One of the most profound mysteries about the universe is whether gravity is a quantum notion, and scientists are working on an experiment to test this theory.
Image shows a laser beam in Gavin Morley’s lab probes the quantum properties of a diamond. Image Credit: Gavin Morley
The two most fundamental descriptions of nature are general relativity and quantum mechanics. General relativity explains gravity on macroscopic scales, but quantum mechanics describes atomic and molecular behavior.
The proper approach to combine these two ideas-to discover whether gravity functions on a quantum level - is arguably the most significant unsolved problem in fundamental physics. While the theoretical study has presented numerous prospects, investigations are required to properly comprehend gravity’s behavior.
For a century, it appeared impossible to conduct tests on the quantum nature of gravity. However, researchers from the Universities of Warwick, UCL, Yale (USA), Northwestern (USA), and Groningen (Holland) will now collaborate to explore this paradox.
Their novel concept involves suspending two microdiamonds in a vacuum and putting them in a quantum superposition where they are simultaneously in two locations. A key component of quantum physics is its paradoxical behavior.
Each diamond is like a little version of Schrödinger’s cat.
Schrödinger’s cat is a thought experiment pointing out that it would be really weird if everyday objects (and pets!) could be in a quantum superposition of being in two places at once. We want to test the limits of this idea. 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.
Gavin Morley, Principal Investigator and Professor, Department of Physics, University of Warwick
Morley added, “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.”
There are several obstacles to achieving this concept, which the team will study during the project.
For example, we need to eliminate all interactions between the nanoparticles other than gravity, which is incredibly challenging since gravity is so weak.
Dr. David Moore, Assistant Professor, Physics, Yale University
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.”
Professor Sougato Bose, UCL, added, “It is hard to overstate how significant it would be for physicists to have experiments that could probe the correct way to combine quantum mechanics and general relativity. People working on theories of quantum gravity such as string theory typically focus on what’s happening at high energies, near black holes and at the big bang.”
Bose stated, “In contrast, our work is in the low-energy regime right here on Earth, but it would also provide invaluable information about whether gravity is quantum. Also the experiment can be regarded as the verification of a generic prediction of any quantum theory of gravity at low energies.”
Professor Anupam Mazumdar, University of Groningen, added, “On the way to understanding the quantum nature of gravity, we may be able to test other aspects of fundamental physics such as exotic deviations from Newtonian gravity as short distances.”
Andrew Geraci, Associate Professor of Physics, Northwestern University, stated, “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.”
“MAST-QG: Macroscopic superpositions towards witnessing the quantum nature of gravity” is the name of the project.