Weak Force - in what sense is it a force?

[jbar18]

Hi,

I don't know very much about the weak force, but gravity, EM and the strong force all seem to apply an actual F = ma type of force (at least, I think the strong force does). But my limited knowledge of the weak force is just that it is involved in radioactive decay. Maybe this is why some people are reluctant to call it the weak force (and use "interaction" instead)? I'm just wondering in what sense the weak force is a force.

Thanks

 

[mfb]

Maybe this is why some people are reluctant to call it the weak force (and use "interaction" instead)?

Right.
If an interaction changes the particle types, it is not useful to call it "force". The Z boson can exchange momentum without changing the particle types, but it has a very short range, it does not lead to a classical (macroscopic) force.
It is similar for the strong interaction.

 

[llynne]

I read something that described the weak force like this...the protons within the nucleus would repel each other with such energy that the strong force wouldn't be able to hold them. Each proton is holding a number of (damn I don't know what to call them) but like a catch ball game they pass this ball back and forth between protons and neutrons. This is the weak nuclear force. It's necessarily so because it allows the nucleus got stay together. I will go look for the reference. But maybe someone can straighten out what I am trying to describe
Obvious that I have no idea...http://hyperphysics.phy-astr.gsu.edu/hbase/forces/funfor.html#c4

 

[Meir Achuz]

The weak force between neutrinos and other particles is much like the electric force between charged particles.
It is only weak at low energies, but it approaches the EM force in strength at energies larger than the W mass.
Neutrinos scatter, just like charged particles at these energies.
The weak force was first seen in decays, but now it is also seen in scattering.

 

[mfb]

The weak force has nothing to do with the stability of nuclei against breaking apart. This is just the strong force. Protons and neutrons consist of quarks and gluons, and the strong force between nucleons (=protons and neutrons) can be described with the exchange of pions.

 

[llynne]

Thanks, as soon as I started I knew I had it wrong

 

[ZapperZ]

Hi,

I don't know very much about the weak force, but gravity, EM and the strong force all seem to apply an actual F = ma type of force (at least, I think the strong force does). But my limited knowledge of the weak force is just that it is involved in radioactive decay. Maybe this is why some people are reluctant to call it the weak force (and use "interaction" instead)? I'm just wondering in what sense the weak force is a force.

Thanks

You need to look at how a "force" is depicted in quantum field theory. It involves the exchange of a "force carrier", which naively can be thought of as an exchange of energy, momentum, and spin between two particles. Thus, in QFT and elementary particles, we seldom use the term "force", but rather use the term "interaction".

It is within that scenario that one considers the weak force as a "force". The exchange of the W's and Z vector bosons are similar enough in the mechanism as the rest of what we call as "force".

Zz.

 

[llynne]

When you say "naively can be thought of as an exchange of energy, momentum, and spin between two particles. " where would I look to improve to a more sophisticated understanding?
The interaction between the bosons w and z changes the particles flavor and colour? Or the momentum, direction and spin are qualities which can be transferred or modified by interaction.?

 

[mfb]

When you say "naively can be thought of as an exchange of energy, momentum, and spin between two particles. " where would I look to improve to a more sophisticated understanding?

Quantum field theory.

The interaction between the bosons w and z changes the particles flavor and colour?

Color is the charge of the strong interactions, the weak interaction does not change it. The W boson can change the particle flavor, the Z cannot (directly).
Momentum can be changed in an interaction, the flight direction is just a result of the momentum. Spin... depends on the interaction.

 

[llynne]

So would I be safe to say the z boson. Does not work alone but as an intermediary?

 

[mfb]

How do you mean that?

The Z boson is a particle which appears in the electroweak interaction, together with the W+, the W- and the photon.

 

[llynne]

So, is it fair to say that all we really know about a boson, (any boson) is the it wasn't there and then it was...at the same time another particle either changes direction/momentum or spin.
Also is it right for me to think that the weak force is really an interaction with the "background" summoning bosons temporarily into being.

 

[mfb]

So, is it fair to say that all we really know about a boson, (any boson) is the it wasn't there and then it was...at the same time another particle either changes direction/momentum or spin.

Well, that is the case in any interactions. Be careful with "a particle is there" - for virtual particles, that is not so well-defined.

Also is it right for me to think that the weak force is really an interaction with the "background" summoning bosons temporarily into being.

That is a strange statement.

 

[Vanadium 50]

Llynne, I don't think that's a terribly useful way of thinking about it.

We know how to mathematically transform the interaction description to the force description. It turns out that the force description is not very useful: the force is almost zero until you get to a very short range (smaller than a proton), and then it suddenly gets almost unimaginably strong. It's sort of like a wall: zero force until you get right up against it, and then no matter how much you push, you can't get closer.

This is very boring behavior, so it's usually not what people think about.