According to current scientific theories, the most likely scenario for the end of the universe is the "heat death" or "Big Freeze" hypothesis. This suggests that as the universe continues to expand, the energy and matter within it will become more and more spread out, eventually reaching a state of maximum entropy and becoming too cold and diffuse to sustain life.
It is likely that the end of the universe will be a gradual process. The "Big Freeze" scenario would take trillions of years to fully unfold, while other theories such as the "Big Rip" or "Big Crunch" also involve gradual changes over time.
While current theories provide estimates for the timeline of the end of the universe, unexpected events or new discoveries in science could potentially change this timeline. However, it is unlikely that the end of the universe would happen significantly earlier than predicted.
Some theories, such as the "Big Bounce" hypothesis, suggest that the universe could undergo a cycle of expansion and contraction, potentially leading to a rebirth of the universe. However, this is still a highly debated topic and there is currently no conclusive evidence for or against this idea.
Since the end of the universe is expected to occur over trillions of years, it is likely that humans and all other forms of life will not exist at that time. However, the end of the universe could potentially have an impact on our current understanding of physics and the laws of the universe as we know them.