Once it becomes measurable, then you can implant emotions into AI agents. Once you an AI identity that is emotionally indistinguishable from us non-AI identities and which is infinitely smarter than us, what purpose would we have left to fulfil?
My purpose would remain unchanged. What you’re asking is almost the same as asking, “If a person exists who is better (smarter, stronger, more attractive) than you, what point is there in existing?” Because I experience life subjectively and would prefer to continue doing that.
You make a good point - purpose is very subjective and personal. Maintaining that purpose regardless of outside influence becomes the hard bit!
OTOH what happens if there is a whole species of beings who are smarter, stronger, … than our species? Would our collective purpose become to accept them as our betterment? Our personal purpose would vary greatly from fear to wonderment.
