Our universe became transparent for the first time around 380,000 years after the Big Bang and the first radiation was released. Now astronomers have published the most precise mapping of this cosmic background radiation so far. The recordings of the Atacama Cosmology Telescope (act) in Chile, which were created over the course of five years, represent a “baby picture” of our universe because they show how energy and matter were distributed in this early early days of the cosmos. The new mapping of the microwave background also provides information about crucial cosmological parameters such as the age of the universe, the shares of matter, dark matter and dark energy as well as the Hubble constant and the rate of cosmic expansion in this early era.
In the first hundreds of thousands of years after the Big Bang, our universe was extremely bright, hot and opaque. Because the first particles had not yet united. As a result, the radiation had no free track, it was distracted, absorbed and emitted by the invited particles of the primordial plasma. That only changed around 380,000 years after the big bang after the universe had cooled further and had already expanded. Because the first atoms arose, the electromagnetic radiation was able to decouple from the matter and spread freely – the universe was for the first time transparent. Remains of this first radiation have been preserved to this day, albeit strongly stretched and moved into the microwave area. This cosmic background radiation can be demonstrated everywhere and in all directions, but is very weak. Nevertheless, the subtle differences in this radiation carpet provide valuable information about the original state of the cosmos and the distribution of matter and energy at that early days – almost a baby picture of our universe.
Funfach higher resolution than the Planck mapping
Now astronomers have published the clearest picture of cosmic background radiation so far. For their mapping, they evaluated five years of the observations of the Atacama Cosmology Telescope (ACT) in Chile, a telescope on the 5,190 meter high Cerro Toco in Chile. The current mapping is based on data that the telescope used with optimized recipients in its last observation phase from 2017 to 2022. The pictures of the strange microwave background created from this show the universe when it was about 380,000 years old. “By looking back at the time when things were much easier, we can reconstruct the story of how our universe has developed into the rich and complex place where we are today,” explains the head of the act analysis, Jo Dunkley from Princeton University.
The new recordings complement previous maps of cosmic background radiation with the south polelescop or the European satellite Planck. This had created the most comprehensive and precise map of the microwave background in 2013. “Act has five -time resolution of Planck and greater sensitivity,” says Sigurd Naess from the University of Oslo. As a result, the new “baby picture” not only shows the distribution pattern of early radiation and thus indirectly also of matter, it also shows the polarization of the background radiation more direct and more precisely than before. This allows conclusions to be drawn about how the primordial gases were moving: “In the past, we could see where things were, and now we also see how they move,” says act director Suzanne Staggs from Princeton University. “As with tides that suggest the presence of the moon, the movement pursued by the polarization of light shows how strong the attraction of gravity was in different parts of the room.” There are other telescopes that showed the polarization of the microwave background as clearly, but none of them could cover such a large sky area as Act.
Age, mass shares and rate of expansion
The new mapping of the cosmic background radiation enables astronomers to check some essential properties of the cosmos. The first is the age of the universe, which can be seen in the size of certain wave patterns in the data. The new data confirms with an uncertainty of only 0.1 percent that the universe is 13.8 billion years old. “A younger universe should have expanded faster to reach its current size, and the pictures we measure would appear closer,” explains Mark Devlin from the University of Pennsylvania. “In this case, the apparent extent of the waves in the images would be greater, just as a ruler near the face appears larger than one that is kept an arm length away.” The measurement data also allow the masses and parts of different forms of material to break down more precisely in the cosmos. “According to the measurements, the observable universe extends almost 50 billion light years in all directions from us and contains around 1,900 Zetta sonnen masses-almost two trillion trillion sun mass,” reports Erminia Calabrese from Cardiff University. The mass of normal matter only takes around 100 Zetta sonnen masses, another 500 Zetta sonnen masses are eliminated on the dark matter. The rest of around 1,300 Zetta sonnen masses largely corresponds to the dark energy, a still puzzling force that drives the universe apart.
The act mapping also brings new findings to cosmic expansion, the Hubble constant, closely linked to it and to the discrepancies in the measurements. Because measurement data that are derived from the strange background radiation, including the Planck mapping, consistently showed a Hubble constant of 67 to 68 kilometers per second per megaparsec. Astronomical studies based on distance measurements of supernovae, variable stars, red giants and other cosmic objects, on the other hand, provide almost all a significantly higher value for the Hubble constant of up to 73 to 74 km/s/MPC. The new act data does not clarify this discrepancy, but confirm: “It was a bit surprising for us that we did not even partially find evidence to support the higher value,” says Staggs. Instead, the Hubble constant derived from the new mapping agrees with the values based on Planck and other values based on the background radiation. This speaks the new mapping against models that postulate a higher expansion rate or the existence of still undiscovered effects in the early cosmos. “The acts of acts show no evidence of such new signals.
Source: Act Collaboration, Global Physics Summit 2025; Journal of Cosmology and Astroparticle Submitted