Space wasn't infinitely small when the hot Big Bang began

Light from the earliest hot Big Bang was emitted about 13.8 billion years ago and is observed today after traveling through an expanding universe. Because space itself expands during the light’s journey, the same ancient light corresponds to objects currently located about 46.1 billion light-years away. As time passes, more distant light will arrive, allowing observations of objects up to roughly 61 billion light-years away at the farthest observable limit. At any moment, there remains a finite boundary to what can be seen, implying the universe’s size in the past was also finite and smaller than today. Tracing back to the very beginning does not require an infinite-density singularity; instead, a smallest possible universe size exists, and gravity-based laws are used to determine it.

"At the farthest reaches of our observable limits, the most ancient light we can see was emitted a whopping 13.8 billion years ago: corresponding to the hot Big Bang itself. Today, after traveling through our expanding Universe, that light finally arrives here on Earth, carrying information about objects that are presently located some 46.1 billion light-years away. It's only due to the expanding fabric of space that the most ancient light we can see corresponds to distances that exceed 13.8 billion light-years."

"As time continues to march forward, we'll be able to see even farther away, as light that's still on its way eventually reaches us: ultimately revealing objects that are presently up to 61 billion light-years distant. Nonetheless, at any given time, there's always a limit to how far away we can see: a limit to the observable Universe. This also means that if we went back to any point in the distant past, our Universe would also have a finite, quantifiable size: smaller than it is today, dependent on how much time has passed since the hot Big Bang."

"But what if we went all the way back: back to the very beginning, and the very first moment of the hot Big Bang itself? Surprisingly, it doesn't give us a singularity, where the Universe reaches infinite densities and temperatures at an infinitesimal size. Instead, there's a limit: a smallest possible size that the Universe could have had. Here's why that limit exists, and how we can figure out the minimum size of the early Universe."

"In our Universe, if we want to know anything about either what it will do in the future or what it was doing in the past, we need to understand the rules and laws that govern it. For the Universe, and in particular for how the fabric of the Universe evolves with time, those rules are set forth by our theory of gravity: Einstein'"

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