## Space-time by quantum entanglement

A group of physicists has made an important step towards the unification of general relativity and quantum mechanics. And what emerges from a study published in Physical Review Letters that sheds light on the relationship between quantum entanglement and the microscopic structure of space through a series of precise and meticulous calculations.

Thanks to collaboration between physicists and mathematicians has taken an important step towards the unification of general relativity and quantum mechanics. In a paper published in Physical Review Letters Editor’s Suggestion “for potential interest in terms of results and in the success of the item in communicating its message, especially for those readers who specialize in other fields of study,” the authors, led by Hirosi Ooguri, principal investigator at the University of Tokyo’s Kavli IPMU and co-author of the study in collaboration with an Italian mathematician, Matilde Marcolli Caltech, and with his students Jennifer Lin, lead author of the study, and Bogdan Stoica, space-time would emerge from entanglement quantum part of a more fundamental theory.

**Credit:** H. Ooguri

Physicists and mathematicians are pursuing a long-standing theory of everything that can unify general relativity and quantum mechanics. General relativity and quantum mechanics are now the two theories more complete and more accurate that allow us to describe, respectively, the severity and the physical phenomena on a large scale, as the dynamics of stars and galaxies, and phenomena from microscopic subatomic scales up in molecular ones. Nevertheless, the two theories are in conflict with one another. The world of quantum mechanics is weird, full of quirks and where you can only predict the probability that a given physical phenomenon occurs. Einstein always doubted that the universe behaves in a random and unpredictable because he believed instead that there were strict rules that govern the laws of physics.

The holographic principle is by far considered an essential feature of a theory entirely successful. It states that in a three-dimensional volume gravity can be described by quantum mechanics on a two-dimensional surface surrounding this 3D volume. In particular, the three dimensions should emerge from the two dimensions of the surface. Anyway, the problem to understand the mechanism leading to the formation of the three dimensions has remained quite elusive. Today, however, Ooguri and his collaborators have found that quantum entanglement can be the key to solving this problem. Starting from quantum mechanics, which does not include gravity, the authors show how to calculate the energy density, which is the source of gravitational interactions in three dimensions, using data of quantum relative to the two-dimensional surface. It’s a bit like analyzing the human body X-ray examining the two-dimensional sheets. This allowed the researchers to interpret the universal properties of quantum entanglement in terms of conditions on the energy density that would be described in a consistent manner by any theory of quantum gravity that do not explicitly include the severity.

**Credit:** Jennifer Lin et al. 2015

The importance of quantum entanglement is already known but its precise role in the mechanism that leads to the emergence of space it was not clear before this study. The quantum entanglement is a phenomenon where quantum states, such as the spin or polarization of the particles located in different positions, cannot be described independently. Perform therefore a measure of a particle implies a consequent action of another particle, a phenomenon that Einstein himself defined it as “spooky action at a distance”. The work of Ooguri and collaborators shows that the phenomenon of quantum entanglement generating extra space dimensions of the theory of gravity.

“We know that quantum entanglement is related to the deeper issues that revolve around the attempt to unify general relativity and quantum mechanics, such as the information paradox of black holes. Our work sheds light on the relationship between quantum entanglement and the microscopic structure of space-time through precise and meticulous calculations. The interface between gravity and quantum information science is becoming increasingly important. One of my goals is just to go on following this path for future research, “concludes Ooguri.