On the other hand, my understanding is that QFT itself doesn’t exist in a rigorous form yet, either.
Depends on what you mean by rigorous. (OTOH, it’s not fully compatible with general relativity, so we know it doesn’t exactly describe the world—or that GR doesn’t, or that neither does.)
Depends on what you mean by rigorous. (OTOH, it’s not fully compatible with general relativity, so we know it doesn’t exactly describe the world—or that GR doesn’t, or that neither does.)