Oz was depressed. He had been trying to figure out the answer to the remaining question, but it just wasn't coming.
Said G. Wiz, "Anyway, you can certainly finish up this test - you're almost done - and then I can show you some of the scary formulas I have been hiding thus far, and we can see a bit more about how one actually uses them to do physics."
The Wiz had come out of his mathematicave for a cup of coffee. Whilst Wiz and Oz waited for the alembic to boil they fell into a short discussion.
"Um." said Oz hesitantly in his usual lucid way "You know this black hole question you asked?"
"Yeeess." said Wiz suspiciously "the one you are making very heavy weather over. Yes."
"Well," continued Oz, "You remember at the beginning of the course you told me to forget all I thought I knew about Gr, space, time and anything else even vaguely connected with it."
"No I don't, but it's the sort of thing I might have said. There is so much misinformation going about, you would be better off forgetting it." Said Wiz sternly and even more suspiciously.
"Well I did, as per instructions. So I figure that you only want answers more or less derivable from your course notes," mumbled Oz as he blew hard on the embers to get a bit of flame going.
"Erg seems to think the same way and it's not really very straightforward, see. I even tried handwaving but that didn't meet with your approval. It didn't even get a quick blast of ire back."
"So? You gotta wave your hands the right way for the magic to happen," snapped Wiz curtly as he picked up the alembic, poured himself some coffee, and swept into his cave. Oz thought it was nice to see Wiz sweeping occasionally, if only regally, and went to get his broom.
Just as he picked up, the Wiz poked his head out again. "Ahem. While you're sweeping, why don't you meditate a bit on the concept of dust."
"Ashes to ashes, dust to dust, that sort of thing?" asked Oz. It surprised him that G. Wiz would be giving him spiritual exercises instead of the usual mathematical ones.
"Not exactly. Imagine a sphere of dust particles in outer space interacting only through gravity. Each one in free fall. What will happen?"
"Well, they'll fall in..." blurted out Oz.
"Right. Can you show that a singularity will form? A place where the curvature becomes infinite? You know.... a BLACK HOLE?"
Oz thought and took a sip of coffee. Yech! The coffee was full of coffee grounds, since there weren't any filters around. Coffee grounds... what did that remind him of....