# Unraveling the quantum nature of gravity • Earth.com

Gravity, the force that keeps our feet on the ground and the planets in their orbit, is an integral part of our daily lives. Despite its ubiquity, the true nature of gravity remains a mystery. Scientists are still grappling with the question of whether gravity is essentially a geometric phenomenon, as proposed by Einstein, or whether it is governed by the laws of quantum mechanics.

In a study published in *Physical Assessment X*researchers from Amsterdam and Ulm have proposed an innovative experiment that could shed light on this age-old question.

Ludovico Lami, a mathematical physicist at the University of Amsterdam and QuSoft, and his colleagues have designed a new approach that circumvents the challenges faced by previous experimental proposals.

## Quantum gravity riddle

The quest to unify quantum mechanics and gravitational physics is one of the most important challenges in modern science. Progress in this area has been hampered by the inability to conduct experiments in regimes where both quantum and gravitational effects are relevant.

As Nobel laureate Roger Penrose once said, we don’t even know whether a combined theory of gravity and quantum mechanics will require a “quantization of gravity” or a “granitization of quantum mechanics.”

“The central question, initially posed by Richard Feynman in 1957, is to understand whether the gravitational field of a massive object can enter a so-called quantum superposition, where it would be in several states at the same time,” Lami explains.

“Before our work, the main idea to answer this question experimentally was to look for gravitationally induced entanglement – a way in which distant but related masses could share quantum information. The existence of such an entanglement would falsify the hypothesis that the gravitational field is purely local and classical,” he continued.

## Overcoming the offshoring dilemma

The main obstacle to previous experimental proposals was the creation of distant but related massive objects, known as delocalized states.

The heaviest object for which quantum delocalization has been observed to date is a large molecule, which is significantly lighter than the smallest source mass whose gravitational field has been detected. This discrepancy has pushed hopes for an experimental realization decades into the future.

## Designing a new experiment to beat the odds

Lami and his colleagues have proposed a possible solution to this impasse. Their experiment aims to reveal the quantum force of gravity without causing any entanglement.

“Our team designed and investigated a class of experiments using a system of enormous ‘harmonic oscillators’ – for example the torsion pendulum, which is essentially similar to the one Cavendish used in his famous 1797 experiment to measure the strength of gravity ,” explains Lami. .

“We place mathematically rigorous limits on certain experimental signals for quantumness that a local classical gravity should not be able to overcome. We have carefully analyzed the experimental requirements necessary to implement our proposal in actual experiments, and have concluded that, while some degree of technological advancement is still needed, such experiments may soon be truly within reach.

## The power of entanglement theory

Surprisingly, the researchers still rely on the mathematical machinery of entanglement theory in quantum information science to analyze their experiment, despite the absence of physical entanglement.

Lami clarifies, “The reason is that even though entanglement is not there physically, it is still there in the mind – in a precise mathematical sense. It is sufficient that entanglement could have arisen.”

## New era of quantum gravity research

In summary, the research of Lami and his colleagues from Amsterdam and Ulm opens a new chapter in the quest to unravel the quantum nature of gravity.

Their innovative experimental proposal, which relies on the mathematical framework of entanglement theory without requiring physical entanglement, brings us closer to answering the fundamental question posed by Richard Feynman more than sixty years ago.

As technological advances continue, the realization of this experiment becomes increasingly feasible and promises to shed light on one of the most profound mysteries in modern physics.

The implications of this research extend far beyond the realm of theoretical physics, as a deeper understanding of the quantum-gravity relationship could radically change our perception of the universe and our place in it.

The full study was published in the journal *Physical Assessment X*.

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