Short answer: there are six quark flavours: up, down, charm, strange, top and bottom. They come in three pairs. Only up and down quarks are found in everyday matter. The other four are heavier and only appear for a split second in special conditions.
The six flavours at a glance
- Up: electric charge +2/3. Very light. Found inside every proton and neutron.
- Down: electric charge −1/3. Very light. Found inside every proton and neutron.
- Charm: electric charge +2/3. Much heavier than up. Found in 1974.
- Strange: electric charge −1/3. Heavier than down. Appears in particles like kaons. Read more in our strange quark guide.
- Top: electric charge +2/3. The heaviest known elementary particle, with a weight close to a whole gold atom. Found in 1995.
- Bottom: electric charge −1/3. Heavy and short-lived. Found in 1977.
Three pairs, called generations
- First pair: up and down (the lightest)
- Second pair: charm and strange
- Third pair: top and bottom (the heaviest)
Scientists do not yet know why quarks come in exactly three pairs. It is one of the open questions in physics.
What does “flavour” mean?
It has nothing to do with taste. Physicists simply needed a word for “type”, and “flavour” stuck.
Why do we only see up and down quarks?
Heavier quarks are unstable. They turn into lighter quarks within a tiny fraction of a second. So the only ones that last are up and down, and that is why protons and neutrons are made only from those two.
- Proton: two up quarks and one down quark
- Neutron: one up quark and two down quarks
Where do we see the heavy quarks?
Scientists make them in particle accelerators, and they also appear naturally when cosmic rays hit our atmosphere. Each one lives for a very short time before changing into something lighter.
What about “colour”?
Quarks also have a property called colour charge, with labels red, green and blue. These are just names, not real colours. The names help scientists describe how quarks stick together through the strong force.
Quick FAQ
How many quarks are there?
Six kinds, plus an opposite version of each called an antiquark.
Which quark is the heaviest?
The top quark.
Which quarks make up a proton?
Two up and one down.
Next: the top quark, quark vs atom or the question of what is smaller than a quark. Back to the science section