I'm really not sure what natural means. If something happens, it's natural.
You have reduced the natural strength of the language to an absurdity.
We use words to communicate ideas. You are just saying that everything obeys the laws of physics without any context.
I would say that 'natural' would mean anything that doesn't require further explanation about the event or the scenario in which it occurred.
For example if a sinkhole opens up under your bedroom and swallows you up, then of course all the laws of physics are obeyed, but the event itself would draw some level of shock to people as being an 'unnatural' occurance. Most people would have some degree of W.T.F. upon hearing that. Nobody would insist 'it can't happen.'
You are confusing 'unnatural' with 'impossible.'