In cosmology, the concept of a "Big Crunch" refers to a hypothetical scenario in which the universe, in a closed system, undergoes a reversal of the expansion that started with the Big Bang. According to this scenario, if the universe's density is high enough, gravitational forces would eventually overcome the expansion, causing the universe to contract.
Assuming a closed universe where a Big Crunch occurs, what happens next is a matter of theoretical speculation, as our current understanding is limited. One possibility is that the universe could experience a cyclical pattern of expansion and contraction, with a series of Big Bangs and Big Crunches occurring repeatedly. This idea is known as the oscillating universe model.
In this cyclic model, the Big Crunch would lead to a contraction of the universe, eventually reaching a highly dense and hot state. From there, it is theorized that a new Big Bang could initiate a new cycle of expansion, leading to the formation of a new universe.
However, it's important to note that the concept of a Big Crunch and the subsequent fate of a closed universe is highly speculative and still an area of active research and debate among cosmologists. The discovery of the accelerating expansion of the universe, as evidenced by observations of distant supernovae, has led to the prevailing theory of dark energy, which suggests that the expansion of the universe may continue indefinitely, resulting in a different future fate for the universe.
It's worth mentioning that the current leading cosmological model, called the Lambda-CDM model, suggests that our universe is not closed but rather spatially flat or possibly even open, and it predicts a future in which the expansion continues to accelerate. However, the ultimate fate of the universe remains a topic of ongoing scientific investigation and exploration.