Answer:
Gravity causes gas in space to come together and form stars. As the star becomes denser and denser, the pressure and temperature at its core become high enough to initiate nuclear fusion reactions, where hydrogen atoms fuse together to form helium, releasing a huge amount of energy. This energy keeps the star hot and shining for millions or billions of years. Without gravity, nuclear fusion would not occur, and the universe as we know it would not exist.
Step-by-step explanation:
Gravity played a crucial role in causing fusion reactions to occur between hydrogen and helium. In the early universe, after the Big Bang, there were only light elements such as hydrogen and helium, and gravity was the main force that brought these elements together to form stars. As a large amount of hydrogen gas began to accumulate in one area, the force of gravity caused the gas to contract and become denser and denser. As the density and temperature of the gas increased, the pressure in the core of the gas cloud became high enough to initiate nuclear fusion reactions.
During nuclear fusion, the extreme temperature and pressure in the star's core caused hydrogen atoms to fuse together to form helium. This fusion process released a huge amount of energy in the form of light and heat, which kept the star hot and shining for millions or even billions of years. Without the force of gravity to bring hydrogen atoms together, fusion reactions would not occur, and the formation of heavier elements, including those necessary for life, would not be possible. Therefore, gravity is the cause that initiated the fusion reactions, leading to the formation of heavier elements and eventually the complex universe we observe today.