For when the agent gets here
So as Sigmund says, the point is that if there is (what looks like) convincing evidence of ‘God’ we will not be able to tell whether it is simply evidence of an advanced alien technology. My similar point is that we won’t know of any way to distinguish between a natural intelligent agent and a ‘god’ of whatever sort.
I think that observation is hard to get around. We could of course say that it could be a ‘god’ – that we don’t know that it’s not a god, that it has powers that seem to us to be what is called ‘miraculous.’ But could we say ‘this is supernatural for sure’? I don’t think so. It seems like the kind of thing we couldn’t know, in the nature of the case.
Another, and perhaps more relevant, thing we couldn’t know is that the agent/god had legitimate authority over us. Believers take that idea for granted – ‘God’ is great, God is bigger and stronger and better than we are, God made us and the flowers too, therefore God is the boss of us. Non-believers however don’t take that for granted. Lots of people are bigger and stronger than I am, but I don’t consider them to have legitimate authority over me. An agent with miraculous-seeming powers might have the ability to force us to obey it, but that’s not at all the same thing as legitimate authority.
But that’s not it, the devout listeners in the audience murmur to each other; it’s not just superior strength, it’s also infinite wisdom and goodness. That’s what makes the authority legitimate.
Well – I’ll suspend judgment on that point until I meet such an agent…or until someone gives me a good argument. One of those.