From 2007 to 2022, the Atacama Cosmology Telescope (ACT) focused on the millimeter and microwave universe. Its primary mission was to study the cosmic microwave background (CMB)—the afterglow of the Big Bang. This ancient light helps us understand the universe’s early moments.
Recently, the ACT team released final data, highlighting a major issue with our understanding of the universe. At the center of this debate is the Hubble Constant, which measures how quickly the universe is expanding. Scientists can measure this in a couple of ways, especially by looking at nearby galaxies and the CMB. However, these methods are giving conflicting results.
This conflict is known as the Hubble Tension. Ideally, both methods should yield similar values, but they don’t. The CMB data comes from ESA’s Planck satellite, which ACT has now confirmed. According to Colin Hill, a cosmologist at Columbia University, “Our new results demonstrate that the Hubble constant inferred from the ACT CMB data agrees with that from Planck… making the Hubble discrepancy even more robust.”
To address this tension, some astronomers propose new theoretical models. However, the latest ACT data suggests that many of these theoretical models lack support. Erminia Calabrese from Cardiff University noted, “We assessed them completely independently… and the result is clear: the new observations have virtually removed the scope for this kind of exercise.”
One significant aspect of ACT’s work is its focus on polarization—the way light waves oscillate. Understanding the polarization of the CMB offers new insights into the universe’s infancy, which regular mapping can’t provide. ACT has improved these polarization maps significantly because its larger size (six meters compared to Planck’s 1.5 meters) increases image sharpness and sensitivity.
This doesn’t make Planck’s data irrelevant; both sources complement each other. These findings deepen our knowledge of the universe’s early days, as the CMB was emitted just 380,000 years after the Big Bang.
Interestingly, this debate over the Hubble Constant has garnered attention on social media, with users sharing theories and discussing its implications for understanding our universe. The excitement around these discoveries continues, as scientists explore the lingering questions about our cosmic surroundings.
For further insights into these exciting findings, you can check the full papers published in the Journal of Cosmology and Astroparticle Physics here, here, and here.
