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As I try to understand the elementary particles,I was reading strong interactions and Isospin from a book.Then I came across this:

Thus,the strong interactions do not distinguish between a proton and a neutron. Consequently, if we imagine a world where only the strong force is present, and the weak and electromagnetic forces are turned off, then in such a world a proton would be indistinguishable from a neutron.

Now,I understand this means there is no difference,fundamental in nature between the protons and neutrons.And the charges are not elementary in nature.I'd like someone to explain it to me,whether I'm right or not.

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They are not same. They ACT same way in strong interactions. Example: every 10 kg object falls same way, thus reacting with a gravitational field of earth in the same manner. Which allows us to say that gravitational mass is independent from other properties of objects. Same story with isospin - it is independent from electrical charge of the particle. –  Asphir Dom Mar 27 at 4:00
    
I don't get the logic in your point....it's not because two persons have the same hair colour that they are identical is it? Same with protons and neutrons, they might have the same interaction under the strong force but other facets of their "personality" such as charge, magnetic spin, mass etc.. tell us they are not the same. –  gatsu Mar 27 at 11:28
    
Definitely wrong. There are two easily seen fundamental differences: charge and constituent particles (i.e., quarks). Protons have charge; neutrons do not. Protons are made of 2 up quarks and 1 down quark; neutrons are made of 1 up quark and 2 down quarks. –  Kyle Kanos Mar 27 at 13:38
    
ok.i get it although it is still not clear how can quarks have non integral charge,yet charges are quantized.I think I'll put it up in another question. –  vivek Mar 27 at 16:39

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