If you realize all the time what's kind of wonderful - that is, if we expand our experience into wilder and wilder regions of experience - every once in a while, we have these integrations when everything's pulled together into a unification, in which it turns out to be simpler than it looked before.

Quarks came in a number of varieties - in fact, at first, only three were needed to explain all the hundreds of particles and the different kinds of quarks - they are called u-type, d-type, s-type.

Investigating the forces that hold the nuclear particles together was a long task.

Richard P. Feynman Quotes