A study published in Physical Review D uses quantum relative entropy to link quantum mechanics and general relativity. The two theories seem to clash despite being both key to understanding the universe.

The author or the study is Ginestra Bianconi, professor of mathematics at Queen Mary University. She sees the metric of spacetime as a quantum operator. She applies quantum relative entropy to describe the interplay between spacetime and matter. This creates a bridge between the two theories.

“The study introduces a new entropic action, which quantifies the difference between the metric of spacetime and the metric induced by matter fields,” explains a Queen Mary University press release. “This approach leads to modified Einstein equations that, in the low coupling regime i.e. low energies and small curvature, reduce to the classical equations of general relativity.”

The cosmological constant

“However, the theory goes further, predicting the emergence of a small, positive cosmological constant,” continues the press release. The value of the cosmological constant derived from the theory “aligns with experimental observations of the universe’s accelerated expansion much better than for other pre-existing theories.”

The cosmological constant affects how fast the universe expands. In theory, quantum mechanics predicts a huge value for it, based on energy in empty space. But when we estimate it from the universe’s real expansion, the value of the cosmological constant is much smaller.

A “G-field” acts like a math adjuster in the equations and tweaks gravity’s rules.

This research ties gravity to quantum information theory and hints at a full quantum gravity theory. The G-field might also unlock dark matter’s secrets. The conclusions of the study express the “hope that this approach can help identify the deep connections among gravity, quantum mechanics and statistical physics.”

“This work proposes that quantum gravity has an entropic origin and suggests that the G-field might be a candidate for dark matter,” explains Bianconi.

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