Sciencemadness Discussion Board

How are neutrons held in the nucleus?

Gooferking Science - 5-11-2013 at 14:42

Hello. I was wondering how neutrons were held in the nucleus of an atom. I googled this subject, and it came up with information telling me that they are held in the nucleus by "the strong force". It said that it is one of the four major forces and is much stronger than gravity. However it only works across VERY small (nuclear) distances. That's great and all, but how does it work!? What causes such an incredibly strong force to just happen?

DraconicAcid - 5-11-2013 at 14:55

You explain to me how gravity works, and I'll tell you how the strong force works.

vulture - 5-11-2013 at 15:09

I'm not well versed in particle physics, so I can't really answer this for you. However, this is one of the hot topics in physics today and ties in to the Higgs boson etc.

You might get some answers by reading up on subatomic particles or by applying for a job at the LHC :D

This is one of those questions where Nobelprizes are waiting...

[Edited on 5-11-2013 by vulture]

[Edited on 5-11-2013 by vulture]

Random - 5-11-2013 at 15:43

One of unsolved questions in physics. Check on wikipedia for them. There is also entire page on Theory of everything.

halogen - 5-11-2013 at 16:03

"Why?" will continue indefinitely: "what can we observe?" is more complete.

ElectroWin - 5-11-2013 at 19:01

didnt this get asked on freenode irc ##physics recently? i recall a very good answer:
just imagine that 3D space is an emergent property, and that space in the vicinity of small dense objects is not really flat, but you have little pockets of this non-flatness. then lines of force could curl up into tiny circles instead of being allowed to stretch out over long distances.

Lambda-Eyde - 5-11-2013 at 19:46

To anyone who has these types of questions pop up in their heads now and then, watch this video: http://www.youtube.com/watch?v=wMFPe-DwULM

MrHomeScientist - 6-11-2013 at 06:15

At first glance, the strong force appears to have two facets to it. It's the force that binds quarks together inside a subatomic particle, and it is also the force that holds protons and neutrons together in an atomic nucleus. In reality both are the result of the same single force. The latter case (and the OP's question) can be thought of as the residual strong force - the "leftovers" of the force holding the quarks together that bleeds outside of the nucleon and acts on and attracts adjacent nucleons. The strong force is very interesting and unique in that it actually increases in strength with increasing distance, up to a limiting distance where it remains at a constant value no matter how much farther apart the quarks get. This limiting distance is about the size of the particle that the quarks comprise.

Nominally, the so-called "color charge" of quarks making up a nucleon cancels completely and no strong force would be seen outside the particle. The cancellation isn't quite perfect, though, which leads to the residual strong force, or nuclear force, that binds protons and neutrons together. This residual force does quickly diminish with distance (since it is mostly cancelled out within the nucleons). This is also the reason larger atoms are more prone to be unstable and radioactive. In large atoms, there is a strong electromagnetic repulsion between protons but not enough strong nuclear force to compensate. Thus these atoms tend to break apart.

If you google "strong force," the wikipedia page in the first hit explains this all pretty well.


Edit: The video above is really excellent; I've seen that posted here before. Definitely recommend watching it.

[Edited on 11-6-2013 by MrHomeScientist]

watson.fawkes - 6-11-2013 at 07:08

Finally. A reply worth engaging with.
Quote: Originally posted by MrHomeScientist  
The strong force is very interesting and unique in that it actually increases in strength with increasing distance, up to a limiting distance where it remains at a constant value no matter how much farther apart the quarks get. This limiting distance is about the size of the particle that the quarks comprise.
The effect you're describing is call quark confinement. It's not quite right to describe a "limiting" distance. What happens is that longer/larger confinements, while they exert constant force, require ever higher energies. At some point this energy is large enough to create new particles, and the confinement decays. In an accelerator, this gives rise to hadron jets. But there's no automatic limit about when the decay occurs.

testimento - 6-11-2013 at 11:39

What is the density of the hypothetical neutronium per cm3?

Random - 11-12-2013 at 11:07

Quote: Originally posted by testimento  
What is the density of the hypothetical neutronium per cm3?


Very dense, check for neutron soup or neutron stars.

Jmap science - 11-12-2013 at 14:06

I bet string theory has something to say about the :D