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"These atheists are not saying that they can't determine the source of the universe, they are saying the source of the universe is chemical/electrical processes. They refuse to ask the question, "Where did these processes come from?", "How did they begin?" They have no answer as to the origin of the processes. Period. Yet, they believe they have "the ultimate answer"."
These people, by and large, do not exist.
They're a fantasy of religious types.
The questions you ask above are asked all the time by physicists and philosophers who refuse to accept the easy answer that "God did it." Some of those physicists and philosophers think those questions are fundamentally unanswerable. Others think the answer is not meaningful. (The logic of the anthropic principle suggests that there is no "why" - nothing special about our universe. To suggest otherwise is to shoot an arrow blindly, then draw a target around where it hit and call yourself a marksman.)
The difference is that the we don't conflate the absence of an answer with certainty. That's the realm of faith, not science.
To suggest that someone who calls himself an atheist is uninterested in those questions and yet claims to have the answer to everything is akin to saying that someone who believes that Jesus was the son of god therefore believes that god created the world in six days. The primary difference is that there actually are thousands of people for whom the latter assumption would prove accurate. There aren't for the former.