An international team of physicists from the US and Japan has found that when gravity is combined with quantum mechanics, no global symmetry is possible. Out of four fundamental forces in nature: gravity, electromagnetism, strong force, and weak force, gravity remains the least justifiable to be explained at the quantum level.

“Many physicists believe that there must a beautiful set of laws in Nature and that one way to quantify the beauty is by symmetry,” says Hirosi Ooguri, Director of the Kavli Institute for the Physics and Mathematics of the Universe, and an author of the paper in a news release. “Some of the symmetries may be hidden in our world, but they should manifest themselves if we look at Nature at a more fundamental level. We showed that this expectation is wrong once we take into account the gravity.”

Even deploying Newtonian model, or relativity is out of question. And, combining the fundamental, quantum properties of mass, energy and space-time to create the phenomenon is still wide of the mark.

Much like how the photons fuel electromagnetism with the energy and momentum they carry, there ought to be particles that propagate the gravitational force. However, we do not have a shred of proof that those hypothetical particles, which physicists call gravitons, exist. So in this new study, the team hinges on at the holographic principle to combine the gravity and quantum mechanics successfully.

The holographic principle, in a way, chucks out imagery of the gravitational systems that surrounds the entire universe, and it’s pretty much comparable to how the hologram projects three-dimensional images out from a two-dimensional screen. The AdS/CFT correspondence proposed by Juan Maldacena in late 1997, has been particularly useful in this regard as it gives a precise mathematical definition of the holographic principle, and also provides a powerful toolkit for explaining quantum field theories.

In the new paper published in the journal *Physical Review Letters *Ooguri and Daniel Harlow, Assistant Professor at Massachusetts Institute of Technology confirmed that no symmetry is achievable in a gravitational theory if it complies with the holographic principle.

Prior work by the same team had found the holographic principle bears a profound correspondence to quantum error correcting codes, which secures information in a quantum computer. However, the new study showed that such quantum error correcting codes are not compatible with any symmetry, confirming that no symmetry is possible in quantum gravity.

Researchers say the finding has several important consequences, and in particular, it goes to show that protons are stable against decaying into other elementary particles. And that magnetic monopoles exist.

The study was published in *Physical Review Letters* on May 17, and it’s titled “Constraints on Symmetries from Holography”

Source: Kavli Institute for the Physics and Mathematics of the Universe

Disproven theories (and assumptions) are exciting because, while at first they throw everything into disarray, they are, in fact, the first step toward discovering something we hadn’t previously even known to look for.

Cool