The universe has been expanding for 13.8 billion years, but some theories suggest that it may not continue forever. Two leading theories are the Big Freeze and the Big Crunch.
According to Henry Tye, a professor emeritus of physics at Cornell University, the most likely scenario is the Big Freeze. In this theory, the universe’s expansion will become faster and continue for 100 billion years or forever, eventually leading to “heat death” where all activity comes to an end.
However, another theory suggests that the positive de Sitter space may decay into negative energy, reversing the direction of the universe and leading to a Big Crunch. This scenario, proposed by Antonio Padilla, would essentially reverse the expansion of the Big Bang and erase our universe.
Some models predict that a Big Crunch could begin as soon as 100 billion years from now, driven by dark energy. Conversely, other studies suggest that the universe has at least another trillion years left before it ends completely.
Even if none of these theories is correct, there may still be an expiration date for regular matter in the universe due to spontaneous radiation predicted by Stephen Hawking. According to a 2025 study, everything in the universe could slowly evaporate to nothing over 1 quinvigintillion years.
Ultimately, cosmologists must improve existing models of our universe and extrapolate them infinitely to gain a better understanding of complicated topics like dark energy and string theory.
Source: https://www.livescience.com/space/cosmology/when-will-the-universe-die