Now if a proton is really made out of three quarks you'd think that if you hit one hard enough the quarks ought to come popping out. Nor would they be hard to recognize carrying as they do the conspicious label of fractional charge. [...] Moreover at least one of the quarks should be absolutely stable; what could it decay into since there is no lighter particle with fractional charge?

(D.J. Griffiths)

There exist rituals called Hund's Rules.

(D.J. Griffiths)

By 1950 there was compelling theoretical evidence for the existence of neutrinos but there was still no direct experimental verification. A skeptic might have argued that the neutrino was nothing but a bookkeeping device - a purely hypothetical particle whose only function was to rescue the conservation laws. It left no tracks, did not decay, in fact no one had ever seen a neutrino do anything.

(D.J. Griffiths)

How many bodies are required before we have a problem? G.E. Brown points out that this can be answered by a look at history. In the 18th-century Newtonian mechanics, the three-body problem was insoluble. With the birth of relativity around 1910 and quantum electrodynamics in 1930, the two- and one-body systems became insoluble. And within modern quantum field theory, the problem of zero bodies (vacuum) is insoluble. So, if we are out after exact solutions, no body at all is already too many!

(R.D. Mattuck)

Nature has always looked like a horrible mess, but as we go along, we see patterns and put theories together; a certain clarity comes and things get simpler.

(R. Feynman)

In QED as in other quantum field theories we can use the little pictures invented by my colleague Richard Feynman which are supposed to give the illusion of understanding what is going on in quantum field theory.

(M. Gell-Mann)

I would be delinquent if I failed to mention the archaic nomenclature for atomic states, because all chemists and most physicists use it (and people who make up the Graduate Record Exam love this thing). For reasons best known to nineteenth century spectroscopists, l=0 is called s (for "sharp"), l=1 is p (for "principal"), l=2 is d ("diffuse"), and l=3 is f ("fundamental"); after that I guess they ran out of imagination, because it now continues alphabetically (g, h, i, but skip j - just to be utterly perverse, k, l, etc.).

(D.J. Griffiths)

Die Wissenschaft hat ewig Grenzen, aber keine ewigen Grenzen.

(P. du Bois-Reymond)

Wie für jedes Metall werden in Folge Fehlanpassung der Wellenwiderstände an der Grenzfläche Vakuum/Metall fast alle einfallenden Photonen reflektiert.

(Ch. Kittel)