• Question: What causes the nuclear strong force? From what I know, it seems we have conveniently invented a force to explain why nucleons stick together.

    Asked by freddie to Adam, Geoff, Rob, Sheila, Suzie on 21 Mar 2011 in Categories: .
    • Photo: Geoff McBride

      Geoff McBride answered on 18 Mar 2011:

      I can see why you’s say this but the universe the a system of balanced forces, energy, and matter with minor in balances leading to change. There is no cause if you like only effects for us to measure. Some scientists have talked of other universes with different forces but they don’t last long as they are so inbalanced [no evidence for this from what I understand].

    • Photo: Suzie Sheehy

      Suzie Sheehy answered on 18 Mar 2011:

      Inside nucleons are subatomic particles called quarks. The force that holds them together is governed by QCD – quantum chromodynamics and involves other particles called gluons, which are like the photon (which is the particle which makes electrodynamics work), but they make the nuclear strong force work.

      It happens that you can never observe a ‘naked’ quark but they are always bound together in various states by gluons.

      It might seem sometimes like we just invent things like this to explain why things work the way they do, and to a certain extent – theorists do! But that’s how science works: they come up with an idea of how things work, it gets tested against experiment and if it doesn’t hold up, it gets thrown away.

      QCD is a very strong theory and it has been widely tested by some of the most rigorous experiments!

      It took me 4 years of an undergraduate degree before I even got to the point where I started to look at the maths and theory of QCD – this stuff isn’t easy! Sometimes it can be misleading if someone explains it in a book or on TV because they miss out the intricacies that really make the theory work.

      I know from your questions that you’re really into this stuff so I can only encourage you to go on studying it and hope that you’ll get to the point where you can sit down and work through the physics yourself and convince yourself of whether you think it’s right or not!

    • Photo: Adam Tuff

      Adam Tuff answered on 18 Mar 2011:

      Interesting question! Well, as we understand it, the forces arse caused by mediating particles – in the case of nuclear reactions, they are caused by an exchange particle called the gluon – which have actually been detected.

    • Photo: Sheila Kanani

      Sheila Kanani answered on 20 Mar 2011:

      That is about right! Most of quantum physics is ‘made up’ as far as I can tell 😀

    • Photo: Robert Simpson

      Robert Simpson answered on 21 Mar 2011:

      Isn’t that exactly what we’ve done with the other forces? You could just as easily ask why electric charges stick together or why gravity attracts things. We have excellent models, backed up by evidence, for describing the interaction of subatomic particles that create the forces – all of them except gravity. The strong and weak forces are far beyond our everyday experience and thus seem strange and bizarre.

      Your question is a a good one – suspicion is the first step to accepting quantum mechanics 🙂