Nightfall

Life would be impossible on such a planet. It wouldn't get enough heat and light, and if it rotated there would be total darkness half of every day. There wouldn't be any native inhabitants. You couldn't expect life---which is fundamentally dependent on light---to develop under such extreme conditions of light deprivation. Half of every axial rotation spent in Darkness! No, nothing could exist under conditions like that.

It was a long time since he'd done any actual clinical work, and obviously his sojourn among the academics at Saro University had attenuated the professional detachment that allows members of the healing arts to confront the ill without being overwhelmed by compassion and sorrow. He was surprised at that, how tenderhearted he seemed to have become, how thin-skinned.

It's one thing to predict [the complete breakdown of civilization]. It's something else again to be right in the middle of it. It's a very humbling thing...for an academic like me to find his abstract theories turning into concrete reality... It was all just so many words to me, really, just a philosophical exercise, completely abstract.

[The theory of universal gravitation] is not cast-iron. No theory is, and there is always room for improvement. Isn't that so? Science is constructed out of approximations that gradually approach the truth. . . Well, that means all theories are subject to constant testing and modification, doesn't it? And if it eventually turns out that they're not quite close enough to the truth, they need to be replaced by something that's closer. Right?

So the universe is not quite as you thought it was. You’d better rearrange your beliefs, then. Because you certainly can’t rearrange the universe.