Gravity is one of the four fundamental forces that bind matter in the universe. The other three forces (electromagnetic, weak nuclear, and strong nuclear) are explained through the exchange of force-carrying elementary particles, leading theorists to believe there is a similar quantum explanation for gravity.
The force carriers for the electromagnetic force are photons, while the weak nuclear force has W-, W+, and Z0 bosons as force carriers, and the strong nuclear force has eight types of gluons. On the other hand, the hypothetical carrier of gravitational force is known as the graviton.
The properties of the graviton are deducible in quantum theory. The amount of energy required to summon a force-carrying particle from the vacuum determines how quickly it must be recovered. Since gravity has an infinite range and does not require energy to create a graviton, the mass of the graviton must be zero.
Additionally, gravitons are expected to have a spin of 2, as only spin 2 particles interact with all matter, which is characteristic of universal gravity. This is in contrast to quarks and leptons, which have a spin of 1/2, and the non-gravitational force carriers, which have a spin of 1.
While gravity may not be fully explained by the exchange of gravitons, most physicists believe it can be quantized. String theory offers a potential framework where fundamental particles are envisioned as vibrations of mass-energy strings, with each vibrating string having the properties of a graviton.
However, string theory faces challenges due to its complexity and inability to make testable predictions. Detecting gravitons is difficult due to the extremely weak nature of gravity and the rare interactions gravitons have with matter.
Despite the challenges in detecting gravitons, recent advancements in experimental exploration, such as the discovery of spin-2 particle properties in a liquid analogue system, provide hope for a better understanding of gravitons and the eventual unification of fundamental forces into a single theory.
About our experts
Tony Rothman: A theoretical physicist who has taught at Princeton and Harvard Universities, he has published non-fiction and fiction novels and written various stage plays outside of his academic career. He has contributed to publications like Physics Basics, European Journal of Physics, and Astrophysics and Space Sciences.
Source: www.sciencefocus.com
