You don't know that
OK and how about just simulating the universe? There is a legitimate question about computability there - it does seem plausible that aspects of simulating the universe could be uncomputable.
Suppose that this is case - well it's still an open question as to whether or not this spells doom for the simulation route. The uncomputable bits are going to be some quantum this or that, and it's not at all clear that such low-level bits are fundamentally required for human-level intelligence; that the high-level process of intelligence is inseparable from the underlying processes which give rise to human intelligence.
Personally, I find it a highly unlikely that intelligence is inseparable/has no reduced model, for whatever my prognostication is worth.
BUT even if it is inseparable, there's still a strong argument to be made that you could construct AGI through means of so-called 'embodied computation', just like biology does.
If we can empirically quantify the behavior of an irreducible entity, which seems plausible, then the hypothesis is scientific.
Or are you saying only AGIs can have conversations? That's begging the question.
Also that assumes that the goal is some general AI. We're just getting started here