&gt; It&#x27;s inconsistent to state that we believe that the Big Bang theory is a theory about the origin of the Universe and in the same time state that before some point in time we don&#x27;t know what happened.<p>If that rule were in force, mathematics would disintegrate because it&#x27;s built on a foundation of axioms. But scientific theories are often predicated on axioms whose consequences are examined, but whose existence are accepted without explanation until a more encompassing, more global, theory is created. Like relativity replacing Newtonian gravitation -- the new theory still has axioms, but the theory explains and encompasses more.<p>&gt; If we don&#x27;t know what happened before some time t, then we don&#x27;t know the origin, by definition.<p>A scientific theory is by definition a testable, falsifiable explanation of what can be observed. For each such theory, there are limits to what can be observed.<p>&gt; Back then it very much is possible the Universe was still infinite in space anyway ...<p>Yes, unless (imagine time running in reverse) spacetime collapsed to a point, as is often claimed, and as relativity theory requires. In that case, an infinite universe would occupy no space or time at all. The notion of infinity doesn&#x27;t require infinite size.