WE ARE ALL DESIGNIST NOW:

The AdS/CFT duality connects a theory of gravity in a space-time region called anti-de Sitter space (which curves differently than our universe) to an equivalent quantum field theory describing that region's gravity-free boundary. Everything there is to know about AdS space--often called the "bulk" since it's the higher-dimensional region--is encoded, like in a hologram, in quantum interactions between particles on the lower-dimensional boundary. Thus, AdS/CFT gives physicists a "holographic" understanding of the quantum nature of gravity.

That's the idea that space-time and everything in it emerges like a hologram out of information stored in the entangled quantum states of particles. [...]

What do you see as the relationship between math and physics?

I prefer not to give you a cosmic answer but to comment on where we are now. Physics in quantum field theory and string theory somehow has a lot of mathematical secrets in it, which we don't know how to extract in a systematic way. Physicists are able to come up with things that surprise the mathematicians. Because it's hard to describe mathematically in the known formulation, the things you learn about quantum field theory you have to learn from physics. [...]

The other night I was reading an old essay by the 20th-century Princeton physicist John Wheeler. He was a visionary, certainly. If you take what he says literally, it's hopelessly vague. And therefore, if I had read this essay when it came out 30 years ago, which I may have done, I would have rejected it as being so vague that you couldn't work on it, even if he was on the right track.

You're referring to Information, Physics, Quantum, Wheeler's 1989 essay propounding the idea that the physical universe arises from information, which he dubbed "it from bit." Why were you reading it?

I'm trying to learn about what people are trying to say with the phrase "it from qubit." Wheeler talked about "it from bit," but you have to remember that this essay was written probably before the term "qubit" was coined and certainly before it was in wide currency. Reading it, I really think he was talking about qubits, not bits, so "it from qubit" is actually just a modern translation.

Don't expect me to be able to tell you anything useful about it--about whether he was right. When I was a beginning grad student, they had a series of lectures by faculty members to the new students about theoretical research, and one of the people who gave such a lecture was Wheeler. He drew a picture on the blackboard of the universe visualized as an eye looking at itself. I had no idea what he was talking about. It's obvious to me in hindsight that he was explaining what it meant to talk about quantum mechanics when the observer is part of the quantum system. I imagine there is something we don't understand about that.

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