30 models of the universe proved wrong by final data from groundbreaking cosmology telescope
After a decades-long mission to understand the nature of the universe, a telescope perched on the mountainous plateaus of northern Chile bid farewell in 2022. Today, its final data reveals the telescope’s legacy: a field in tension.
In October 2007, the Atacama Cosmological Telescope (ACT) saw its first light. But it wasn’t the light of a star, or even a distant galaxy. Instead, ACT was designed to search for microwaves, particularly the type of microwaves left over from some of the earliest epochs of the universe. This “fossil” light, known as cosmic microwave background (CMB), was emitted when the universe was only 380,000 years old.
ACT has been particularly effective at studying the polarization of the CMB, which tells us a lot about the state of the early universe. If you change the amount of dark matter in the cosmos, how it is distributed, how much neutrinos there is, or any other dozen properties of the cosmos, you change the appearance of CMB light.
final ACT
In November, the ACT team released its sixth and final public dataset like three items published in the Journal of Cosmology and Astroparticle Physics. While cosmologists will continue to mine the data for many years to come, the core team has also provided its final round of analyzes and studies before saying goodbye for good.
Their conclusions match what investigations like Planck’s had already identified: something funny is happening with the expansion of the universe. Measurements of the current expansion rate, known as the Hubble rate or Hubble constant, taken with early universe probes like Planck and ACT, reveal a number that is somewhat slower than estimates based on nearby measurements, such as supernova attenuation.
This gap is now known as Hubble voltageand it is perhaps the greatest unsolved mystery of modern cosmology. But ACT not only confirmed the existence of tension; it also destroyed some really good ideas.
ACT axis 30 cosmic models
Cosmologists have endeavored to concoct numerous theoretical explanations for the Hubble tension. Many of these are called “extended” cosmological models, because they take the standard cosmological picture and add a few additional ingredients or forces to the universe.
But these ingredients and these forces do not only exist today; they must also have existed when the CMB was first issued. So, the exquisite view of the CMB offered by ACT allowed the team to test many of these models – around 30 in fact –.
All failed.
But in science, you only lose if you don’t learn anything, and the negative results of the ACT help cosmologists in their research. In other words, you can only know the correct answer once you have crossed out all the wrong answers.
