David Toms, a theoretical physicist at Newcastle University, UK, has found that gravity seems to calm the electromagnetic force at high energies. The finding could make some calculations easier, and is a rare case in which gravity seems to work in harmony with quantum mechanics, the theory of small particles.
For decades, theoretical physicists have been able to explain the Universe in terms of four fundamental forces: the electromagnetic force, which causes electricity and magnetism; the weak nuclear force, which moderates some nuclear decays; the strong nuclear force, which binds quarks together inside atomic nuclei; and gravity. All except gravity have been incorporated into a ‘standard model’ of particle physics.
There are signs that an even more fundamental theory may be out there. At high energies, electromagnetism and the weak force merge into a single ‘electroweak’ force; and, at even higher energies, some as yet untested theories known as supersymmetry combine the electroweak and strong nuclear force. Theorists hope that the world’s most powerful particle accelerator, the Large Hadron Collider near Geneva, Switzerland, will provide evidence for this combined strong and electroweak force.
But gravity remains a stubborn holdout against efforts to create a theory of everything. The force is too weak at low energies to fit with the others, and it becomes too strong at high energies to be included in a single theory. Moreover, theories which attempt to describe gravity in quantum mechanical terms lead to nonsensical infinities in the equations. “That is a very serious problem,” says Toms.
But Toms’s equations have now shown that gravity can sometimes help, rather than hinder. He included a quantum formulation of gravity in a calculation of quantum electrodynamics (QED), a theory that describes how electrons interact with light particles, known as photons. The theory normally breaks down at high energies, because these interactions seem to grow far too strong to be calculated using conventional methods.
In Toms’s work, gravity soothes the interaction, making the force between the electron and photon nearly zero at high energies (1015–1019 GeV). This weakening of the force means that theorists can calculate the behaviour of high-energy electrons and photons after all. “What gravity seems to do is make things better for you,” says Toms.