Causality is a scientific question. We look at the world of nature and uncover mechanisms at work which cause the world to function and appear as it does.
Having said this, when it comes to the philosophical distinction between primary and secondary causes, science not only cannot, but need not know whether its subject – the natural world – is secondary or not. Science can still uncover natural mechanisms whether the universe is self-caused or ‘other’-caused.
…but then again; technically, the assumption of nature’s regularity (that the same experimental conditions, subjects and controls, etc. will always yield the same experimental result) is a way of being aware of primary causal factors beyond the actual subjects of study themselves.