The concept of the universe's beginning and its current state can be complex and challenging to comprehend fully. However, I'll do my best to provide an explanation based on our current understanding of cosmology.
The prevailing scientific model for the origin of the universe is the Big Bang theory. According to this theory, approximately 13.8 billion years ago, the universe began as an extremely hot and dense point called a singularity. At this singularity, the laws of physics, as we understand them, break down, and our current understanding cannot precisely describe what occurred at that point. It is often referred to as a moment of "cosmic inflation."
The universe rapidly expanded and cooled down after the Big Bang, eventually leading to the formation of matter, energy, and the fundamental forces that govern the universe. The expansion of the universe continues to this day, although the rate of expansion has been found to be accelerating.
Now, the idea of the universe being infinite refers to the spatial extent of the universe. It is currently unknown whether the universe is truly infinite or has a finite but unbounded size. Observations suggest that the universe is at least much larger than the observable universe, which is the part we can see and study.
The expansion of the universe does not imply that it started from nothing and became infinite within a finite period of time. The expansion describes the increase in the scale of the universe over time, but it doesn't necessarily mean that the universe was once confined to a finite size and then expanded to become infinite. It's important to note that the concept of infinity can be challenging to grasp, and our understanding of the universe's size and its behavior is still an active area of scientific research.
In summary, the Big Bang theory describes the early stages of the universe and its expansion from a hot and dense state. Whether the universe is truly infinite or has a finite but unbounded size is still a topic of scientific investigation. The concept of the universe's beginning and its current state involves complex theories and ongoing research, and our understanding continues to evolve as new evidence and observations become available.