Early universe after the big bang
Pro Research Analysisby 
Searched over 200M research papers
The Planck Era and Post-Planck Era in the Early Universe
The earliest moments after the Big Bang are divided into two main periods: the Planck era (up to 10^-43 seconds after the Big Bang) and the post-Planck era (from 10^-43 to about 10^-10 seconds). During the Planck era, the universe was so hot and dense that current physics, including quantum gravity theories like string theory, are needed to describe it. After the Planck era, in the post-Planck or Grand Unified Theory (GUT) era, quantum theory and general relativity can be used to study the universe's evolution Louis2021Julie2023.
Hot Big Bang and the Expansion of the Universe
The Big Bang theory explains that the universe began as an extremely hot, dense point about 13.8 billion years ago. All matter and energy were concentrated in this single point, and the universe has been expanding ever since. This expansion is still ongoing, and the Big Bang theory also addresses why the universe's expansion is accelerating .
Inflation and the Early Universe’s Problems
Shortly after the Big Bang, the universe is believed to have undergone a brief period of rapid expansion called inflation. Inflation helps solve several problems in early universe cosmology, such as the horizon problem (why distant regions of the universe look similar), the flatness problem (why the universe appears nearly flat), and the relic problem (why we don’t see certain predicted particles). Inflationary models suggest that the universe became highly homogeneous and isotropic during this phase Ling2024Guth1985Nastase2019.
Formation of Structure: Galaxies and Stars
Despite the chaotic beginnings, structures like galaxies and stars began to form relatively quickly. Observations show that spiral galaxies with distinct features such as disks, bulges, and spiral arms existed as early as 1.4 billion years after the Big Bang. This suggests that galaxy formation and internal structure development happened much earlier than previously thought . Additionally, evidence indicates that star formation began as early as 250 million years after the Big Bang, marking the emergence of the first galaxies and influencing the intergalactic medium .
Matter, Antimatter, and Dark Matter in the Early Universe
The early universe was dominated by radiation, and theories suggest that the universe before and after the Big Bang could be mirror images, potentially explaining the matter-antimatter asymmetry and the abundance of dark matter. Some models propose that heavy neutrinos could account for dark matter, and that the universe’s evolution naturally leads to the observed matter content .
Phase Transitions and Gravitational Waves
The origins of matter and radiation are linked to phase transitions in the early universe. Some cosmological models propose that the Big Bang itself was a result of a strong first-order phase transition, which could produce gravitational waves detectable by current and future experiments. These phase transitions are crucial for understanding the creation of matter, radiation, and possibly dark matter .
Conclusion
The early universe after the Big Bang was marked by extreme conditions, rapid expansion, and the formation of the first structures. Theories and observations continue to refine our understanding of this period, from the Planck era and inflation to the emergence of galaxies and the possible origins of dark matter. While many details remain uncertain, ongoing research and new observations are helping to piece together the universe’s earliest moments Louis2021Kolb1990Tsukui2021+7 MORE.
Sources and full results
Most relevant research papers on this topic