I suppose I should really go tell it to Timothy M. O'Brien over at O'Reilly Media, but here I am right now; every time Mr. O'Brien transcribes "white walls" in the snippet of that quite fascinating interview you quote, Mr. Cox is most certainly actually saying "white dwarfs", only in an accent Americans find unintelligible (think of the announcer from BBC "Wild" News). So, Mr. Noah, please do your part to limit the spread of dandruff caused by head scratching and change that to "white [dwarfs]". Thanks!