Experiments on a quantum material have revealed for the first time what might be a particle similar to the hypothetical graviton particle. This elementary particle could be the missing link between Einstein’s theory of general relativity, which explains gravity, and quantum mechanics.
There is a divide in physics.
Three of the four fundamental forces of nature – electromagnetism, the nuclear strong force and the nuclear weak force – operate in the same way. Matter moving through force fields experience the forces through “force carrier” particles.
When matter interacts with these fields in particular ways, it causes “excitations” in the force fields which leads to energy being translated in waves through the field. The force carriers are the ‘quantisation’ of this energy, according to quantum mechanics.
For example, electromagnetism is translated through the photon created when the electromagnetic field is excited into electromagnetic waves.
This Standard Model of Particle Physics explains how matter and forces combine to make the universe as we know it. But there is a gaping hole in the Standard Model where gravity should be.
It has long been theorised that there should be a “graviton” particle which is the ‘quantisation’ of gravity waves and carries the gravitational force. However, it is difficult to test this theory because of how relatively weak gravity is. Detecting a single graviton has proven virtually impossible. But that may just have changed.
An international team of researchers has presented the first experimental evidence of “chiral graviton modes” (CGMs) in a semiconductor, virtual particles which are “graviton-like.”
Their findings are published in Nature.
“Our experiment marks the first experimental substantiation of this concept of gravitons, posited by pioneering works in quantum gravity since the 1930s, in a condensed matter system,” says senior author Lingjie Du, a former postdoctoral researcher at Columbia University, US.
The CGMs were detected in a fractional quantum Hall effect liquid. These systems of strongly interacting electrons occur at high magnetic fields and temperatures approaching absolute zero.
Electrons in this kind of condensed matter had previously been predicted to give rise to CGMs in response to light.
An experimental setup pioneered by the late Columbia physicist Aron Pinczuk has now revealed results which could be signatures of CGMs – their spin-2 nature, characteristic energy gaps between ground and excited states, and dependence on so-called “filling factors” which relate the number of electrons to the magnetic field.
These characteristics are shared between CGMs and gravitons. Future experiments using this new setup may find the elusive graviton.
