Quantum gravity

I recently asked an eminent physicist [Don Page] a question about the relationship between Relativity and quantum mechanics. Here's the exchange:

I was reading an interview with Roger Penrose from 10 years ago:

http://discovermagazine.com/2009/sep/06-discover-interview-roger-penrose-says-physics-is-wrong-string-theory-quantum-mechanics

The idea of parallel universes—many worlds—is a very human-centered idea, as if everything has to be understood from the perspective of what we can detect with our five senses. 

The trouble is, what can you do with it? Nothing. You want a physical theory that describes the world that we see around us. That’s what physics has always been: Explain what the world that we see does, and why or how it does it. Many worlds quantum mechanics doesn’t do that. Either you accept it and try to make sense of it, which is what a lot of people do, or, like me, you say no—that’s beyond the limits of what quantum mechanics can tell us. Which is, surprisingly, a very uncommon position to take. My own view is that quantum mechanics is not exactly right, and I think there’s a lot of evidence for that. It’s just not direct experimental evidence within the scope of current experiments.

You have called the real-world implications of quantum physics nonsensical. What is your objection?

Quantum mechanics is an incredible theory that explains all sorts of things that couldn’t be explained before, starting with the stability of atoms. But when you accept the weirdness of quantum mechanics [in the macro world], you have to give up the idea of space-time as we know it from Einstein. The greatest weirdness here is that it doesn’t make sense. If you follow the rules, you come up with something that just isn’t right.

Of course, this debate has raged for decades, with competing interpretations of quantum mechanics.  Penrose offes an interesting criticism, but it seems to beg the question. What if the world we see around us isn't all there is because there's more than one universe? In that case, the theory shouldn't describe or predict just one outcome, should it? 

Suppose both theories are true, only Relativity is true for our universe while quantum mechanics is true for more than one universe, including ours? Maybe Relativity accurately describes the space-time structure of our universe, but the quantum world is more fundamental than the macro world, which is generated by the quantum world, and the rules for the quantum world transcend the macro world of our particular universe? Our universe represents one set of quantum outcomes, but there are others. The rules of Relativity are specific to our universe, unlike the rules of quantum mechanics. Both theories would be mutually consistent because they describe distinct, overlapping domains. Perhaps the quantum structure of a universe is variable, so quantum mechanics must be more flexible to accommodate the variance, which makes it probabilistic in reference to any particular universe, since it doesn't single out any particular universe.  Does that make any sense? 

I tend to agree with you.  Roger Penrose seems to be among what I think is a small minority (which does not prove that he is wrong, though on this issue I tend to agree with the majority) that spacetime and general relativity is more fundamental than quantum theory.  My tentative position is that quantum theory is universally true (at least as what I see as the most conservative option), and that it implies that general relativity is not universally true but has a limited range of validity, though that range does seem to include most of our observable universe (the part we can observe, taking the very early universe, where GR may not apply, not to be observable by us).