What is Colour (in terms of Quarks)?

FeDeX_LaTeX

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Hello;

What is colour? Is it like the charge between quarks? I can't conceptually understand it, probably because of the wording.

Thanks.
 

mathman

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Colo(u)r has no deeper meaning than simply a way of saying there are three possibilities for this property. In that sense it is analogous to charge, which has two possibilities.
 

FeDeX_LaTeX

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How could they have discovered that quarks possess a colour and an anti-colour? So, one side of the quark has 1 colour, the other side has another?
 

tiny-tim

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So, one side of the quark has 1 colour, the other side has another?
No, there's red and anti-red, blue and anti-blue, magenta and anti-magenta, and so on.

One quark has one colour.

(but a meson, for example, is made of two quarks, which can be a red quark and an anti-red quark)

You can think of red as being positive red charge, and anti-red as being negative red charge.
 
As others have pointed out, color is the "charge" of the strong interactions, and is largely analogous to electric charge. On a superficial level, that's all you probably need to know, but it may be useful to note that the symmetry structure is a little more complicated. The analogy with electric charge makes it easy to see how a quark and an anti-quark could combine into an overall color-neutral configuration.

But you can also combine three quarks together into an overall neutral configuration, which is harder to understand if you're used to just adding together positive and negative electric charges to find the total electric charge. I believe this is where the "color" term comes from, since it's reminiscent of combining red, green, and blue light to get white light. The color analogy is also a pretty loose analogy, though, so don't get too hung up on the term "color".

And yes, a quark has a single color label that can take on three values. Similarly with an anti-quark. A gluon, on the other hand, is usually written with two color labels that can take on 8 different combinations. To fully understand how it all works you would have learn about irreducible representations of SU(3), although suffice to say it's a bit more complicated than electric charge.

Oh, and I think the correct Wikipedia entry would be this, which is probably a good place to start reading:
http://en.wikipedia.org/wiki/Color_charge
 
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mathman

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No, there's red and anti-red, blue and anti-blue, magenta and anti-magenta, and so on.

One quark has one colour.

(but a meson, for example, is made of two quarks, which can be a red quark and an anti-red quark)

You can think of red as being positive red charge, and anti-red as being negative red charge.
This not quite accurate. Quarks and anti-quarks are matter and antimatter. For mesons to be color neutral they need an quark and and anti-quark of the same color.
 

tiny-tim

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Hi mathman! :smile:
For mesons to be color neutral they need an quark and and anti-quark of the same color.
Isn't that what I said? :confused:
 

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