Gravity can turn itself into light, but only if space-time behaves in just the right way, a research team has found.
Under normal circumstances, you cannot get something from nothing. Specifically, the Standard Model of particle physics, the reigning theory that explains the subatomic zoo of particles, usually forbids the transformation of massless particles into massive ones. While particles in the Standard Model constantly change into each other through various reactions and processes, the photon — the massless carrier of light — cannot normally change into other particles. But if the conditions are just right, it is possible — for example, when a photon interacts with a heavy atom, it can spontaneously split off to become an electron and a positron, both of which are massive particles.
With this well-known example in hand, a team of theoretical physicists, writing in a paper posted March 28 to the preprint database arXiv, asked if gravity itself could transform into other particles. We normally think of gravity through the lens of general relativity, where bends and warps in space-time influence the motion of particles. In that picture, it would be very difficult to imagine how gravity could create particles. But we can also view gravity through a quantum lens, picturing the gravitational force as carried by countless invisible particles called gravitons. While our picture of quantum gravity is far from complete, we do know that these gravitons would behave like any other fundamental particle, including potentially transforming.
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