Atheists who believe in the Big Bang typically attribute the origins of the universe to natural processes rather than invoking the notion of someone or something "lighting the fuse." The Big Bang theory describes the expansion of the universe from a highly dense and hot state around 13.8 billion years ago. According to this scientific theory, the universe originated from a singularity—a point of infinite density and temperature—and has been expanding ever since.
Atheists who accept the Big Bang theory generally view the event as a natural occurrence governed by physical laws rather than as the result of a deliberate act by a supernatural being. They might explain the origins of the universe through scientific principles such as quantum mechanics or cosmology. It's important to note that atheism itself refers to the lack of belief in gods or deities and doesn't inherently prescribe specific views on cosmology or the origins of the universe. Different atheists may hold different explanations or hypotheses about the origins of the universe, as their beliefs can vary widely.