Bob Park is a legitimate authority regarding physics. Therefore, using what I understand to be an acceptable understanding of the logical fallacy known as "appeal to authority", quoting Bob Park as an authority in physics on a matter that is about physics does not constitute commission of that fallacy.
No, that is not a requirement for an appeal to authority:
Wikipedia wrote:There are two basic forms of appeal to authority, based on the authority being trusted.... The second form, citing a source who is actually an authority in the relevant field, carries more subjective, cognitive weight.... experts can still be mistaken, wilfully deceptive, subject to pressure from peers or employers, have a vested financial interest in the false statements, or have unusual views (or views that are widely criticized by other experts) within their field, and hence their expertise does not always guarantee that their arguments are valid.
Furthermore, and rather devastatingly for your case, the claim "every observable effect has a physical cause" isn't a physics claim anyway - it's a philosophical one. There is no law of physics that says that "every observable effect has a physical cause". It's even a fairly nebulous idea in philosophy:
Stanford Encyclopedia of Philosophy wrote:For a variety of reasons this approach is fraught with problems, and the reasons explain why philosophers of science mostly prefer to drop the word “causal” from their discussions of determinism. Generally, as John Earman quipped (1986), to go this route is to “… seek to explain a vague concept — determinism — in terms of a truly obscure one — causation.” More specifically, neither philosophers' nor laymen's conceptions of events have any correlate in any modern physical theory.[1] The same goes for the notions of cause and sufficient cause. A further problem is posed by the fact that, as is now widely recognized, a set of events {A, B, C …} can only be genuinely sufficient to produce an effect-event if the set includes an open-ended ceteris paribus clause excluding the presence of potential disruptors that could intervene to prevent E. For example, the start of a football game on TV on a normal Saturday afternoon may be sufficient ceteris paribus to launch Ted toward the fridge to grab a beer; but not if a million-ton asteroid is approaching his house at .75c from a few thousand miles away, nor if the phone is about to ring with news of a tragic nature, …, and so on. Bertrand Russell famously argued against the notion of cause along these lines (and others) in 1912, and the situation has not changed. By trying to define causal determination in terms of a set of prior sufficient conditions, we inevitably fall into the mess of an open-ended list of negative conditions required to achieve the desired sufficiency.