"There wasn't any explosion."
"But we saw it with our own eyes!"
"You don't know what you saw. That wasn't an explosion, it was a collapse. Remember, Arthur, what I told you of Hop science? That they had neglected what they regarded as theoretical and useless branches?"
"You say their planet collapsed?"
"Yes, that's the clue. It was calculated long ago that when the mass of a body exceeded a certain maximum, the force of gravity would overcome those structural forces that tended to maintain the existence of ordinary types of matter. Ordinary molecules would collapse, and even atoms and nuclei, as we know them, would be unable to maintain their separate existence. The whole mass would fall into a single, compact, giant molecule."
"I seem to remember something we were taught in school. Vaguely, though."
"Yes, it's a commonplace to us now. But the twentieth century astrophysicists were tremendously excited by their discovery at first, although their original calculations were considerably off the mark, as far as the mass required was concerned. We've fixed a more accurate figure since then.
"Through the course of millennia, as a result of conquest and loot, the mass of their planet grew. Our astronomers calculated that it wasn't far from its critical collapse mass. And so as we couldn't hope to win in a direct struggle, our own hope was to build up that mass until the collapse actually took place. That's why we were in such a hurry to send them our heaviest equipment."
His wife said painfully, "And you couldn't have let me know—not even hinted—"
"No, dear. We couldn't afford to take any chances. Not even the members of the Council were informed."