A new project is developing an experiment to test whether gravity is quantum – one of the deepest questions about our Universe.
While theoretical work has previously proposed many possibilities, experiments are needed to understand whether gravity is quantum.
General relativity and quantum mechanics are fundamental descriptions of nature. General relativity explains gravity, and quantum mechanics explains the behaviour of atoms and molecules.
To understand the quantum nature of gravity, these two theories must be brought together.
The project, ‘MAST-QG: Macroscopic superpositions towards witnessing the quantum nature of gravity,’ aims to understand if gravity can behave in a quantum manner.
Testing the quantum nature of gravity
The new project aims to bring the two theories together by levitating two microdiamonds in a vacuum, putting each into a quantum superposition of being in two places at the same time. The behaviour is a fundamental feature of quantum mechanics.
Each diamond can be thought of as a smaller version of Schrödinger’s cat. This thought experiment poses that it would be strange if everyday objects could be in a quantum superposition of being in two places at once. The team tested the limits of this idea.
Principal Investigator Professor Gavin Morley of the Department of Physics at the University of Warwick said: “Atoms and molecules have been successfully put into such a superposition state, but we want to do this with much larger objects. Our diamonds are made up of one billion atoms or more. To test the quantum nature of gravity, we would look for interactions between two such diamonds due to gravity.
“If gravity is quantum, then it would be able to entangle the two diamonds. Entanglement is a unique quantum effect where two things are linked more strongly than is possible in our everyday life. For example, if two coins could be entangled then you might find that whenever you flip them, they both land the same way up even if it’s impossible to know in advance if they will both be heads or both tails.”
‘The most important problem in physics’
There are challenges with the experiment that the team will investigate. This includes eliminating all interactions between the nanoparticles other than gravity. This is hard because gravity is so weak.
Andrew Geraci, Associate Professor of Physics at Northwestern University, said: “This is a challenging experiment, and this project is a pathfinder to address some of the key technical challenges to make these tests of quantum aspects of gravity a reality.”
Professor Morley added: “For me, the most important problem in physics right now is to develop an experiment that can test the quantum nature of gravity. This new project is an acceleration in our exciting journey towards this.”
