Concerning the Big Bang, how can nothingness produce mass and energy?

Science is primarily about OBSERVATION: we can only model from what we see. By observing how things interact, we try to understand our universe.

Although many observations can currently be explained by the "Big Bang" theory of universal generation, there are still many unanswered questions, and there is no assurance that this theory is even the best one.

Visit https://tutor.hix.ai for a more thorough discussion of what and why we believe we know.

additionally, https://tutor.hix.ai which discusses the implications of the "multiverse."

For the best non-theological discussions of universal origins, I strongly advise everyone to read Dr. Stephen Hawking's extremely readable books "A Brief History of Time," "A Briefer History of Time," and "The Grand Design": https://tutor.hix.ai

Energy was transformed into particles of matter during the early universe's explosive expansion, or inflation, which was caused by variations in the energy fields in the vacuum of space, which produced both mass and energy.