Mapping the forces inside protons

You might be surprised to hear that there’s anything “inside” a proton.

But scientists have mapped the forces between the quarks inside protons in unprecedented detail, adding to the understanding of fundamental characteristics of the universe and potentially leading to future proton-based technologies.

Atoms are made of electrons, protons and neutrons. Protons and neutrons are each made up of a collection of quarks.

Quarks are bound together to form protons through one of the 4 fundamental forces of nature: the strong nuclear force.

“We have used a powerful computational technique called lattice quantum chromodynamics to map the forces acting inside a proton,” says Ross Young – an associate professor in physics at Australia’s University of Adelaide – who is a co-author of a paper on the new research published in the Physical Review Letters.

The approach breaks space and time up into a grid to simulate on a computer how the strong force acts in different regions of the proton. They examined what would happen if high-energy photons were fired at the quarks.

By the way – a proton has a radius of about 0.8–0.9 femtometres about 100,000 times smaller than an atom. This means the grid the scientists are working on is very small indeed.

“Our findings reveal that even at these minuscule scales, the forces involved are immense, reaching up to half a million Newtons, the equivalent of about 10 elephants, compressed within a space far smaller than an atomic nucleus,” says first author Joshua Crawford, a PhD student at the University of Adelaide.

“These force maps provide a new way to understand the intricate internal dynamics of the proton, helping to explain why it behaves as it does in high-energy collisions, such as those at the Large Hadron Collider, and in experiments probing the fundamental structure of matter.”

“As researchers continue to unravel the proton’s inner structure, greater insight may help refine how we use protons in cutting-edge technologies,” says Young. “One prominent example is proton therapy, which uses high-energy protons to precisely target tumours while minimising damage to surrounding tissue.

“Just as early breakthroughs in understanding light paved the way for modern lasers and imaging, advancing our knowledge of proton structure could shape the next generation of applications in science and medicine.

“By making the invisible forces inside the proton visible for the first time, this study bridges the gap between theory and experiment.”