Again you have a problem here dictating what science can accommodate because the universe may have arised spontaneously. It's cause therefore can never be described by science. That shows the limitations of science rather than the possibility of the spontaneous appearance of the universe.
I've long accepted the philosophical limitations of science. Those same limitations apply to every phenomena we experience, whether we currently have a scientific explanation for them or not. Gravity could be an intrinsic function of the interaction of Higgs Bosons within atoms with the background Higgs Field, or it could be a remarkably coincidental series of spontaneous events.
Science MUST presume the philosophical naturalism of cause and effect, or none of its conclusions mean anything. The justification for accepting those conclusions is that, from them, predictions have been made which have proven to be validated by further experiment. So long as reality continues to behave consistently, science will continue to be validated, updated and relevant.
Nothing in science, history, nature or philosophy has ever changed the possiblity of a spontaneous universe: it's a possibility now, it was a possibility when it was first posited, and there's no way to quantify the likelihood.
We can therefore never be certain that a spontaneous event cannot happen anytime anywhere.
Which is why scientific findings are always provisional. There is always the possibility of data which disrupts the current paradigm. There is, also, the possibility of phenomena which are spontaneous, which don't comply with the assumption of philosophical materialism. Science does not ignore the phenomena, but it doesn't accept 'it just happened' as an answer, it hypothesises and then tries to develop tests to validate or disprove the hypothesis.
Philosophical naturalism is opinion
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Philosophical naturalism is a philosophy. The findings of science, which are based on that philosophy are - to varying degrees - validated hypotheses and conjectures as to the nature of reality.
Philosophical naturalism is 'opinion' to the extent that any philosophy is only opinion - we lack sufficient scope of sense and experience to adequately determine any absolutes as reference for any philosophy.
O.