Short excerpt from a 2019 YouTube interview with Sean Carroll discussing how to experimentally test interpretations of quantum mechanics and ideas of emergent spacetime. Carroll notes that ongoing experiments test whether wavefunctions spontaneously collapse — which, if observed, would falsify the Many-Worlds Interpretation — and that hidden-variable theories are thought to make the same predictions as standard quantum mechanics, though Carroll expresses some personal skepticism about the generality of that theorem. On emergent spacetime, he emphasizes the theoretical immaturity: there is no fully worked-out theory yet, so concrete experimental predictions are unclear; possible signals (speculative) include violations such as wavelength-dependent light speed or effects at very high energies or speeds.
Even outside of quantum computers, some of the theories that we've been talking about. What's your hope? What's most promising to test these theories? What are, what are kind of experiments we can conduct, whether in simulation or in the physical world, that would validate or disprove or expand these theories?
Well, I think for there's two parts of that question. One is many worlds and the other one is sort of emergent space time. For many worlds, there are experiments ongoing to test whether or not wave functions spontaneously collapse. And if they do, then that rules out many worlds, and that would be falsified. If there are hidden variables, there's a theorem that seems to indicate that the predictions will always be the same as many worlds. I'm a little skeptical of this theorem. I'm not completely. I haven't internalized it. I haven't made it in part of my intuitive view of the world yet. So there might be loopholes to that theorem. I'm not sure about that. I of me thinks that there should be different experimental predictions if there are hidden variables, but I'm not sure. But otherwise it's just quantum mechanics all the way down. And so there's this cottage industry in science journalism of writing breathless articles that say, quantum mechanics shown to be more astonishing than ever before thought. And really it's the same quantum mechanics we've been doing since 1926. Whereas with the emergent space time stuff, we know a lot less about what the theory is. It's in a very primitive state. We don't even really have a safely written down, respectable, honest theory yet. So there could very well be experimental predictions we just don't know about yet. That is one of the things that we're trying to figure out.
But for emergence space time, you need really big stuff, right?
Well, or really fast stuff or really energetic stuff. We don't know. That's the thing. So there could be violations of the speed of light if you have emergent space time not going faster than the speed of light, but the speed of light could be different for light of different wavelengths. Right. That would be a dramatic violation of physics as we know it. But it could be possible or not. I mean, it's not an absolutely prediction. That's the problem. The theories are just not well developed enough yet to.
