The nature of space-time and the extent of the universe are still active areas of research and debate in astrophysics and cosmology. While it is true that current observational data suggests that the universe is spatially flat on large scales, indicating that space-time is not significantly curved, it does not necessarily imply that the universe extends infinitely.
The concept of a multiverse, which hypothesizes the existence of multiple universes beyond our observable universe, is a speculative idea that arises from various theories, such as inflationary cosmology and string theory. In some versions of these theories, it is proposed that our observable universe is just a small part of a much larger structure, often referred to as the multiverse.
However, it is important to note that the multiverse hypothesis is still highly speculative and lacks direct empirical evidence. It remains a topic of ongoing research and theoretical exploration. Scientists are actively studying cosmological data, such as the cosmic microwave background radiation and large-scale structure of the universe, to gain insights into the fundamental nature of space-time and the structure of the cosmos.
So, while the concept of an infinite multiverse is a possibility in some theoretical frameworks, its existence and the nature of our universe beyond the observable region are still open questions that require further investigation and observational evidence.