May 9, 2021


What If Gravity Is Actually a Double Copy of Other Forces? (Charlie Wood, 5/09/21, Wired)

"There's a schism in our picture of the world, and this is bridging that gap," said Leron Borsten, a physicist at the Dublin Institute for Advanced Studies.

While this unproven mathematical relationship between gravity and the quantum forces has no clear physical interpretation, it's allowing physicists to pull off nearly impossible gravitational calculations and hints at a common foundation underlying all the forces.

John Joseph Carrasco, a physicist at Northwestern University, said anyone who spends time with the double copy comes away believing "that it's rooted in a different way of understanding gravity."

On one side of the fundamental physics divide stand the electromagnetic force, the weak force and the strong force. Each of these forces comes with its own particle carrier (or carriers) and some quality that the particle responds to. Electromagnetism, for instance, uses photons to push around particles that possess charge, while the strong force is conveyed by gluons that act on particles with a property called color.

Physicists can describe any event involving these forces as a sequence of particles scattering off each other. The event might start with two particles approaching each other, and end with two particles flying away. There are, in principle, infinitely many interactions that can happen in between. But theorists have learned how to make frighteningly accurate predictions by prioritizing the simplest, most likely sequences.

On the other side of the divide stands gravity, which rebels against this kind of treatment.

Gravitons react to themselves, generating looping, Escher-like equations. They also proliferate with a promiscuity that would make a bunny blush. When gravitons mingle, any number of them can emerge, complicating the prioritization scheme used for other forces. Just writing down the formulas for simple gravitational affairs is a slog.

But the double copy procedure serves as an apparent back door.

It's whatever physicists convince themselves it is.
Posted by at May 9, 2021 11:09 AM