In physics, symmetry means the conservation of physical laws, or of certain quantities, under transformations or operations. For many years, theorists have been convinced that the fundamental laws describing our Universe, from stars to particles, are necessarily based on symmetries. However, gravity could escape this rule. Indeed, two physicists have shown that on the quantum scale, gravity has no symmetry. If this conception proves to be correct, the current theoretical models which are limited to describing quantum gravity should be modified.

There are four basic interactions: electromagnetism, strong and weak nuclear interactions, and gravity. Gravity is the only force that does not yet have a description at the quantum level. Its effects on large objects, such as planets or stars, are relatively easy to describe, but things get complicated when the effects of gravity manifest on a quantum scale.

### The holographic principle to describe gravity on a quantum scale

To try to understand gravity at the quantum level, Hirosi Ooguri, director of the Kavli Institute for Physics and Mathematics of the Universe in Tokyo, and Daniel Harlow, assistant professor at the Massachusetts Institute of Technology (MIT), started with the holographic principle. This principle explains the three-dimensional phenomena influenced by gravity on a flat two-dimensional space not influenced by gravity.The researchers have shown that symmetry only affects the hatched areas of the diagram, not the surroundings of the point in the middle, so there can be no overall symmetry. Credits: KAVLI |

It is not a real representation of our universe, but it is close enough to help researchers study its fundamental aspects. Earlier work by Harlow and others had found a precise mathematical analogy between the holographic principle and quantum error correction codes, which protect information in a quantum computer.

Ooguri and Harlow have shown that these quantum error correction codes are not compatible with any symmetry, which means that symmetry would not be possible in quantum gravity.

### Better understand quantum gravity and its potential lack of symmetry

This work began over four years ago, when Ooguri discovered an article on holography and its relationship to quantum error correction codes by Harlow, who was then a post-doctoral fellow at Harvard University. Shortly after, the two met at the Institute for Advanced Study in Princeton, when Ooguri was on sabbatical and Harlow came to give a seminar.*“ I went to his seminar, prepared with questions. We talked a lot afterwards, then we started to think that the idea he had developed could perhaps be used to explain one of the fundamental properties of quantum gravity, about the lack of symmetry "*explains Ooguri.

Their result has several important consequences. In particular, he predicts that protons are stable and do not disintegrate into other elementary particles, and that there are magnetic monopoles.

Although the two theorists have provided theoretical proof of the absence of symmetry in the context of quantum gravity, this preliminary work still needs to be deepened. If these works were generally well received by their peers, the researchers recall that the theoretical framework they used must be developed further.

Bibliography: Constraints on Symmetries from Holography Daniel Harlow and Hirosi Ooguri Phys. Rev. Lett. 122, 191601 DOI:https://doi.org/10.1103/PhysRevLett.122.191601 |

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