, if you count all possible color/anti-color pairs, you will get the number 9
. But brainwave
is still right, there are only 8 gluon
s. The reason
for this is somewhat obscure
, buried as it is in the intricacies of group theory
, and it ends up sounding like a rather Tolkeinesque
myth. It turns out that if all nine gluons existed then quarks would not be subject to confinement
, and free color charge would be everywhere and the world would be completely dominated by the strong nuclear force
, rather than the electromagnetic force
as it is now. The absence of one combination forces quarks to be confined, and hence the strong force to have a very limited range.
Unfortunately, explaining which one is missing is kind of complicated. It is easiest to talk about gluons as if they were straight color/anti-color pairs like rb* (red/anti-blue) or gg* (green/anti-green). But it seems that the physical gluons are actually combinations of these such as (rb* + br*)/sqrt(2). The ninth, "missing", gluon is (rr* + bb* + gg*)/sqrt(3).