The Nebular Hypothesis and the Big Bang theory are both theories that explain the formation and evolution of the universe, but they have some key differences.
One similarity is that both theories propose that the universe began in a hot and dense state, and that it has been expanding and cooling over time.
One key difference is the starting point of each theory. The Big Bang theory proposes that the universe began as a singularity, an infinitely hot and dense point, and has been expanding ever since. The Nebular Hypothesis, on the other hand, proposes that the universe began as a cloud of gas and dust, which collapsed under its own gravity to form the sun and planets.
Another difference is the way in which the Big Bang theory explains the formation of the elements, through a process known as nucleosynthesis. In contrast, the Nebular Hypothesis explains the formation of the elements through the process of planetary nebula, where elements heavier than helium are formed in stars and then spread out into space through supernovae explosions and planetary nebulae.
Finally, the Big Bang theory is supported by a wealth of observational evidence, including the cosmic microwave background radiation, the large scale structure of the universe, and the abundance of light elements. The Nebular Hypothesis, on the other hand, is more of a hypothesis of how the solar system formed, and does not explain the large scale structure of the universe.