Science does not tell you "why" because "why" is (respectfully) a stupid question. Just because you can ask a question does not mean it has an answer. What is the colour of anxiety? You understand the question, but it is nonsense. Such is the nature of the question "What is the meaning of our lives" in any context outside the meaning you yourself give it. Meaning is a human mental construct, looking for meaning in nature is futile. Just because you want the universe to have meaning does not make it so; the universe does not care what you want. In fact, the universe does not care at all.
Our moral compulsion to live a good life seems perfectly coherent in the context of the evolutionary biology of social primates. There has been no shortage of science on the subject in the past few years.
Particle physics has a pretty good idea of the physics of how the Big Bang "Banged". Unfortunately, the supporting math and science is pretty difficult for the layman to understand (I'm not sure why we would assume the underpinnings universe should be easily explainable or should conform to common sense). Physicists are on the doorstep of unlocking the history and the building blocks of the cosmos, and like all scientific discovery before it, the light of science will send the god(s) scurrying into another gap in scientific knowledge.
The term fundamentalist atheist is kind of incomprehensible to me, but I would support the description of "fundamentalist rationalist". I see nothing wrong with basing your beliefs on the foundation that if they are not reasonable and supported by evidence, that they are not valid.
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