For many years, researchers have struggled to fully comprehend the mechanism behind the force that unites the core components of atoms. Recent developments in mathematical techniques are now helping to address this longstanding puzzle.
Simon Danaher
At this moment, the atoms in your body—and indeed all atoms throughout the universe—are under immense internal pressure to disintegrate. Fortunately, this has not occurred since the universe began.
This instability stems from the nucleus, a compact cluster at the heart of each atom. Within it, protons are densely packed, each bearing a positive charge that drives them to separate from one another. If only electromagnetic forces were at play, the cosmos would have ended in a fleeting burst of energy.
However, another force intervenes—one far more powerful than electromagnetism. This force preserves the stability of matter by securing the fundamental elements of atoms.
As scientists have delved deeper into this force, its complexities have become more apparent. The equations describing it appear straightforward, but they lead to a paradox: a framework starting with massless elements results in particles with evident mass.
Resolving this discrepancy would not only refine our grasp of the force that stabilizes atomic nuclei but also strengthen a cornerstone of contemporary physics. It might also shed light on the origins of mass in the observable universe.
Following over two decades of limited advancement, experts in physics and mathematics believe they are making headway. ‘It seems like a promising period,’ notes Ajay Chandra from Purdue University in Indiana.
The Enigma of Nuclear Binding
Atoms consist largely of vacant space, but their centers house incredibly dense nuclei composed of protons and neutrons in close proximity. This setup creates a clear challenge: protons, with their positive charges, should strongly push away from each other. What prevents the nucleus from breaking apart?
By the 1930s, scientists hypothesized a novel natural force—stronger than electromagnetism—that could maintain nuclear integrity despite proton repulsion.
Subsequent experiments involving particle collisions uncovered the inner workings of atoms. Protons and neutrons were found to consist of tinier units called quarks, bound by an unidentified agent. In the early 1950s, researchers started to define this nuclear adhesive.
At Brookhaven National Laboratory in New York, Chen-Ning Yang and Robert Mills explored whether the math of electromagnetism and quantum mechanics could apply here. In 1954, they formulated new equations.
These suggested the force was mediated by a particle later named the gluon, which conveys the strong nuclear force. Similar to the photon that transmits light, it was initially thought to lack mass.
Almost 20 years later, tests at the Stanford Linear Accelerator in California involved breaking protons. Scientists anticipated quarks confined by intense forces, but they moved freely instead. ‘The unexpected finding was that quarks inside a proton acted unbound, as if unaffected,’ explains David Tong from the University of Cambridge. ‘Yet they remain contained within the proton, suggesting powerful constraints.’
This initially baffled experts, but in 1973, Frank Wilczek, David Gross, and David Politzer demonstrated that the Yang-Mills equations accounted for it. At extremely close ranges inside a proton, the strong force diminishes, permitting quark movement. Slightly farther apart, the force intensifies, akin to a stretching elastic band.
Importantly, this force operates only within the nucleus and vanishes beyond it. In quantum theory, short-range interactions typically involve massive particles, such as the W and Z bosons of the weak force. Yet the original model used massless particles, implying mass emerges mathematically from nothing.
Protons and neutrons comprise three quarks secured by gluons.
