How do we know the Universe had a beginning?

Our current Universe appears to be 13.75 billion years old. The cosmic microwave background radiation (CMBR) is today about 48 billion light years away from us in terms of coordinates that move along with the expansion. This is the limit of our vision because before then, our Universe was opaque. So we really have no idea what lies beyond the CMBR. Even that gives us a staggeringly large Universe having an observable radius of 48 billion light years, or a “diameter” of 96 billion light years. Of course, it would be incorrect to think of the Universe as centered about us and having an actual diameter. Instead, we think that if we were at what appears to us to be its “edge” it would appear from there to be centered about that point of observation as well. Clearly, we are dealing with a morphology that is very different from an inflated beach ball, which appears to us to be an actual sphere that does have a true center.

Given that we can’t see back to its beginning, and certainly can’t see beyond the beginning, how can we have any confidence that this Universe had any beginning? Isn’t it just as possible that it is infinite and cyclical?