It is important to clarify that atheism, by definition, is not a claim about the origin of the universe. Atheism is simply the absence of belief in deities or gods. It does not inherently imply a specific position on the origin of the universe or any other scientific or philosophical questions.
As for the question of how the universe began, scientific understanding regarding the origin of the universe is an ongoing and active area of research. The current leading scientific explanation for the origin of the universe is the Big Bang theory, which suggests that the universe originated from a highly dense and hot state approximately 13.8 billion years ago. However, the exact nature of the initial conditions and the events that preceded the Big Bang remain areas of active scientific investigation.
It is important to note that scientific explanations are based on empirical evidence, observation, and rigorous analysis, and they continue to evolve as new evidence emerges. Admitting what we don't know and acknowledging the limits of our current understanding is a fundamental part of the scientific process. Scientists and researchers are constantly pushing the boundaries of knowledge and refining their understanding based on new data and discoveries.
Atheists, like people with any other worldview, may hold various opinions and levels of knowledge regarding the origins of the universe. Some may accept the scientific explanations available, while others may have different perspectives or await further scientific progress before forming a conclusion. It is not accurate to make a generalized statement about when atheists or any other group will or should admit to not knowing something, as individuals have different perspectives and approaches to knowledge.