30 Models of the Universe Proved Wrong by Final Data from Groundbreaking Cosmology Telescope
After decades of research, a telescope perched atop the mountain plateaus of northern Chile bid farewell in 2022, leaving behind a treasure trove of data. This final data release unveils the telescope's legacy: a field in tension.
The Atacama Cosmology Telescope (ACT) first saw the light in October 2007, but not the light of stars or distant galaxies. Instead, ACT was designed to detect microwaves, particularly the ancient microwaves that linger from the universe's earliest moments. This "fossil" light, known as the cosmic microwave background (CMB), emerged when the universe was just 380,000 years old.
ACT's specialty lay in studying the CMB's polarization, which offers valuable insights into the early universe's state. Altering the amount of dark matter, its distribution, or the number of neutrinos, among other cosmic properties, directly influences the appearance of the CMB's light.
Final ACT Data Release
In November, the ACT team unveiled their sixth and final public dataset in three articles published in the Journal of Cosmology and Astroparticle Physics. While cosmologists will continue to extract insights from the data for years, the core team also presented their final suite of analyses and studies before bidding farewell.
Their findings aligned with previous surveys like Planck, indicating a peculiarity in the universe's expansion. Measurements of the present-day expansion rate, known as the Hubble rate or Hubble constant, taken with early-universe probes like Planck and ACT, reveal a significantly slower rate than estimates based on nearby measurements, such as supernova dimming.
This discrepancy, dubbed the Hubble tension, stands as one of the most enigmatic puzzles in modern cosmology. However, ACT not only confirmed the tension's existence but also shattered several well-regarded theories.
ACT Challenges 30 Cosmic Models
Cosmologists have proposed numerous theoretical explanations for the Hubble tension, many of which are "extended" cosmological models. These models enhance the standard cosmological picture by introducing additional ingredients or forces to the universe.
However, these ingredients and forces didn't materialize overnight; they were present when the CMB was first emitted. ACT's exceptional view of the CMB enabled the team to test these models, and a staggering 30 of them failed to withstand scrutiny.
Despite these setbacks, science thrives on learning from failures. ACT's negative results provide valuable insights to cosmologists, guiding them closer to the truth. In essence, understanding the correct answer becomes possible only after eliminating all the wrong ones.
