Consider say the proton. It is seems to be universally stated that a proton is "composed of three quarks, 2 up and a down, and you must have the three different 'colors'".

So, you can have blue-up, red-up and green-down, or maybe green-up, red-up and blue-down, and so on. You need only glance at the wikipedia page for an example illustration of this.

Something I don't understand is, imagine "some particular" proton (say inside one particular hydrogen atom). Is is the case that

(A) .. that particular proton is made of some combination. (Say, red-up, green-up, blue-down.) And then for all time, or for a long time, that particular proton is indeed made of that combination.

or, is it the case that

(B) .. that particular proton is continuously changing between the various possible combinations.

Which is it?

I generally understand the idea of color change - how gluons mediate the change of color between two quarks. This is explained widely for the general reader example, example.

However as I ask above, it is to me completely unclear whether that happens only occasionally (when?) or whether it is something that happens continuously (if so - exactly how often? 10 times a second? More, less?)

Furthermore. I was enjoying this excellent answer by John Rennie. The trouble is, that answer essentially says that the idea of a proton "being composed of three quarks" is in fact nonsense. Note too that this answer by another expert literally says ""red, blue or green" quarks do not exist".

What's the deal with this? For example, in particle accelerators, does one ever say "oh look ..... that proton there seemed to be a red-up, blue-up and green-down style of proton..". Or, in fact is this image:

enter image description here

... largely nonsense in terms of literally "what is a proton 'made' of"? Is it quite simply "utterly wrong" in any meaningful sense??

Again, even within that descriptive mode, which of "A" versus "B:" above is true??

  • $\begingroup$ Related: Is color charge a quantum mechanical observable? $\endgroup$
    – ACuriousMind
    Commented Nov 8, 2015 at 17:46
  • $\begingroup$ Gotchya. I still wanna know which of "A" or "B" is (in some sense) correct... one could say, given the "fiction" of the typical explanation (as in the diagram), which of "A" or "B" is correct within that, let us say, scale of meaning? $\endgroup$
    – Fattie
    Commented Nov 8, 2015 at 17:52
  • $\begingroup$ "composed of three quarks, 2 up and a down, but the colors must 'add' to white" should be understood as a shorthand for describing the valence content of the proton. Secondly, while there is no physical significance to a color assignment as ACouriousMind writes, there is nothing that stops you from making an arbitrary assignment for convenience of communication; its just that this assignment can have no physical consequences. $\endgroup$ Commented Nov 8, 2015 at 18:05
  • $\begingroup$ Hi DM. I completely understand, of course, that the "color" language is nothing more than a convenient choice of terms due to the analogy with light. (The "add" and so on is in quotes.) $\endgroup$
    – Fattie
    Commented Nov 8, 2015 at 18:15
  • $\begingroup$ B is somehow correct ... I prefer C , the proton components are indistinguishable until a decay, then there is : 3 quarks ( white ensemble ) of which 2 up and 1 down . $\endgroup$
    – user46925
    Commented Dec 16, 2015 at 4:59

1 Answer 1


Indeed protons and neutrons in the nucleus are very different than isolated. E.g. the neutron is assumed to be unstable isolated (~15mn lifetime) while they are say "stable" in the nucleus. But indeed in the nucleus protons and neutrons are quickly "blinking" all the time, exchanging genders as they exchange mesons (a pair quark-antiquark). So you might say that as a balance the nucleus is made of "such amount of protons and neutrons", plus at any time there do exist temporary grouping of 3 quarks (you can see the cross section then shooting high energy electrons). So there is "something", but not as material and stable we learn in young classes :-)

  • 1
    $\begingroup$ Hi Fabrice. I don't totally follow your answer unfortunately. (What is a 15 "mn" by the way??) I will try to study your answer carefully. I mentioned a proton as an example: I can see from your answer that in a nucleus even that is too simplified. What about the case of a hydrogen atom (just the one proton -- unless I misunderstand that!) In that case, in some particular hydrogen atom, regarding the proton in it, which of my "A" or "B" apply ??? $\endgroup$
    – Fattie
    Commented Nov 8, 2015 at 18:20
  • $\begingroup$ mn = minute. $$$$ $\endgroup$ Commented Nov 8, 2015 at 23:03

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