Is the ground state of matter strange?
Ordinary stuff (i.e., everything you'll ever see unless you stick your head in a particle beam) is made of up and down quarks. But it's known that strange matter - stuff made out of up, down, and strange quarks - is more tightly bound, more stable. This came up the other day at lunch - I guessed that it's a consequence of the Pauli exclusion principle (spin 1/2 particles don't like to be in the same place, and having a third quark gives an extra degree of freedom), and apparently that's right. The link has a stronger statement which I didn't know - that the effect is stronger than the extra mass contributed by the strange quark (which is heavier than normal quarks). People are of course looking for this stuff (even if they don't understand their background noise). I think it's the case that a small stable black hole would take more or less forever to eat the entire earth, so presumably we're safe from any strange nuggets that wander by. Anyway, something to worry about if you feel so inclined.