The process by which two protons fuse to form helium is known as proton-proton fusion, and it is one of the primary nuclear reactions that powers stars, including our Sun. Scientists have gained knowledge of this process through a combination of theoretical understanding, laboratory experiments, and observations of stars.
Theoretical Understanding: The process of proton-proton fusion is well understood within the framework of nuclear physics and the Standard Model. Scientists have developed mathematical models and equations that describe the behavior of particles and their interactions at the subatomic level. These models, which include quantum mechanics and nuclear physics, provide a theoretical basis for understanding how nuclear reactions occur.
Laboratory Experiments: Scientists have conducted experiments in laboratories to study nuclear reactions and verify the theoretical predictions. These experiments involve creating conditions similar to those found in the cores of stars to observe and measure the fusion reactions. While it is challenging to recreate the extreme temperatures and pressures of stellar environments, scientists have been able to study the behavior of atomic nuclei and measure the rates of fusion reactions under controlled conditions. These experiments have provided valuable data that support the understanding of proton-proton fusion.
Observations of Stars: Observations of stars, including our Sun, provide indirect evidence of proton-proton fusion. Scientists can analyze the light and other radiation emitted by stars to infer the processes occurring in their cores. The observed energy output of stars, their spectral characteristics, and the abundance of elements can be used to deduce the nuclear reactions taking place. In the case of the Sun, the observed neutrino flux, which is produced as a byproduct of the proton-proton fusion process, provides strong evidence for the occurrence of this reaction.
Combining theoretical understanding, laboratory experiments, and observations of stars, scientists have built a comprehensive picture of the proton-proton fusion process. While it is not possible to directly observe individual fusion events in stars, the collective evidence from these different sources supports the understanding that two protons can fuse to form helium, releasing energy in the process.