A Theory of everything? How Spacetime is Built by Quantum Entanglement

Credit: Hirosi Ooguri
This is an illustration of the concept of the holography. 

Most people know that quantum mechanics and the theory of relativity each explain how different aspects of the universe work, and, most people know that Albert Einstein, the creator of both concepts, spent the last years of his life working to figure out how the two theories worked together to explain everything in one neat package aka a Theory of Everything.

Over the years since Einstein's death in 1955, theoretical physicists have continued to struggle to merge the two into one.  While it's obviously a tough problem, I'm willing to bet that the answer when found is going to be quite simple and what mathematicians call, elegant.

Not that I'd come close to understanding what they're talking about in all but the simplest, most remedial terms.

Now it seems we're one step closer to solving the theory of everything based on an idea, if I understand it right, that if you look at the universe as being two dimensional, there are complex computations that show that gravity in three dimensions can be explained as an effect of what Einstein called "spooky action at a distance", or quantum entanglement. 

Quantum entanglement, an idea of quantum mechanics, says that if a person tweeks a particle here, the effect of your tweek can be seen in a paired particle over there, something that was theory until March of this year when it was announced that  Professor Howard Wiseman of Griffith University's Centre for Quantum Dynamics and his experimental collaborators at the University of Tokyo did exactly that.

With me so far?  Good, because now you know all that I know about the subject.

So, without further ado, here's the story:

Theory of everything?
How spacetime is built by quantum entanglement
 
A collaboration of physicists and a mathematician has made a significant step toward unifying general relativity and quantum mechanics by explaining how spacetime emerges from quantum entanglement in a more fundamental theory.
Physicists and mathematicians have long sought a Theory of Everything (ToE) that unifies general relativity and quantum mechanics. General relativity explains gravity and large-scale phenomena such as the dynamics of stars and galaxies in the universe, while quantum mechanics explains microscopic phenomena from the subatomic to molecular scales.

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The holographic principle is widely regarded as an essential feature of a successful Theory of Everything. The holographic principle states that gravity in a three-dimensional volume can be described by quantum mechanics on a two-dimensional surface surrounding the volume. In particular, the three dimensions of the volume should emerge from the two dimensions of the surface. However, understanding the precise mechanics for the emergence of the volume from the surface has been elusive.

The paper announcing the discovery by Hirosi Ooguri, a Principal Investigator at the University of Tokyo's Kavli IPMU, with Caltech mathematician Matilde Marcolli and graduate students Jennifer Lin and Bogdan Stoica, will be published in Physical Review Letters as an Editors' Suggestion "for the potential interest in the results presented and on the success of the paper in communicating its message, in particular to readers from other fields."

Now, Ooguri and his collaborators have found that quantum entanglement is the key to solving this question. Using a quantum theory (that does not include gravity), they showed how to compute energy density, which is a source of gravitational interactions in three dimensions, using quantum entanglement data on the surface. This is analogous to diagnosing conditions inside of your body by looking at X-ray images on two-dimensional sheets. This allowed them to interpret universal properties of quantum entanglement as conditions on the energy density that should be satisfied by any consistent quantum theory of gravity, without actually explicitly including gravity in the theory.

The importance of quantum entanglement has been suggested before, but its precise role in emergence of spacetime was not clear until the new paper by Ooguri and collaborators.

Quantum entanglement is a phenomenon whereby quantum states such as spin or polarization of particles at different locations cannot be described independently. Measuring (and hence acting on) one particle must also act on the other, something that Einstein called "spooky action at distance." The work of Ooguri and collaborators shows that this quantum entanglement generates the extra dimensions of the gravitational theory.

"It was known that quantum entanglement is related to deep issues in the unification of general relativity and quantum mechanics, such as the black hole information paradox and the firewall paradox," says Hirosi Ooguri. "Our paper sheds new light on the relation between quantum entanglement and the microscopic structure of spacetime by explicit calculations. The interface between quantum gravity and information science is becoming increasingly important for both fields. I myself am collaborating with information scientists to pursue this line of research further."

Related posts:
Story Source:  Materials provided by University of Tokyo. Jennifer Lin, Matilde Marcolli, Hirosi Ooguri, and Bogdan Stoica. Locality of gravitational systems from entanglement of conformal field theories. Physical Review Letters, 2015
 

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