One of the big issues in physics is that quantum mechanics and relativity don’t work well together. This is mostly due to the fact that we don’t know how to express gravity as a quantum force. Many scientists have proposed ways to reconcile the theories, but so far we haven’t found a conclusive way to do so.
Now, an interesting experiment suggests a new way to actually test if gravity is a quantum force. The international team of researchers, led by Professor Sougato Bose from the University College London, want to use gravity to entangle particles. We are a bit short of the tech to test such an idea, but it has found support in the theoretical community as a sound approach to resolve the issue, according to New Scientist.
Entanglement is one of the “head-scratching” phenomena of quantum mechanics, which at first sight shows that the properties of a particle are instantaneously influenced by a distant one without an apparent contact. A more accurate view sees the two particles (in this case) as being part of a single quantum system, and even when the single components are at a significant distance, the properties of the system depend on the whole and not the part.
Particles cannot be entangled without a quantum force acting between them, and so Bose and collaborator suggest an experiment where gravity is used to create such an entanglement. To do this, two very small masses (about 0.01 nanograms) would be dropped under gravity through a magnetic field. Inside the masses, there would be a material that possesses spin, a quantum mechanics property not found in the “regular-sized” world. By using a magnetic field, it is possible to make the mass take one of two paths, depending on if the spin is “up” or “down”. The spin would also be manipulated with microwave pulses, changing the paths that the particles take.
One specific path would bring the masses close together (but no less than 200 microns to avoid other influences), so that if gravity is indeed a quantum force, it will be capable of entangling the spins of the two particles.
The experiment seems straightforward enough, but it is still beyond our capabilities. We have never put in superposition an object as big as that and it is still minuscule by our human standard. And as Bose explains in the paper, even if the entanglement is not produced, it doesn’t mean gravity is not quantum.
Regardless of whether we are immediately able to test this setup, it is interesting to hear new approaches to solving the quantum gravity conundrum. The paper is available on the arXiv, and will soon be published in Physical Review Letters.
[H/T: New Scientist]