model of cosmology.
By confirming that the Hubble constant behaves differently at various distances, ACT has helped guide future research. It’s no longer just a matter of figuring out if Hubble’s number is consistent across the cosmos. Researchers have tested competing models, and the results have narrowed the field significantly. Calabrese remarked that these new observations limit the theoretical possibilities for cosmologists.
The implications of ACT’s work extend beyond just numbers. It invites a deeper understanding of the universe’s timeline, including what happened in those early moments after the Big Bang. With each discovery, we inch closer to unraveling the cosmos’ greatest mysteries.
For those interested in diving deeper, the full research and companion papers are available on arXiv.
