The Strong Force Is the Least Known of Nature's Four Forces — Until Now
How strong is the strong interaction?
The strong coupling α_s, which governs the force between quarks and gluons, has been measured to only 1% precision, while electromagnetism is known to a billionth. Now, a lattice QCD calculation published in Nature has reduced its uncertainty to five parts per mille using only low-energy input, so the value can enter collider predictions without being fitted to collider data. This milestone comes after decades of algorithmic and computational advances, and it matters for the High-Luminosity LHC and future Higgs factories, where new physics may hide in small discrepancies.
While the fine-structure constant of electromagnetism has been measured to better than one part in a billion, the strong coupling α s is only known to one in a hundred.
- davidhyde
For those looking for a more satisfying answer implied by the simple title here goes. The “αs” number quoted is a dimensionless unit so let’s pick a distance of 1 femtometer so that we can use newtons. The strong force between two gluons is about 150,000N at this distance, compared to 230N for electromagnetism. Electromagnetism weakens with the square of the distance and the strong force does a similar thing up to a point and then it becomes constant. At about 1.1 - 1.5 fm it “snaps”. The energy in the tension is enough to create another pair of gluons. To put it in perspective, the width of a proton is 0.85 fm. It’s all waves down there so my layman view is probably oversimplified.