Creation of the Universe: For Scientists and Philosophers

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When scientists are conducting an experiment, they understand that there are many parameters that are out of their control. There are many factors that cannot be measured or quantified. So they need to suppose many things and approximate many other things while conducting an experiment. If the results of those experiments do not match the real world results then they can always go back and change the things they supposed.
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Similarly the thinkers and philosophers don’t spend their time and energies in proving certain things that are already accepted by most if not all. They consider those things to be self-evident. Like the great thinkers who wrote the constitution of America, stated at the beginning of the constitution that “we hold these truths to be self-evident, that all men are created equal, that they are endowed by their creator with certain unalienable rights, that among these are life, liberty and pursuit of happiness.”
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So what I don’t understand is, that when certain philosophers and scientists talk about the creation of the universe, why do they fanatically insist that there is no God?
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I understand that there is no way to prove that God exists. But there is also no way to prove that God doesn’t exist. Not believing in God is as much a dogma and blind faith as believing in God.
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God is an unknown parameter in the creation of the universe. So why don’t they suppose that there is a God and see if that makes the creation of the universe easier? Then they can suppose that if there is no God, would that make the creation easier than the first case?
Which is more likely? An intelligent design of a creator? Or blind forces of probability that need everything to come together right at the exact moment to make life possible? (I read somewhere that the odds of that happening by chance is 1 in 10^50 or more). You can make up your own mind by comparing the two probabilities.
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Similarly when philosophers ask the question that if everything is created by God, then who created God? Why can’t they consider this to be self-evident that there is an un-created God who created everything?
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I mean, doesn’t that make everything simple to understand?