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How Our Universe Could Emerge as a Hologram
The fabric of space and time is widely believed by physicists to be emergent, stitched out of quantum threads according to an unknown pattern. And for 22 years, they've had a toy model of how emergent space-time can work: a theoretical "universe in a bottle," as its discoverer, Juan Maldacena, has described it.
The space-time filling the region inside the bottle—a continuum that bends and undulates, producing the force called gravity—exactly maps to a network of quantum particles living on the bottle's rigid, gravity-free surface. The interior "universe" projects from the lower-dimensional boundary system like a hologram. Maldacena's discovery of this hologram has given physicists a working example of a quantum theory of gravity.
But that doesn't necessarily mean the toy universe shows how space-time and gravity emerge in our universe. The bottle's interior is a dynamic, Escheresque place called anti–de Sitter (AdS) space that is negatively curved like a saddle. Different directions on the saddle curve in opposite ways, with one direction curving up and the other curving down. The curves tend toward vertical as you move away from the center, ultimately giving AdS space its outer boundary—a surface where quantum particles can interact to create the holographic universe inside. However, in reality, we inhabit a positively curved "de Sitter (dS) space," which resembles the surface of a sphere that's expanding without bounds.
Ever since 1997, when Maldacena discovered the AdS/CFT correspondence — a duality between AdS space and a "conformal field theory" describing quantum interactions on that space's boundary—physicists have sought an analogous description of space-time regions like ours that aren't bottled up. The only "boundary" of our universe is the infinite future. But the conceptual difficulty of projecting a hologram from quantum particles living in the infinite future has long stymied efforts to describe real space-time holographically.
[...] Patrick Hayden, a theoretical physicist and computer scientist at Stanford who studies the AdS/CFT correspondence and its relationship to quantum error correction, said he and other experts are mulling over Dong, Silverstein and Torroba's dS/dS model. He said it's too soon to tell whether insights about how space-time is woven and how quantum gravity works in AdS space will carry over to a de Sitter model. "But there's a path—something to be done," Hayden said. "You can formulate concrete mathematical questions. I think a lot is going to happen in the next few years."
(Score: 4, Interesting) by Anonymous Coward on Wednesday February 27 2019, @05:03PM
The holographic principal is a result of this idea that quantum properties result in physical objects when the quantum particles are kept on an external boundary.
I have to be honest when I read the AdS/CFT papers I think they are right to a point, but I don't think the correspondence is a physical one.
We have an interesting math result, but it fails to describe our universe in its current form, but certain properties we find in our universe do emerge.
Nevertheless this negative curvature issue is not physically realizable, that makes this a very interesting thought experiment and maybe one day it will cause something to click in the next Einstein, but right now it is causing a lot of physicists to bark up what is clearly the wrong tree.
I read these papers though and I think to myself, you know this sounds an awful lot like a data problem.
If I build a 3D movie or game in blender and then burn it to a DVD, the pits and peaks form 1s and 0s and these 1s and 0s form the instructions to the hardware causing it to render.
These 1s and 0s correspond quite well to quantum particles and the boundary here is the interface between the storage substrate called data space and the abstract mathematical space inside the computer called rule space. You and I know that there is quite a lot in between those. That boundary is huge and complex, the math going on at every level could fill libraries. But really there is only data space and rule space. In order to compute anything, data must exit data space, transit rule space and as it does so, the game or movie emerges, but the place it emerges is in rule space and it is still constituted of data.
That isn't to say that I believe the universe is a simulation. I'm quite certain it isn't. But it is most definitely computational in nature. Information transforms things here. Ergo we are in rule space. But the data needs to be coming from somewhere.
Or does it?
If you look at any minecraft world, you can regenerate the entire world with a simple 128bit seed number. After that seed is generated, the data is fed back in on itself over and over again until the world is rendered. We do this with such a tiny fraction of the computing power available in the universe that it is hardly worth mentioning. This isn't even getting into self evolving cellular automata, where the rules themselves are derived from the data.
Whatever else our universe is, it seems to be fine tuned for the purpose of computation. Everything computes and almost everything can be used as a computer. Ergo perhaps everything is information, or really everything is data in a state of being processed through rule space and we are what has emerged.