I am a pretty good physicist, but don't undstand a lot of the engineering nitty gritty.
It may well be that I am committing a logical fallacy (accepting an argument from authority?)
If you're a physicist, then you're a scientist. That means you understand the scientific method common to all fields of science (and with significant application in engineering and medicine). So even if you don't personally know the field in question, you can at least check that the experts are following the scientific method in theirs.
I've had to think about this recently while debating some global-warming deniers. I have enough personal expertise in physics, engineering and other fields relevant to space flight to not have to take anybody else's word that Apollo was real, but I most definitely
don't in climate research. Besides, we don't have any major life decisions to base on Apollo's reality. For climate change, we do.
Oh, I understand the basic physics of radiative heat transfer and the general mechanism of global warming from greenhouse gas emissions, but that's
far from being able to independently evaluate the claims that the earth's average temperature will rise X degrees in 10, 50 or 100 years and what that will mean. I really have to trust the judgment of those who do work in that field.
But I can still walk around and "kick the tires". I can see that many researchers are active in the field. I can look at their credentials and see that they have what seem like the relevant skills and experience. I can see that their raw data and computer models are open to inspection and verification. I can see that they publish formal papers in open journals, present them at conferences and answer questions. I can see that they review each others' work before it is formally presented. I can see that dissenting views are encouraged and accepted or rejected after a proper evaluation.
To a limited extent I can also look at their track record: have their short-term predictions been accurate?
So when this process produced a strong consensus, I thought it reasonable to accept the experts' conclusions, to base decisions on them and advocate that others do the same. But that acceptance is always tentative.