An international team of theoretical physicists has found that when gravity is combined with quantum mechanics, no global symmetries are possible.

“There are four kinds of fundamental forces in Nature: electromagnetism, strong force, weak force, and gravity,” said MIT researcher Daniel Harlow and Hirosi Ooguri from Caltech and the University of Tokyo.

“Of the four, the gravity is the only one still unexplainable at the quantum level.”

“We believe the holographic principle is an important hint to combine the gravity and quantum mechanics successfully.”

The holographic principle allows physicists to study gravitational systems by projecting them on a boundary that surrounds the entire Universe.

The anti-de Sitter/conformal field theory (AdS/CFT) correspondence, developed in the 1990s by the Argentine-American theoretical physicist Juan Maldacena, has been particularly useful because it gives a precise mathematical definition of the holographic principle.

In the new paper, published in the journal Physical Review Letters, Professor Ooguri and Dr. Harlow proved that no symmetry is possible in a gravitational theory if it obeys the holographic principle.

“Our previous work had found a precise mathematical analogy between the holographic principle and quantum error correcting codes, which protects information in a quantum computer,” they said.

“In the new paper, we showed such quantum error correcting codes are not compatible with any symmetry, meaning that symmetry would not be possible in quantum gravity.”

“This result has several important consequences,” they added.

“In particular, it predicts that the protons are stable against decaying into other elementary particles, and that magnetic monopoles exist.”

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Daniel Harlow & Hirosi Ooguri. 2019. Constraints on Symmetries from Holography. Phys. Rev. Lett 122 (19): 191601; doi: 10.1103/PhysRevLett.122.191601