The Atacama Large Millimeter Array, located in the middle of the desert in northern Chile, has concluded 15 years of observations and released its final research data. Scientists succeeded in capturing the 'infant universe' shortly after the birth of the cosmos 13.8 billion years ago, before the formation of stars and galaxies in clouds of hydrogen and helium gas.
An international research team led by Professor Joe Dunkley of Princeton University announced on the 18th (local time) that they had observed cosmic microwave background radiation (CMB) emitted about 380,000 years after the universe was born in the Big Bang.
In the early universe after the Big Bang, matter was filled with a plasma state where electrons and nuclei were separated at extremely high temperatures, creating an opaque space where light could not travel freely. As the universe cooled, hydrogen and helium atoms formed, allowing light to traverse the cosmos unimpeded. The light emitted at this point is the CMB, which still fills the entire universe today.
The most significant achievement of this study is the high-resolution data containing the subtle features of the CMB and the specific directionality of light known as "polarization." Polarization refers to the phenomenon where an electric field vibrates in a specific direction when light hits a surface. This polarization data has a resolution five times higher than that provided by the previous Planck satellite.
The researchers noted that based on this data, they could glimpse the process by which hydrogen and helium gas in the early universe clumped together under gravity to form the first stars and galaxies. They measured changes in density and the velocity of gas in the early universe through data analysis.
Professor Dunkley explained, "In this study, we meticulously analyzed the fine structure and polarization patterns of the CMB, allowing us to verify potential anomalous physical phenomena that might have occurred in the early universe and piece together how the cosmos evolved into its complex form today."
The research team verified the standard cosmological model 'Lambda Cold Dark Matter (LCDM)' theory, which explains the evolution of the universe. Modern physics explains that even when combining all the stars that emit light, they make up only 5% of the entire universe. Scientists believe that dark matter, which has gravity but does not emit light, accounts for 27% of the universe. The remainder is estimated to consist of dark energy, which has a repulsive effect instead of gravitational pull.
LCDM assumes the existence of dark matter and dark energy in the universe. The researchers confirmed that, as posited by LCDM, the proportion of ordinary matter in the universe is extremely low, with the majority of the mass composed of dark matter and dark energy. However, this study did not uncover any clues to solve one of astronomy's greatest mysteries, the "Hubble tension."
Modern physics suggests that the universe has been expanding ever since it was born in the Big Bang. Hubble tension refers to the phenomenon where different measurement methods yield varying values for the Hubble constant, which indicates the rate of the universe's expansion. The expansion rate can be directly measured by observing galaxies or predicted by using CMB data to find the conditions of the early universe. However, the values of the Hubble constant derived from both methods do not match, leading to debates among scientists.
The research team utilized high-resolution CMB data to measure a new Hubble constant but still obtained results consistent with the CMB-based value. They considered the possibility that new physical laws could explain the expansion rate of the universe and examined various alternative theories, but so far, no signals supporting these have been found.
Professor Colin Hill of Columbia University stated, "We attempted to verify whether new particles exist in the field through CMB data, but we only found results consistent with the existing cosmological model," adding that this demonstrates that the current cosmological model continues to provide a robust explanation.
Following the Atacama Large Millimeter Array, a new successor telescope known as the Simons Observatory has commenced operations at the same site. This telescope is equipped with even more precise instruments, enabling deeper exploration of the CMB. Upcoming new research is expected to further unveil the secrets of the early universe.