“I think I know the real reason.” “Which is?” “Alcohol in the dust clouds. Goddamn stuff is everywhere. Any lousy species ever invents the telescope and the spectroscope and starts looking in between the stars, what do they find?” He knocked the glass on the table. “Loads of stuff, but much of it alcohol.” He drank from the glass. “Humanoids are the galaxy’s way of trying to get rid of all that alcohol.”
Just as the spectroscope opened up a new astronomy by enabling the astronomer to determine some of the constituents of which distant stars are composed, so the seismograph, recording the unfelt motion of distant earthquakes, enables us to see into the earth and determine its nature with as great a certainty, up to a certain point, as if we could drive a tunnel through it and take samples of the matter passed through.