How strong is the strong interaction? (cerncourier.com)

38 pointsby EA-3167a day ago6 comments

davidhyde 13 hours ago

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.

pavel_lishin 2 hours ago

> 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.

That sort of makes intuitive sense, right? If the force were weaker so that it "snapped" at 10 femtometers, you'd expect protons themselves to be somewhere in that size range as well.

(Or am I totally wrong?)

sigmoid10 24 minutes ago

The actual size is not defined by this "snapping" point, but by the equilibrium between the kinetic energy from the Heisenberg uncertainty of the quarks pushing outwards and the strong force pulling inwards. It's actually the same concept as for the size of an atom, where the kinetic energy of the electron and the electromagnetic force define what you would call "size."

EA-3167 2 hours ago

It’s pretty intuitive in the context of confinement theory. Intuitively we imagine something like a rubber band, as you add energy in the form of tension the material passes a threshold and as you say snaps. For confinement however as you add energy to the system it doesn’t snap, you simply reach the moment when you’ve added enough energy to the system to create a new particle pair that are also confined.

This is the explanation for why when we collide beams of protons at near c they don’t produce a new higher energy particle, but a massive shower of secondary and tertiary particles like pions and kaons as a result of the decay chain from initial pair production.

kadoban 2 hours ago

Do you have the weak force number as well? I'm curious.

I _think_ I expect it to be quite high. My understanding is it's "weak" because it falls off quickly, past a certain distance, due to the force carrier having mass.

quchen an hour ago

The weak force is weak in two ways. One is as you mention the massive-ness of the W/Z resulting in exponential decrease of force over distance, but there's also the fact that at our usual energy scales, creating a (virtual/off-shell) W/Z is close to impossible - so it's not only weak over distance, but also very rare.