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The Fantastic Journey of the Initial Universe: How Was Helium-4 Born?
In the early days of the universe, a series of mysterious and magical processes occurred, the most eye-catching of which was Big Bang nucleosynthesis (BBN). This process refers to the creation of light elements, especially helium-4, in the short time after the Big Bang. Through this process, we can unravel part of the mystery of the origin of the universe.
Big Bang nucleosynthesis made our universe about 25% helium-4, a prediction that is still supported by observations today.
From 10 seconds to 20 minutes after the Big Bang, the temperature and density of the universe were very high, which made various nuclear reactions become violent. The study pointed out that the formation of helium-4 was one of the important results of this period. Compared with other elements such as hydrogen, deuterium, helium-3 and lithium-7, helium-4 occupies a dominant proportion in the universe. In this process, the production of helium-4 mainly relies on neutrons and protons. of mutual reactions.
In the early stages of the universe, the neutron-proton ratio played a key role. The determination of this ratio in the moments after the Big Bang laid the foundation for subsequent nucleosynthesis. Over time, as temperatures gradually dropped and the universe expanded, the stability of free neutrons weakened, allowing more neutrons to combine with protons to form helium-4. The formation of helium-4 is more stable than other nuclides in the nucleosynthesis process, which also explains why most neutrons eventually fused into helium-4 shortly after the big bang nucleosynthesis.
As the universe expands and cools, helium-4 is created, and the key to this process lies in the formation and stability of deuterium.
The production of helium-4 will undergo multiple transformations from hydrogen to deuterium and then to helium during the nucleosynthesis process. However, an important bottleneck phenomenon appeared in this process: deuterium is formed at extremely high temperatures. susceptible to damage at temperatures. This phenomenon is also known as the "deuterium bottleneck." As the universe cooled, deuterium survived longer, allowing helium-4 to form. Once the right conditions are reached, a vigorous helium-4 reproduction occurs.
Throughout the BBN process, some unstable isotopes are also produced, such as tritium and beryllium-7, which later decay into helium-3 and lithium-7. Therefore, although the process of Big Bang nucleosynthesis was relatively short-lived, its impact on the chemical composition of the universe was profound.
Research shows that the observed content of helium-4 in the universe is highly consistent with the results predicted by Big Bang nucleosynthesis, which consolidates the basis of the Big Bang theory.
The existence and abundance of helium-4 is not only an important basis for the Big Bang theory, but also helps us understand the evolution of the universe. However, although helium-4 occupied a relatively high proportion in the original universe, it cannot explain the production of other heavy elements in the universe. These heavy elements, such as carbon, oxygen, etc., are mainly produced through the nucleosynthesis process after the evolution and death of stars. This process is called stellar nucleosynthesis.
As time progresses, the theoretical model of BBN has also changed. When faced with current observational data, previous models have shown some differences, especially in terms of lithium abundance, which is likely to be a hot spot for future research. To explain these differences, scientists are conducting more sophisticated calculations and new hypothetical modeling, hoping to further clarify the chemical composition of the universe and its formation process.
The conclusion is that the birth of helium-4 is a fantastic journey, and through this process, scientists are gradually unraveling the mysteries of the universe. This raises an interesting question: In future cosmic research, will there be new discoveries that reveal deeper mysteries of the universe?
